title: Rheumatoid factor inhibition of in vitro binding of IgG complexes in the human glomerulus.
abstract: We studied the effects of rheumatoid factor (RF) on binding of immune complexes to activated C3 (C3b) receptors in vitro. IgM fraction of serum containing RF activity (IgM-RF), IgM isolated from pooled normal human serum and have no RF activity (IgM-control), bovine serum albumin, and Veronal buffered saline solutions were used in a C3b assay system consisting of aggregated human IgG (AggHuIgG) coupled to sheep erythrocytes (SRBC) with guinea pig and normal human serum complement. The number of glomerular bound AggHuIgG-SRBC with IgM-control and bovine serum albumin or Veronal buffered saline was similar, while the number of bound cells with IgM-RF was reduced significantly, This effect was seen with both guinea pig and normal human serum complements. Supernatant hemolytic complement activity was maintained with IgM-RF, but reduced with control solutions. The blocking factor was shown to be RF by serial dilutions of IgM-RF resulting in inverse correlations with latex flocculation and inhibition of SRBC binding, absorption of blocking from IgM-RF with insolubilized AggHuIgG, and failure of IgM-control to block binding. IgM-RF did not directly interfere with activation of complement, but blocked attachment of C3 to AggHuIgG and formation of C3b capable of reacting with glomerular receptors. These results showed that IgM-RF can inhibit binding of AggHuIgG complexes to human glomeruli. This in vitro phenomenon may represent a possible protective mechanism of RF in vivo in diseases with immuno complexes.
mesh_terms: D000936:Antigen-Antibody Complex / Q000276:immunology*; D003179:Complement C3b / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D007075:Immunoglobulin M / Q000276:immunology; D066298:In Vitro Techniques; D007678:Kidney Glomerulus / Q000276:immunology*; D012217:Rheumatoid Factor / Q000502:physiology*
chemical_list: D000936:Antigen-Antibody Complex; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D003179:Complement C3b; D012217:Rheumatoid Factor