Antibodies specific for human T lymphocytes in cold agglutinin and lymphocytotoxic sera

Sera of patients with cold agglutinin disease (anti‐I,i), systemic lupus erythematosus, infectious mononucleosis or cryoglobulinemia contained cold IgM antibodies cytotoxic for a subpopulation of normal lymphocytes. Evidence was obtained that the antibodies were specific for T lymphocytes. There was an enrichment of cells reacting with the sera after removal of Ig‐bearing cells on immuno adsorbent columns. Absorption studies with adult and cord erythrocytes revealed a minimum of three antigenic determinants on the lymphocyte membrane, viz. i,I and a third specificity which was unique to T cells. Antibodies to this third specificity were present, at high titer, in sera which were monoclonal for the i antigen.