TNF and its receptor antibody agonist differ in mediation of cellular responses.

TNF binds to two distinct receptors designated p60 and p80. Because Abs to the p60 receptor (anti-p60) can mimic TNF, we therefore compared the cellular signaling of TNF with that of anti-p60. We demonstrate both qualitative and quantitative differences between TNF and anti-p60. HepG2 cells, which express the p60 receptor, were found to be completely resistant to TNF but highly sensitive to the antiproliferative effects of anti-p60. In contrast, normal fibroblasts were found to be several fold more sensitive to TNF than to anti-p60. Several other epithelial cell lines that also express primarily the p60 receptor showed quantitative differences in mediation of cellular responses by TNF and anti-p60. The blocking of the p60 receptor by TNF had no effect on the response of HepG2 cells to anti-p60, suggesting a difference in their binding sites. Anti-p60, however, inhibited the effect of TNF on fibroblasts. Ab against the p80 receptor had no effect by itself or on the effect of TNF and anti-p60. The difference in the response to TNF and anti-p60 could not be correlated to the differences in the level of expression of p60 receptor on these cells. Furthermore, cycloheximide potentiated the TNF-mediated effect but not that mediated through anti-p60, thus also indicating a difference in the mechanism of action of these two agents. Overall, these results demonstrate that TNF and anti-p60, although both working through the p60 receptor, differ in their cellular signaling.