AGALACTOSYL IGG IN AGGREGATES FROM THE RHEUMATOID JOINT

It has been postulated that agalactosyl immunoglobulin G (IgG) self-as sociates to form pathological aggregates in the rheumatoid joint. To e xamine this hypothesis, IgG aggregates from synovial fluid (SF) of 22 patients with RA were prepared by precipitation with polyethylene glyc ol (PEG) 6000. The PEG precipitates and SFs were reduced with 2-mercap toethanol (2ME) and bound to protein G. This procedure isolated the Ig G in the PEG precipitates from other contaminating glycosylated protei ns. The levels of galactose and N-acetylglucosamine (GlcNAc) residues present on the reduced IgG were quantified by their ability to bind th e lectins Ricinus communis (RCA)(120) and Bandeiraea simplicifolia (BS ) II. Proportionally less galactose (expressed as a ratio of bound RCA (120) to BS II) was present on the IgG from the PEG precipitates than on the IgG in the paired SF (P = 0.001). However, in many cases more R CA(120) as well as BS II bound to IgG from PEG precipitates than from the corresponding SF. It is considered that agalactosyl IgG occurs pre ferentially in RA SF PEG precipitates and that this IgG may also exhib it increased Fab glycosylation.