A role of IgM antibodies in monosodium urate crystal formation and associated adjuvanticity (135.71)

Abstract

Uric acid is a product of purine metabolism that is secreted from injured or dying cells and can act as an endogenous adjuvant. However, uric acid must crystallize to monosodium urate (MSU) before it can activate dendritic cells and cause gouty inflammation. At normal serum uric acid levels, crystallization of uric acid is not observed in vitro. The crucial question therefore is how the crystals form and cause inflammation. It has been reported that serum from rabbits immunized with MSU, increased uric acid precipitation rates. When C57BL6 or Balb/c mice were immunized with MSU, they produced serum factors which bind to MSU crystals, a phenomenon absent in mu chain deficient IgH (or muMT) mice. These observations show that antibodies may be involved in MSU crystallization. Antibodies produced via B cell hybridomas, were observed to precipitate uric acid in vitro, with the variable region acting as the binding domain. Most importantly, the presence of antibody was instrumental in significantly increasing the basal level of inflammation and mediating the adjuvant effect of uric acid in antigen dependent T cell cytotoxicity in B cell deficient mice. Therefore, we have identified a factor in determining uric acid precipitation and possibly its ability to function as an endogenous adjuvant. This finding suggests a new mechanism of the pathogenesis of gouty arthritis and uric acid induced immune activation.