Lectin-binding profile of serum IgA in women suffering from systemic autoimmune rheumatic disorders.
In many pathological states changes in the carbohydrate part of serum glycoproteins occur, the etiopathogenic role or diagnosis significance of these abnormally glycosylated glycoproteins being relevant in many instances. The aim of this study was to determine the glycosylation pattern of the serum immunoglobulin A (IgA) in young women suffering from systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), by comparison with that in healthy ones. We used lectin proteins as bivalent reagents to selectively and specifically recognize and bind the different oligosaccharides at the surface of the IgA molecules and precipitate them. The serum IgA level in the SLE and RA women included in this study was of 4 and respectively 6 times greater than in control women. Our experiments revealed for the IgA isolated from SLE women a very low degree of glycosylation, as follows: in the Fc region, we detected a markedly reduced level of the unbisected, biantennary oligosaccharides (by 72.8%) and of the unbisected, tri- and tetraantennary oligosaccharides (by 40%), accompanied by a slightly increased level of the bisected (by 14.7%) and fucosylated (by 13.3%) oligosaccharides; in the hinge region, a marked degalactosylation (by 74.4%) of the oligosaccharides was revealed; the sialylation degree of the IgA molecules was thus reduced by 71.2%. Related to it, it is reasonable to presume a certain role of the degalactosylated IgA fraction in renal tissue deposition of IgA in SLE patients, as it has been ascribed to this fraction in IgA nephropathy. Referring to the IgA isolated from RA women, we showed that it selectively bound the lectins, but lacked the property to be lectin-precipitated, most probably due to an altered arrangement of the oligosaccharide chains at the surface of the glycoprotein.