Partial chemical characterization of Ia antigens derived from murine thymocytes.

Abstract

The question of whether Ia [immune response associated] antigens exist on thymocytes (defined as thymus cells that bear a T [thymus-derived] cell marker) was studied by isolating strain C3H thymocytes free of other contaminating cells (using the fluorescence-activated cell sorter) and then chemically testing the purified populations for Ia antigens. Immunoglobulin-negative thymus cells and thymus cells selected with a rabbit antiserum to mouse brain were the 2 populations of thymocytes labeled with [3H]leucine after sorting. Radiolabeled proteins were solubilized with the non-ionic detergent Nonidet P-40, reacted with anti-Ia antiserum and analyzed by electrophoresis on discontinuous sodium dodecyl sulfate/polyacrylamide gels. Ia antigens were recovered from both cell populations. These antigens were synthesized by thymocytes and were found on molecules composed of 2 chains of MW 33,000 and 25,000, respectively, similar to Ia antigens derived from spleen cells. Assuming that all thymocytes bear similar amounts of Ia antigens, thymocytes probably have approximately 1/50 the amount of Ia antigens that spleen cells do.