Ia antigen turnover. II. The kinetics of biosynthesis and release of Ia alpha- and beta-chains by murine spleen cells in culture.

The kinetics of biosynthesis, release, and turnover of Ia antigens were determined by 3H-leucine labeling, immunoprecipitation and SDS-PAGE analysis. Continuous incorporation and pulse-chase experiments demonstrated that the half-life of the total cell Ia pool was 8 hr, with radiolabeled Ia antigens released from the cell within 4 hr of culture initiation. Both Ia alpha- and beta-chains were released by the cells. I-A antigen turnover was more rapid than I-E antigen turnover. However, detailed comparison of I-A and I-E alpha- and beta-chain biosynthesis demonstrated that the E beta (Ae) chains were synthesized more rapidly than E alpha chains, at rates similar to A alpha- and A beta-chains. Once assembled, however, E alpha- and E beta (Ae)- chains were turned over at the same rate. This kinetic anomaly may reflect post-translational association of polypeptides coded by separate genes into complete I-E antigens.