Immunochemical and ultrastructural characterization of serum proteins associated with monosodium urate crystals (MSU) in synovial fluid cells from patients with gout.

Immunoelectron microscopic (IEM) analysis of the surface coats of intracellular and extracellular monosodium urate (MSU) crystals in synovial fluid (SF) in gouty arthritis was performed using the ferritin-bridge method. Cells from patients with acute gout were fixed in 1% glutaraldehyde containing 0.05% saponin to permeabilize membranes for access of immunochemicals to intracellular antigens. Intracellular MSU crystals were observed in phagosomes of greater than 75% of both polymorphonuclear (PMNs) and mononuclear cells. Coating of crystals with IgG was more prominent than with IgM or IgA. Other proteins such as C3, and fibrinogen were also found to a lesser extent. Albumin was not detected in appreciable amounts on MSU crystals. Extracellular crystals also showed IgG to be bound more prominently than other proteins. The various proteins, shown here for the first time to be clearly associated with intracellular crystals by EM, and other materials associated with MSU crystals may influence the phlogistic properties of these crystals.