Natural Thymocytotoxic Autoantibodies in Autoimmune and Normal Mice

Natural thymocytotoxic autoantibodies (NTA) were found in all mouse strains. Among those strains that show autoimmune syndromes resembling human systemic lupus erythematosus (SLE), the NZB and NZB×NZW had high levels of NTA, the BXSB had moderate levels, and the MRL/1 and MRL/n had very low levels. In addition, some normal strains had high levels, sometimes even higher than the autoimmune strains. The NTA were mostly IgM and were present, but not concentrated, in the cryoprecipitates of the autoimmune mouse strains. In most strains, they were directed toward an antigen shared by thymocytes and brain. The failure to find high levels of NTA in all autoimmune mouse strains, as well as the finding of very high levels in some normal strains, make it unlikely that such autoantibodies are a fundamental etiologic factor in all murine SLE.