RECOMBINANT SOLUBLE HUMAN FC-GAMMA-RII - PRODUCTION, CHARACTERIZATION, AND INHIBITION OF THE ARTHUS REACTION

A recombinant soluble form of human FcgammaRII (rsFcgammaRII) was gene tically engineered by the insertion of a termination codon 5' of seque nces encoding the transmembrane domain of a human FcgammaRII cDNA. Chi nese hamster ovary cells were transfected with the modified cDNA and t he secreted rsFcgammaRII purified from the tissue culture supernatant (to >95%, assessed by SDS-PAGE) using heat aggregated human immunoglob ulin G (IgG) immunoaffinity chromatography. The IgG-purified rsFcgamma RII was relatively homogeneous (approximately 31,000 M(r)) whereas the total unpurified rsFcgammaRII secreted into the tissue culture supern atant was heterogeneous relating to N-linked glycosylation differences . Functional in vitro activity of the rsFcgammaRII was demonstrated by : (a) ability to bind via the Fc portion of human IgG and mouse IgG (I gG2a>IgG1>>IgG2b); (b) complete inhibition of binding of erythrocytes sensitized with rabbit IgG to membrane-bound FcgammaRII on K562 cells; and (c) inhibition of the anti-Leu4-induced T cell proliferation assa y. Blood clearance and biodistribution studies show the rsFcgammaRII w as excreted predominantly through the kidney in a biphasic manner, wit h an alpha-phase (t1/2 approximately 25 min) and a beta-phase (t1/2 ap proximately 4.6 h); the kidneys were the only organs noted with tissue -specific accumulation. In vivo, the administration of rsFcgammaRII si gnificantly inhibited the immune complex-mediated inflammatory respons e induced by the reversed passive Arthus reaction model in rats. There was a specific and dose-dependent relationship between the amount of rsFcgammaRII administered, and the reduction in the size and severity of the macroscopic inflammatory lesion. Histological analysis of the s kin showed a diffuse neutrophil infiltrate in both control and rsFcgam maRII-treated rats, however the perivascular infiltrate and the red ce ll extravasation was less intense in the rsFcgammaRII-treated group. I t is likely that complement activation leads to neutrophil chemotaxis, but neutrophil activation via FcgammaRII, which results in inflammato ry mediator release, is inhibited. The data indicate that rsFcgammaRII is a potential therapeutic agent for the treatment of antibody or imm une complex-mediated tissue damage.