Properties and reactivity of immune complexes in rheumatoid synovial fluid

Fractionation of immune complexes (IC) from rheumatoid synovial fluid revealed the presence of three different fractions of IC. The largest molecular weight form, fraction I (above 1000 Kdaltons) was predominately composed of IgG and IgM and contained both IgM-RF and IgG-RF. The other IC, fraction II (480 Kdaltons) and fraction III (330 Kdaltons), contained predominately IgG with some IgA and only significant amounts of IgG-RF. All three fractions of IC can bind Clq and stimulate human monocyte prostaglandin E (PGE) production. Fraction I IC bound Clq most readily while fraction III IC were the most effective stimulators of monocyte PGE production. IC stimulation of monocyte PGE production was inhibited by staphylococcus protein A suggesting mediation via activation of Fc receptors. It remains to be determined whether this IC reactivity has any pathologic significance.