Lepra (leprosy) - What's going on?

The development of various morphoclinical types of leprosy caused by the same pathogen is determined by the characteristics (level) of T-cell immunity, the ability to react with DTH to M. leprae antigens. In case of failure of the cellular immune response in combination with active production of humoralantibodies develops the lepromatous type of leprosy, and with intense cellularresponse to the Th1 type - tuberculoid type of leprosy. Since M. leprae are obligate intracellular parasites of cells of the mononuclear phagocyte system(SMF), the macrophage occupies a central place in the immune response system in leprosy. In the lepromatous type of leprosy, the SMF cells are represented by both ordinary macrophages and large cells containing large quantities of M. leprae with varying degrees of cytoplasm vacuolization ("leprosy cells" or "Virchow cells"), and in the tuberculoid type of leprosy, i.e. in low-bacterial forms, by epithelioid cells and typical Langhans cells. In the tuberculoid type of leprosyclear foci of epithelioid cells are surrounded by a lymphoid border (tuberculous tubercle); the granuloma directly reaches the epidermis, signs of hypersensitivity are noted (deep erosion of the epidermis, thickening and central caseation of the cutaneous nerves, fibrinoid necrosis in the dermis, the presence of giant Langhans cells). Small nerves are usually not determined, since they are destroyed or heavily infiltrated. M. leprae is difficult to detect as single cells in the tissue of the thickened nerve or they are not detected.

In the undifferentiated form of leprosy, granuloma does not develop, but an infiltrate of a simple inflammatory structure with a large or small content of M. leprae located intracellularly appears.

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