Increased expression of Ia and Thy-1 antigens on mitogen-activated murine spleen lymphocytes.

The amount of Ia antigens expressed on mitogen-stimulated spleen lymphocytes was measured in a cellular radioimmunoassay optimized for murine Ia antigens. 125I-RAM-Fc, which reacts specifically with alloantibodies bound to cell surface antigens while reacting minimally with surface Ig, was used as the anti-immunoglobulin reagent. Stimulation of spleen cells, in vitro, with the B cell mitogen, lipopolysaccharide (LPS), caused an augmentation in the expression of Ia antigens. This phenomenon was seen with all haplotypes tested, and all Ia specificities detected on spleen cells were found on LPS lymphoblasts. Culturing a cell suspension from one mouse spleen in vitro for 60 to 64 hr with LPS increases its Ia content (total units derived per spleen) by 13-fold. This augmentation is very significant from the point of view of purification of the antigens from murine tissues where quantity of material available is limited. The T cell mitogens, concanavalin A (Con A) and phytohemagglutinin (PHA), also stimulated increased Ia expression in all haplotypes tested; all Ia specificities found on spleen cells were observed on Con A and PHA blasts. Stimulation by Con A and PHA also resulted in an increased expression of Thy-1 antigen, equivalent to that observed for Ia antigens. The increase in Ia expression observed after stimulation of spleen cells by Con A could not be attributed to contaminating B cells in the cultures. In view of their increased level of Ia antigens and decreased expression of surface Ig, Con A blasts are better target cells than spleen lymphocytes in the Ia CRIA.