Bordetella spp. block eosinophil recruitment to suppress lung iBALT formation

A characteristic that differentiates pathogenic and opportunistic bacteria is that pathogens have been selected by their ability to suppress host inflammatory responses allowing colonization and persistence. Bordetella spp. are respiratory pathogens characterized for the arsenal of mechanisms they use to manipulate host immune responses. We have previously characterized a B. bronchiseptica mutant, RB50{Delta}btrS, that is not able to suppress host immune responses, resulting not only in rapid clearance of the infection but also long-term lung sterilizing immunity against reinfection with the three classical Bordetella spp. Interestingly, this strong immune response requires eosinophils. In this work our results indicate that wildtype B. bronchiseptica, RB50, blocks eosinophil pro-inflammatory functions to prevent the rapid recruitment of B and T cells to the lung that results in iBALT formation. Moreover, eosinophils promote a TH17 microenvironment within the iBALT that might be responsible for the long-term robust protective immunity generated by infection with this mutant. Overall, this work provides a novel role for eosinophils as promoters of adaptive immune responses and protective immunity, while also indicating that bacteria actively manipulate those cells to promote long-term persistence and reinfection.