UC Irvine

Most human cells express two TNF and lymphotoxin (LT) membrane receptors (TNF-R), of 55 and 75 kDa. The regulatory effect of these two receptors on intercellular adhesion molecules (ICAM-1) expression was examined in various human cell lines in vitro, including human lymphokine-activated killer T cells (T-LAK) cells and HL-60 cells. Rabbit antihuman TNF-R antisera specific for each receptor were employed as probes to selectively stimulate 55- and 75-kDa TNF/LT membrane receptor production. These antisera compete with TNF/LT binding to each specific cell membrane receptor and have been found to bind to specific membrane receptors on various human cell lines in vitro. In the present study, we demonstrated biologic activity for anti-55-kDa TNF-R antiserum. For example, antibodies that bind to the 55-kDa TNF-R caused cytolysis of HeLa and ME-180 human cervical cancer cells and induced proliferation of MRC-5 human fibroblasts. In contrast, however, anti-75-kDa TNF-R antiserum demonstrated no bioactivity in these assays. In addition, no synergy or costimulation was observed when a combination of both anti-55- and anti-75-kDa TNF-R antisera were tested in these assay systems. Anti-55-kDa TNF-R antiserum up-regulated ICAM-1 expression on human HL-60, T-LAK, and THP-1 cells, whereas anti-75-kDa TNF-R antiserum had no effect. Unexpectedly, however, ICAM-1 expression was greatly enhanced by the addition of anti-75-kDa TNF-R to the anti-55-kDa TNF-R containing culture. This enhancing effect was also observed with human T-LAK cells and THP-1 monocytic leukemia cell, in vitro.