Ultrastructural study of human synovial membrane with immunoperoxidase.

An ultrastructural immunoperoxidase study of human synovial membrane biopsies performed in 16 patients with rheumatoid synovitis and in 14 control patients showed that: (1) plasma immunoglobulins have an intercellular distribution and seem to diffuse mainly by an intercellular rather than by a transcellular pathway; and (2) there is a difference in the distribution of plasma IgG and IgM. IgG was found in intravascular and extravascular spaces in all biopsies. IgM was found only in intravascular spaces in control biopsies, but in rheumatoid synovitis it was present in both intravascular and extravascular spaces. This difference in distribution may be due to increased vascular permeability in inflammatory synovitis.