bluuebunny/crossref_metadata_2025 huggingface dataset:
Dominance not richness determines invasibility of tallgrass prairie
Authors: Smith Melinda D. , Wilcox Julia C. , Kelly Theresa , Knapp Alan K.
Published: July 2004

Many recent studies suggest that more diverse communities are more resistant to invasion. Community characteristics that most strongly influence invasion are uncertain, however, due to covariation of diversity with competition and crowding. We examined separately the effects of species richness and dominance on invasion by an exotic legume,Melilotus officinalis, in intact, native Kansas grassland. We manipulated dominance of C4grasses by reducing their abundance (i.e. ramet densities) by ∼25 and 50%. In addition, richness was reduced by removing species that were mainly rare and uncommon as might be expected with environmental changes such as drought and fragmentation. In both years of the study (2001–2002), invasibility, measured as peak establishment ofMelilotus, was not affected by a 3‐fold reduction in species richness, nor was there an interaction between loss of species and reduced dominance on invasion. In contrast, reductions in abundance of the dominants significantly reduced invasibility of the grassland plots in both years. Because the abundance of dominants was highly correlated with measures of competition (i.e. ratio of dominant biomass to total biomass) and crowding (total stem densities), this pattern was opposite to that expected if competition were indeed limiting invasion. Rather, invasion appeared to be facilitated by the dominant species, most likely because reduced dominance increased environmental stress. Our results suggest that dominance is the key community characteristic determining invasibility, because highly competitive and space‐filling species can either enhance or reduce susceptibility to invasion depending on whether dominants create a more competitive environment or alleviate stressful conditions.
Shrubs, granivores and annual plant community stability in an arid ecosystem
Authors: Wilby Andrew , Shachak Moshe
Published: July 2004

Compensatory population dynamics among species stabilise aggregate community variables. Inter‐specific competition is thought to be stabilising as it promotes asynchrony among populations. However, we know little about other inter‐specific interactions, such as facilitation and granivory. Such interactions are also likely to influence population synchrony and community stability, especially in harsh environments where they are thought to have relatively strong effects in plant communities. We use a manipulative experiment to test the effects of granivores (harvester ants) and nurse plants (dwarf shrubs) on annual plant community dynamics in the Negev desert, Israel. We present evidence for weak and inconsistent effects of harvester ants on plant abundance and on population and community stability. By contrast, we show that annual communities under shrubs were more species rich, had higher plant density and were temporally less variable than communities in the inter‐shrub matrix. Species richness and plant abundance were also more resistant to drought in the shrub under‐storey compared with the inter‐shrub matrix, although population dynamics in both patch types were synchronised. Hence, we show that inter‐specific interactions other than competition affect community stability, and that hypothesised mechanisms linking compensatory dynamics and community stability may not operate to the same extent in arid plant communities.
Prey selection by wild birds can allow novel and conspicuous colour morphs to spread in prey populations
Authors: Thomas Robert J. , Bartlett Laura A. , Marples Nicola M. , Kelly David J. , Cuthill Innes C.
Published: July 2004

Conspicuous warning coloration helps to protect prey because it signals to potential predators that the prey is unprofitable. However, such signals only work once predators have come to associate the conspicuous colour with the unprofitability of the prey. The evolution of warning coloration is generally considered to be paradoxical, because it has traditionally been assumed that the first brightly coloured individuals would be at an immediate selective disadvantage because of their greater conspicuousness to predators that are naïve to the meaning of the signal. As a result, it has been difficult to understand how a novel conspicuous colour morph could ever avoid rapid extinction, and instead survive and spread in the population until predators have become educated about the signal. In the present study, we experimentally simulated the appearance of a single novel coloured mutant in small populations (20 individuals) of palatable artificial pastry “prey”. The colour morph frequencies in each “generation” of prey (presented on successive days of a trial) were determined by the relative survival of the previous generation under predation by free‐living birds. We found that the novel colour morphs regularly persisted and increased from a starting frequency of 1/20 to reach fixation (100%), despite being fully palatable, even when the novel morph was much more conspicuous against the background than the familiar morph. This was true for both green (not normally considered a warning colour) and red (a classic warning colour) novel morphs. Novel colours reached fixation significantly faster than could be accounted for by random drift, indicating differential predation in relation to prey colour by the birds. Our experiments show that the immediate demise of a fully palatable new prey morph is not an inevitable outcome of predator behaviour, because even very conspicuous prey can gain protection from conservative foragers, simply by being novel.
Incidental predation, enemy‐free space and the coexistence of incidental prey
Authors: Schmidt Kenneth A.
Published: July 2004

Many communities consist of a generalist predator that consumes multiple prey species whose persistence is thereby threatened through the indirect effect of apparent competition. However, uncommon and/or ephemeral prey may be encountered only incidentally through the predator's effort expended to consume primary prey. In such instances, the functional response to incidental prey is driven entirely through the density of primary prey. Moreover, rarity and brevity in the predator's diet precludes a numerical response to incidental prey. Instead, the persistence of incidental prey may be critically linked to gaps in space unexploited by predators, i.e. enemy‐free space. I use optimal foraging theory to derive a mechanism by which enemy‐free space is created as a result of a predator's forging aptitude and patch‐use behavior. In non‐competitive environments enemy‐free space provides a behavioral refuge for incidental prey that may prevent their extinction. In competitive environments, greater enemy‐free space is associated with higher incidental prey densities and concomitantly greater competitive effects. As a result, incidental prey diversity declines with an increase in enemy‐free space.
Habitat selection in a seasonally variable environment: test of the isodar theory with the fat sand rat, Psammomys obesus, in the Negev Desert, Israel
Authors: Shenbrot Georgy
Published: July 2004

Isodar theory was applied to the analysis of habitat selection by a diurnal folivorous gerbil species, Psammomys obesus, in the Central Negev Desert, Israel. In this site, the species demonstrated seasonal habitat shifts, from densely vegetated and well protected dry river beds (wadi) in winter and spring to open and less protected flat terraces in summer and autumn. These shifts were associated with different phenologies of the main foraging plants in the two microhabitats (winter vegetation of Atriplex halimus in the first and summer vegetation of Anabasis articulata in the second). The life history of P. obesus, thus, suggests that in winter and spring the wadi is better both quantitatively and qualitatively, whereas in summer and autumn, river beds are quantitatively poorer but qualitatively better than the flat terraces. Thus, the winter distribution of P. obesus should fit the divergent model of population regulation for quantitatively different habitats while the summer distribution should fit the convergent or crossover model. The analysis of long‐term data supports the predictions for summers and winters following dry autumn conditions but supported the divergent model of population regulation for winters following autumn seasons with high precipitation. The result is consistent with foraging by P. obesus in winters after wet autumns not only on Atriplex and Anabasis, but also on fresh annual plants that are abundant during such winters in both habitats. This assumption was tested and supported by the analysis of annual data on micro‐habitat distribution and diet composition. Thus, the isodar analysis can be used not only as a descriptive technique for habitat selection patterns, but also as a powerful tool for natural history studies. The tight connection between food plants and habitat use is clear evidence that foraging and habitat selection are linked through their joint interactions with the ultimate mechanism maximizing fitness.
Larval growth history determines juvenile growth and survival in a tropical marine fish
Authors: McCormick Mark I. , Hoey Andrew S.
Published: July 2004

Processes that occur around the transition between larval and juvenile life‐stages can have a major effect on the population dynamics of organisms with complex life cycles. We explore the roles of larval history and selective post‐settlement mortality in determining the growth and survival of newly settled individuals of the damselfish,Pomacentrus amboinensis(Pomacentridae). Specifically, we determine whether the direction and intensity of selection on the recruits differs among various size‐classes of predators. A mark‐recapture study showed that individuals who survived 9 or more days were significantly larger at settlement than those that died within the first day (12.3 vs 11.9 mm SL), when mortality was highest (25% d−1). Censuses revealed that the species and size composition of piscivores differed markedly between two reef habitats whereP. amboinensiswas common. A cage experiment, conducted in both habitats, manipulated the sizes of predators that could access newly settledP. amboinensisto determine whether the resulting mortality of the recently settled fish was influenced by larval growth history or size at settlement. Ten days after the start of the experiment individuals that grew slowly in the second half of their larval life had been lost from most of the experimental treatments. Small fish were also selectively lost from the coarse‐mesh cage on the reef base. Significant positive relationships between pre‐ and post‐settlement growth rates were found in both habitats for the fine mesh cages, cage controls and open patch reefs. This relationship was reversed in the coarse mesh cages in both habitats. This growth compensation was facilitated through the action of a particular size range of predators, whose impact was disrupted or masked in the open treatments by the action of a diverse predator pool. The present study underscores the complexity of the processes that influence the early post‐transition growth and survival in organisms with complex life‐histories.
The effect of limited visibility on vigilance behaviour and speed of predator detection: implications for the conservation of granivorous passerines
Authors: Whittingham M. J , Butler S. J , Quinn J. L , Cresswell W.
Published: July 2004

Foraging animals frequently change their pattern of vigilance when they move from a patch with a clear view to one with a relatively obstructed view. This has been widely interpreted as compensation for a reduced ability to detect approaching predators in obstructed habitats. We test the extent to which changes in vigilance may compensate for the effect of reduced visibility on an animal's ability to detect predators. We measured the vigilance, foraging and speed of predator‐response behaviours of lone chaffinches Fringilla coelebs that fed on seeds (800 per m2) scattered on artificial stubble habitats (with either a clear view of surroundings or an obstructed view). On both treatments, individuals with more rapid head‐up rates responded more quickly to a flying model sparrowhawk Accipiter nisus (P=0.04); as did individuals with shorter food‐search times (P=0.02). However, neither head‐up rate nor food‐search period varied with obstruction. Based on research previously published using this system, we suggest that this is because individuals are constrained in their ability to increase head‐up rate because doing so is largely determined by their individually determined foraging efficiency. Instead chaffinches increased the duration of their head‐up periods by 13% in the visually obstructed treatment (long stubble) and peck rates were 13% lower. Despite this presumed attempt to compensate for reduced visibility, duration of head‐up period had no effect on response time of the fast‐moving predator in our experiment and birds were 24% slower to respond in the long stubble. Rather than being maladaptive, increasing head‐up duration may have been related to enhanced detection of other predator types, for example stalkers. Our results have implications for the conservation of wild granivorous birds. They support the view that agroeconomic decisions that affect micro‐habitat structure over a large scale could affect predation risk, habitat choice and the conservation status of granivorous birds.
Seedling growth rate and survival do not predict invasiveness in naturalized woody plants in New Zealand
Authors: J. Bellingham P. , P. Duncan R. , G. Lee W. , P. Buxton R.
Published: July 2004

We tested if plant species invasiveness (measured as rate of geographic spread in New Zealand) was positively associated with seedling relative growth rate (RGR) and survival, among 33 naturalized woody plant species in four families (Fabaceae, Mimosaceae, Pinaceae, Rosaceae). Eight disturbance and fertilization treatments were applied to seedlings in pots to mimic conditions the species are likely to encounter in the wild. We tested if seedlings of more invasive species have higher RGR and greater survival under these conditions. We also tested whether more invasive species had wider tolerance of the conditions to which they were subjected. There were no significant relationships between seedling RGR or survival and invasiveness for any of the treatments. Measures of tolerance (a species’ relative performance across all treatments), based on both RGR and survival, also failed to explain differences in invasiveness. Our findings contrast with those from a recent study by Grotkopp et al. (2002) showing a positive correlation between seedling RGR and invasiveness in Pinus species, even though our study included 12 Pinus species. The findings of the two studies may differ because they focus on different stages in the invasion process. Our study tested whether RGR (and survival) was associated with the rate of spread of invasive species following naturalization, whereas Grotkopp et al. primarily tested whether RGR was associated with the probability of naturalization. We caution that relationships between RGR and measures of invasiveness are likely to be confounded with human introduction effort. Among pines, species with high RGR are more likely to have been widely cultivated, for purposes such as timber production, providing more opportunities for naturalization and spread. Associations between RGR, invasiveness and human introduction effort need to be partitioned out before we can reliably infer causal relationships.
Does increased habitat complexity reduce predation and competition in coral reef fish assemblages?
Authors: Almany Glenn R.
Published: July 2004

Greater habitat complexity is often associated with a greater abundance and diversity of organisms. High complexity habitats may reduce predation and competition, thereby allowing more individuals to occupy a given area. Using 16 spatially isolated reefs in the Bahamas, I tested whether increased habitat complexity reduced the negative effects of resident predators and competitors on recruitment and survival of a common damselfish. Two levels of habitat complexity were cross‐factored with the presence or absence of two guilds of resident fishes: predators (sea basses and moray eels) and interference competitors (large territorial damselfishes). I monitored subsequent recruitment and recruit mortality for 60 days. Residents had strong negative effects on recruitment regardless of habitat complexity. In the presence of residents, recruits suffered high mortality immediately after settlement that was similar on low and high complexity reefs, although high complexity reduced mortality of recruits that survived this early postsettlement period. Comparisons between shelter hole diameters and the sizes of residents suggest that territorial damselfishes and small resident predators could access most shelter holes, whereas large resident predators were excluded from many shelter holes. This study demonstrates that whether habitat complexity reduces predation and competition may depend on several key factors, such as the availability of appropriate shelter, behavioral attributes of interactors, and developmental stage of prey/inferior competitors.
Importance of large and small mammalian herbivores for the plant community structure in the forest tundra ecotone
Authors: Olofsson Johan , E. Hulme Philip , Oksanen Lauri , Suominen Otso
Published: July 2004

Both theoretical arguments and empirical evidence suggests that herbivory in general and mammalian winter herbivory in particular is important in arctic–alpine ecosystems. Although knowledge of the effect of herbivores on specific plants and communities is quite extensive, little is known about the relative impact of large and small vertebrate herbivores and how it might vary among different habitats. To address this key issue, we established exclosures with two different mesh sizes in forest and nearby tundra at three different sites in four contrasting locations in the forest–tundra ecotone in northernmost Sweden and Norway. Plant community composition was recorded annually in three permanent plots within each exclosure and an unfenced control. Local densities of vertebrate herbivores were estimated in spring and autumn from 1998 to 2002.

Reindeer (Rangifer tarandus) were the most abundant large vertebrate while Norwegian lemmings (Lemmus lemmus) and grey‐sided voles (Clethrionomys rufocanus) were the most common small vertebrates. The study reveals that voles and lemmings have larger effects on the vegetation than reindeer in both habitats in all four locations, even though densities of reindeer differ between locations and only two locations experienced lemming peaks during the period of the experiment. The relative abundance of five of the fifteen most common species was significantly influenced by voles and lemmings whereas only a single species was significantly influenced by reindeer. Different analyses give contrasting results on the importance of herbivory in forest versus open heathlands. A principal component analyses revealed that herbivory influenced the vegetation more in open heathlands than in forests. However, an importance index of herbivores did not differ between forest and open heathlands. Moreover, none of the plant species responded differently in the two habitats, when herbivores were removed. Our results suggest that intense and localised selective foraging by small mammals may have a more marked effect on vegetation than transient feeding by reindeer.
Maternal effects and offspring performance: in search of the best method
Authors: Krist Miloš , Remeš Vladimír
Published: July 2004

Traditionally, maternal effects have been treated as a source of troublesome environmental variance that confounds our ability to accurately estimate the genetic basis of the traits of interest. However, the adaptive significance of maternal effects is currently at the centre of the attention of ecologists. Thus, in turn, the genetic basis of traits has become a troublesome source of the genetic resemblance that confounds our ability to accurately estimate the maternal effects of interest. This fact is, however, less widely realized among ecologists. We demonstrate this on the example of studies investigating egg‐size effects on offspring performance in birds. Traditionally this relationship is being studied by cross‐fostering of eggs or young and it is claimed that this design is able to separate the effects of egg size per se. However, a positive covariation between the direct effects of genes and the maternal effects exists for many studied traits, which may result in overestimation of the egg‐size effects on offspring performance in cross‐fostering studies. Within‐clutch comparisons or direct experimental manipulation of the egg size are the approaches that do not suffer from such covariation and therefore give less biased estimates of the egg‐size effects than cross‐fostering studies.
Transnational Migration and the Gender Politics of Scale: Indonesian Domestic Workers in Saudi Arabia
Authors: Silvey Rachel
Published: July 2004

Recent research has begun to explore the dynamics of transnational migration from a feminist perspective, and studies of migrant domestic workers have played a prominent role in pushing forward this work. Emerging simultaneously, but largely separately, are explicit debates within geography about the politics of scale, the social construction of scale, and the gender dimensions of scale. This article develops an analysis of the gender politics of the production of scale, specifically, the ‘transnationalisation’ of Indonesian activist approaches to overseas migrant domestic workers' issues. Based on fieldwork in an Indonesian community in West Java that has recently become a sending area for migrants to Saudi Arabia and interviews with activists representing Indonesian migrant women, the article examines the various gender‐specific ways in which migrant women's rights activists construct and deploy the scales of the body, the nation and the transnational. It argues that activist approaches to migrant domestic workers' rights and the ways in which activists mobilise migrant women's narratives represent sophisticated feminist theoretical approaches to scale. By identifying and exploring the scale theory embedded in activist strategies, the analysis highlights the imbrication of feminist theory with practice, and underscores activists' agency in producing the meanings of specific scales. In so doing, the article is aimed more broadly at elaborating the ambivalent relationship between feminist activism/theory and transnationalism.
Inhabiting the Imaginary: Factory Women at Home on Batam Island, Indonesia
Authors: Mack Jennifer
Published: July 2004

Batam Island, Indonesia, located a short ferry ride away from Singapore, is a place where tourism and industry have been developed simultaneously and a border area where “developed” and “developing” nations meet. Government officials, investing international corporations and the “factory women” who work in the island's industrial estates arrive in Batam ‐ native to none of them ‐ with their own preconceptions and goals. When challenges not foreseen through master planning arise, the authorities cling ever more tightly to their physical and structural development model: the nearby city‐state of Singapore. Conversely, the factory workers who travel intranationally to work in this export processing zone (EPZ) find their objectives contested in the face of the Master Plan, corporate agendas and ethnic fusions characterising this transnational capitalist space.

Entering into the homes of three groups of women migrants living and working in Batam, the relationship between the private realm that they inhabit and the social contexts in which they participate publicly is investigated. Some of the choices that women make at and about home are identified, and their ability to “micro‐resist” these external structures is explored. At home, the dynamic relationship between the Batam development project and the women's own hopes and visions of the place ‐ sometimes parallel and sometimes incongruous ‐ are revealed. As they experience life on Batam, their “social imaginaries” of it are shaped into various new realities, and their homes, removed from the confines of the factory floor, thus become spaces of release from these tensions.
Runaway Brides: Anxieties of Identity among Trafficked Filipina Entertainers in South Korea
Authors: Yea Sallie
Published: July 2004

Although the migration of Filipinas to the Republic of Korea has only a short history, some Filipinas have already begun to form incipient communities around the largest United States military bases there. These communities are formed by an increasing number of women who run away from the military camptown clubs where they work as entertainers, to marry or live in cohabitation/de facto relationships with the enlisted American army personnel (or GIs) whom they meet and develop relationships with while working as entertainers in the GI clubs. Drawing on ethnographic research and interviews with the women in one such camptown, this paper documents their experiences and the dynamics of their marriages as they attempt to negotiate their transition from “trafficked entertainers” to “runaway brides”. Their experiences illustrate the daily tribulations of women who wish to improve their prospects, or more ambitiously, transform their identity whilst abroad, by entering into marriages or similar arrangements, but who continue to be encumbered with the stigma attached to being trafficked entertainers. The discussion in this paper aims to contribute to the literature on Filipina migrants' anxieties about identity in the context of transnational migration.
When the Light of the Home is Abroad: Unskilled Female Migration and the Filipino Family
Authors: Asis Maruja Milagros B. , Huang Shirlena , Yeoh Brenda S.A.
Published: July 2004

The migration of women engaged in transnational domestic work reveals how the uneven impacts of globalisation have intruded into the micro‐world of families and households. In this age of globalisation and migration, family membership has become multisited or transnational, with members dispersed in space. The migration of workers and the separation this entails has raised challenges to notions and ideals of “being family”. Unlike other workers on the move, the migration of domestic workers has some distinctive characteristics. It can be framed in terms of women moving between families and households; workers whose departure from their family of origin and insertion into their family of employment reconstitute the structure and content of family relationships in both material and imagined ways. Drawing on in‐depth interviews conducted in the Philippines and Singapore, we explore how migrant women and their family members define and negotiate family ideals, gender identities and family relationships, given the family's transnational configuration. Our findings provide some support to the notion that individual members in transnational families resort to “relativising” in fashioning responses to their situation.
Gender and Migration Policies in Southeast and East Asia: Legal Protection and Sociocultural Empowerment of Unskilled Migrant Women
Authors: Piper Nicola
Published: July 2004

This paper is concerned with how existing migration policies affect individual migrant women's choices, in particular, with the advancement, or consolidation, of a migrants' rights perspective. The focus is thereby on those migrants classified as unskilled, who constitute the largest and most vulnerable category among migrants. The analysis of migration policies has conventionally been approached from a state/government‐centred viewpoint that sees states as the key actors. This paper, however, emphasises a larger number of actors ‐ governmental and non‐governmental ‐ as well as the power relations among them to argue that protection through “legal regulation” in the absence of actual implementation is an incomplete solution to alleviate unfair labour conditions that migrants in general, and migrant women specifically, experience. Measures designed to “protect” migrants must be accompanied by measures that empower them, a role that has largely been taken on by existing migrant worker non‐governmental organisations (NGOs). Focussing on intra‐Asian migration flows in which Southeast Asia is the main labour sender and East Asia the receiver of Southeast Asian migrants, the paper explores the nexus between law and civic activism in the specific subject area of international labour migration and its gender implications.
Cytolytic Capabilities of Lamina Propria and Intraepithelial Lymphocytes in Normal and Chronically Inflamed Human Intestine
Authors: Melgar S. , Hammarström S. , Öberg Å. , Danielsson Å. , Hammarström M.‐L.
Published: July 2004

Cell‐mediated lymphocyte cytotoxicity in ileum and colon of patients with ulcerative colitis (UC), Crohn's disease (CD) and controls was investigated. Frequencies of cells expressing perforin and Fas‐ligand (FasL) were determined by immunomorphometry. mRNA expression of perforin, granzyme B and FasL in T cells and subsets was assayed by reverse transcriptase‐polymerase chain reaction. Cytotoxicity of intraepithelial and lamina propria lymphocytes was analysed without ex vivo activation in three functional assays: (1) anti‐CD3‐dependent T‐cell receptor (TCR)‐/CD3‐mediated redirected cytotoxicity, (2) Fas‐/FasL‐mediated TCR‐/CD3‐independent cytotoxicity and (3) natural killer (NK) cell cytotoxicity. Inflammation in ileum of CD patients caused increased frequency of perforin‐expressing cells and enhanced perforin‐dependent TCR‐/CD3‐mediated cytotoxicity. In contrast, lymphocytes in the inflamed colon of UC or Crohn's colitis patients did not display this cytotoxicity nor did lymphocytes of normal colon. Normal colon lymphocytes showed spontaneous Fas‐/FasL‐mediated cytotoxicity. This activity was retained but not enhanced in inflamed UC colon. In contrast, a significant increase of FasL‐expressing cells was seen in situ. Inflammation did not induce NK cell activity in colonic lymphocytes. Intestinal lymphocytes comprise effectors active in two different cytolytic processes. ‘Classical’ cytotoxic T lymphocytes in small intestine and lymphocytes executing TCR‐/CD3‐independent FasL‐/Fas‐mediated killing of unknown biological role present throughout the intestinal mucosa. Ongoing normal cytolytic processes seem to be enhanced by chronic inflammation.
Anti‐Class II Antibodies, but not Cytotoxic T‐Lymphocyte Antigen 4–Immunoglobulin Hybrid Molecules, Prevent Rejection of Major Histocompatibility Complex Class II‐Negative Myeloma in T‐Cell Receptor‐Transgenic Mice
Authors: Dembic Z. , Hofgaard P. O. , Omholt H. , Bogen B.
Published: July 2004

We have previously shown that tumour‐specific CD4+ T cells protect against subcutaneous injections of major histocompatibility complex (MHC) class II‐negative MOPC315 myeloma cells. Here, we have interfered with the immunologic events that lead to successful rejection of MOPC315 challenges in T‐cell receptor (TCR)‐transgenic mice. The CD4+ T cells have a transgene‐encoded TCR specific for a MOPC315 V‐region idiotypic (Id) peptide presented on the MHC class II molecule Ed. A side‐by‐side comparison indicated that DNA‐recombination‐deficient TCR‐transgenic mice were better protected against MOPC315 tumour development than recombination‐sufficient counterparts, suggesting that B cells or endogenous TCR chains might facilitate tumour progression in this model. Intraperitoneal injections of Ed‐specific antibodies over a period of initial 24 days, abrogated protection against tumours in both strains of mice. By contrast, injections of anticostimulatory molecules (cytotoxic T‐lymphocyte antigen 4–immunoglobulin hybrid molecules) had no effect. The findings demonstrate that tumour rejection depends on the presence of MHC class II molecules, despite the fact that MOPC315 tumour cells themselves do not express them. The results are consistent with the idea that secreted myeloma protein is processed and presented by class II+ antigen‐presenting cells to Id‐specific naïve CD4+ T cells that become activated and kill the myeloma cells by a bystander mechanism. While Id presentation on class II molecules is absolutely required for tumour rejection, costimulatory CD80/CD86 molecules might be dispensible in this process.
The Potential Role of Mannan‐Binding Lectin in the Clearance of Self‐Components Including Immune Complexes
Authors: Saevarsdottir S. , Vikingsdottir T. , Valdimarsson H.
Published: July 2004

Mannan‐binding lectin (MBL) is a pattern recognition receptor in the innate immune system. It recognizes certain sugar residues arranged in a pattern that enables MBL to bind with sufficient strength. Such sugar patterns are common on the surface of many microorganisms, and MBL has therefore been considered to be an agent that can discriminate between self and nonself. There is, however, increasing evidence supporting that MBL, like many membrane‐bound C‐type lectin‐like receptors, also helps to dispose of various outworn or abnormal body components. Most self‐components are protected with sialic acid or galactose that disrupt the pattern of the sugars that MBL can bind, but MBL may be significantly involved in the elimination of self‐components that have lost these protective terminal residues. The role of MBL in the clearance of invading pathogens has previously been thoroughly reviewed. Here, we review some findings that support the notion that MBL may contribute to noninflammatory removal of immune complexes and abnormal cells by the reticuloendothelial system. Defects in this clearance mechanism may cause an accumulation of potentially dangerous self‐components, thereby increasing the likelihood of chronic inflammation and autoimmunity.
Statin Drugs Do Not Affect Serum Complement Activation In Vitro
Authors: Lappegård K. T. , Hvassing T. , Mollnes T. E.
Published: July 2004

Statin drugs prevent coronary heart disease through anti‐inflammatory mechanisms in addition to the well‐known reduction of low‐density lipoproteins. The complement system plays an essential role in the inflammatory response and has been postulated to be modified by statins. A direct role for statins in complement activation, however, has not been previously investigated. We therefore studied the effect of statins on in vitro complement activation. Pravastatin, atorvastatin and the active metabolite of the latter, ortho‐hydroxy atorvastatin, were added to normal human serum and incubated for 1 h in the absence or presence of aggregated immunoglobulin (classical pathway activation) or cobra venom factor (alternative pathway activation). The degree of complement activation, as detected by specific complement‐activation products for the classical pathway (C1rs‐C1‐inhibitor complexes), the combined classical and lectin pathway (C4bc), the alternative pathway (C3bBbP) and the final common pathway (C3bc and TCC), was not affected by pre‐incubation of the serum with any of the statins. Statins do not affect complement activation directly, but indirect effects in vivo may well be operative.
Apoptotic Effect of Rituximab on Peripheral Blood B Cells in Rheumatoid Arthritis
Authors: Szodoray P. , Alex P. , Dandapani V. , Nakken B. , Pesina J. , Kim X. , Wallis G. L. , Wilson P. C. , Jonsson R. , Centola M.
Published: July 2004

Rituximab (RTX) has proven efficacious in the treatment of rheumatoid arthritis (RA). Herein, we assessed the apoptosis‐inducing capability of RTX in vitro on RA peripheral blood B‐cell subsets and also compared the effects of RTX on B cells from rheumatoid factor‐positive (RF+) and RF– patients. The likely relevance of B cells in disease was assessed by measuring B‐cell‐modulating serum cytokines. Peripheral blood B cells were isolated and cultured with the presence or absence of RTX. The levels of apoptosis within the naïve, memory and IgD+CD27+ B‐cell subpopulations were determined by cytofluorometric analysis and caspase 3/7 assays. Levels of serum cytokines were measured with a multiplex cytokine array system. RTX induced significant apoptosis in all B‐cell subsets in both RA and controls. In naïve and memory B cells from RA patients, RTX induced significantly higher levels of apoptosis than in controls. RTX induced apoptosis of B cells in RF+ and RF– patients. Serum levels of interleukin‐1β (IL‐1β), IL‐4, IL‐10 and IL‐13 were profoundly increased in RF+ patients compared to RF− patients and controls. Although our cohort was small (10 RA patients), the data suggest that RTX induces apoptosis in all investigated subsets of B cells from RA patients. Interestingly, memory B cells from RA patients were more sensitive to RTX than memory cells from normal controls, suggesting that the delay in treatment response to RTX observed in clinical trials may be due in part to memory cell depletion. The apoptotic effects of RTX were similar in RF+ and RF– patients, but serum levels of B‐cell‐activating cytokine levels were only elevated in RF+ but not RF– patients. These data suggest that RTX is less effective in RF– RA because B cells play a less significant role in RA pathogenesis in RF– patients.
Interleukin‐2, But Not Interleukin‐15, is Required to Terminate Experimentally Induced Clonal T‐Cell Anergy
Authors: Bendiksen S. , Rekvig O. P.
Published: July 2004

It has been demonstrated that T cells stimulated with nucleosome–polyomavirus T‐antigen (self–nonself) complexes, but not nucleosomes, activate autoimmune nucleosome‐specific T cells. As these cells may be naïve, such observations do not show that anergic T cells are reactivated. To understand the regulation of autoimmunity, this is important to assess, and this is the focus of this study. T‐Cell anergy was induced by antigen stimulation in the presence of antibodies to the costimulatory molecules CD80/CD86. Requirements for the reactivation of anergic T cells were analysed by the ability of antigen and interleukin‐2 (IL‐2) or IL‐15 to increase T‐cell proliferation and IL‐2 transcription. Data demonstrate that stimulation of T cells with T‐antigen and anti‐CD80/86 antibodies promotes long‐lasting clonal T‐cell anergy. While T‐antigen did not reactivate anergic T cells, proliferation and upregulation of IL‐2 gene transcription was initiated by stimulation with antigen, costimulation and IL‐2 added to the cultures. Proliferation per se was not sufficient to promote the reactivation of anergic T cells, as both IL‐2 and IL‐15 induced proliferation, while antigen and IL‐2, but not IL‐15, upregulated IL‐2 mRNA levels. These data demonstrate that the innate immune system and IL‐2 are central to the initiation and termination of T‐cell anergy.
Antigen‐Specific In Vitro Suppression of Murine Helicobacter pylori‐Reactive Immunopathological T Cells by CD4+CD25+ Regulatory T Cells
Authors: Raghavan S. , Suri‐Payer E. , Holmgren J.
Published: July 2004

A Helicobacter pylori‐specific in vitro coculture system was established and used to study the role of CD4+CD25+ regulatory T cells (Treg) in gastritis development in mice with H. pylori infection. Effects of therapeutic immunization against H. pylori infection on the Treg function were also studied to better understand the mechanisms leading to postimmunization gastritis in these mice. Depletion of Treg led to extensive proliferation to H. pylori antigens of CD4+ T cells isolated from either naïve, H. pylori‐infected or H. pylori‐immunized mice. Using the Treg‐depleted CD4+ T cells from immunized mice as effector cells, we compared the suppressive efficacy of Treg isolated from naïve, infected or immunized mice and found that Treg from naïve mice, and slightly less efficiently from infected mice, suppressed the CD25– effector T‐cell response and in most cases were distinctly more efficacious than Treg isolated from immunized mice. The suppressive efficacy of Treg isolated from the differently treated mice correlated closely with production of interleukin‐5 (IL‐5) by the Treg and suppression of interferon‐γ and IL‐2 production by the CD25– effector T cells. Our study is the first to demonstrate in H. pylori‐induced chronic infection, antigen‐specific Treg with differential efficacy in suppressing H. pylori proinflammatory T effector cells.
Monocytes Stimulated with Group B Streptococci or Interferons Release Tumour Necrosis Factor‐Related Apoptosis‐Inducing Ligand
Authors: Halaas Ø. , Liabakk N.‐B. , Vik R. , Beninati C. , Henneke P. , Sundan A. , Espevik T.
Published: July 2004

Tumour necrosis factor (TNF)‐related apoptosis‐inducing ligand (TRAIL) is a cytotoxic member of the TNF family. Some reports have shown that TRAIL is released from cells in a soluble form. In this work, we have investigated the mechanism of release of TRAIL from monocytes. First, we show that whole gram‐positive, gram‐negative and mycoplasmal bacteria as well as lipopolysaccharide (LPS), interferon‐α (IFN‐α), ‐β and ‐γ all induced upregulation of TRAIL on the surface of human monocytes. Next, we show that IFN‐α, ‐β and ‐γ all induced a dose‐dependent release of TRAIL, giving significant amounts of soluble TRAIL after 2 days. Of the bacteria, only the Group B streptococcus COH‐1 (GBS) induced release of TRAIL and concomittantly induced IFN‐α. Monocytes stimulated with GBS or IFN‐α also showed extensive cell death. When monocyte apoptosis was prevented by interleukin‐1, GM‐CSF, LPS or the caspase inhibitor zVADfmk, the IFN‐α‐induced release of TRAIL was reduced, whereas agents inducing necrosis caused increased release of TRAIL. LPS also prevented release of TRAIL from GBS‐stimulated monocytes. The release of TRAIL from IFN‐α‐stimulated monocytes was reduced by inhibitors of both cysteine and metalloproteases. We conclude that bacteria and IFN induce upregulation of membrane TRAIL and that release of TRAIL is associated with cell death.
If the ‘Adaptive’ Immune System Can Recognize a Significant Portion of the Pathogenic Universe to Which the ‘Innate’ Immune System is Blind, Then…
Authors: Cohn M.
Published: July 2004

The ‘adaptive’ immune repertoire functionally recognizes pathogens (and their toxic products) that the ‘innate’ defense system misses. This requires that the self–nonself discrimination and the regulation of effector output be dependent primarily on somatic learning mechanisms (i.e. on the somatically generated, large, random ‘adaptive’ immune paratopes repertoire).
Characterization of Ribosomal P Autoantibodies in Relation to Cell Destruction and Autoimmune Disease
Authors: Ersvær E. , Bertelsen L.‐T. , Espenes L. C. , Bredholt T. , Bøe S. O. , Iversen B. M. , Bruserud Ø. , Ulvestad E. , Gjertsen B. T.
Published: July 2004

Autoantibodies against the ribosomal P proteins are related to cell death and tissue destruction and are frequently exhibited in patients with systemic lupus erythematosus (SLE). In an attempt to explore the effect of tissue destruction on the induction of anti‐P autoantibodies, we searched for anti‐P autoantibodies by enzyme‐linked immunosorbent assay in 201 antinuclear antibody (ANA)‐positive individuals, in 10 patients with treated kidney SLE and in 45 acute leukaemia patients undergoing intensive chemotherapy. The autoantibody reactivity was further characterized using one‐ and two‐dimensional immunoblot analysis and immunofluorescence. Anti‐P were detected in 5.5% (11/201) of ANA‐positive individuals, but not in kidney‐affected SLE patients or in patients with leukaemia. Seven of 11 anti‐P‐positive patients had SLE (3/11), primary Sjögrens's syndrome (1/11) and other autoimmune diseases (3/11). A relation between disease activity and anti‐P was suggested by follow‐up examinations in one SLE patient, supported by the absence of anti‐P autoantibodies in the 10 treated kidney SLE patients. Anti‐P autoantibodies were detected by immunoblot in one patient with SLE indicating anti‐P2 predominance and in the patient with Sjögrens's syndrome indicating anti‐P1 predominance. Diverging humoral responses in these ANA‐ and anti‐P‐positive patients were further illustrated by immunofluorescence, elucidating varying nuclear reactivity and anti‐P pattern. The observation of anti‐P in individuals with active autoimmune disease, but not in patients with chemotherapy‐induced cell damage, suggests that anti‐P antibodies are part of a specific disease process, and not elicited as a response to cell destruction per se.
Response to Cohn: The Immune System Rejects the Harmful, Protects the Useful and Neglects the Rest of Microorganisms
Authors: Dembic Z.
Published: July 2004

The immune system is seen as a guardian of tissue integrity. It would analyse the extent and quality of damage and respond adequately. If no ill effects were found, the system would ignore disturbance, but if beneficial effects were found, it could protect certain microorganisms (establishing commensalism), perhaps via regulatory cells. The Integrity hypothesis proposes three basic groups of intercellular signals for cells of all tissues and assumes that they govern communication between dendritic cells, T cells and B cells. Signal‐1 would be the main information source resulting with generation of intracellular mediators that are bound to travel into the nucleus to achieve reaction. Signal‐2 represents the generation of additional signal transducers representing a modifier at the level of cytosol. And, signal‐3 would be a modifier at nuclear level, perhaps guarding accessibility to chromosome or genetic locus.
Citrullination of Self‐Proteins and Autoimmunity
Authors: Rubin B. , Sønderstrup G.
Published: July 2004

Citrullination (deimination is an enzymatic, posttranslational conversion of arginine residues to citrulline residues) of joint‐associated self‐proteins may be a possible mechanism in the induction of autoimmune CD4 T‐cell responses in rheumatoid arthritis. We have studied the immune response to normal or deiminated human fibrinogen (hFBG) in mouse strains expressing major histocompatibility complex (MHC) class II antigens similar to either RA‐susceptible or non‐susceptible HLA‐DR4 alleles. Upon immunization with deiminated hFBG, all mouse strains analysed produced high amounts of anti‐FBG antibodies, while relatively low levels of anti‐citrulline antibodies and little or no anti‐FBG antibodies crossreactive with mouse FBG (mFBG) were obtained. Mice immunized with normal hFBG also produced high amounts of anti‐hFBG antibodies. However, whereas mice with MHC class II molecules similar to RA‐non‐susceptible HLA‐DR4 alleles produced low levels of anti‐hFBG antibodies with crossreactivity to mFBG, mouse strains with RA‐susceptible HLA‐DR4‐equivalent MHC class II molecules contained high levels of such crossreactive anti‐mFBG antibodies. Similar results were obtained with HLA‐DR4*0401, human CD4‐double‐transgenic mice. However, none of the more than 600 mice investigated developed arthritis. These data indicate that the quality and/or quantity of anti‐FBG autoantibodies or of anti‐citrulline antibodies, produced in the studied mouse strains, are insufficient to induce arthritis.