FN1 and rheumatoid arthritis: In our further experiments however, we assessed the antigen-specific effects of purified IgG in the presence of FcγR blockade, we found that both SLE- and RA-IgG were able to enhance β1 integrin activation, measured by adhesion to immobilised fibronectin, but only SLE-IgG significantly enhanced αMβ2-mediated adhesion to PMA stimulated neutrophils.