CROSS-LINKING OF HLA CLASS-II ANTIGENS MODULATES THE RELEASE OF TUMOR-NECROSIS-FACTOR-ALPHA BY THE EBV-B LYMPHOBLASTOID CELL-LINE JY

In addition to their functional role as peptide-binding proteins HLA c lass II Ag can also act as signal-transducing molecules. The present s tudy showed that cross-linking of HLA class II Ag by the anti-HLA-DR m Ab L243 or by the anti-HLA-DR,-DP mAb IVA12 significantly (p < 0.05) i ncreased the release of TNF-alpha by the EBV-B lymphoblastoid cell lin e JY. In contrast, the anti-HLA-DR mAb 2.06 or the superantigens staph ylococcal exotoxin toxic shock syndrome toxin-1 and staphylococcal ent erotoxin B that bind to HLA-DR,-DQ Ag did not affect the release of TN F-alpha by JY cells. The accumulation of TNF-alpha in the culture medi um of JY cells peaked at 24 h, decreased thereafter, and was found to be dependent on the dose of mAb L243 or mAb IVA12 used to cross-link H LA class II Ag. mAb L243 or staphylococcal exotoxin toxic shock syndro me toxin-1 enhanced the spontaneous homotypic aggregation of JY cells and mediated a dose-dependent inhibition of JY cell proliferation. The se phenomena were not mediated by TNF-alpha released in response to cr oss-linking of HLA class II Ag; polyclonal anti-TNF-alpha neutralizing antibody did not affect JY cell aggregation and the inhibition of JY cell proliferation mediated by mAb L243. In contrast, TNF-alpha secret ed by JY cells enhanced a nuclear factor-kB-like activity through the binding to the 75-kDa TNF-alpha receptor. These results demonstrate an additional role of HLA class II Ag as signal-transducing molecules re gulating the production of bioactive TNF-alpha by EBV-B cells. The rel ease of TNF-alpha after the triggering of HLA class II molecules could be relevant to different aspects of B cell biology and might play a r ole in the pathogenesis of human diseases in which antibodies cross-re active to HLA class II Ag have been identified.