Ly-A and Ly-B: two systems of lymphocyte isoantigens in the mouse

Abstract

Two systems of isoantigens confined to thym ocytes and lymphocytes have been defined in the mouse by cytotoxic isoantisera. The two genetic loci have been designated Ly-A and Ly-B . Typing of 25 mouse strains and sublines indicates that each system comprises only 2 alleles, determining alternative isoantigens Ly-A. 1 or Ly-A. 2, and Ly-B. 1 or Ly-B. 2, respectively. There is no evidence of multiple alleles or that either locus is compound. Tests for genetic linkage were performed by serological typing of mice from segregating generations. None of the four loci H -2 (group IX ), θ, Ly-A and Ly-B is closely linked to any other of the four. Ly antigens are found in high concentration on thymocytes and in lesser amounts on lymphocytes. The small absorptive capacity of bone marrow cell suspensions is probably due to the presence of mature lymphocytes rather than thymocyte-lymphocyte precursors, which according to preliminary evidence lack Ly antigens. Ly-B. 1 is exceptional in that the disparity between thymocytes and lymphocytes in content of antigen is greater than that of the three other antigens. When Ly antiserum is injected into mice of the relevant Ly type, under conditions which give complete absorption of H-2 antibody in vivo , Ly antibody is not extensively absorbed ; this is to be expected from the limited tissue distribution of Ly antigens. Absorption of Ly and θ iosantibodies in vivo is reduced by treatment of the recipients with cortisone or lethal total-body irradiation. The reduction in titre of Ly and θ antibodies in such mice may be no more than that resulting from dilution. Absorption of injected H-2 antibody also may be reduced by treatment of the recipients with cortisone but in this case the effect of corti­sone does not approach the virtual abolition of absorption that is seen with Ly and θ anti­bodies. The thymocytes and lymphocytes of chimeras formed by restoring lethally irradiated mice with allogeneic bone marrow have the Ly-A type, Ly-B type and θ type o f the donor. The content of Ly antigens on cells of different leukaemias varies widely and shows no correlation with presence or absence of TL (thymus-leukaemia) antigen; TL + leukaemias may be Ly — or Ly + and TL — leukaemias may be Ly — or Ly + . Five systems of isoantigens are now demonstrable on mouse thymocytes by means of cytotoxic isoantisera. Of these, TL is an exclusively thymic antigen. Ly-A and Ly-B antigens occur also on lymphocytes. θ occurs on thymocytes, on lymphocytes, and in brain. The fifth antigen, H-2. is still more widely distributed and differs from the other four in being repre­sented less strongly on thymocytes than on lymphocytes.