[The titers and complement-activating abilities of anticentromere antibody in systemic sclerosis, other connective tissue diseases, and other related conditions].

The anticentromere antibody is considered to be a useful serologic marker for the CREST syndrome. But this antibody also appears in other related conditions less frequently. We classified 29 patients with anticentromere antibodies into 3 groups: (1) 16 patients with systemic sclerosis or Raynaud's phenomenon alone; (2) 7 patients with other connective tissue diseases; (3) 6 patients with other conditions. Ig class reactivities and complement-fixing abilities of anticentromere antibody were measured by the indirect immunofluorescence test. The whole Ig titers were high (1025 or more) in all patients belonging to group 1. However, the properdin-fixing anticentromere antibody titers of these patients were relatively low (256 or less). In contrast, the patients in group 2 and 3 were shown to have higher C3- and properdin-activating abilities which were determined by the ratios of the titers of C3- and properdin-fixing anticentromere antibody to the IgG titers although the whole Ig titers of these patients were widely distributed. These data suggest that the patients who have low whole Ig titers and/or high properdin-fixing titers do not belong to the scleroderma spectrum and that the patients without clinical features of scleroderma have high C3- and properdin-activating abilities.