Laminin and vascular proliferation in rheumatoid arthritis

Laminin is a high molecular weight basement membrane structural glycoprotein. In rheumatoid arthritis and other arthropathies immunoreactive laminin was prominent in synovial blood vessel basement membranes and acted as a marker for them. It codistributed with collagen type IV. Immunohistological reactivity to laminin showed extensive vascular proliferation in rheumatoid arthritis together with basement membrane reduplication, which was confirmed ultrastructurally. Parallel histological studies showed vascular proliferation was predominantly in the subintimal rheumatoid synovium, where it was related to connective tissue proliferation but not to the inflammatory cell infiltrate. Vascular proliferation was also seen in relation to connective tissue changes in biopsies from cases of haemophilic arthritis, osteoarthritis, and meniscal tears. We suggest connective tissue activation is non-specific reaction associated with vascular proliferation. This involves laminin and other structural proteins. It occurs in rheumatoid arthritis and other arthropathies but is distinct from inflammatory cell infiltration.