Failure to induce delayed-type hipersensivity to Mycobacterium leprae in long-term treated lepromatous leprosy patients

Lepromatous leprosy (LL) patients whose bacillary load has decreased to almost undetectable levels by long-term chemotherapy failed to develop delayed-type hypersensitivity (DTH) to Mycobacterium leprae antigen following immunization with killed armadillo-derived m. leprae. When these LL patients were immunized with killed M. leprae in a mixture with live BCG, only DTH to purified protein derivative (PPD) was induced. These results are further evidence that immunological unresponsiveness to the leprosy antigen of patients with lepromatous leprosy is antigen-specific and non-reversible.

The histopathology of lepromatous leprosy in the nose

On the basis of clinical, histological and bacteriological assessments, 31 patients in Central India were selected and classified as having active but early lepromatous leprosy and 4 patients as having early borderline leprosy. From the nose of each patient an average of 4 biopsies were taken from particular sites of the septum and turbinates either by punch biopsy or dissection with a scalpel. The nasal tissues from all the lepromatous patients contained many acid-fast bacilli; no bacilli or abnormalities were seen in the nasal tissues from the borderline patients. The histopathology of these highly bacilliferous tissues is described. Bacilli were universally seen in macrophages , but they were also seen in blood monocytes and polymorphs, fibroblasts, squamous and pseudo-columnar epithelium, kerati, peri- and endo-neurial cells of tiny nerve bundles, erectile tissue, vascular plain muscle, perivascular histiocytes and frequently and abundantly in the cytoplasm of endothelial lining cells of lymphatics and of small blood vessels and free within the lumina of these vessels. Five basic mechanisms of scape of bacilli from the sunbmucosa on to the surface, and thus into the external environment, are described. Secondary infection, in the presence of an expansile lepromatous infiltrate, together with simple trauma to the surface epithelium, are the main factors in the discharge of bacilli. These histopathological observations are consistent with the findings from other recent studies on the nose in leprosy regarding (1) the large mumbers of morphologically intact and viable Myco. leprae excreted in the nasal mucus of lepromatous patients; (2) the clinical changes observed in the nose of such patients, and (3) the similar nasal involvement and excretion of Myco. leprae from the nose of mice inoculated with leprosy bacilli of human origen. On particular interest was the frequency and intensity of bacilli within the endothelial lining cells of small blood and lymph vessels and the presence of bacilli free within the lumina of these vessels or within monocytes and polymorphs. The possible dynamic significance of these observations in the pathogenesis of leprosy is discussed. The significance of all these observations in relation to (1) the spresd of leprosy; (2) local factors in the nose which might favour the growth of Mico. leprae, and (3) the nose as a portal of entry, are discussed.