Demonstration of mycobacterial antigens in nerve biopsies from leprosy patients using peroxidase-antiperoxidase immunoenzyme technique.

Peripheral nerve biopsies from patients with leprosy were stained with anti-Mycobacterium bovis (BCG) in a peroxidase-antiperoxidase (PAP) system to demonstrate intraneural mycobacterial antigens. Most M. leprae antigens have been shown to cross-react with BCG. Of the 30 biopsies from borderline tuberculoid (BT) patients 18 had acid-fast bacilli while 26 of them had demonstrable mycobacterial antigens in their nerves. All borderline lepromatous (BL) and lepromatous leprosy (LL) nerve biopsies had both M. leprae and mycobacterial antigens within them. Most of the antigens in the BT patients were seen to be extracellular. In BL and LL patients antigens were seen both extracellularly and intracellularly in Schwann cells and infiltrating macrophages. Mycobacterial antigens in BT nerves were always seen to be surrounded by a mononuclear cell reaction while in the BL and LL patients antigens could be seen with minimal cellular infiltrate and the neural architecture was more or less preserved. While bacilli could not be seen in BT patients who had been released from treatment for more than 4 years, mycobacterial antigens could still be seen in some patients who had been released from treatment for up to 5 years. Patients with no skin lesions but with large, painful, or tender nerves were found to have intraneural inflammation surrounding mycobacterial antigens, while those with a similar clinical picture but without tender or painful nerves showed no marked inflammation within their nerves despite the presence of mycobacterial antigens. From these findings it was concluded that immunologically mediated inflammatory response toward intraneurally located M. leprae antigens in conjunction with other host factors may be necessary for nerve damage in the BT leprosy patients. In the BL and LL patients the mechanisms of nerve damage are still unknown with certainty but local effects and immune-complex damage secondary to abundant M. leprae antigens are worth exploring. The use of immunohistological techniques should offer a new approach in the study of the immunopathology of leprosy.