Increased cell surface expression of histocompatibility class II I-A(d) in c-fos transfected clones of the P388D1 murine macrophage cell line.

Numerous biological functions of the monocyte-macrophage lineage are affected by the presence of immunomodulators. Enhancement in transcription of c-fos has been shown in the murine P388D1 macrophage line treated by LPS, TPA, Ca++ ionophore or dibutyryl cAMP. In order to study the effects of an increased c-Fos protein level on macrophage functions, we previously have established stable c-fos-overexpressing clones in the P388D1 cell line. Here we report that the expression of class II MHC antigens (I-A(d) antigen) is increased in these clones, particularly after IFN-gamma treatment. No variation in the cell surface expression of IFN-gamma receptor was observed. The increase of I-A(d) cell surface expression was well correlated with the level of I-A(d) mRNA. No inducible NO synthase activity and no increase of TNF-alpha release were observed in c-fos transfected cells. A slight increase of the basal expression of the main class II MHC transcription factor CIITA which is further amplified by IFN-gamma treatment, was observed in the c-Fos overexpressing clones. This suggests that the increased I-A(d) expression in clones could result from a transactivating action of the c-Fos protein on the CIITA factor.