Presence of soluble, Mycobacterium leprae-derived antigen in the inflammatory exudate of reactional lepromatous leprosy

By immunofluorescence techniques, immunocomplexes deposition in the wall and periphery of dermal blood vessels have been demonstrated in 8 leprosy-reaction lesions (4 ENL, 4 Lucio's phenomena). Two additional ENL lesions were negative for the presence of immunocomplexes with anti-IgM, IgG, IgA, C3 and C1q antisera. The 10 leprosy reaction lesions, however, were positive for the presence of Mycobacterium leprae-derived soluble antigen. This antigen, visualized with a potent human anti-M. leprae antiserum, was often found in and around the dermal blood vessels showing vasculitis and always in the macrophages (Virchow's cells) present in the leprous granulomas. This finding was independent of the presence of intact or fragmented M. leprae in those locations. The role of mycobacteria derived material in the genesis of type-2 leprosy reactions is discussed.