Study on the roles of CD4+ and CD8+ T cells in the expression of host resistance to Mycobacterium leprae infection induced in athymic nude mice

The contribution of CD4+ or CD8+ T cells in the host resistance to Mycobacterium leprae was investigated. Athymic BALB/c nude mice were infected subcutaneously with M. leprae into the foot pads 1 or 3 weeks after adoptive transfer with whole, CD4 T cell-depleted, or CD8 T cell-depleted lymphocyte fractions prepared from spleen cells (SPCs) of euthymic BALB/c mice. SPCs from all of the recipient mice showed nearly the same levels of proliferative responses to phytohemagglutinin (PHA) and lipopolysaccharide, except that those of mice transferred with CD4 T cell depleted lymphocytes showed somewhat reduced mitogenic responses to PHA. Significantly potentiated host resistance to the infection was seen, as evidenced by the obviously reduced bacterial growth in all three groups of recipient mice compared to that seen in control mice, that is, 4.7- to 6.4-log unit decreases in the bacterial loads were observed. Levels of the reduction conferred by CD 4 T cell-depleted lymphocytes were comparable to that of CD8 T cell-depleted lymphocytes. This suggests that both CD4 and CD8 T cells are important for the expression of resistance to M. leprae infection.