C3 receptors on granulocytes from patients with rheumatoid arthritis and Felty's syndrome.

The expression of receptors for the third component of complement (C3R) on polymorphonuclear cells (PMN) from patients with rheumatoid arthritis (RA) or Felty's syndrome (FS) and healthy controls (HC) was studied by means of a rosetting technique using ox erythrocytes coated with rabbit IgM and mouse complement. The percentage of rosette forming PMN (RF-PMN) was found to be increased in patients with FS (59%) and patients with RA (47%) compared to HC (18%), when measured directly after cold isolation of PMN. Incubation at 37 degrees C of cold isolated cells increased the percentage of RF-PMN in all three groups, although the values were significantly higher during the first 45 min of incubation in both patient groups. When incubated with serum from patients with FS at 37 degrees C, cold isolated donor PMN formed significantly more rosettes than after incubation with donor serum. This increase was shown to be due to the presence of circulating immune complexes in the patient sera and could be mimicked by incubating donor PMN with aggregated human IgG. As a result of these experiments it was demonstrated that the increased percentages of PMN with C3R in patients with FS or RA are most likely caused by a previous in vivo activation of PMN by immune complexes. The possible effect of such an increase in C3R expression in relation to PMN function in these patients is discussed.