Control of Ia antigen expression on phagocytic cells of the thymic reticulum by interferon‐gamma and prostaglandins

Phagocytic cells of the thymic reticulum (P-TR) spawned in the microenvironment of primary thymic stroma cultures express class II antigens on their membranes. We can show that Ia-antigen expression is regulated by the local secretion of interferon-gamma (IFN-gamma): (a) early primary culture supernatants contain IFN as tested by a cytopathogenic inhibition test after concentration of IFN activity; (b) the addition of a specific anti-IFN-gamma antiserum to primary cultures reduces Ia expression on P-TR suggesting that IFN-gamma produced in situ is implicated in Ia expression; (c) the percentage of Ia+ cells declines as primary cultures age. This phenomenon parallels the disappearance of thymocytes which are the supposed candidate for IFN-gamma secretion. (d) When isolated from their stromal environment and replated in secondary cultures, P-TR lose their membrane Ia antigen which can be re-expressed in the presence of recombinant IFN-gamma, but not IFN-alpha/beta. The decline of Ia expression on P-TR during the aging of primary cultures may be delayed by the inhibition of prostaglandin secretion.