Recombinant soluble FcγRII inhibits immune complex precipitation

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Abstract
SUMMARY: Control of IgG immune complex formation and deposition is important in determining the nature and extent of subsequent immune effector responses, and appears to be aberrant in some autoimmune diseases. In this study we demonstrate that recombinant soluble FCγRII (rsFcγRII) is an effective modulator of immune complex formation, delaying immune precipitation in a manner which is dose-dependent, and can be specifically inhibited by anti-FcγRII MoAb Fab’ fragments. This inhibitory role in immune precipitation also provides a possible mechanist explanation for our previous demonstration of the efficacy or rsFcγRII as an inhibitor of immune complex-induced inflammation in the Arthus reaction in vivo. RSFcγRH inhibited immune complex precipitation in two different experimental systems. First, rsFc7RII inhibited the precipitation of 125I-bovine serum albumin (BSA)-anti-BSA complexes in a dose-dependent manner, while an irrelevant protein (soybean trypsin inhibitor) had no effect on the precipitation of the immune complexes. Moreover. RsFcγRII inhibited the precipitation of ovalbumin (OVA) anti-OVA complexes as determined by turbidimetric analysis, where the inhibition of immune complex precipitation by rsFc7RII was dose-dependent and was specifically blocked by prior ineubation with Fab’ fragments of a blocking MoAb to FcγRII. RSFcγRII could inhibit the precipitation of BSA anti-BSA complexes in the presence of excess bystander IgG and did not inhibit complement-mediated prevention of immune precipitation, demonstrating that rsFcγRII did not block C1 binding to the BSA anti-BSA complex. Unlike complement. RSFC7RIL could not cause re-solubilization of pre-formed precipitated BSA- anti-BSA complexes. Soluble FcγRS have been detected in biological fluids of normal and inflammatory disease patients., yet the role of SFcγR is still unclear. However, they now play a potential role in the modulation of immune complex solubility.