We have examined the formation, participation and functional specialization of virus-reactive Foxp3+ regulatory T cells (Tregs) in a mouse model of influenza virus infection. “Natural” Tregs generated intra-thymically based on interactions with a self-peptide proliferated in response to a homologous viral antigen in the lungs, and to a lesser extent in the lung-draining mediastinal LN (medLN), of virus-infected mice. By contrast, conventional CD4+ T cells with identical TCR specificity underwent little or no conversion to become “adaptive” Tregs. The virus-reactive Tregs in the medLN and the lungs of infected mice upregulated a variety of molecules associated with Treg activation, and also acquired expression of molecules (T-bet, Blimp-1 and IL-10) that confer functional specialization to Tregs. Notably, however, the phenotypes of the T-bet+ Tregs obtained from these sites were distinct, since Tregs isolated from the lungs expressed significantly higher levels of T-bet, Blimp-1 and IL-10 than did Tregs from the medLN. Adoptive transfer of antigen-reactive Tregs led to decreased proliferation of anti-viral CD4+ and CD8+ effector T cells in the lungs of infected hosts, while depletion of Tregs had a reciprocal effect. These studies demonstrate that thymically-generated Tregs can become activated by a pathogen-derived peptide and acquire discrete T-bet+ Treg phenotypes while participating in and modulating an antiviral immune response.

We have examined the formation, participation and functional specialization of virus-reactive Foxp3+ regulatory T cells (Tregs) in a mouse model of influenza virus infection. “Natural” Tregs generated intra-thymically based on interactions with a self-peptide proliferated in response to a homologous viral antigen in the lungs, and to a lesser extent in the lung-draining mediastinal LN (medLN), of virus-infected mice. By contrast, conventional CD4+ T cells with identical TCR specificity underwent little or no conversion to become “adaptive” Tregs. The virus-reactive Tregs in the medLN and the lungs of infected mice upregulated a variety of molecules associated with Treg activation, and also acquired expression of molecules (T-bet, Blimp-1 and IL-10) that confer functional specialization to Tregs. Notably, however, the phenotypes of the T-bet+ Tregs obtained from these sites were distinct, since Tregs isolated from the lungs expressed significantly higher levels of T-bet, Blimp-1 and IL-10 than did Tregs from the medLN. Adoptive transfer of antigen-reactive Tregs led to decreased proliferation of anti-viral CD4+ and CD8+ effector T cells in the lungs of infected hosts, while depletion of Tregs had a reciprocal effect. These studies demonstrate that thymically-generated Tregs can become activated by a pathogen-derived peptide and acquire discrete T-bet+ Treg phenotypes while participating in and modulating an antiviral immune response.