Association of C1q- and Conglutinin-Binding Immune Complexes with High Consumption of Alpha-2-Macroglobulin in Synovial Fluids of Patients with Rheumatoid Arthritis

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Abstract
The consumption of alpha-2-macroglobulin (a2M) by proteinases in synovial fluids (SF) was indirectly measured by determining trypsin binding to solid-phase immunoadsorbed SF-a2M. In addition immune complexes (IC) were assessed by the solid-phase C1q-binding assay as well as the solid-phase conglutinin binding assay in rheumatoid (RA; n = 25) and osteoarthritic (OA; n = 9) SF. Elevated levels were found as follows: a2M · proteinase complexes (a2M P) in 73.5% (RA, n = 20; OA, n = 5), solid-phase C1q-binding IC (C1q-IC) in 52% (13 out of 25 RA-SF) and bovine conglutinin binding IC (KgB-IC) in 54% (13 out of 24 RA-SF). All OA-SF were in either IC assay negative. Consumption of a2M in OA-SF and seronegative RA-SF was not more than 15% of total SF-a2M, showing a mean value of 19.5 and 13.5 μg a2M P/ml SF. Seropositive RA-SF had an a2M P mean value of 96.4 μg/ml SF, which differed significantly (p ≤ 0.05) from the former two groups. Similarly, RA-SF which were negative in either IC assay had a low a2M · P mean value (20.0 μg/ml SF). This contrasted sharply with the a2M P · means obtained in IC-positive RA-SF, which amounted to 131.5 μg a2M P/ml SF in C1q-IC positive RA-SF and to 110.4 μg a2M · P/ml SF in KgB-IC positive RA-SF, respectively. These values differed significantly (p≤0.0005) from the a2M · P mean in IC-negative RA-SF. The presence of IC in the synovial compartment may directly or indirectly enhance liberation of an array of proteinases as reflected by the augmented consumption of the multifunctional proteinase inhibitor a2M.

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