Protective immunity wanes rapidly after immunization of children with acellular pertussis (aP) vaccines and these vaccines do not prevent nasal colonization or transmission of Bordetella pertussis in baboons. In this study, we examined the role of tissue-resident memory T (T RM ) cells in persistent protective immunity induced by infection or immunization with aP and whole-cell pertussis (wP) vaccines in mice. Immunization of mice with a wP vaccine protected against lung and nasal colonization, whereas an aP vaccine failed to protect in the nose. IL-17 and IFN-γ-secreting CD69 + CD4 + T RM cells were expanded in the lung and nasal tissue after B. pertussis challenge of mice immunized with wP, but not aP vaccines. However, previous infection induced the most persistent protection against nasal colonization and this correlated with potent induction of nasal tissue T RM cells, especially IL-17-secreting T RM cells. Blocking T cell migration to respiratory tissue during immunization with a wP vaccine impaired bacterial clearance, whereas transfer of T RM cells from convalescent or wP-immunized mice conferred protection to naïve mice. Our findings reveal that previous infection or wP vaccination are significantly more effective than aP vaccination in conferring persistent protective immunity against B. pertussis and that this is mediated by respiratory T RM cells.

Recent studies have suggested that the innate immune system can display characteristics of immunological memory and this has been called “innate immune memory” or “trained immunity.” Certain fungal products have been shown to induce epigenetic imprinting on monocytes/macrophages that results in heightened inflammatory responses to subsequent stimuli. Here we report that innate immune cells can be trained to be more anti-inflammatory following exposure to products of a helminth pathogen. Macrophages trained in vitro with Fasciola hepatica total extract (FHTE) had enhanced IL-10 and IL-1RA, but reduced TNF production upon re-stimulation with FHTE or TLR ligands and this was reversed by inhibitors of DNA methylation. In contrast, macrophages trained with β-glucan or Bacillus Calmette–Guérin had enhanced TNF production upon re-stimulation with Pam3cys or LPS. Furthermore, FHTE-trained macrophages had enhanced expression of markers of alternative activated macrophages (AAM). Macrophages from mice treated with FHTE expressed markers of AAM and had heightened IL-10 and IL-1RA production in response to FHTE or TLR ligands and had suppressed TNF and IL-12p40 production. Macrophages from mice treated with FHTE had reduced APC function and inhibited IL-17 production and the encephalitogenic activity of T cells in the experimental autoimmune encephalomyelitis (EAE) model. In addition, mice pre-treated with FHTE were resistant to induction of EAE and this was associated with a significant reduction in IL-17-producing γδ and CD4 T cells infiltrating the CNS. Our findings reveal that cells of the innate immune system can be trained in vitro or in vivo to be more anti-inflammatory by exposure to helminth products and this protects mice against the induction of a T cell-mediated autoimmune disease.

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Understanding the mechanism of protective immunity in the nasal mucosae is central to the design of more effective vaccines that prevent nasal infection and transmission of Bordetella pertussis. We found significant infiltration of IL-17-secreting CD4+ tissue-resident memory T (TRM) cells and Siglec-F+ neutrophils into the nasal tissue during primary infection with B. pertussis. Il17A−/− mice had significantly higher bacterial load in the nasal mucosae, associated with significantly reduced infiltration of Siglec-F+ neutrophils. Re-infected convalescent mice rapidly cleared B. pertussis from the nasal cavity and this was associated with local expansion of IL-17-producing CD4+ TRM cells. Depletion of CD4 T cells from the nasal tissue during primary infection or after re-challenge of convalescent mice significantly delayed clearance of bacteria from the nasal mucosae. Protection was lost in Il17A−/− mice and this was associated with significantly less infiltration of Siglec-F+ neutrophils and antimicrobial peptide (AMP) production. Finally, depletion of neutrophils reduced the clearance of B. pertussis following re-challenge of convalescent mice. Our findings demonstrate that IL-17 plays a critical role in natural and acquired immunity to B. pertussis in the nasal mucosae and this effect is mediated by mobilizing neutrophils, especially Siglec-F+ neutrophils, which have high neutrophil extracellular trap (NET) activity.

Tissue‐resident memory CD4 T (TRM) cells induced by infection with Bordetella pertussis persist in respiratory tissues and confer long‐term protective immunity against reinfection. However, it is not clear how they are maintained in respiratory tissues. Here, we demonstrate that B. pertussis‐specific CD4 TRM cells produce IL‐17A in response to in vitro stimulation with LPS or heat‐killed Klebsiella pneumoniae (HKKP) in the presence of dendritic cells. Furthermore, IL‐17A‐secreting CD4 TRM cells expand in the lung and nasal tissue of B. pertussis convalescent mice following in vivo administration of LPS or HKKP. Bystander activation of CD4 TRM cells was suppressed by anti‐IL‐12p40 but not by anti‐MHCII antibodies. Furthermore, purified respiratory tissue‐resident, but not circulating, CD4 T cells from convalescent mice produced IL‐17A following direct stimulation with IL‐23 and IL‐1β or IL‐18. Intranasal immunization of mice with a whole‐cell pertussis vaccine induced respiratory CD4 TRM cells that were reactivated following stimulation with K. pneumoniae. Furthermore, the nasal pertussis vaccine conferred protective immunity against B. pertussis but also attenuated infection with K. pneumoniae. Our findings demonstrate that CD4 TRM cells induced by respiratory infection or vaccination can undergo bystander activation and confer heterologous immunity to an unrelated respiratory pathogen.