A recombinant soluble form of human Fc gamma RII (rsFc gamma RII) was genetically engineered by the insertion of a termination codon 5' of sequences encoding the transmembrane domain of a human Fc gamma RII cDNA. Chinese hamster ovary cells were transfected with the modified cDNA and the secreted rsFc gamma RII purified from the tissue culture supernatant (to > 95%, assessed by SDS-PAGE) using heat aggregated human immunoglobulin G (IgG) immunoaffinity chromatography. The IgG-purified rsFc gamma RII was relatively homogeneous (approximately 31,000 M®) whereas the total unpurified rsFc gamma RII secreted into the tissue culture supernatant was heterogeneous relating to N-linked glycosylation differences. Functional in vitro activity of the rsFc gamma RII was demonstrated by: (a) ability to bind via the Fc portion of human IgG and mouse IgG (IgG2a > IgG1 > > IgG2b); (b) complete inhibition of binding of erythrocytes sensitized with rabbit IgG to membrane-bound Fc gamma RII on K562 cells; and © inhibition of the anti-Leu4-induced T cell proliferation assay. Blood clearance and biodistribution studies show the rsFc gamma RII was excreted predominantly through the kidney in a biphasic manner, with an alpha-phase (t1/2 approximately 25 min) and a beta-phase (t1/2 approximately 4.6 h); the kidneys were the only organs noted with tissue-specific accumulation. In vivo, the administration of rsFc gamma RII significantly inhibited the immune complex-mediated inflammatory response induced by the reversed passive Arthus reaction model in rats. There was a specific and dose-dependent relationship between the amount of rsFc gamma RII administered, and the reduction in the size and severity of the macroscopic inflammatory lesion. Histological analysis of the skin showed a diffuse neutrophil infiltrate in both control and rsFc gamma RII-treated rats, however the perivascular infiltrate and the red cell extravasation was less intense in the rsFc gamma RII-treated group. It is likely that complement activation leads to neutrophil chemotaxis, but neutrophil activation via Fc gamma RII, which results in inflammatory mediator release, is inhibited. The data indicate that rsFc gamma RII is a potential therapeutic agent for the treatment of antibody or immune complex-mediated tissue damage.