Cold-reactive lymphocytotoxic antibodies in mixed connective tissue disease

Eighty-one sera from 18 patients with mixed connective tissue disease (MCTD) and high titers of antibody to ribonucleoprotein (RNP) were investigated for the presence of lymphocytotoxic antibodies. These were found in 59% sera from 14 patients but in only one of 40 normal subjects. Although lymphocytotoxic activity tended to be higher when the disease was active or there was lymphopenia, the correlation was not statistically significant. The lymphocytotoxic antibodies were found to be cold-reactive, and located in the IgM and/or IgG-containing elution fractions from DEAE cellulose columns. IgM-containing fractions tended to be more cytotoxic. Lymphocytotoxic antibodies were partially absorbed out with cerebral cortex but not with ENA-coated sheep red blood cells. Although attention has been focused on the anti-RNP antibodies found in MCTD, other autoantibodies are also present in a high proportion of patients.