Factors mediating the binding of immune complexes to cryostat sections of psoriatic lesions

Sheep erythrocytes sensitized with rabbit IgG, or complexes of horseradish peroxidase (HRP) and rabbit IgG antibodies to HRP bound to cryostat sections of psoriatic and other skin lesions (lichen planus, discoid lupus erythematosus, sarcoidosis, and mycosis fungoides). Immune complexes with reduced and alkylated IgG (RA-IgG) reacted with preparations of soluble rheumatoid factors (RF) and with sections of RF-coated sheep erythrocytes equally well as did untreated IgG. However, RA-IgG did not react with sections containing FcR-positive cells. These complexes bound either weakly or not at all to skin sections. IgG inhibited the binding of immune complexes to all skin control sections, while RA-IgG only inhibited the binding of complexes to sections of RF-coated cells. Anti-Clq did not inhibit the binding of immune complexes to any section. Periodic acid and formaldehyde abolished FcR activity, whereas neither the activity of soluble RF nor of RF in sections was affected. Only sections of lesional skin from patients with highly active psoriasis and sarcoidosis showed some binding of immune complexes after treatment with periodic acid or formaldehyde. Apparently, the binding of immune complexes in vitro to sections of psoriatic and other skin lesions is mainly mediated by FcR.