The localization of immune complexes in epidermis and upper dermis: electron microscopic studies on reversed passive Arthus reaction.

A reversed passive Arthus reaction was induced in guinea pigs using horseradish peroxidase as antigen. An electron microscopic study on the cutaneous localization of the immune complexes was performed applying a peroxidase reaction. Precipitates of immune complexes were found within the walls of small blood vessels and among the collagen bundles in the dermis. The adherence of immune complexes to numerous eosinophils was observed and some of immune complexes were phagocytosed by neutrophils. The adherence of immune complexes to fibroblasts and the deposits of immune complexes in some areas of the basement membrane zone, especially in the zona diffusa, were found in the upper dermis and in the papillae. In the lower layers of the epidermis, we observed immune complexes adhering to the cell membranes of keratinocytes.