Granulomatous hypersensitivity induced by sensory peripheral nerve

Abstract

THE nature of granulomas remains uncertain. In sarcoidosis and Crohn's disease of the ileum, the aetiology is unknown. Even where a causative organism has been identified, as in tuberculosis and non-lepromatous leprosy, the role the mycobacteria play in the development of the granuloma is obscure¹. There is no animal model available for the study of granulomatous hypersensitivity. But in susceptible human subjects it is possible to produce granulomas with tubercle formation by skin testing with zirconium² or beryllium³. Similarly, in sarcoidosis, granulomas with tubercles occur in patients skin-tested with Kveim antigen (sarcoid spleen or lymph node suspension). These reactions are specific for each antigen and independent of dose. Thus, chronic states of altered tissue reactivity or granulomatous hypersensitivity can be found in humans⁴. We have shown that rabbits develop skin lesions after injection with homogenates of peripheral sensory nerve⁵. Now we report that these lesions sometimes possess organised granulomas in tubercles, and that similar granulomas can be produced by skin-testing rabbits sensitised with sensory nerve, using cutaneous nerve as the challenging antigen. These results suggest that granulomas may sometimes be an autoimmune response to tissue antigens: in the case of non-lepromatous leprosy, to an antigen in peripheral nerve containing sensory fibres⁵. A specific diagnostic test for leprosy is therefore a possibility.