IgG and rheumatoid factor at a glance

The presence of rheumatoid factors in both sero-positive and seronegative rheumatoid arthritis patients is well established. Immune complexes are formed through the binding of IgM, IgG or IgA rheumatoid factors to the Fc fragment of IgG. IgG rheumatoid factor is of particular interest in that being both antigen and antibody, it can self-associate to form immune complexes. It has recently been shown that there is a decrease in the galactose content in the Fc oligosaccharides of IgG leading to a vacant pocket where the galactose moiety normally resides. One of the mechanisms through which IgG can potentially self-aggregate is by the insertion of galactose of the Fab oligosaccharides of one IgG molecule into the galactose free pocket of a second IgG molecule.