Analysis of the immune responses in experimental and human Mycobacterial infections
Lagrange, P.H. (1983) Analysis of the immune responses in experimental and human Mycobacterial infections. Indian Journal of Tuberculosis, Supplement, 30 (3). pp. 12-23.
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In a susceptible host, inoculation of pathogenic mycobacteria induces, through its own multiplication in macrophages, specific and non specific immune responses. The specific responses are well characterised by mechanisms which prevent further multiplication of the mycobacteria in phagocytic mononuclear cells and inhibit further dissemination. This event, called macrophage activation, is specific in its induction but it is non specific in its expression. The specificity of the immune response to pathogenic mycobacteria or for intracelluiar multiplying bacteria, has been shown to be mediated by thymus-dependant lymphocytes (T. lymphocytes) which become stimulated in the T cell area of the draining lymphoid tissue during the induction phase occurring after inoculation of the bacteria. Simultaneously, at the site of entry of the mycobacteria, the host develops a local granulomatous reac-tion which is mediated by the systemic cell hypersensitivity. This sensitivity is also called Delayed-type Hypersensitivity (DTH) and is expressed locally when the circulating specific committed T cells are able to recognize in the tissues the specific antigen presented by the antigen-presenting cell (ARC). In the case of mycobacterial antigens, the APC are mostly macrophages. The development of the specific DTH reaction is usually associated with the occurrence of an acquired resistance to subsequent virulent challenge of the same or related mycobacteria. This acquired resistance and hypersensitivity are transferable in normal recipients with T cells harvested from immune donors; however, in contrast to adoptive DTH, resistance is better expressed if the recipient mice have been non-lethally irradiated before the cell transfer. Non specific immunity, increased during mycobacterial infection, represents another hallmark of the development of cell-mediated immunity (CMJ) and can be detected in vivo or in vitro by measuring the increase in resistance of mononuclear phagocytes against unrelated intracellular multiplying pathogens (‘such as listeria). Quantitative and qualitative variations in the expression of these CMI parameters have been described in experimental animals and also in human beings during mycobacterial infections. The purpose of this review is to attempt to analyse observations obtained in human beings infected naturally with Mycobacterium tuberculosis or after being vaccinated with BCG and in experimental infections in animals in order to define general principles responsible for the variability of the immune responses after mycobacterial infections. According to these observations, deductions are made to explain the variability in effectiveness of BCG vaccination in humans and recommendations can be formulated to integrate the prophylaxis against mycobacterial diseases in general eradication campaigns.
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