The autoimmune antigen Me is distinct and related to undifferentiated connective tissue disease.

Using prototype Me serum, a new autoantibody-antigen system has been identified by Ouchterlony immunodiffusion and indirect immunofluorescence. Although immunologically distinct, the Me antigen has physiochemical and biochemical properties similar to those of the Sm antigen. Immunoblot assays indicate that Me sera commonly recognize 4 peptides of molecular weights approximating 100K, 65K, 21K, and 16K. The last of these may be identical to the D peptide recognized by Sm antibodies. The Me antigen may be associated with the RNP-Sm macromolecular complex. Me-positive patients have few clinical symptoms, and the most common diagnosis is undifferentiated connective tissue disease.