Superantigen-driven, CD8+ T cell-mediated down-regulation: CD95 (Fas)-dependent down-regulation of human Ig responses despite CD95-independent killing of activated B cells.
Staphylococcal superantigens, including staphylococcal enterotoxin B (SEB), promote vigorous T cell-dependent Ig responses at low dose (0.01 ng/ml). In contrast, more mitogenic high dose SEB (100 ng/ml) profoundly inhibits the Ig responses. To assess the contribution of CD8+ T cells to this inhibition, high dose SEB-dependent killing of activated B cells and down-regulation of Ig responses were determined. Rapid killing (4 h) of activated B cells was effected by high dose SEB-activated CD8+ T cells (CD8*), but not by high-dose SEB-activated CD4+ T cells (CD4*), and required the presence of high dose SEB during the cytotoxicity assay. This killing was abrogated by chelation of extracellular calcium or by treatment with concanamycin A but was only modestly affected by treatment with brefeldin A, suggesting a perforin-based pathway of killing. Despite their widely disparate abilities to rapidly kill activated B cells, CD8* and CD4* demonstrated similar quantitative abilities to effect high dose SEB-dependent down-regulation of Ig responses. Antagonist anti-CD95 mAb substantially reversed high dose SEB-dependent downregulation effected by CD8* but had no appreciable effects on high dose SEB-dependent killing of activated B cells. These observations strongly suggest that the small fraction of activated B cells that secrete Ig are selectively sensitive to CD95-based killing but resistant to CD95-independent killing. This finding may help explain why clinical autoimmunity associated with increased titers of autoantibodies is a predominant feature of defects in CD95 or CD95 ligand.
Department of Medicine, University of Southern California, Los Angeles 90033, USA. stohl@hsc.usc.edu
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W
Stohl
D H
DH
Lynch
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GC
Starling
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Kiener
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D019138:Antibodies, Blocking / Q000494:pharmacology; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D000921:Antibody-Producing Cells / Q000276:immunology; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002118:Calcium / Q000502:physiology; D016923:Cell Death / Q000187:drug effects / Q000276:immunology; D003602:Cytotoxicity, Immunologic / Q000187:drug effects / Q000276:immunology; D004306:Dose-Response Relationship, Immunologic; D015536:Down-Regulation / Q000276:immunology*; D004768:Enterotoxins / Q000276:immunology / Q000494:pharmacology; D006801:Humans; D007136:Immunoglobulins / Q000096:biosynthesis*; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology; D018942:Macrolides; D013211:Staphylococcus aureus / Q000276:immunology; D018089:Superantigens / Q000276:immunology / Q000494:pharmacology*; D019014:fas Receptor / Q000276:immunology / Q000502:physiology*
D000900:Anti-Bacterial Agents; D019138:Antibodies, Blocking; D000911:Antibodies, Monoclonal; D004768:Enterotoxins; D007136:Immunoglobulins; D018942:Macrolides; D018089:Superantigens; D019014:fas Receptor; C031818:enterotoxin B, staphylococcal; C036978:concanamycin A; D002118:Calcium