Isolation and analysis of immune complexes from sera of patients with polymyalgia rheumatica and giant cell arteritis

Serum samples were obtained from patients with polymyalgia rheumatica (PMR: n = 10) or giant cell arteritis (GCA; n = 7), or both. Samples were taken either before treatment or within one week of starting prednisolone. Immune complexes (IC) were concentrated by polyethylene glycol (PEG) precipitation then purified with either IgG anti-C1q-Sepharose or IgG anti-C3c-Sepharose. Complex components were separated by sodium dodecyl sulphate (SDS) gradient polyacrylamide gel electrophoresis then transferred to nitrocellulose by Western blotting. Identification of proteins was carried out using specific antisera. All the IC contained IgM (mu chain), some contained IgA (alpha chain), and IgG (gamma chain). C1r, C1s, C1q, C3, C4, and C reactive protein (CRP), where tested, were found in most but not all IC. The occurrence of properdin, factor B, alpha 2 macroglobulin (alpha 2M), factor H (beta 1H), C1 esterase inhibitor, and C4 binding protein was also investigated. Immune complexes in PMR and GCA differed from those previously characterized in rheumatoid arthritis (RA)1 purified by anti-C1q-Sepharose which contained immunoglobulins and C1q only. No properdin or factor B were detected in RA IC purified with either anti-C1q-Sepharose or anti-C3c-Sepharose.