Phagocytosis and degradation of DNA-antiDNA complexes by human phagocytes. Influence of rheumatoid factors.

We studied the influence of sera that contain rheumatoid factor (RF) or purified RF of the IgM and IgG class on the size and the processing (phagocytosis plus degradation) of DNA-antiDNA complexes by human phagocytes. Low concentrations of fresh serum with IgM RF increased the size of small DNA-antiDNA complexes, but at higher concentrations prevented formation of large complexes. The latter effect resulted from interaction of the complexes with complement. By increasing the size of the complexes, purified IgM RF enhances the processing by monocytes and neutrophils of small DNA-antiDNA complexes, prepared at antigen excess. IgM RF inhibited the processing of large DNA-antiDNA complexes, probably by blocking the Fc parts of the IgG antiDNA. IgM RF had a biphasic influence on the processing of small DNA-antiDNA complexes, prepared at antibody excess: an increasing effect due to an increase in size of the complexes and, at higher concentrations of RF, a decreasing effect due to the covering of Fc parts. The inhibiting effect on complex processing was abolished by opsonization with C3. Purified IgG RF increased the size of small DNA-antiDNA complexes, and in parallel the processing of these complexes. IgG RF hardly affected the processing of large DNA-antiDNA complexes.