Increased cell surface expression of class III-A(d) in c-Fos transfected clones of the P388D1 murine macrophage cell line

wNumerous biological functions of the monocyte-macrophage lineage are affec ted 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 inc reased c-Fos protein level on macrophage functions, we previously have esta blished 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 in creased in these clones, particularly after IFN-gamma treatment. No variati on in the cell surface expression of IFN-gamma receptor was observed. The i ncrease of I-A(d) cell surface expression was well correlated with the leve l of l-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 o f 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-Fo s 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.