Expression of MHC class II antigens is modulated by ouabain

Ouabain enhances a modulation effect of lipopolysaccharide (LPS) on the expression of MHC class II antigens. A similar but lesser effect than that of ouabain, which increases intracellular concentration of sodium ions, has been observed when treating cells with ionophores quercetin which increases [Ca2+]i or valinomycin which increases [K+]i. These findings confirm the role of ion flux in cellular activation and differentiation. Optimal concentration of ouabain is 10(-7) M with 10 micrograms of LPS/ml for human and pig peripheral blood cells. The increase in radioactivity of mononuclear human blood cells after the binding of 125I-anti-MHC class II monoclonal antibody is at the fourth hour of cultivation with LPS and ouabain, the number of immunofluorescently positive cells rises at the twelfth hour. A similar modulation has been observed on pig kidney cell line. It can be concluded that the expression of class II antigens on the plasma membrane can be induced by cumulative effect of LPS and agents alterating ion transport.