Recombinant human tumor necrosis factor increases mRNA levels and surface expression of HLA-A,B antigens in vascular endothelial cells and dermal fibroblasts in vitro.

Recombinant human tumor necrosis factor (TNF), purified to greater than 99% homogeneity, increases surface expression of class I major histocompatibility complex (MHC) antigens to a maximum of 9-fold on cultured human endothelial cells (HEC) and human dermal fibroblasts (HDF). The increase is concentration dependent (peak 20-100 units/ml) and time dependent (nearly maximal by 4 days); expression remains elevated in the continued presence of TNF and requires greater than 7 days to return to basal levels upon TNF withdrawal. The increase in surface expression appears to result from increases in steady-state mRNA levels for the class I antigens, although the increase in mRNA is proportionately greater than for surface expression. No surface expression of or mRNA for class II MHC antigens is detectable in either control or TNF-treated HEC or HDF. These effects are similar to those produced by leukocyte or fibroblast (type I) interferons (IFNs). The protein synthesis inhibitor cycloheximide (CHX), when added coincidentally with type I IFNs, leads to superinduction of mRNA for class I MHC antigens and, unexpectedly, leads to the appearance of mRNA for class II MHC antigens. CHX has no effect by itself upon mRNA levels for class I or class II MHC antigens, nor does it modulate the increases in mRNA produced by immune (type II) IFN. Most interesting, CHX blocks the increase in mRNA for class I MHC antigens induced by TNF. Thus TNF appears to act on MHC gene expression through a newly synthesized protein intermediate. Our results provide direct evidence that TNF can modulate gene expression in normal (untransformed) cell types and contribute to understanding the complex nature of MHC gene regulation. Finally, they suggest that TNF may act in vivo as an immunoregulatory molecule.