Transient immune deposits in the papillary dermis and in the epidermis. A light-microscopical study on the experimental Arthus reaction.

To have as further insight into the localizations of immune deposits in the skin the reversed passive and the passive Arthus reactions were carried out in the foot-pads skin of guinea-pigs using horseradish peroxidase as antigen. The transient localizations of immune deposits in the papillary dermis and in the epidermal cell layer were observed in the skin of the reversed passive Arthus reaction, but not in the skin of the passive Arthus reaction. Following the immune deposits in the papillae including the capillary walls and the dermoepidermal junction, the papillary dermis became widened, swollen, and edematous, being infiltrated by PMN's. In the epidermal layer, the immune deposits were found as fine granular aggregates adhering to the epidermal cells or to the dendritic cells. Although the immune deposits disappeared promptly from the papillae and the inflammatory reactions were slightly and transient, the epidermal cell layer became thickened, and several mitotic figures of the epidermal cells were observed.