Whooping cough is a highly contagious respiratory disease caused by Bordetella pertussis (Bp). Recently, the prolonged nature of whooping cough has been associated with a delay in Th17 responses, which are essential to resolve the infection. While investigating the IFNα-driven delay in Th17 responses during Bp infection, we noted a parallel rise of Th17-like Tregs secreting IL-17. Similar T cell hybrids have demonstrated either inflammatory or suppressor function. In this study we phenotypically and functionally characterized Th17-like Tregs in mice infected with Bp to test the hypothesis that these cells are derived from Tregs and display a suppressor role to specifically control the robust rise in Th17 inflammation during late stages of infection. Phenotypic analysis of the Th17-like Tregs revealed high frequencies expressing cytokines and trafficking markers similar to that of Th17. However, the abundance of Th17-like Treg expressing regulatory markers such as CTLA-4, OX-40 and PD-1, resemble a Treg profile. Furthermore, Th17-like Tregs express the thymic-derived nTreg marker, Helios, and were detected in the lungs during late infection but not in the blood or thymus, which suggests their derivation from lung nTregs. When IFNα was spiked into a Th17-polarized allogeneic assay, T-cell differentiation skewed towards Th17-like Tregs. In vitro functional analyses of these cells confirmed their suppressive nature. These data imply that there is a balance between IFNα Treg-favoring conditions and a Th17-polarizing environment that push Tregs to a Th17-like state during Bp infection. This study contributes valuable information about adaptive IL-17 responses that are crucial to the resolution of whooping cough.

Whooping cough is a highly contagious respiratory disease caused by Bordetella pertussis (Bp). The prolonged nature of whooping cough has been associated with delayed Th17 responses, which are essential to resolve the infection. Regulatory T cells (Treg) are historically immunosuppressive, but have recently been demonstrated to facilitate proper immune responses during certain infections and to occasionally adapt proinflammatory phenotypes. Because Treg and Th17 cells are considered “brothers in arms,” we evaluated the role of Tregs during immune response to B. pertussis. Here, we test the hypothesis that Tregs are crucial for generating a proinflammatory response that resolves whooping cough. We show that homeostatic lung Tregs acquire a highly proliferative Th17 phenotype during Bp infection in mice and that the frequency of this Th17-like Tresg (T17reg) population raises in parallel with Th17 influx and expansion at late phases of infection. Our data suggests that the frequency of lung T17reg may be modulated by levels of IFNa and IL-2 in the lung. Depleting Foxp3+ cells throughout Bp infection resulted in decreased MHC class II expression on dendritic and endothelial cells, suggesting reduced APC maturation. Additionally, Treg knockout lead to increased lung IL-2 levels (which may diminish Th17 differentiation/accumulation) and compromised IL-17 secretion. Moreover, infected mice lacking Treg had an increased Bp load in the lungs. Our data support Tregs facilitating and assisting Th17 immune responses to Bp to help resolve the infection.