Hidden antiglobulins in rheumatic disorders.

Sera from thirty-five patients with rheumatoid arthritis, fourteen patients with osteoarthritis, eleven patients with juvenile rheumatoid arthritis, ten patients with ankylosing spondylitis, twenty-two patients with arthritis of various etiologies and seven healthy subjects were studied for the presence of hidden IgM antiglobulins. The whole sera and the chromatographically separated IgM fractions were tested for antiglobulin activity against human and rabbit IgG. Significant antiglobulin activity was not detected in any of the whole sera, but was found in thirteen isolated IgM fractions. Of the thirteen patients with hidden antiglobulins, seven had rheumatoid arthritis, three had osteoarthritis, one had ankylosing spondylitis, one had subacute bacterial endocarditis and one was apparently healthy. All hidden antiglobulins reacted with human IgG, but only the rheumatoid sera contained antiglobulins directed against determinants on rabbit IgG. Antiglobulin titres were generally greater in those with rheumatoid arthritis as compared to the non-rheumatoid group. These data indicate that hidden IgM antiglobulins, particularly those with specificity for human and rabbit IgG, occur most frequently and in highest titre in patients with rheumatoid arthritis.