Bystander activation of Bordetella pertussis-induced nasal tissue-resident memory CD4 T cells confers heterologous immunity to Klebsiella pneumoniae.

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-1ß 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.

Type 1 interferons promote Staphylococcus aureus nasal colonization by inducing phagocyte apoptosis.

Staphylococcus aureus is an important human commensal which persistently colonizes up to 30% of the human population, predominantly within the nasal cavity. The commensal lifestyle of S. aureus is complex, and the mechanisms underpinning colonization are not fully understood. S. aureus can induce an immunosuppressive environment in the nasal tissue (NT) by driving IL-10 and IL-27 to facilitate nasal colonization, indicating that S. aureus has the capacity to modulate the local immune environment for its commensal habitation. Mounting evidence suggests commensal bacteria drive type 1 interferons (IFN-I) to establish an immunosuppressive environment and whilst S. aureus can induce IFN-I during infection, its role in colonization has not yet been examined. Here, we show that S. aureus preferentially induces IFN signaling in macrophages. This IFN-I in turn upregulates expression of proapoptotic genes within macrophages culminating in caspase-3 cleavage. Importantly, S. aureus was found to drive phagocytic cell apoptosis in the nasal tissue during nasal colonization in an IFN-I dependent manner with colonization significantly reduced under caspase-3 inhibition. Overall, loss of IFN-I signaling significantly diminished S. aureus nasal colonization implicating a pivotal role for IFN-I in controlling S. aureus persistence during colonization through its ability to induce phagocyte apoptosis. Together, this study reveals a novel strategy utilized by S. aureus to circumvent host immunity in the nasal mucosa to facilitate nasal colonization.

Staphylococcus aureus suppresses the pentose phosphate pathway in human neutrophils via the adenosine receptor A2aR to enhance intracellular survival.

IMPORTANCE: Staphylococcus aureus is one of the leading causes of antimicrobial-resistant infections whose success as a pathogen is facilitated by its massive array of immune evasion tactics, including intracellular survival within critical immune cells such as neutrophils, the immune system's first line of defense. In this study, we describe a novel pathway by which intracellular S. aureus can suppress the antimicrobial capabilities of human neutrophils by using the anti-inflammatory adenosine receptor, adora2a (A2aR). We show that signaling through A2aR suppresses the pentose phosphate pathway, a metabolic pathway used to fuel the antimicrobial NADPH oxidase complex that generates reactive oxygen species (ROS). As such, neutrophils show enhanced ROS production and reduced intracellular S. aureus when treated with an A2aR inhibitor. Taken together, we identify A2aR as a potential therapeutic target for combatting intracellular S. aureus infection.