Mature peripheral T cells are important to preserve thymus function and selection of thymocytes during Mycobacterium tuberculosis infection.

Evaluation of: Nobrega C, Nunes-Alves C, Cerqueira-Rodrigues B et al. T cells home to the thymus and control infection. J. Immunol. 190, 1646-1658 (2013). It is well documented that the thymus is a target organ for a large variety of pathogens (virus, bacteria, fungi and protozoa). Moreover, the presence of pathogen-derived antigens in the thymus of infected mice seems to interfere with the capacity of mature T cells to respond to the invading organism. In this way, Nobrega and colleagues demonstrated in 2010 that Mycobacterium avium infection in the thymus leads to the appearance of differentiated T cells tolerogenic for bacterial antigens. In the present and elegant study, the same group demonstrates that T-cell recirculation from the periphery to the thymus is a mechanism that allows the immune system to respond to thymic infection. A Mycobacterium-infected thymus increases the production of Th1-effector chemokines, such as CXCL9 and CXCL10, which in turn recruit CXCR3(+) peripheral T cells involved in intrathymic bacterial control. Taken together, these findings may represent an important issue of the host response, in terms of different pathogens able to infect the thymus.