TNF-ALPHA INHIBITS ANTI-IGM-MEDIATED APOPTOSIS IN RAMOS CELLS

We have examined the effects of tumor necrosis factor-alpha (TNF-alpha ) as an inducer or modulator of necrosis and/or apoptosis in B cell li nes. TNF-alpha does not induce either necrosis or apoptosis in EBV-pos itive or -negative cell lines, regardless of the culture conditions of the cells or the presence or absence of cytokines. By contrast anti-I gM induces apoptosis in two EBV-negative cell lines (Ramos and ST486) but not in EBV-positive cell lines. Since TNF receptor and CD40 belong to the TNF receptor superfamily and anti-CD40 is a known inhibitor of apoptosis, we tested for TNF-alpha's effects on the inhibition of apo ptosis induced by anti-IgM. Our results indicate that TNF-alpha inhibi ts apoptosis induced by anti-IgM in Ramos cells but not in ST486. The effects are dose and time dependent; the degree of apoptosis achieved and the selectivity of the effect among cell lines are strikingly simi lar for both TNF-alpha and anti-CD40. Furthermore when both agents are tested together no additivity in the inhibition is observed. The inhi bition of apoptosis is a direct effect of TNF-alpha and not a permissi ve effect of another cytokine, since it is observed in defined medium. Although anti-IgM induces both TNF-alpha secretion and TNF receptors in Ramos cells, the concentration of secreted TNF-alpha is too low to affect apoptosis. Inhibition does not involve perturbation of the cell cycle distribution of Ramos cells. Furthermore rapid induction of c-f os and the decrease in c-myc observed after anti-IgM treatment are bot h unaltered by TNF-alpha. Our results suggest that TNF-alpha is an inh ibitor of apoptosis in Ramos cells, that its overall pattern of inhibi tion is similar to that of anti-CD40, and that both agents act at some point distal to the alteration of c-fos and c-myc by anti-IgM. (C) 19 96 Academic Press, Inc.