Serum alpha 1-antitrypsin (alpha 1AT) is an acute-phase glycoprotein which contains three carbohydrate side chains, N-glycosidically linked to the asparagine molecules (Asn46, Asn83 and Asn247) of the single polypeptide unit. "Microheterogeneity", which is a varying proportion of bi- or triantennary heteroglycans attached to the glycosylation sites, has been observed in various inflammatory states including rheumatoid arthritis (RA), and may influence the properties of alpha 1AT.
In this study, we used affinity immunoelectrophoresis with the lectin concanavalin A (ConA) to investigate the possible role of alpha 1AT microheterogeneity in IgA-alpha 1AT complex formation. The concentrations of alpha 1AT and its glycosylation variants, the level of immunoglobulin A (IgA), and concentration of IgA-alpha 1AT complex were determined in the sera of 43 patients with RA.
In seven patients, high concentrations of the IgA-alpha 1AT complex were found. This group did not differ from the remaining patients in sex, age, or disease activity. However, significantly higher concentrations of both the alpha 1AT variant 1a+1b (with a predominance of triantennary heteroglycan side chains) and IgA were found in patients with an elevated complex compared to those with low serum levels of IgA-alpha 1AT complex (p < 0.05 for both variables). In the entire group, there was a significant correlation between the IgA-alpha 1AT complex level and both serum IgA and the concentrations of alpha 1AT variants 1a+1b and 2 (r = 0.3473, p < 0.05; r = 0.4604, p < 0.005; r = 0.3176, p < 0.05, respectively).
The results suggest that the microheterogeneity of alpha 1AT may play a part in the formation of the IgA-alpha 1AT complex in RA.