Tumour necrosis factor-like activity on paraformaldehyde-fixed monocyte monolayers.

A tumour necrosis factor (TNF)-related protein appears to be associated in part with the monocyte surface membrane, since paraformaldehyde-fixed monocyte monolayers induced cytolysis of WEHI 164 clone 13 cells. Cytolysis was inhibited by neutralizing antisera raised against recombinant TNF (rTNF) and against the monocyte-derived cytotoxic factor, CF, which presumably is identical to natural TNF. Moreover, crude monocyte membrane preparations also contained cytotoxic activity, which was inhibited by antisera raised against rTNF and CF, and this activity was associated with particulate structures as it did not pass through filters with a pore size of 0.2 micron. Gamma-interferon (gamma-IFN)-activated monocytes fixed with paraformaldehyde had more TNF-like activity than fixed unactivated monocytes, and the crude membrane preparations from gamma-IFN-activated monocytes contained about five times more TNF-like activity than preparations from unactivated monocytes.