The epitope specificity and idiotypy of monoclonal rheumatoid factors

Monoclonal rheumatoid factors (MRF) of the Wa idiotypic family have been studied for Fc gamma epitope specificity and the expression of idiotopes recognized by murine monoclonal antibodies. The majority of MRF recognized the Ga antigen or a closely similar iso-allotypic epitope expressed on IgG1, 2, 4 and IgG3.G3m(s.t.) proteins. MRF having the iso-allotypic specificity expressed a similar profile of V-region sub-group and idiotypic serological markers. One protein, Kas, whilst recognizing a distinct Fc gamma epitope also expressed these V-region markers and was highly homologous, from primary sequence analysis, with a MRF of Ga specificity. We conclude that these MRF recognize overlapping non-identical epitopes possibly including the same immuno-dominant residue and consequently demonstrate restricted V-gene usage.