In mild cases of leprosy there is frequently an associated immunological suppression that is specific for M. leprae antigens. At present, little is known of the mechanisms by which pathogens inhibit immune responses. It seems probable that it is due to interference with the immune functions of B cells, T cells or macrophages. Since many intracellular bacteria infect macrophages, it might be expected that they compromise the role of these cells in an immunological response. Perhaps this is why it does not seem to be a commonly used strategy of the bacteria.
Some pathogens can avoid exposing themselves to immune forces.
Intracellular pathogens can evade host immune responses as long as they stay inside of infected cells and they do not allow microbial Ag to form on the cell surface. This is seen in macrophages infected with Brucella , Listeria or M. leprae . The macrophages support the growth of the bacteria and at the same time give them protection from immune responses. Some pathogens persist on the luminal surfaces of the GI tract, oral cavity and the urinary tract, or the lumen of the salivary gland, mammary gland or the kidney tubule. If there is no host cell destruction, the pathogen may avoid inducing an inflammatory response, and there is no way in which sensitized lymphocytes or circulating antibodies can reach the site to eliminate the infection.