SOLUBLE AND MEMBRANE-BOUND TNF-ALPHA ARE INVOLVED IN THE CYTOTOXIC ACTIVITY OF B-CELLS FROM TUMOR-BEARING MICE AGAINST TUMOR TARGETS

Splenic B cells from BALB/c mice bearing mammary adenocarcinomas are c apable of performing Ab-dependent cellular cytotoxicity. Effector-targ et conjugation after 18 h results in minimal cytoplasmic damage, where as extensive nuclear disintegration is observed. To determine whether splenic B cells from tumor-bearing mice can effect direct cytotoxicity against tumor cells, L929 and WEHI 164 cells were used as targets. B lymphocytes from tumor-bearing mice, but not from normal animals, were capable of lysing these two types of tumor cells. However, only a low level of cytotoxicity could be detected when the nontumorigenic 3T3 c ells were used as targets. To elucidate the mechanism of cytotoxicity of these killer B cells, RNase protection assays were performed using perforin, granzyme A, TNF-alpha, and lymphotoxin probes. No perforin, granzyme A, or lymphotoxin RNA could be detected in purified preparati ons of B cells from normal and tumor-bearing mice. B cells from normal mice did not have TNF-alpha RNA. In contrast, B cells from tumor bear ers expressed TNF-alpha RNA. TNF-alpha could be detected in supernatan ts from both unstimulated and stimulated tumor bearers' splenic B cell s, as measured by ELISA, and its lytic activity was neutralized by ant i-TNF-alpha Ab. Western blots revealed the presence of TNF-alpha on th e surface of the killer B cells. Paraformaldehyde-fixed B cells from t umor-hearing mice but not from normal animals were able to lyse TNF-al pha-sensitive tumor targets. This cytotoxicity was neutralized by anti -TNF-alpha Ab. These results suggest that TNF-alpha in soluble and mem brane-bound forms may be involved in the mechanism of cytotoxicity exe rted by B cells from tumor-bearing mice.