Cytokine generation by human basophils
Authors: John T. Schroeder, Donald W. MacGlashan, Anne Kagey-Sobotka, Jane M. White, Lawrence M. Lichtenstein
Journal: Journal of Allergy and Clinical Immunology (1994)

The concept that basophils and mast cells participate in acute allergic reactions is based in part on evidence from studies demonstrating the rapid release of inflammatory mediators including histamine, leukotrienes, and prostaglandins after the activation of these cells by various stimuli. The role that basophils play in complex allergic disease states is less well understood, yet might best be explained by their role in the "late phase response" (LPR) to antigen. After the description of this phenomenon in the early 1970s by Dolovich et al.1Dolovich J Hargreave FF Chalmers R Shier KJ Gauldie J Bienenstock J Late cutaneous allergic responses in isolated IgE-dependent reactions.J Allergy. 1973; 52: 3846Google Scholar and, later, independently by Solley et al.,2Solley GO Gleich GJ Jordan RE Schroeter AL The late phase of the immediate wheal and flare skin reaction: its dependence upon IgE antibodies.J Clin Invest. 1976; 58: 408-420Crossref PubMed Scopus (458) Google Scholar LPRs were soon recognized as clinically relevant models of chronic allergic inflammatory conditions, such as asthma and rhinitis. A prominent feature of these late reactions with regard to cellular infiltrates was the selective migration of eosinophils into reaction sites several hours after challenge with specific antigens. On the basis of the work by Okuda and Ohtsuka3Okuda M Ohtsuka H Basophilic cells in allergic nasal secretions.Arch Otorhinolaryngol. 1977; 214: 283-289Crossref PubMed Scopus (73) Google Scholar in the mid 1970s, which clearly demonstrated that basophils migrate into the nasal mucosa in response to antigen challenge and during the pollen season, it was soon recognized that basophils share similar characteristics with eosinophils. During the past decade extensive work in our laboratory has been directed to the study of this phenomenon and has expanded the concept that basophils actively participate in the LPR. Our results support the involvement of basophils in these chronic inflammatory conditions and provide evidence that these cells infiltrate and secrete their mediators at specific reaction sites in the skin, nose, and lung.4Charlesworth EN Hood AF Soter NA Kagey-Sobotka A Norman PS Lichtenstein LM Cutaneous late-phase response to allergen: mediator release and inflammatory cell infiltration.J Clin Invest. 1989; 83: 1519-1526Crossref PubMed Scopus (247) Google Scholar, 5Bascom R Wachs M Naclerio RM Pipkorn V Galli SJ Lichtenstein LM Basophil influx occurs after nasal antigen challenge: effects of topical corticosteroid pretreatment.J ALLERGY CLIN IMMUNOL. 1988; 81: 580-589Abstract Full Text PDF PubMed Scopus (191) Google Scholar, 6Guo C-B Liu MC Galli SJ Bochner BS Kagey-Sobotka A Lichtenstein LM Identification of IgE-bearing cells in the late phase response to antigen in the lung as basophils.Am J Resp Cell Mol Biol. 1993; 10: 384-390Crossref Scopus (135) Google Scholar Whereas the exact nature of this recruitment remains unclear, this review, with a primary focus on cytokine generation by basophils, aims to expand our understanding of the role these cells play in chronic allergic inflammation. The evidence for cytokine production from cells expressing the high affinity receptor for IgE (FcϵRI) is relatively recent, having originated in studies that were performed with various murine mast cell lines. In the mid 1980s, Chung et al.7Chung SW Wong PMC Shen-Ong G Ruscetti S Ishizaka I Eaves CJ Production of granulocyte-macrophage colony-stimulating factor by Abelson virus–induced tumorigenic mast cell lines.Blood. 1986; 68: 1074-1081PubMed Google Scholar showed that Abelson murine leukemia virus–transformed mast cell lines spontaneously produced granulocyte-macrophage colony-stimulating factor (GM-CSF), as demonstrated by the ability of culture supernatants to support the growth of the FDC/P1 hemopoietic precursor cell line despite the presence of neutralizing antibody to interleukin 3 (IL-3). Additional studies performed by Brown et al.,8Brown MA Pierce JH Watson CJ Falco J Ihle JN Paul WF B cell stimulatory factor-1/interleukin-4 mRNA is expressed by normal and transformed mast cells.Cell. 1987; 50: 809-818Abstract Full Text PDF PubMed Scopus (328) Google Scholar who screened many different cell types, indicated that both transformed and nontransformed mast cell lines expressed mRNA for IL-4. Plaut et al.9Plaut M Pierce JH Watson CJ Hanley HJ Nordan RP Paul WE Mast cell lines produce lymphokines in response to cross-linkage of Fc epsilon RI or to calcium ionophores.Nature. 1989; 339: 64-70Crossref PubMed Scopus (1145) Google Scholar and Wodnar-Filopowicz et al.10Wodnar-Filipowicz A Heusser CH Moroni C Production of the haemopoietic growth factors GM-CSF and interleukin-3 by mast cells in response to IgE receptor-mediated activation.Nature. 1989; 339: 150-152Crossref PubMed Scopus (465) Google Scholar then used IL-3–dependent nontransformed cell lines to show that cytokine production by mast cells could result from the cross-bridging of IgE/receptor complexes or by activation with calcium ionophore. The significance of this functional process, by which FcϵRI-positive cells secrete cytokines after the interaction of receptor-bound IgE with antigen, was strengthened by data showing that the cytokine profile produced by these mast cells (i.e., IL-4, IL-3, IL-5, GM-CSF, IL-1, and IL-6) very much resembled that previously described for activated Th2 lymphocytes.11Mossman TR Cherwinski H Bond MW Giedlin MA Coffman RL Two types of murine helper T-cell clones. I. Definition according to profiles of lymphokine activities and secreted protein.J Immunol. 1986; 136: 2348-2357PubMed Google Scholar Because IL-4 had been shown to have a role in class switching to IgE12Vercelli D Jabara HH Arai K-I Geha RS Induction of human IgE requires interleukin-4 and T/B cell interactions involving the T cell receptor/CD3 complex and MHC class II antigens.J Exp Med. 1989; 169: 1295-1307Crossref PubMed Scopus (356) Google Scholar, 13Del Prete G Maggi E Parronchi P et al.IL-4 is an essential factor for the IgE synthesis induced in vitro by human T cell clones and their supernatants.J Immunol. 1988; 140: 4193-4198PubMed Google Scholar and IL-5 had potent eosinophil growth and differentiation properties,14Sanderson CJ Campbell HD Young IG Molecular and cellular biology of eosinophil differentiation factor (interleukin-5) and its effect on human and mouse B cells.Immunol Rev. 1988; 102: 29-34Crossref PubMed Scopus (238) Google Scholar the production of these cytokines from mast cells and basophils, in concert with the inflammatory mediators commonly released by these cells, supported the concept that these cells might help to amplify and maintain allergic inflammatory responses. The observations that murine mast cell lines generated several cytokines inspired additional studies in mice to test various organ systems for the presence of non–T cells with similar properties. Of the possible cytokines to target, IL-4 was chosen because of the frequency of its appearance in the mast cell lines, its unique biologic properties with regard to allergic inflammation, and because it could be readily assayed by supporting proliferation of the CT.4S T lymphocyte cell line. Using naive mice, Ben-Sasson et al.15Ben-Sasson SZ Le Gros G Conrad DH Finkelman FD Paul WE Cross-linking Fc receptors stimulates splenic non-B, non-T cells to secrete interleukin-4 and other lymphokines.Proc Natl Acad Sci USA. 1989; 87: 1421-1425Crossref Scopus (179) Google Scholar reported cytokine production from a cell population found in spleen after the depletion of T and B lymphocytes. These "non-T, non-B cells" were shown to secrete IL-4 when cultured in microtiter plates that contained wells precoated with IgE and in the presence of IL-3. Culture wells precoated with IgG1, IgG2a, or IgG2b antibody also induced cytokine production from these splenic cells; however, synthesis was very much dependent on IL-3 as a costimulant. Plate-bound IgM and IgA failed to stimulate IL-4 production from these cells. Because soluble IgE inhibited the secretion of IL-4 from these cell cultures, the need for receptor cross-linkage for the induction of protein synthesis was implied and suggested to be mediated through FcϵRI. Subsequent studies reported that splenic non-T, non-B cells, prepared from mice infused with IL-3, showed enhanced IL-4 secretion when stimulated with plate-bound IgE.16Le Gros G Ben-Sasson SZ Conrad DH et al.IL-3 promotes production of IL-4 by splenic non-B, non-T cells in response to Fc receptor cross-linkage.J Immunol. 1990; 145: 2500-2560PubMed Google Scholar Passive sensitization of splenic cells with IgE antibody specific for trinitrophenyl-ovalbumin resulted in IL-4 generation on stimulation with specific antigen, thus providing additional evidence for receptor signalling. An interesting physiologic observation revealed that striking enhancement (up to 10-fold) of the percentages of these non-T, non-B splenic cells occurred in animals after injection with anti-IgD antibody or infection with the helminthic parasite Nippostrongylus brasiliensis, conditions known to elicit an immune response marked by large amounts of polyclonal IgE.17Conrad DH Ben-Sasson SZ Le Gros G Finkelman FD Paul WE Infection with Nippostrongylus brasiliensis or injection of anti-IgD antibodies markedly enhances Fc-receptor–mediated interleukin 4 production by non-B, non-T cells.J Exp Med. 1990; 171: 1497-1508Crossref PubMed Scopus (87) Google Scholar The non-T, non-B splenic cell population closely resembled the mast cell lines discussed previously with respect to the effect of IL-3 treatment and the dependency on IgE-mediated activation for cytokine generation. However, because mature mast cells are not commonly found in the spleen and because these IL-4–producing cells lacked many specific mast cell markers, the exact identification of these "non-T, non-B lymphocytes," which represented approximately 5% of the total cells found in the spleens of naive mice, could not readily be determined. The possibility that these cells represented immature basophils was suggested by studies performed by Seder et al.18Seder RA Paul WE Dvorak AM et al.Mouse splenic and bone marrow cell populations that express high-affinity Fcε receptors and produce interleukin-4 are highly enriched in basophils.Proc Natl Acad Sci USA. 1991; 88: 2835-2839Crossref PubMed Scopus (266) Google Scholar By morphologic analysis with electron microscopy, cytoplasmic granules were seen in many of the cells found in the FcϵR–positive fraction isolated from non-T, non-B spleen and bone marrow cell suspensions that resembled those found specifically in mature basophils. However, because many investigators have disputed the existence of murine basophils, additional studies were conducted to demonstrate whether basophil or mast cell lineages were responsible for the IL-4 production from these non-T, non-B splenic cells. In these experiments, culture conditions were developed favoring either basophil (medium with IL-3) or mast cell (medium with IL-3 and the c-kit ligand) maturation. Stimulation with ionomycin resulted in IL-4 generation only in the basophil cultures. Mast cell cultures, which showed quite homogeneous staining with antibodies specific for the c-kit receptor and FcϵRI, failed to produce IL-4 on activation.19Seder RA Cytokine production by FcεR+ cells.in: Asthma: physiology, immunopharmacology, and treatment. : Academic Press, London1993: 187-196Google Scholar Finally, the identification of "non-T, non-B" cells in human bone marrow that had similar morphologic and physiologic features as those described in mice supported the idea that mature human basophils might generate IL-4.20Piccinni M-P Macchia D Parronchi P et al.Human bone marrow non-B, non-T cells produce interleukin-4 in response to cross-linkage of Fcε and Fcγ receptors.Proc Natl Acad Sci USA. 1991; 88: 8656-8660Crossref PubMed Scopus (101) Google Scholar Studies in several different laboratories have shown the generation and secretion of IL-4 by human basophil cultures after IgE-dependent activation. To date, IL-4 is the only known cytokine reported to be produced by human basophils, and they are a consistent source of high levels of this protein. Brunner et al.21Brunner T Heusser CH Dahinden CA Human peripheral blood basophils primed by interleukin-3 (IL-3) produce IL-4 in response to immunoglobulin E receptor stimulation.J Exp Med. 1993; 177: 605-1110Crossref PubMed Scopus (351) Google Scholar were the first to publish evidence for the release of IL-4 in normal blood basophil cultures with use of suspensions prepared by combining countercurrent elutriation and negative selection techniques to achieve purities ranging from 50% to 97%. In their study the absence or minimal levels of IL-4 protein were reported in cultures treated with anti-IgE receptor antibody alone, despite the use of a wide concentration range of stimulus. However, IL-4 protein levels increased substantially (199 ± 10 pg/106 basophils), as did leukotriene C4 (LTC4) generation (nearly sevenfold), if basophil cultures were pretreated with IL-3 for 18 hours before stimulation. With the exception of a few donors, IL-4 was not detected in cultures receiving only IL-3. The secretion of IL-4 by IL-3–primed basophils was observed over a broad range of anti-IgE receptor antibody concentrations (0.1 to 1000 ng/ml), with optimal production occurring at 5 ng/ml. Related cytokines, such as IL-5 and GM-CSF, did not have the same priming effect that IL-3 had on basophil-derived IL-4. In a study by Arock et al.22Arock M Merle-Beral H Dugas B et al.IL-4 release by human leukemic and activated normal basophils.J Immunol. 1993; 151: 1441-1447PubMed Google Scholar that used human leukemic and bone marrow–derived basophils, IL-3 was also found to be essential for the development of cells expressing IL-4 message and secreting protein. Contrary to these findings, we found that long pretreatment with IL-3 before stimulation with anti-IgE antibody was not an absolute requirement for the secretion of IL-4 from pure (88% to 99%) basophils.23MacGlashan Jr, DM White JM Huang S-K Ono SJ Schroeder JT Lichtenstein LM Secretion of interleukin-4 from human basophils: the relationship between IL-4 mRNA and protein in resting and stimulated basophils.J Immunol. 1994; 152: 3006-3016PubMed Google Scholar However, the IL-4 levels in cultures that received no IL-3 or a short (15-minute) pretreatment with this cytokine were nearly tenfold less than those from highly purified cells pretreated for 18 hours. The kinetics of IL-4 secretion in basophil cultures suggest that this cytokine is generated de novo on activation with stimulus and is not stored and released on degranulation, as has been suggested for some mast cell–derived cytokines.24Gordon JR Galli SJ Mast cells as a source of both preformed and immunologically inducible TNF-α/cachectin.Nature. 1990; 346: 274-276Crossref PubMed Scopus (938) Google Scholar Unlike the rapid release of inflammatory mediators that occurs during degranulation or within minutes after stimulation, 1 to 2 hours are needed before IL-4 protein is first detected in basophil cultures, with levels peaking at 4 to 6 hours.21Brunner T Heusser CH Dahinden CA Human peripheral blood basophils primed by interleukin-3 (IL-3) produce IL-4 in response to immunoglobulin E receptor stimulation.J Exp Med. 1993; 177: 605-1110Crossref PubMed Scopus (351) Google Scholar, 23MacGlashan Jr, DM White JM Huang S-K Ono SJ Schroeder JT Lichtenstein LM Secretion of interleukin-4 from human basophils: the relationship between IL-4 mRNA and protein in resting and stimulated basophils.J Immunol. 1994; 152: 3006-3016PubMed Google Scholar In addition, the ability of cycloheximide to completely ablate the secretion of IL-4 protein indicates that protein synthesis is necessary for the generation of this cytokine in basophils. However, the time required for IL-4 protein release is considerably less than the 12 to 16 hours required for IL-4 production by antigen-stimulated T lymphocytes.25Gagnon R Akoum A Hebert J Lol p I–induced IL-4 and IFN-γ production by peripheral blood mononuclear cells of atopic and nonatopic subjects during and out of the pollen season.J ALLERGY CLIN IMMUNOL. 1993; 91: 950-956Abstract Full Text PDF PubMed Scopus (27) Google Scholar That the cytokine message for IL-4 is rapidly translated in basophils is demonstrated by our data indicating that resting blood basophils constitutively express IL-4 mRNA (approximately 10 to 50 copies per cell), as shown by Northern blot and reverse transcriptase polymerase chain reaction analysis. In addition, we have data indicating that IL-4 mRNA accumulates in response to stimulation, although the precise stimulation index has not been quantitated. In contrast, interferon-γ mRNA was not detected in any of the basophil preparations tested, which mimicked studies in murine mast cell lines and bone marrow mast cells that show that only cytokines of the Th2-like profile are secreted after IgE-mediated stimulation.23MacGlashan Jr, DM White JM Huang S-K Ono SJ Schroeder JT Lichtenstein LM Secretion of interleukin-4 from human basophils: the relationship between IL-4 mRNA and protein in resting and stimulated basophils.J Immunol. 1994; 152: 3006-3016PubMed Google Scholar As was true for the murine non-T, non-B cells, it was not clear whether basophils represented the sole source of secreted IL-4 or whether activated basophils promoted the generation of this cytokine from the few contaminating mononuclear cells also present in these suspensions. To address this question, we used cultures in which the percentage of basophils was varied while the total cell number was kept constant and found that the presence of both IL-4 protein and mRNA was strictly a function of the basophil purity, with no contribution by the contaminating cells.23MacGlashan Jr, DM White JM Huang S-K Ono SJ Schroeder JT Lichtenstein LM Secretion of interleukin-4 from human basophils: the relationship between IL-4 mRNA and protein in resting and stimulated basophils.J Immunol. 1994; 152: 3006-3016PubMed Google Scholar Because the methods used for the purification of blood basophils often affect the responsiveness of these cells to various stimuli and thus might influence our findings, we investigated several parameters of IgE-dependent IL-4 generation with enriched basophil suspensions (5% to 30%), prepared rapidly from whole blood.26Schroeder JT MacGlashan Jr, DW Kagey-Sobotka A White JM Lichtenstein LM IgE-dependent IL-4 secretion by human basophils: the relationship between cytokine production and histamine release in mixed leukocyte cultures.J Immunol. 1994; 153: 1808-1817PubMed Google Scholar Histamine was measured in parallel with IL-4 to allow comparisons with cytokine production. As with very pure basophils, no significant correlation was found (r = 0.21, p = 0.34) between the basophil purity and the amount of IL-4 detected in these mixed cell cultures, which is consistent with the notion that contaminating cells do not contribute to the measurable IL-4 released after IgE-dependent stimulation. Importantly, activation of these same basophil-enriched cultures with a nonspecific stimulus (such as calcium ionophore [A23187]) that can stimulate all peripheral blood mononuclear cells, caused secretion of IL-4 that could essentially be accounted for on the basis of the basophil content. Experiments investigating the dose-response relationship of anti-IgE stimulation showed that IL-4 secretion is optimal at lower concentrations than those necessary for optimal histamine release. Maximal IL-4 generation routinely occurred at 10 ng/ml of anti-IgE, whereas histamine release peaked at 100 ng/ml. As a result, IL-4 production had a relatively sharp dose response curve (Fig. 1). These IL-4 curves reproduced our observations using pure basophil suspensions23MacGlashan Jr, DM White JM Huang S-K Ono SJ Schroeder JT Lichtenstein LM Secretion of interleukin-4 from human basophils: the relationship between IL-4 mRNA and protein in resting and stimulated basophils.J Immunol. 1994; 152: 3006-3016PubMed Google Scholar and were very similar to the distinctive antigen dose-response patterns observed with murine mast cell lines.9Plaut M Pierce JH Watson CJ Hanley HJ Nordan RP Paul WE Mast cell lines produce lymphokines in response to cross-linkage of Fc epsilon RI or to calcium ionophores.Nature. 1989; 339: 64-70Crossref PubMed Scopus (1145) Google Scholar Cross-linking of IgE/receptor complexes with anti-IgE alone led to abundant IL-4 synthesis in these mixed cell cultures, yielding up to 400 pg of IL-4 protein/106 basophils, nearly 10-fold higher than that from pure basophil cultures receiving the same stimulus. Unlike the studies by Brunner et al.,21Brunner T Heusser CH Dahinden CA Human peripheral blood basophils primed by interleukin-3 (IL-3) produce IL-4 in response to immunoglobulin E receptor stimulation.J Exp Med. 1993; 177: 605-1110Crossref PubMed Scopus (351) Google Scholar IL-3 pretreatment again was not an absolute necessity for IL-4 secretion. However, protein levels were consistently enhanced by 40% to 130% (as was histamine release) when cultures were pretreated with IL-3 for just 15 minutes. On the basis of these observations, it appears likely that basophils subjected to the stresses occurring during purification produce less IL-4 protein in response to IgE-dependent stimulation than do those in freshly isolated enriched cultures and that IL-3 pretreatment may simply function to restore cytokine releasability after purification. To our surprise, these basophil-enriched suspensions, which were prepared by Percoll density gradient centrifugation, generated less IL-4 in response to IgE-mediated stimulation if primed with IL-3 for more than 15 minutes. Cultures treated for an additional 45 minutes (1 hour total) with IL-3 produced 90% ± 3% of that produced when cultures were primed for 15 minutes, and IL-4 synthesis was reduced to 42% ± 7% of control IL-4 after 4 hours. After 18 hours of IL-3 priming, the cultures almost completely lost the ability to secrete IL-4, dropping to 13% ± 5% of the control IL-4.26Schroeder JT MacGlashan Jr, DW Kagey-Sobotka A White JM Lichtenstein LM IgE-dependent IL-4 secretion by human basophils: the relationship between cytokine production and histamine release in mixed leukocyte cultures.J Immunol. 1994; 153: 1808-1817PubMed Google Scholar Although the reason for this effect is unclear, preliminary experiments that used very pure basophils to which various cell fractions were "added back" indicate that basophils pretreated for 18 hours with IL-3 in the presence of monocytes lose the ability to secrete IL-4 on activation with anti-IgE; this is not seen when basophils are cocultured with B or T lymphocyte containing fractions (J. T. Schroeder, unpublished observations, March 1994). These results suggest that some product of monocytes can down-regulate IL-4 production in human basophils; we are currently investigating this hypothesis. In additional studies of IgE-dependent IL-4 secretion from basophil-enriched cultures, no significant differences between cytokine levels generated from basophils of allergic and nonallergic persons were seen.26Schroeder JT MacGlashan Jr, DW Kagey-Sobotka A White JM Lichtenstein LM IgE-dependent IL-4 secretion by human basophils: the relationship between cytokine production and histamine release in mixed leukocyte cultures.J Immunol. 1994; 153: 1808-1817PubMed Google Scholar Challenge with an optimal dose (10 ng/ml) of anti-IgE in donors with similar histamine releasability caused release of approximately 190 pg/106 basophils from nonatopic donors (range = 30 to 540 pg/106 cells, n = 8/9) and 200 pg/106 basophils in the atopic group (range =40-630 pg/106 cells, n = 7/8). As expected, only with atopic donor cells did IL-4 secretion occur using specific antigens, which provides additional support for the role of IgE/receptor cross-linking signals in cytokine production by basophils. Although a body of evidence suggests an association between histamine release and the ability to generate IL-4, we believe that the mechanisms controlling these two activities in basophils diverge at some point in the signal transduction network. Whereas the dissociation of the anti-IgE dose response curves for histamine release and cytokine production first suggested separate control, additional observations support this hypothesis. First, the IgE-independent secretogogues, N-formyl-methionyl-leucyl-phenylalanine and C5a, although potent activators of histamine release, induce little to no IL-4 generation in basophil cultures.26Schroeder JT MacGlashan Jr, DW Kagey-Sobotka A White JM Lichtenstein LM IgE-dependent IL-4 secretion by human basophils: the relationship between cytokine production and histamine release in mixed leukocyte cultures.J Immunol. 1994; 153: 1808-1817PubMed Google Scholar The lack of cytokine production was evident in both enriched and highly purified basophil cultures that used several different concentrations of these stimuli (Fig. 2). Secondly, the amount of IL-4 secreted in basophil cultures could be enhanced two- to three-fold by increasing the extracellular calcium levels from 1.4 mmol/L to 5.0 mmol/L, with no significant increases in the percentage of histamine released.26Schroeder JT MacGlashan Jr, DW Kagey-Sobotka A White JM Lichtenstein LM IgE-dependent IL-4 secretion by human basophils: the relationship between cytokine production and histamine release in mixed leukocyte cultures.J Immunol. 1994; 153: 1808-1817PubMed Google Scholar Third, in studies that we have begun to investigate the pharmacologic control of IL-4 secretion by basophils, drugs that are known to increase intracellular levels of cyclic adenosine monophosphate (e.g., 3-isobutyl-1-methylxanthine, Forskolin, and N6,O2′-dibutyryladenosine 3′-5′-cyclic monophosphoric acid [dbcAMP]) and which have been previously shown to inhibit histamine (and LTC4) release actually augment (by 20% to 60%) IgE-dependent IL-4 protein generation in basophils more highly purified (50% to 80%) using elutriation/Percoll density centrifugation and pretreated 18 hours with IL-3.27Schroeder JT MacGlashan Jr, DW Kagey-Sobotka A Lichtenstein LM IgE-dependent IL-4 secretion by basophils in mixed leukocyte cultures.J ALLERGY CLIN IMMUNOL. 1994; 93 ([Abstract]): 214Google Scholar In contrast, in enriched cell cultures (5% to 30% basophils) prepared from whole blood and pretreated for just 15 minutes with IL-3, these same drugs inhibit both histamine release and IL-4 secretion (J. T. Schroeder, unpublished observations, March 1994). These findings, taken together, suggest that prolonged exposure to IL-3, as might occur in chronic inflammation, may have profound effects on signal transduction in basophils. In addition, differences in the mechanisms that control cytokine generation versus those necessary for the release of other mediators suggest that the pharmacologic control of these various proinflammatory properties may require the targeting of individual pathways in basophils. As alluded to previously, it is our conviction that basophils participate in chronic inflammation by selectively infiltrating sites of allergic reactions, as suggested by their participation in the clinically relevant LPR to antigen. It was originally thought that the mediators released (histamine and LTC4) from basophils during chronic reactions might function directly to prolong the inflammatory response. Because basophils represent an acute source of IL-4 (and possibly additional cytokines), these cells are also capable of influencing the immune response of other cells, perhaps acting to amplify the overall inflammatory reaction. Thus the synthesis of IgE and IgG4 antibodies from human peripheral blood mononuclear cells, which is dependent on the costimulatory effects of IL-4,28Vercelli D Geha RS Regulation of IgE synthesis in humans: a tale of two signals.J ALLERGY CLIN IMMUNOL. 1991; 88: 285-295Abstract Full Text PDF PubMed Scopus (114) Google Scholar suggests that basophil-derived cytokines may have a role in this production. A more direct function of basophil-derived IL-4 might be its effects on eosinophils and T lymphocytes. Because the adherence and selective transmigration of eosinophils are partially controlled by the actions of IL-4 on endothelium,29Moser R Fehr J IL-4 controls the selective endothelium-driven transmigration of eosinophils from allergic individuals.J IMMUNOL. 1992; 149: 1432-1438PubMed Google Scholar, 30Schleimer RP Sterbinsky SA Kaiser J et al.IL-4 induces adherence of human eosinophils and basophils but not neutrophils to endothelium.J Immunol. 1992; 148: 1086-1092PubMed Google Scholar the accumulation of these cells at sites of allergic inflammation may be dependent on basophil activation. In addition, a substantial amount of evidence now indicates that the development of Th2 and Th1 CD4 + lymphocytes is regulated by the actions of IL-4 and interferon-γ, respectively, on naive cells.31Abehsira-Amar O Gilbert M Jolly M Theze J Jankovic D.Lj IL-4 plays a dominant role in the differential development of Th0 into Th1 and Th2 cells.J Immunol. 1992; 148: 3820-3829PubMed Google Scholar, 32Swain SL Weinberg AD English M Huston G IL-4 directs the development of Th2-like helper effectors.J Immunol. 1990; 145: 3796-3806PubMed Google Scholar Thus the cytokine profile at sites of allergic inflammation may be significantly affected by basophil-derived IL-4, because of the fact that there is a predominance of cells of the Th2-like phenotype. In this scenario, basophils capable of responding to allergen, coinfiltrating with lymphocytes, could indeed serve as an amplification mechanism because (although generally perceived to represent a small percentage of the infiltrate) they would most likely outnumber the antigen-specific T cells entering these sites. However, whether one or more of these hypotheses holds up, the fact that basophils release both potent inflammatory mediators and immunoregulatory cytokines underscores their important role in chronic allergic inflammation and suggests that studies of basophil activation and its pharmacologic control will lead to useful therapies for allergic and inflammatory disorders.