Evidence for complement activation by the alternate pathway in the arthritis of hypogammaglobulinemic patients.

The chronic, rheumatoid synovitis in four patients (two children and two adults) with immunodeficiency was studied by means of immunopathological examination of synovial tissues and fluids. Their immunodeficiencies were extensively studied, with various tests for humoral and cell-mediated immunity. The two children were boys with Bruton's disease. One adult, female, had common variable immunodeficiency. One adult male had severe hypogammaglobulinemia. All patients had isolated deposits of complement component C3 in their synovial membranes, usually without traces of immunoglobulins. Depressed levels of complement component C3 were found in the joint fluid, in contrast to high levels in the corresponding serum in one patient. Components of the alternate pathway, properdin and C3A, were found in the tissues, but not components of the classic pathway, C1q and C4. The findings suggest that chronic, rheumatoid arthritis in hypogammaglobulinemic patients may be related to activation of C3 by the alternate pathway.