Modulation of macrophage I-A expression: lack of effect of prostaglandins and glucocorticoids on macrophages that continuously express I-A.

The ability of prostaglandins, glucocorticoids and lipopolysaccharide to modulate I-A expression on macrophages that continuously or transiently express I-A was compared. We found that neither prostaglandins nor glucocorticoids affected I-A expression by macrophages that continuously expressed I-A. In contrast, prostaglandin E2 (PGE2) inhibited the lymphokine-induced maintenance of I-A on macrophages that transiently expressed I-A while glucocorticoids inhibited both the induction and expression of I-A. Lipopolysaccharide caused a loss in the expression of Class II molecules on macrophages that continuously expressed I-A by a prostaglandin-independent mechanism. The lack of effect of PGE2 and glucocorticoids may be related to our observation that continuous expression of I-A does not require its continued synthesis.