Immunoglobulin inclusions in rheumatoid arthritis polymorphonuclear cells: lack of correlation with circulating immune complexes.

A discriminating direct immunofluorescent test has been used to identify immunoglobulin inclusions in polymorphonuclear leucocytes (PMNs) isolated from the blood of patients with rheumatoid arthritis. These inclusions are thought to represent phagocytosed immune complexes, since normal PMNs incubated in RA sera known to contain raised levels of immune complexes developed similar immunoglobulin inclusions. Inclusions did not develop in normal PMNs incubated in normal serum. No correlation was found between the percentage of either RA blood PMNs with immunoglobulin inclusions or normal PMNs developing inclusions after incubation in RA sera, and levels of immune complexes in the corresponding sera. Using heat-aggregated IgG as a laboratory model of immune complexes, a simple relationship has been demonstrated between the uptake of IgG aggregates by normal PMNs and the concentrations of IgG aggregates in the test solutions over a concentration range of 12.5-200 micrograms . ml-1. These results indicate that the C1q- PEG test gives no measure of the actual amounts of immune complexes available in serum for phagocytosis.