Responses to Mycobacterium leprae by lymphocytes from new and old leprosy patients: role of exogenous lymphokines.

Lepromatous leprosy patients generally have reduced response to Mycobacterium leprae antigens in an in vitro lymphocyte transformation test, which could be due to insufficient generation of reactions or to active suppression of any reaction generated. We could detect 3 types of lack of reactivity: one which could be restored by the addition of supernatants from healthy, PHA-stimulated lymphocyte cultures, one which could not thus be restored and one in which the culture supernatant contained factors able to suppress mitogen responses of healthy cells. We compared responses of cells from untreated patients, patients treated for 12-20 months with multiple drug therapy and patients with up to 20 years of dapsone treatment; all types of the disease were represented. Untreated patients of all types had low responses which were not always reconstituted by lymphokine-rich supernatants, but they did not produce the non-specific soluble suppressive factors. In most cases, including BL/LL types, after the initial months of treatment, antigen response improved and was further increased by the addition of supernatants containing lymphokines. Most of the long-term-treated, stable patients had a lymphokine-reconstitutable antigen response, and in most cases also produced non-specific suppressive factor(s). The question as to why leprosy patients do not respond to M. leprae antigen is a complex one; our results suggest that it is related to the activity of the infection in each group of patients.

Mycobacterium leprae-burdened macrophages are refractory to activation by gamma interferon.

Mycobacterium leprae grows to enormous numbers in the nu/nu mouse footpad, producing granulomas resembling those of lepromatous leprosy in humans. Footpad granuloma cells gorged with M. leprae were established in primary cell culture to examine their functional capabilities. These cells were classified as macrophages by the following criteria: positive staining for nonspecific esterase, reduction of Nitro Blue Tetrazolium during phagocytosis of Candida albicans, possession of Fc receptors, and possession of Mac-1 antigen. Footpad macrophages also phagocytized and supported the intracellular growth of Toxoplasma gondii. However, unlike peritoneal macrophages, footpad macrophages could not be activated to kill or inhibit T. gondii by macrophage-activating factor produced by mitogen-stimulated spleen cells or by recombinant gamma interferon. Thus, although the lepromatous macrophages appeared to be normal in many of their functions, they were defective in response to macrophage-activating signals.

Mechanism of immunosuppression in leprosy: presence of suppressor factor(s) from macrophages of lepromatous patients.

Human peripheral blood mononuclear cell proliferation induced by Mycobacterium leprae could be inhibited by the suppressor factor in the lysate of the macrophages of lepromatous leprosy patients. Macrophages from normal subjects and tuberculoid patients did not show production of a suppressor factor. Inhibition occurred only when the factor was present in the initial stages of lymphocyte culture. The factor is heat stable and nondialyzable. Proliferation induced by some mycobacteria and concanavalin A could also be blocked by the factor. Interestingly, blastogenic response by a few other antigens and phytohemagglutinin could not be inhibited by the suppressor factor. Mononuclear cells pretreated with such lysate from lepromatous macrophages for 24 h could induce suppressive activity in the cells in vitro in an autologous system. Treatment of these cells with carbonyl iron after the induction phase, to remove phagocytic cells, did not abolish their suppressive activity. The lepromatous macrophage lysate also generated suppressive activity in a T-lymphocyte-enriched population of normal subjects. These studies are interpreted to indicate that immunosuppression in lepromatous patients is produced by both macrophages and T lymphocytes. The exact phase in which either of these cells acts as a suppressor may be different. Specific suppression by macrophages to M. leprae can be an early event, and nonspecific suppression by T lymphocytes may be a later event in the course of lepromatous leprosy.

Mechanism of immunosuppression in leprosy: presence of suppressor factor(s) from macrophages of lepromatous patients

Human peripheral blood mononuclear cell proliferation induced by Mycobacterium leprae could...

In-vitro modification of membrane receptors on cells of the mononuclear phagocyte system.

EA and EAC receptors have been studied on non-elicited and paraffin-induced macrophages, under a variety of culture conditions in vitro, for up to 7 days. A large decrease in the number of macrophages showing EAC receptors was found after treatment of the cells with BCG, but not "inert" particles such as latex and zymosan. This was reversible by 7 days. In the presence of a toxic material, Al(OH)3, both EA and EAC receptors were partially lost. The results obtained have been related to previous results obtained with cryostat sections of human leprosy skin lesions.