Plasma from rheumatoid arthritis patients does not contain abnormally high levels of α2‐macroglobulin–proteinase complexes

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Abstract
We measured the levels of α2‐macroglobulin (α2M)–proteinase complexes in the plasma of 18 patients with classic rheumatoid arthritis, 11 age‐matched patients with noninflammatory back pain and osteoarthritis, and 8 healthy volunteers. In contrast with previous reports, we found no evidence of α‐proteinase complexes in the plasma samples from individuals in any of the groups. In our assays, all activity that might have been the result of the presence of such complexes in the plasma samples proved instead to be an artifact attributable to contamination of the anti–α2M antibody immobilized on the AffiGel solid phase with a trypsin‐like proteinase. When the contaminating activity was eliminated by pretreatment of the antibody with 1 mM diisopropyl fluorophosphate, no degradation of substrate was detected with any of the plasma samples. However, the ability of the solid‐phase assay to detect and quantitate α2M‐proteinase complexes when they are present was confirmed in control experiments with plasma samples to which preformed α2M‐trypsin complexes had been added, or in which α2M‐kallikrein complexes had been generated by activation of Hageman factor (coagulation factor XII). We therefore conclude that neither normal plasma nor that from rheumatoid arthritis patients contains measurable amounts of α2M‐proteinase complexes.

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