induces a strong Th1 response that subsequently declines in C57BL/6 mice.

is a fast-growing species of saprophytic bacteria that is widely distributed. To understand the host immune responses induced by isolated from bovine submaxillary lymph nodes, C57BL/6 mice were infected with reference strain Bacillus Calmette-Guérin (BCG) and isolated using intraperitoneal injections. Comparison of the bacterial replication and organ pathology between and BCG revealed that was more malignant than in mice. We also demonstrated that serum from the -infected mice contained a higher expression level of gamma-interferon (IFN-γ), tumor necrosis factor alpha, monocyte chemoattractant protein-1, interleukin (IL)-4, IL-12, IL-10 and transforming growth factor beta than did the other groups, especially after week 4. Furthermore, when the numbers of CD3⁺CD4⁺IFN-γ⁺ and CD3⁺CD4⁺IL4⁺cells in the infected mice were observed by flow cytometry, we found that a powerful T helper 1 (Th1) response was induced by infection, which was associated with the emergence of CD3⁺CD4⁺IFN-γ⁺cells. However, the Th1 response declined over time, which was associated with appearance of the CD4⁺CD25⁺FoxP3⁺ and CD4⁺CD25⁺CD152⁺Treg cell reaction. In addition, a strong Th2 response was found. Finally, we found that infection increased the production of type I IFNs, which was associated with a reduced Th1 response.