Ultrastructural features of epithelioid cell granuloma induced by intradermal injection of xenogeneic nerve tissue.

Epithelioid cell granulomas were induced in rabbits previously sensitised with human sensory peripheral nerve extract by skin testing with homogenate of sural nerve. Ultrastructurally some of the cells contained in their cytoplasm abundant and dilated rough endoplasmic reticulum filled with a moderately dense product while the cytoplasm of other cells contained numerous membrane-bound vesicles. These cells show all the ultrastructural characteristics of epithelioid cells found in human granulomatous disease and in human states of granulomatous hypersensitivity. Thus we have developed an animal model which supports the concept of granulomatous hypersensitivity as a distinct entity in humans to be differentiated from foreign body and delayed-type hypersensitivity reactions. The model may also prove important in elucidating the pathogenesis of granuloma formation in non-lepromatous leprosy and other granulomatous disease and in defining the nature of the products of epithelioid cells.