Interaction between fibronectin, rheumatoid factor and aggregated gamma globulins.

Fibronectin (Fn) was detected in 12/14 2.5% polyethylene glycol precipitates of rheumatoid serum positive for rheumatoid factor (RF). This association led to an investigation of the capacity of Fn to interact with IgM RF and heat aggregated human IgG. Our data suggest that Fn can interact directly with both of these substances at a site in the Fc fragment of the immunoglobulin molecule. The exact cite of the interaction is still to be defined but evidence indicates that it is probably distinct from sites binding staphylococcal protein A and complement.