Differences in lymphocyte subpopulations from peripheral blood and lymphoid organs in natural caprine tuberculosis infection

Although the cell-mediated immune response is known to be a critical factor in host defence against intracellullar mycobacterial infection, the different components of the T-cell response are unclear, particularly in caprine infection. In this study we examine the differences in the lymphocyte population of peripheral blood, spleen and mediastinal and superficial lymph nodes in 11 naturally infected goats showing positive reactions in the comparative tuberculine intradermal test. According to the different types of lesion showing, the goats were classified into proliferative or exudative tuberculosis. The results obtained by fflow cytometry analysis indicated that the main differences in peripheral blood were in the CD4 T-cell population, which decreased markedly in goats with exudative tuberculosis, while the CD8 and B cells increased in number. The gamma/delta T cells did not show significant differences in either type of tuberculosis, while interleukin-2 receptor cells decreased slightly in the exudative tuberculosis. The CD4 : CD8 ratio was higher than 1 in goats with proliferative tuberculosis and lower than 1 in goats with exudative tuberculosis. In general, the lymphoid organs of the goats with exudative tuberculosis showed a significant increase in the number of CD8 T cells (CD4: CD8 ratio of less than 1) whereas no significant differences were observed in the CD4 T population between either type of tuberculosis.