An IgG thymolytic autoantibody in rats which has specificity for a subpopulation of T cells.

A cytotoxic anti-thymocyte IgG auto-antibody is present in Lewis rats which, in the presence of autologous complement, destroys (in vitro) 12-28 per cent of isologous or autologous thymocytes, a smaller number of lymph node cells and splenocytes, but not bone marrow or circulating lymphocytes. The labile cells in the thymus represent a finite subpopulation which is autologous antithymocyte antibody (ATS) sensitive and steroid resistant. The presence of the autoantibody is randomly distributed in outbred animals whereas in inbred Lewis rats, a strain in which the induction of some autoimmune reactions is under genetic control, the antibody is always present. In this strain, the susceptible T cells and the quantity of circulating autoantibody is significantly depressed during the productive phase of a T-cell mediated disease (adjuvant polyarthritis) and returns to normal after the disease becomes stabilized. There is a direct relationship between the amount of susceptible cells in the thymus and the amount of antibody in circulation, suggesting that the antibody could serve as a marker for a specific subpopulation of thymocytes which may have a regulatory influence on T-cell reactivity.