Study of peripheral blood cell populations involved in the immune response of goats naturally infected with Mycobacterium caprae

Tuberculosis in goats caused by Mycobacterium bovis and Mycobacterium caprae has noteworthy sanitary and economic implications. Current diagnostic assays are based on cellular immunity and although they have demonstrated a high sensitivity, some animals remain undetected. In the present study, flow cytometry has been used to determine changes in CD4+, CD8+ and CD25+ T cell populations in peripheral blood from naturally infected goats. Proportion of lymphocytes producing PPD-specific interferon-gamma (IFN-γ) was calculated and an ELISA for detection of PPD-specific IFN-γ was performed to measure the cytokine in plasma. The infected goats showed percentages of CD4+ T cells between 27.31% and 47.23% and there were not significant differences (p = 0.113) with the non-infected control goats although the mean percentage was lower in this group. Regarding CD8+ T cells, a higher percentage was observed in healthy goats compared to controls (p = 0.081). The mean percentage of lymphocytes expressing CD25 without antigen stimulation (30.65 ± 3.91) was higher in lesion and/or culture-positive animals than in the controls (21.84 ± 1.21; p = 0.053). The percentage of CD4+/IFN+ T cell population stimulated with bovine PPD was a reliable marker of infection, since the mean percentage in the infected goats was significantly higher than in the controls (p < 0.05). Tuberculosis in goats caused by M. caprae induced changes in cellular populations similar to those described for M. bovis in cattle.