Cell-mediated immunological processes in leprosy.

A large number of organisms such as viruses, protozoa, helminths, fungi and bacteria, especially mycobacteria, need cell-mediated immunological processes for their elimination. As well as being involved in protection, cell-mediated immunological processes are also involved in a number of allergic reactions to products derived from mycobacteria. Cell-mediated immunological processes can be demonstrated by a number of in vitro reactions. Leprosy can present with a wide range of different clinical patterns. The clinical spectrum of leprosy can be shown to depend on the degree of the cell-mediated immune response of the host against Mycobacterium leprae. Thus in tuberculoid leprosy there is a high degree of cell-mediated immune response whereas in lepromatous leprosy such a response is virtually absent. There appears to be a constitutional predisposition to lepromatous leprosy. In addition to a specific loss of cell-mediated immune response against Myco. leprae, there is also a non-specific drop in the ability of patients with lepromatous leprosy to show other aspects of cell-mediated immune response, e.g., contact sensitivity and skin homograft rejection. There is also a relative impairment of the ability of lymphocytes to react in vitro. Lymph nodes from patients with lepromatous leprosy show a deficiency in those areas associated with the development of cell-mediated immune responses.The article includes a discussion on the possible causes of deficiencies in cell-mediated immune responses in lepromatous leprosy.