TNF-alpha is not the sole mediator of WEHI-164 tumour cell killing in natural cytotoxicity.

Using a mAb to NC-1.1, a receptor involved in recognition of tumour targets, the authors have examined the dogma that murine natural cytotoxicity (NC) is exclusively mediated by TNF-alpha. Three different NC-1.1+ spleen cells, WEHI-3BR1 myelomonocytic cells and an uncloned mast cell line-MCL) were reacted with NC-sensitive WEHI-164 targets in vitro, and the induction of TNF-alpha mRNA, surface expression of TNF-alpha, and the appearance of apoptotic bodies in the culture were simultaneously measured. NC-1.1+ spleen cells and WEHI-3BR1 cells showed marked induction of TNF-alpha mRNA within 30 min and this was maintained for up to 18 h. Only transient TNF-alpha mRNA induction was observed in MCL cells at 30 min. Surface TNF-alpha was detected on WEHI-3BR1 cells by 4 h, but was not detected on MCL cells. All three effector cell types mediated NC against WEHI-164 targets within 18 h, but they responded differently to the addition of anti-TNF-alpha mAb: anti-TNF-alpha completely blocked WEHI-3BR1 NC, blocked NC-1.1+ spleen cell NC by approximately 70%, and did not block NC by MCL cells. This indicates that TNF-alpha is induced during NC by WEHI-3BR1 effectors and NC-1.1+ spleen cells, is the sole mediator of NC by WEHI-3BR1, and appears to play no role in NC by MCL cells.