Biomedical subjects

Michael B Brenner

Publications and source records attributed to Michael B Brenner.

47 records · Page 3Linked to original sources

PubMed2002

CD1-mediated gamma/delta T cell maturation of dendritic cells.

Immature myeloid dendritic cells (DCs) express only low levels of major histocompatibility complex (MHC) class II but express high levels of CD1 a, b, and c antigen-presenting molecules at the cell surface. As Vdelta1+ gamma/delta T cells are the main tissue subset of gamma/delta T cells and they are known to recognize CD1c in the absence of specific foreign antigen recognition, we examined the possible interaction of these T cells with immature DCs. We show that CD1-restricted gamma/delta T cells can mediate the maturation of DCs. DC maturation required cell-cell contact and could be blocked by antibodies against CD1c. The maturation process was partially mediated by tumor necrosis factor alpha. Importantly, immature DCs matured in the presence of lipopolysaccharide and CD1-restricted gamma/delta T cells produced bioactive interleukin-12p70. In addition, these DCs were able to efficiently present peptide antigens to naive CD4+ T cells. CD1-restricted gamma/delta T cell recognition of immature DCs provides the human immune system with the capacity to rapidly generate a pool of mature DCs early during microbial invasion. This may be an important source of critical host signals for T helper type 1 polarization of antigen-specific naive T cells and the subsequent adaptive immune response.

Antibodies, Monoclonal↗

PubMed2002

Conservation of CD1 intracellular trafficking patterns between mammalian species.

Dendritic cells (DC) are potent APCs that sample Ags from the surrounding environment and present them to naive T cells using cell surface Ag-presenting molecules. The DC in both lymphoid and nonlymphoid tissues express high levels of CD1, a cell surface glycoprotein capable of presenting lipids and glycolipids to T cells. Distinct group 1 CD1 isoforms (CD1a, -b, -c) in man are known to traffic to different parts of the endocytic system where microbial Ags may be sampled. Guinea pigs are the only known rodent species that express the group 1 CD1 proteins. Therefore, we examined the expression and trafficking of guinea pig CD1 (gpCD1) isoforms on isolated DC. Confocal microscopy using mAbs specific for individual gpCD1 isoforms revealed differential trafficking of two distinct CD1b isoforms within DC. Colocalization of MHC class II was observed with the gpCD1b1 isoform, consistent with localization in the late endosomes of DC. In contrast, the gpCD1b3 isoform lacks an endosomal sorting motif and remains on the cell surface. Following incubation with Mycobacterium tuberculosis lipoarabinomannan, colocalization of endocytosed lipoarabinomannan with the gpCD1b1 isoform was observed but not with the gpCD1b3 isoform, which remained primarily on the cell surface. These data demonstrate that guinea pig DC express CD1 isoforms with unique trafficking patterns that recapitulate the patterns seen for human CD1 isoforms. This suggests evolutionary pressure for a conserved mechanism in mammals that allows CD1 to sample lipid Ags from various subcompartments of the endocytic system.

Animals↗

PubMed2002

CD1-dependent dendritic cell instruction.

Both microbial products and T cell factors influence dendritic cell (DC) maturation. However, it is not known which T cells are capable of interacting with DCs at the initiation of adaptive immunity, when foreign antigen-specific T cells are rare. We show here that self-reactive CD1-restricted T cells can promote DC maturation by recognizing CD1 in the absence of foreign antigens. T cell recognition of all four CD1 isoforms can trigger DC maturation, but their distinct mechanisms of costimulation lead to profound differences in concomitant interleukin 12 p70 production. Distinct CD1-reactive T cells may thus differentially direct DC development early in the immune response, thereby controlling subsequent polarization of acquired immunity.

Antigens, CD1↗

PubMed2002

CD1 molecules efficiently present antigen in immature dendritic cells and traffic independently of MHC class II during dendritic cell maturation.

Upon exposure to Ag and inflammatory stimuli, dendritic cells (DCs) undergo a series of dynamic cellular events, referred to as DC maturation, that involve facilitated peptide Ag loading onto MHC class II molecules and their subsequent transport to the cell surface. Besides MHC molecules, human DCs prominently express molecules of the CD1 family (CD1a, -b, -c, and -d) and mediate CD1-dependent presentation of lipid and glycolipid Ags to T cells, but the impact of DC maturation upon CD1 trafficking and Ag presentation is unknown. Using monocyte-derived immature DCs and those stimulated with TNF-alpha for maturation, we observed that none of the CD1 isoforms underwent changes in intracellular trafficking that mimicked MHC class II molecules during DC maturation. In contrast to the striking increase in surface expression of MHC class II on mature DCs, the surface expression of CD1 molecules was either increased only slightly (for CD1b and CD1c) or decreased (for CD1a). In addition, unlike MHC class II, DC maturation-associated transport from lysosomes to the plasma membrane was not readily detected for CD1b despite the fact that both molecules were prominently expressed in the same MIIC lysosomal compartments before maturation. Consistent with this, DCs efficiently presented CD1b-restricted lipid Ags to specific T cells similarly in immature and mature DCs. Thus, DC maturation-independent pathways for lipid Ag presentation by CD1 may play a crucial role in host defense, even before DCs are able to induce maximum activation of peptide Ag-specific T cells.

Antigen Presentation↗

PubMed2002

Mast cells: a cellular link between autoantibodies and inflammatory arthritis.

Previous studies have revealed that autoantibodies, complement components, and Fc receptors each participate in the pathogenesis of erosive arthritis in K/BxN mice. However, it is not known which cellular populations are responsive to these inflammatory signals. We find that two strains of mice deficient in mast cells, W/Wv and Sl/Sld, were resistant to development of joint inflammation and that susceptibility was restored in the W/Wv strain by mast cell engraftment. Thus, mast cells may function as a cellular link between autoantibodies, soluble mediators, and other effector populations in inflammatory arthritis.

Animals↗

PubMed2002

Induction of CD1-restricted immune responses in guinea pigs by immunization with mycobacterial lipid antigens.

Group 1 CD1 molecules have been shown to present lipid and glycolipid Ags of mycobacteria to human T cells. However, a suitable animal model for the investigation of this component of antimycobacterial immunity has not yet been established. Previously, we found that guinea pigs express multiple isoforms of group 1 CD1 proteins that are homologous to human CD1b and CD1c. In this study, we show that CD1-restricted T cell responses can be generated in guinea pigs following immunization with lipid Ags from Mycobacterium tuberculosis. Splenic T cells from lipid Ag-immunized guinea pigs showed strong proliferative responses to total lipid Ags and partially purified glycolipid fractions from M. tuberculosis. These lipid Ag-reactive T cells were enriched in CD4-negative T cell fractions and showed cytotoxic activity against CD1-expressing guinea pig bone marrow-derived dendritic cells pulsed with M. tuberculosis lipid Ags. Using guinea pig cell lines transfected with individual CD1 isoforms as target cells in cytotoxic T cell assays, we found that guinea pig CD1b and CD1c molecules presented M. tuberculosis glycolipid Ags to T cells raised by mycobacterial lipid immunization. These results were confirmed using a T cell line derived from M. tuberculosis lipid Ag-immunized guinea pigs, which also showed CD1-restricted responses and cytolytic activity. Our results demonstrate that CD1-restricted responses against microbial glycolipid Ags can be generated in vivo by specific immunization and provide support for the use of the guinea pig as a relevant small animal model for the study of CD1-restricted immune responses to mycobacterial pathogens.

Animals↗

PubMed2002

Fine specificity of TCR complementarity-determining region residues and lipid antigen hydrophilic moieties in the recognition of a CD1-lipid complex.

alphabeta TCR can recognize peptides presented by MHC molecules or lipids and glycolipids presented by CD1 proteins. Whereas the structural basis for peptide/MHC recognition is now clearly understood, it is not known how the TCR can interact with such disparate molecules as lipids. Recently, we demonstrated that the alphabeta TCR confers specificity for both the lipid Ag and CD1 isoform restriction, indicating that the TCR is likely to recognize a lipid/CD1 complex. We hypothesized that lipids may bind to CD1 via their hydrophobic alkyl and acyl chains, exposing the hydrophilic sugar, phosphate, and other polar functions for interaction with the TCR complementarity-determining regions (CDRs). To test this model, we mutated the residues in the CDR3 region of the DN1 TCR beta-chain that were predicted to project between the CD1b alpha helices in a model of the TCR/CD1 complex. In addition, we tested the requirement for the negatively charged and polar functions of mycolic acid for Ag recognition. Our findings indicate that the CDR loops of the TCR form the Ag recognition domain of CD1-restricted TCRs and suggest that the hydrophilic domains of a lipid Ag can form a combinatorial epitope recognized by the TCR.

Amino Acid Sequence↗

PubMed2002

Adaptive immune response of Vgamma2Vdelta2+ T cells during mycobacterial infections.

To examine the role of T cell receptor (TCR) in gammadelta T cells in adaptive immunity, a macaque model was used to follow Vgamma2Vdelta2+ T cell responses to mycobacterial infections. These phosphoantigen-specific gammadelta T cells displayed major expansion during Mycobacterium bovis Bacille Calmette-Guérin (BCG) infection and a clear memory-type response after BCG reinfection. Primary and recall expansions of Vgamma2Vdelta2+ T cells were also seen during Mycobacterium tuberculosis infection of naive and BCG-vaccinated macaques, respectively. This capacity to rapidly expand coincided with a clearance of BCG bacteremia and immunity to fatal tuberculosis in BCG-vaccinated macaques. Thus, Vgamma2Vdelta2+ T cells may contribute to adaptive immunity to mycobacterial infections.

Animals↗

PubMed2002

Functionally distinct subsets of CD1d-restricted natural killer T cells revealed by CD1d tetramer staining.

CD1d-restricted natural killer (NK)T cells are known to potently secrete T helper (Th)1 and Th2 cytokines and to mediate cytolysis, but it is unclear how these contrasting functional activities are regulated. Using lipid antigen-loaded CD1d tetramers, we have distinguished two subsets of CD1d-restricted T cells in fresh peripheral blood that differ in cytokine production and cytotoxic activation. One subset, which was CD4(-), selectively produced the Th1 cytokines interferon gamma and tumor necrosis factor alpha, and expressed NKG2d, a marker associated with cytolysis of microbially infected and neoplastic cells. This subset up-regulated perforin after exposure to interleukin (IL)-2 or IL-12. In contrast, CD4(+) CD1d-restricted NKT cells potently produced both Th1 and Th2 cytokines, up-regulated perforin in response to stimulation by phorbol myristate acetate and ionomycin but not IL-2 or IL-12, and could be induced to express CD95L. Further, for both CD1d-restricted NKT cell subsets, we found that antigenic stimulation induced cytokine production but not perforin expression, whereas exposure to inflammatory factors enhanced perforin expression but did not stimulate cytokine production. These results show that the various activities of CD1d-restricted T cells in tumor rejection, autoimmune disease, and microbial infections could result from activation of functionally distinct subsets, and that inflammatory and antigenic stimuli may influence different effector functions.

Animals↗

PubMed2002

Failure of trafficking and antigen presentation by CD1 in AP-3-deficient cells.

Endocytosed microbial antigens are primarily delivered to lysosomal compartments where antigen binding to MHC and CD1 molecules occurs in an acidic and proteolytically active environment. Signal-dependent delivery to lysosomes has been suggested for these antigen-presenting molecules, but molecular interactions with vesicular coat proteins and adaptors that direct their lysosomal sorting are poorly understood. Here CD1b but not other CD1 isoforms bound the AP-3 adaptor protein complex. In AP-3-deficient cells derived from patients with Hermansky-Pudlak syndrome type 2 (HPS-2), CD1b failed to efficiently gain access to lysosomes, resulting in a profound defect in antigen presentation. Since MHC class II traffics normally in AP-3-deficient cells, defects in CD1b antigen presentation may account for recurrent bacterial infections in HPS-2 patients.

Adaptor Proteins, Vesicular Transport↗

PubMed2002

Characterization of guinea-pig group 1 CD1 proteins.

CD1 molecules are cell-surface glycoproteins with strong structural similarities to major histocompatibility complex (MHC) class I molecules, and studies in humans and mice have demonstrated that CD1 proteins perform the unique role of presenting lipid antigens to T lymphocytes. Our previous studies have shown that guinea-pigs, unlike the muroid rodents, have an extended family of group 1 CD1 genes. In the current study, we raised monoclonal anibodies (mAbs) against guinea-pig CD1 proteins and generated transfected cell lines expressing individual members of the guinea-pig CD1 family. Our results indicated that multiple members of the guinea-pig CD1 family, including members that are homologous to the human CD1b and CD1c proteins, are expressed at the protein level in transfected cells and in specialized antigen-presenting cells such as monocyte-derived dendritic cells. In addition, CD1 proteins, especially guinea-pig CD1b3, were expressed on a large number of B cells in the guinea-pig, and CD1 expression appeared to be regulated by B-cell maturation or differentiation. Interestingly, three different patterns of intracellular localization were observed for the various guinea-pig CD1 isoforms, a finding that is reminiscent of the distinct patterns of intracellular localization that have been previously demonstrated for human CD1a, CD1b and CD1c. Taken together, these results provide further evidence for substantial similarities between the guinea-pig and human CD1 systems, thus supporting the possibility that the guinea-pig may offer significant advantages as an animal model for the study of the in vivo role of CD1 proteins in infectious and autoimmune diseases.

Animals↗