A recombinant soluble form of human FcγRII (rsFcγRII) was genetically engineered by the insertion of a termination codon 5' of sequences encoding the transmembrane domain of a human FcγRII eDNA. Chinese hamster ovary cells were transfected with the modified cDNA and the secreted rsFcγRII purified from the tissue culture supernatant (to >95%, assessed by SDS-PAGE) using heat aggregated human immunoglobulin G (IgG) immunoaffinity chromatography. The IgG-purified rsFcγRII was relatively homogeneous (∼31,000 Mr) whereas the total unpurified rsFcγRII secreted into the tissue culture supernatant was heterogeneous relating to N-linked glycosylation differences. Functional in vitro activity of the rsFcγRII was demonstrated by: (a) ability to bind via the Fc portion of human IgG and mouse IgG (IgG2a > IgGl≫IgG2b); (b) complete inhibition of binding of erythrocytes sensitized with rabbit IgG to membrane-bound FcγRII on K562 cells; and (c) inhibition of the anti-Leu4-induced T cell proliferation assay. Blood dearance and biodistribution studies show the rsFcγRII was excreted predominantly through the kidney in a biphasic manner, with an or-phase (t1/2 ∼25 min) and a β;-phase (tl/2 ∼4.6 h); the kidneys were the only organs noted with tissue-specific accumulation. In vivo, the administration of rsFc-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 rsFcγRII 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 rsFcγRII-treated rats, however the perivascular infiltrate and the red cell extravasation was less intense in the rsFcγRIItreated group. It is likely that complement activation leads to neutrophil chemotaxis, but neutrophil activation via FcyRII, which results in inflammatory mediator release, is inhibited. The data indicate that rsFcyRII is a potential therapeutic agent for the treatment of antibody or immune complex-mediated tissue damage.