bluuebunny/crossref_metadata_2025_split huggingface dataset:
Central Role for MyD88 in the Responses of Microglia to Pathogen-Associated Molecular Patterns
Authors: Esen Nilufer , Kielian Tammy 
Published: April 2014

Abstract
Microglia, the innate immune effector cells of the CNS parenchyma, express TLR that recognize conserved motifs of microorganisms referred to as pathogen-associated molecular patterns (PAMP). All TLRs identified to date, with the exception of TLR3, use a common adaptor protein, MyD88, to transduce activation signals. Recently, we reported that microglial activation in response to the Gram-positive bacterium Staphylococcus aureus was not completely attenuated following TLR2 ablation, suggesting the involvement of additional receptors. To assess the functional role of alternative TLRs in microglial responses to S. aureus and its cell wall product peptidoglycan as well as the Gram-negative PAMP LPS, we evaluated primary microglia from MyD88 knockout (KO) and wild-type mice. The induction of TNF-α, IL-12 p40, and MIP-2 (CXCL2) expression by S. aureus- and peptidoglycan-stimulated microglia was MyD88 dependent, as revealed by the complete inhibition of cytokine production in MyD88 KO cells. In addition, the expression of additional pattern recognition receptors, including TLR9, pentraxin-3, and lectin-like oxidized LDL receptor-1, was regulated, in part, via a MyD88-dependent manner as demonstrated by the attenuated expression of these receptors in MyD88 KO microglia. Microglial activation was only partially inhibited in LPS-stimulated MyD88 KO cells, suggesting the involvement of MyD88-independent pathways. Collectively, these findings reveal the complex mechanisms for microglia to respond to diverse bacterial pathogens, which occur via both MyD88-dependent and -independent pathways.
The TCR Cβ FG Loop Regulates αβ T Cell Development
Authors: Touma Maki , Chang Hsiu-Ching , Sasada Tetsuro , Handley Maris , Clayton Linda K. , Reinherz Ellis L. 
Published: April 2014

AbstractThe TCRβ chain constant domain contains an unusually elongated, solvent-exposed FG loop. This structural element forms one component of an αβ TCR cavity against which CD3εγ may abut to facilitate Ag-specific signaling. Consistent with this notion, in the present study we show that N15αβ TCR transfectants expressing a FG loop-deleted chain (βΔFG) stimulate less tyrosine protein phosphorylation than those bearing a wild-type β-chain (βwt) upon TCR cross-linking. Furthermore, coimmunoprecipitation studies suggest a weakened association between the CD3εγ heterodimer and the β-chain in TCR complexes containing the βΔFG variant. To further investigate the biologic role of the Cβ FG loop in development, we competitively reconstituted the thymus of Ly5 congenic or RAG-2−/− mice using bone marrow cells from βwt or βΔFG transgenic C57BL/6 (B6) mice. Both βwt and βΔFG precursor cells generate thymocytes representative of all maturational stages. However, βΔFG-expressing thymocytes dominate during subsequent development, resulting in an excess of βΔFG-expressing peripheral T cells with reduced proliferative and cytokine production abilities upon TCR stimulation. Collectively, our results show that the unique Cβ FG loop appendage primarily controls αβ T cell development through selection processes.
A Role for MAPK in Feedback Inhibition ofTcrbRecombination
Authors: Jackson Annette M. , Krangel Michael S. 
Published: April 2014

AbstractThe Tcrb locus is subject to a host of regulatory mechanisms that impart a strict cell and developmental stage-specific order to variable (V), diversity (D), and joining (J) gene segment recombination. The Tcrb locus is also regulated by allelic exclusion mechanisms, which restrict functional rearrangements to a single allele. The production of a functional rearrangement in CD4−CD8− double-negative (DN) thymocytes leads to the assembly of a pre-TCR and initiates signaling cascades that allow for DN to CD4+CD8+ double-positive (DP) differentiation, proliferation, and feedback inhibition of further Vβ to DJβ rearrangement. Feedback inhibition is believed to be controlled, in part, by the loss of Vβ gene segment accessibility during the DN to DP transition. However, the pre-TCR signaling pathways that lead to the inactivation of Vβ chromatin have not been determined. Because activation of the MAPK pathway is documented to promote DP differentiation in the absence of allelic exclusion, we characterized the properties of Vβ chromatin within DP thymocytes generated by a constitutively active Raf1 (Raf-CAAX) transgene. Consistent with previous reports, we show that the Raf-CAAX transgene does not inhibit Tcrb recombination in DN thymocytes. Nevertheless, DP thymocytes generated by Raf-CAAX signals display normal down-regulation of Vβ segment accessibility and normal feedback inhibition of the Vβ to DJβ rearrangement. Therefore, our results emphasize the distinct requirements for feedback inhibition in the DN and DP compartments. Although MAPK activation cannot impose feedback in DN thymocytes, it contributes to feedback inhibition through developmental changes that are tightly linked to DN to DP differentiation.
Growth, Differentiation, and Malignant Transformation of Pre-B Cells Mediated by Inducible Activation of v-Abl Oncogene
Authors: Jacobsen Elizabeth A. , Ananieva Olga , Brown Matthew L. , Chang Yung 
Published: April 2014

Abstract
The nonreceptor tyrosine kinase, encoded by the v-Abl oncogene of Abelson murine leukemia virus induces transformation of progenitor B cells. The v-Abl oncogene promotes cell cycle progression and inhibits pre-B cell differentiation. The temperature-sensitive form of Abelson murine leukemia virus offers a reversible model to study the role of v-Abl in regulating growth and differentiation. Inactivation of v-Abl elevates p27 and Foxo3a levels and activates NF-κB/Rel, which leads to G1 arrest and induction of Ig L chain gene rearrangement, respectively. In turn, v-Abl reactivation reduces p27 and Foxo3a levels, thus permitting G1-arrested cells to reenter the cell cycle. However, the cell lines derived from SCID mice that are defective in the catalytic subunit of DNA-dependent protein kinase retain elevated levels of p27 and Foxo3a proteins despite reactivation of v-Abl. Consequently, these cells are locked in the G1 phase for an extended period of time. The few cells that manage to bypass the G1 arrest become tumorigenic and fail to undergo pre-B cell differentiation induced by v-Abl inactivation. Deregulation of p27, Foxo3a, c-myc, and NF-κB/Rel was found to be associated with the malignant transformation of SCID temperature-sensitive form of Abelson murine leukemia virus pre-B cells.
Identification of a Candidate Regulatory Element within the 5′ Flanking Region of the MouseIghLocus Defined by Pro-B Cell-Specific Hypersensitivity Associated with Binding of PU.1, Pax5, and E2A
Authors: Pawlitzky Inka , Angeles Christina V. , Siegel Andrea M. , Stanton Michelle L. , Riblet Roy , Brodeur Peter H. 
Published: April 2014

AbstractThe Igh locus is controlled by cis-acting elements, including Eμ and the 3′ IgH regulatory region which flank the C region genes within the well-studied 3′ part of the locus. Although the presence of additional control elements has been postulated to regulate rearrangements of the VH gene array that extends to the 5′ end of the locus, the 5′ border of Igh and its flanking region have not been characterized. To facilitate the analysis of this unexplored region and to identify potential novel control elements, we physically mapped the most D-distal VH segments and scanned 46 kb of the immediate 5′ flanking region for DNase I hypersensitive sites. Our studies revealed a cluster of hypersensitive sites 30 kb upstream of the most 5′ VH gene. Detection of one site, HS1, is restricted to pro-B cell lines and HS1 is accessible to restriction enzyme digestion exclusively in normal pro-B cells, the stage defined by actively rearranging Igh-V loci. Sequence motifs within HS1 for PU.1, Pax5, and E2A bind these proteins in vitro and these factors are recruited to HS1 sequence only in pro-B cells. Transient transfection assays indicate that the Pax5 binding site is required for the repression of transcriptional activity of HS1-containing constructs. Thus, our characterization of the region 5′ of the VH gene cluster demonstrated the presence of a single cluster of DNase I hypersensitive sites within the 5′ flanking region, and identified a candidate Igh regulatory region defined by pro-B cell-specific hypersensitivity and interaction with factors implicated in regulating V(D)J recombination.
The Fas-Associated Death Domain Protein Is Required in Apoptosis and TLR-Induced Proliferative Responses in B Cells
Authors: Imtiyaz Hongxia Z. , Rosenberg Stephen , Zhang Yuhang , Rahman Ziaur S. M. , Hou Ying-Ju , Manser Tim , Zhang Jianke 
Published: April 2014

Abstract
The Fas-associated death domain protein (FADD)/Mort1 is a signaling adaptor protein which mediates the activation of caspase 8 during death receptor-induced apoptosis. Disruption of FADD in germ cells results in death receptor-independent embryonic lethality in mice. Previous studies indicated that in addition to its function in apoptosis, FADD is also required in peripheral T cell homeostasis and TCR-induced proliferative responses. In this report, we generated B cell-specific FADD-deficient mice and showed that deletion of FADD at the pro-B cell stage had minor effects on B cell development in the bone marrow, and resulted in increased splenic and lymph node B cell numbers and decreased peritoneal B1 cell numbers. As in T cells, a FADD deficiency inhibited Fas-induced apoptosis in B cells. However, B cell-proliferative responses induced by stimulation of the BCR and CD40 using anti-IgM or anti-CD40 Abs were unaffected by the absence of FADD. Further analyses revealed that FADD-deficient B cells were defective in proliferative responses induced by treatments with dsRNA and LPS which stimulate TLR3 and TLR4, respectively. Therefore, in addition to its apoptotic function, FADD also plays a role in TLR3- and TLR4-induced proliferative responses in B cells.
Precursor B Cell Receptor Signaling Activity Can Be Uncoupled from Surface Expression
Authors: Guloglu F. Betul , Roman Christopher A. J. 
Published: April 2014

AbstractSignals from the precursor BCR (preBCR) cause proliferation and differentiation of progenitor (pro-) B cells into pre-B cells. Given the very low amounts of surface preBCRs and the demonstrated cell autonomy of preBCR signaling, we examined the possible occurrence of preBCR signal propagation from intracellular membranes such as the endoplasmic reticulum (ER) and the trans-Golgi network (TGN) in transformed and primary pro-B cells. PreBCRs composed of normal Ig μ or truncated Dμ heavy chains (HCs) were redirected to intracellular sites via localization sequences appended to the HC cytoplasmic tail. PreBCR complexes retained in the TGN or shunted from the TGN to lysosomes were as or 50% as active as the corresponding wild-type preBCRs in directing preBCR-dependent events, including CD2 and CD22 expression and proliferation in primary pro-B cells. This occurred despite their low to undetectable surface expression in transformed cells, which otherwise allowed significant surface accumulation of wild-type preBCRs. In contrast, ER-retained preBCRs were inactive. These results suggest that preBCR signaling is remarkably tolerant of dramatic changes in its subcellular distribution within post-ER compartments and support the possibility that the preBCR can activate signaling pathways in the TGN as well as the plasma membrane.
Evidence for a Domain-Swapped CD4 Dimer as the Coreceptor for Binding to Class II MHC
Authors: Maekawa Akiko , Schmidt Bryan , Fazekas de St. Groth Barbara , Sanejouand Yves-Henri , Hogg Philip J. 
Published: April 2014

Abstract
CD4 is a coreceptor for binding of T cells to APC and the primary receptor for HIV. The disulfide bond in the second extracellular domain (D2) of CD4 is reduced on the cell surface, which leads to formation of disulfide-linked homodimers. A large conformational change must take place in D2 to allow for formation of the disulfide-linked dimer. Domain swapping of D2 is the most likely candidate for the conformational change leading to formation of two disulfide-bonds between Cys130 in one monomer and Cys159 in the other one. Mild reduction of the extracellular part of CD4 resulted in formation of disulfide-linked dimers, which supports the domain-swapped model. The functional significance of dimer formation for coreceptor function was tested using cells expressing wild-type or disulfide-bond mutant CD4. Eliminating the D2 disulfide bond markedly impaired CD4’s coreceptor function. Modeling of the complex of the TCR and domain-swapped CD4 dimer bound to class II MHC and Ag supports the domain-swapped dimer as the immune coreceptor. The known involvement of D4 residues Lys318 and Gln344 in dimer formation is also accommodated by this model. These findings imply that disulfide-linked dimeric CD4 is the preferred coreceptor for binding to APC.
Development and Selection of Edited B Cells in B6.56R Mice
Authors: Sekiguchi Debora R. , Yunk Lenka , Gary David , Charan Deepshikha , Srivastava Bhaskar , Allman David , Weigert Martin G. , Prak Eline T. Luning 
Published: April 2014

AbstractTolerance to dsDNA is broken in mice with a high-affinity anti-DNA H chain transgene, 56R, on the C57BL/6 background (B6.56R). B6.56R produce more anti-dsDNA Abs than BALBc.56R. To investigate how anti-DNA Abs are regulated on the B6 background, phenotypic and genetic studies were performed. B6.56R have reduced numbers of B cells and phenotypically altered B cell subsets, including relative increases in the proportions of IgM-negative bone marrow B cells, cells with a marginal zone phenotype, and cells with a transitional T3 phenotype. The peripheral B cell repertoire in B6.56R is restricted: most B cells express the 56R H chain and use a similar, limited subset of editor L chains. DNA binding is more common in B6.56R because the repertoire is shifted toward L chains that are more permissive for DNA binding. H chain editing is also observed and is increased in spontaneous as compared with LPS hybridomas. A subset of spontaneous hybridomas appears to lack H chain expression.
Immunologic Consequences ofFrancisella tularensisLive Vaccine Strain Infection: Role of the Innate Immune Response in Infection and Immunity
Authors: Cole Leah E. , Elkins Karen L. , Michalek Suzanne M. , Qureshi Nilofer , Eaton Linda J. , Rallabhandi Prasad , Cuesta Natalia , Vogel Stefanie N. 
Published: April 2014

AbstractFrancisella tularensis (Ft), a Gram-negative intracellular bacterium, is the etiologic agent of tularemia. Although attenuated for humans, i.p. infection of mice with &lt;10 Ft live vaccine strain (LVS) organisms causes lethal infection that resembles human tularemia, whereas the LD50 for an intradermal infection is &gt;106 organisms. To examine the immunological consequences of Ft LVS infection on the innate immune response, the inflammatory responses of mice infected i.p. or intradermally were compared. Mice infected i.p. displayed greater bacterial burden and increased expression of proinflammatory genes, particularly in the liver. In contrast to most LPS, highly purified Ft LVS LPS (10 μg/ml) was found to be only minimally stimulatory in primary murine macrophages and in HEK293T cells transiently transfected with TLR4/MD-2/CD14, whereas live Ft LVS bacteria were highly stimulatory for macrophages and TLR2-expressing HEK293T cells. Despite the poor stimulatory activity of Ft LVS LPS in vitro, administration of 100 ng of Ft LVS LPS 2 days before Ft LVS challenge severely limited both bacterial burden and cytokine mRNA and protein expression in the absence of detectable Ab at the time of bacterial challenge, yet these mice developed a robust IgM Ab response within 2 days of infection and survived. These data suggest that prior administration of Ft LVS LPS protects the host by diminishing bacterial burden and blunting an otherwise overwhelming inflammatory response, while priming the adaptive immune response for development of a strong Ab response.
HIV-1 Adapts to a Retrocyclin with Cationic Amino Acid Substitutions That Reduce Fusion Efficiency of gp41
Authors: Cole Amy L. , Yang Otto O. , Warren Andrew D. , Waring Alan J. , Lehrer Robert I. , Cole Alexander M. 
Published: April 2014

Abstract
Retrocyclin (RC)-101 is a cationic θ-defensin that inhibits HIV-1 entry. Passaging HIV-1BAL under selective pressure by this cyclic minidefensin resulted in only a 5- to 10-fold decrease in viral susceptibility to RC-101. Emergent viral isolates had three amino acid substitutions in their envelope glycoprotein. One was in a CD4-binding region of gp120, and the others were in the heptad repeat (HR) domains of gp41 (HR1 and HR2). Each mutation replaced an electroneutral or electronegative residue with one that was positively charged. These mutations were evaluated either alone or in combination in a single-round viral entry assay. Although the mutation in gp120 did not affect viral entry, the mutation in HR1 of gp41 conferred relative resistance to RC-101. Interestingly, the envelope with the HR2 mutation was less efficient and became codependent on the presence of RC-101 for entry. The adaptive response of HIV-1 to this cationic host defense peptide resembles the responses of bacteria that modulate their surface or membrane charge to evade analogous host defense peptides. These findings also suggest that interactions between θ-defensins and gp41 may contribute to the ability of these cyclic minidefensins to prevent HIV-1 entry into target cells.
PU.1 and a TTTAAA Element in the MyeloidDefensin-1Promoter Create an Operational TATA Box That Can Impose Cell Specificity onto TFIID Function
Authors: Yaneva Mariana , Kippenberger Serena , Wang Nan , Su Qin , McGarvey Margaret , Nazarian Arpi , Lacomis Lynne , Erdjument-Bromage Hediye , Tempst Paul 
Published: April 2014

AbstractDefensins are major components of a peptide-based, antimicrobial system in human neutrophils. While packed with peptide, circulating cells contain no defensin-1 (def1) transcripts, except in some leukemia patients and in derivative promyelocytic leukemia cell lines. Expression is modulated by serum factors, mediators of inflammation, and kinase activators and inhibitors, but the underlying mechanisms are not fully understood. A minimal def1 promoter drives transcription in HL-60 cells under control of PU.1 and a def1-binding protein (“D1BP”), acting through, respectively, proximal (−22/−19) and distal (−62/−59) GGAA elements. In this study, we identify D1BP, biochemically and functionally, as GA-binding protein (GABP)α/GABPβ. Whereas GABP operates as an essential upstream activator, PU.1 assists the flanking “TTTAAA” element (−32/−27), a “weak” but essential TATA box, to bring TBP/TFIID to the transcription start site. PU.1 thus imparts a degree of cell specificity to the minimal promoter and provides a potential link between a number of signaling pathways and TFIID. However, a “strong” TATA box (“TATAAA”) eliminates the need for the PU.1 binding site and for PU.1, but not for GABP. As GABP is widely expressed, a strong TATA box thus alleviates promyelocytic cell specificity of the def1 promoter. These findings suggest how the myeloid def1 promoter may have evolutionarily acquired its current properties.
F4/80+ Alternatively Activated Macrophages Control CD4+ T Cell Hyporesponsiveness at Sites Peripheral to Filarial Infection
Authors: Taylor Matthew D. , Harris Anjanette , Nair Meera G. , Maizels Rick M. , Allen Judith E. 
Published: April 2014

Abstract
Both T cells and APC have been strongly implicated in the immune suppression observed during filarial nematode infections, but their relative roles are poorly understood, particularly in regard to timing and locality of action. Using Litomosoides sigmodontis infection of susceptible BALB/c mice, we have studied the progression of filarial immunosuppression leading to patent infection with blood microfilaremia. Patent infection is associated with decreased immune responsiveness in the draining thoracic lymph nodes (tLN) and intrinsically hyporesponsive CD4+ T cells at the infection site. We now show that we are able to separate, both in time and space, different suppressive mechanisms and cell populations that contribute to filarial hyporesponsiveness. L. sigmodontis infection recruited a F4/80+ population of alternatively activated macrophages that potently inhibited Ag-specific CD4+ T cell proliferative responses even in the presence of competent naive APC. T cell responsiveness was partially restored by neutralizing TGF-β, but not by blocking IL-10 or CTLA-4 signaling. During prepatent infection, the macrophage population was restricted to the infection site. However, once infection became patent with systemic release of microfilariae, the suppressive macrophage activity extended peripherally into the tLN. In contrast, the hyporesponsive CD4+ T cell phenotype remained localized at the infection site, and the tLN CD4+ T cell population recovered full Ag responsiveness in the absence of suppressive macrophages. Filarial immunosuppression, therefore, evolves over time at sites increasingly distal to infection, and the mechanisms of filarial down-regulation are dependent on proximity to the infection site.
Epitopes Derived by Incidental Translational Frameshifting Give Rise to a Protective CTL Response
Authors: Zook Matthew B. , Howard Michael T. , Sinnathamby Gomathinayagam , Atkins John F. , Eisenlohr Laurence C. 
Published: April 2014

AbstractAberrant gene expression can be caused by several different mechanisms at the transcriptional, RNA processing, and translational level. Although most of the resulting proteins may have no significant biological function, they can be meaningful for the immune system, which is sensitive to extremely low levels of Ag. We have tested this possibility by investigating the ability of CD8+ T cells (TCD8+) to respond to an epitope whose expression results from incidental ribosomal frameshifting at a sequence element within the HSV thymidine kinase gene. This element, with no apparent functional significance, has been identified due to its ability to facilitate escape from the antiviral compound acyclovir. Using a recombinant vaccinia virus expression system, we find that in vitro and in vivo TCD8+ responses to the frameshift-dependent epitope are easily discernible. Furthermore, the in vivo response is at a sufficient level to mediate protection from a tumor challenge. Thus, the targets of immune responses to infectious agents can extend beyond the products of conventional open reading frames. On a per-cell basis, responses to such minimally expressed epitopes may be exceedingly effective due to the selective expansion of high avidity TCD8+.