Control of Persistent Salmonella Infection Relies on Constant Thymic Output Despite Increased Peripheral Antigen-Specific T Cell Immunity.

Recent thymic emigrants are the youngest subset of peripheral T cells and their involvement in combating persistent bacterial infections has not been explored. Here, we hypothesized that CD4(+)recent thymic emigrants are essential immune mediators during persistentSalmonellainfection. To test this, we thymectomized adult mice either prior to, or during, persistentSalmonellainfection. We found that thymic output is crucial in the formation of protective immune responses during the early formation of aSalmonellainfection but is dispensable once persistentSalmonellainfection is established. Further, we show that thymectomized mice demonstrate increased infection-associated mortality and bacterial burdens. Unexpectedly, numbers ofSalmonella-specific CD4(+)T cells were significantly increased in thymectomized mice compared to sham control mice. Lastly, we found that T cells from thymectomized mice may be impaired in producing the effector cytokine IL-17 at early time points of infection, compared to thymically intact mice. Together, these results imply a unique role for thymic output in the formation of immune responses against a persistent, enteric pathogen.