TRIGGERING OF HLA-DR ANTIGENS DIFFERENTIALLY MODULATES TUMOR-NECROSIS-FACTOR-ALPHA RELEASE BY B-CELLS AT DISTINCT STAGE OF MATURATION

Triggering of HLA class II antigens by the anti-HLA-DR monoclonal anti body (mAb) L243 significantly (P < 0.05) and differentially enhanced t he release of tumor necrosis factor alpha (TNF-alpha) by the non-Hodgk in's lymphoma cells Ri-I, Ci-I, and Sc-I, which are at a distinct stag e of B-cell differentiation, and by the more mature Burkitt lymphoma c ell Raji; in contrast, it did not induce TNF-alpha release by the pre- B leukemia cells Nalm-6 and BV173, TNF-alpha release peaked at 24 h an d decreased thereafter, and it was dose dependent and preceded by an i ncrease of TNF-alpha mRNA detectable after 3 h of stimulation with mAb L243, Secreted TNF-alpha mediated the enhancement of nuclear factor K B (NF-KB) and activator protein-1 (AP-1) binding activity; in fact, th e triggering of HLA-DR antigens in the presence of antihuman TNF-alpha -neutralizing antibodies did not upregulate NF-kappa B and AP-1, In co ntrast, released TNF-alpha was not responsible for the homotypic aggre gation of Ri-I, Ci-I, Sc-I, and Raji cells induced by mAb L243, and it did not affect the proliferation of B cells investigated. Altogether, our data demonstrate that: (a) the ability of B cells to release TNF- alpha after triggering of HLA-DR antigens depends on their stage of di fferentiation; (b) levels of released TNF-alpha seem to correlate with the stage of a-cell maturation but do not correlate with the amounts of cell surface HLA-DR antigens; (c) secreted TNF-alpha regulates the levels of expression of NF-kappa B and AP-1 by an autocrine loop; and (d) intracellular signals mediating TNF-alpha release by B cells are d istinct from those regulating homotypic aggregation and proliferation.