Nature of cold‐reactive antibodies to lymphocyte surface determinants in systemic lupus erythematosus

Antilymphocyte antibodies in serum from patients with systemic lupus erythematosus (SLE), as detected by microcytotoxicity and indirect immunofluorescence, were predominantly cold reactive and of the IgM class. These IgM antibodies were most active at 4°C. IgG antibodies were infrequent, and were only minimally lymphocytotoxic. Most sera were cytotoxic for autologous lymphocytes and were equally reactive with normal and SLE lymphocytes, as well as with B‐ and T‐cell preparations. Separate T‐ and B‐cell specificities, which appeared not to be related to HL‐A determinants, were identified by differential absorption experiments. The functional significance of these antilymphocyte antibodies is discussed.