A 63 kDa tumor necrosis factor inhibitor released from a human monocytic leukemia cell line, THP-1

A human monocytic cell line, THP-1-S, was cultured in a serum-free medium. The effect of the culture supernatant of THP-1-S on the cytotoxicity of rTN F-alpha to three kinds of cell lines and the binding of rTNF to its recepto r were tested. The supernatant inhibited the cytotoxicity of rTNF-alpha whe n tested by the neutral red uptake method. In addition, the supernatant blo cked the binding of I-125-rTNF-alpha to its receptor. Furthermore, followin g precipitation with PEG we detected complexes between rTNF-alpha and the i nhibitory factor which formed during incubation with the culture supernatan t from THP-1-S cells. However, the supernatant did not bind to or down-regu late the receptor for TNF-alpha on the cell surface of L-M-2d6 cells. This factor eluted,vith an apparent molecular mass of 63,000 Da by gel filtratio n and did not react,vith antibodies against p55 and p75 TNF receptors, Thes e data suggest that human monocytic cells are capable of releasing an inhib itory factor against rTNF-alpha in serum-free culture conditions.