HLA class I antigen downregulation by interleukin (IL)-10 is predominantly governed by NK-kappaB in the short term and by TAP1+2 in the long term.

The present study was designed to determine the molecular mechanisms by which interleukin (IL)-10 prevents the HLA class I antigen expression at the cell surface. In this context, the potential role of transporter associated with antigen presentation 1+2 (TAP1+2) molecules and NF-kappaB transcription factors was addressed. The IL-10 effect was investigated in a human lymphoblastoid cell system defective for TAP1+2 genes (T2 cell line) and in the related TAP1+2 transfectants (T3 cell line). In this experimental system, after 48 h of incubation in the presence of IL-10, the HLA class I antigen downmodulation was observed in the T3 but not in the T2 cell line, suggesting a potential role of TAP1+2 molecules. In the same experimental conditions, the NF-kappaB activity was unaffected. Instead, after 3 h of exposure to IL-10, the HLA downmodulation was observed in both cell lines, the NF-kappaB factors activity being strongly reduced. In addition, the transfection of the inhibitor of NF-kappaB, IkappaBalpha, prevented the IL-10 effect on HLA class I antigen expression in the T3 cell line. This phenomenon was observed after 3 h but not 48 h of IL-10 incubation. These evidences indicate a time dependent involvement of TAP1+2 antigens and of NF-kappabeta activity in the IL-10-induced major histocompatibility complex (MHC) class I downmodulation.