Further immunological studies of sera containing anti-mitochondrial antibodies, type M 5.

All of 15 sera containing anti-mitochondrial antibodies (AMA), type M 5, reacted in ELISA with ssDNA, whereas only four had anti-nuclear antibodies as demonstrated by immunofluorescence technique. Twelve of 15 had biological false-positive seroreaction for syphilis and seven of 11 cases investigated had a positive lupus anti-coagulant test. Cold agglutinins were present in 11 sera. Hyper-gamma-globulinaemia was not a prominent finding, but C4 values below the lower limit were common in spite of C3 within the normal range. Absorption of IgG fractions from three different sera with cardiolipin eliminated the reaction with ssDNA and mitochondria, supporting a certain degree of cross-reactivity among the antibodies. The presence of AMA, type M 5, seemed to discriminate a group of patients with symptoms often consistent with SLE although some of the most prominent findings were often absent.