Properties of solubilized Fc gamma-receptors from psoriatic scales

Extracts from psoriatic scales, prepared using Tris-HCl buffer containing ethylenediaminetetraacetatic acid (EDTA) and 2-mercaptoethanol (ME), agglutinated erythrocytes (E) sensitized with IgG antibodies (A) (EA), but not E or E sensitized with F(ab')2-fragments of IgG. The agglutination was inhibited by IgG and Fc fragments of IgG, but not by IgA, IgM or F(ab')2-fragments of IgG. Partially reduced and alkylated IgG did not inhibit the agglutination, indicating that an inter-heavy-chain disulphide-linked Fc region is required for binding of FcR. The extracts inhibited EA, but not E or EAC rosette formation with mononuclear cells. The results strongly indicated that the extract contained functionally active FcR. The agglutinating activity of the extract was not affected by treatment with periodic acid or formaldehyde, whereas heat reduced the activity. Using a monoclonal antibody (B1D6) a functionally active 40 kDa FcR with low affinity for native IgG was purified from the scale extract. The extracts also contained FcR activity not recognized by B1D6.