Aberrant control of galactosyltransferase in peripheral B lymphocytes and Epstein-Barr virus transformed B lymphoblasts from patients with rheumatoid arthritis.

Abstract

It is now well established that hypogalactosylation of IgG is a molecular marker for rheumatoid arthritis (RA). However, the mechanism for the alteration of the galactosylation status has not been resolved. We compared the galactosyltransferase activities of anti-CD19 selected peripheral B lymphocytes of healthy subjects and patients with RA using ovalbumin as the acceptor substrate. In addition, certain samples of lymphocytes were assayed after Epstein-Barr virus (EBV) transformation and, also, the ability of bovine milk galactosyltransferase to galactosylate IgG in vitro was examined. Our results indicate that there is a significant difference between the galactosyltransferase activities of rheumatoid and control peripheral B lymphocytes and that EBV transformation causes a variable increase (15-1225%) in galactosyltransferase activity, over that present in the peripheral B lymphocytes from which the transformed cells were derived. Also the ubiquitous "lactose synthetase" type galactosyltransferase (EC 2.4.1.38) will galactosylate normal native IgG at concentrations of 500 mU/ml in vitro. We conclude that there is no evidence from our study for an IgG specific galactosyltransferase and that galactosyltransferase is an enzyme that is aberrantly modulated in peripheral B lymphocytes and EBV transformed B lymphoblasts derived from patients with RA.