T-helper cells that produce IL-17 are recognized as a significant subset within cell-mediated adaptive immunity. These cells are implicated in both the pathology of inflammatory disorders as well as the clearance of extracellular infections and the maintenance of the microbiota. However, the dynamic nature of this cell type has created controversy in understanding Th17 induction as well as Th17 phenotyping, since these cells may switch from Th17 to Treg or Th17 to Th1 cytokine profiles under certain conditions. This review highlights recent advances in Th17 cells in understanding their role in commensal regulation, sex difference in immune outcomes and the immunology of pregnancy, as well as inventive experimental models that have allowed for an increased understanding of Th17 regulation and induction.

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Objective We demonstrated the serotype independent immunity of Klebsiella pneumoniae (K. pneumoniae) vaccine. We would like to declare next if the noble effect is dependent on the antibody specific manner. Methods Mice were vaccinated via intranasal with Kp serotype 2 OMPx adjuvanted with heat-labile enterotoxin A1 domain (LTA1) and boosted at 3 weeks after the initial immunization. Protective immunity was compared among the C57Bl/6 mice, STAT3 fl/fl×CD4 Cre mice, and Il21r −/− mice by infecting with K1 strain of K. pneumoniae. Lung T-cell responses were evaluated by FACS and ELISPOT as well as K1 strain specific antibodies were assessed by ELISA. Results CD4+ T-cells of the vaccinated lungs in the CD4+ STAT3 deficient mice were significantly decreased compared to the WT mice and the Il21r −/− mice, and IL17A response by ELISPOT were significantly reduced as well. Meanwhile, K1 strain specific IgG in the serum and IgA in the lung homogenates of vaccinated WT mice were significantly increased in vaccinated mice and these responses were reduced in vaccinated CD4+ STAT3 deficient mice and Il21r −/− mice. Furthermore, vaccine induced protection was compromised in vaccinated CD4+ STAT3 deficient mice whereas the protection as well as antigen elicited lung IL-17 responses were maintained in Il21r −/− mice. Conclusions STAT3 activation in CD4+ T-cells regulated by IL-21R signaling are required for the K. pneumoniae specific antibodies, but these antibody responses were dispensable for the serotype independent immunity LTA1 adjuvanted K. pneumoniae vaccine. However, CD4 STAT3 was essential for Th17 immunity and therapeutic efficacy of the vaccine.

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Objective Multidrug-resistant of Klebsiella pneumoniae (K. pneumoniae) has emerged as a global threat. Vaccination for at high-risk populations could be a promising strategy to prevent and control the disease. Methods Mice were vaccinated via intranasal with a monovalent vaccine encoding Kp serotype 2 OMPx or a quadrivalent vaccine encoding OmpC, OmpW, Omplolb, and Omp36k, adjuvanted with heat-labile enterotoxin A1 domain (LTA1). Protective immunity was assessed by performing a pulmonary challenge with a heterologous mucoid serotype K1 strain of K. pneumoniae. Lung T-cell responses were evaluated mainly by FACS, ELISPOT, and LUMINEX. We also examined inflammatory cell changes by hematoxylin-eosin stain and immunofluorescence. Results Flow cytometry and ELISPOT analysis revealed that CD4+ T cells were significantly increased in the lungs of the monovalent or quadrivalent vaccinated mice and that a considerable fraction of them produced IL17A. And the supernatant of these cells also showed the significant production of IL-17A. Importantly, vaccinated mice showed a significant decrease in CFU in the lung and spleen, compared with mock-vaccinated mice. Finally, we observed that only lungs of intranasally vaccinated mice had lymphocytic structures around bronchi and vessels. Characterization of these structures by immunofluorescence confirmed the presence of inducible bronchus-associated lymphoid tissue (iBALT) – a structure that can not only support local induction of protective immunity but provide a long-term niche for vaccine-induced lymphocytes. Conclusions These data support the therapeutic value of intranasal vaccination strategies to prevent K. pneumoniae infections.

Objective Mucosal immunization with a Klebsiella pneumoniae (Kp) vaccine elicits noble CXCR6+CD4+ T cells that mediate serotype independent immunity, but the stability of this response is unclear. Thus we conducted experiments to determine if these cells circulate and whether they could be depleted by a depleting anti-GK1.5 mAb. Methods Mice were vaccinated via intratracheal with Kp serotype 2 OMPx adjuvanted with heat-labile enterotoxin A1 domain (LTA1) and boosted at 3 weeks after the initial immunization. T-cell responses were evaluated by FACS and ELISPOT. CD4+ T cell depletion in the immunized lung, lymph nodes, and spleen by administering 300ug anti-GK1.5 mAb intraperitoneally was examined using a secondary antibody for anti-GK1.5 mAb. Finally, lung and spleen CD4+ T cells of intratracheally immunized CD45.1+ C57BL/6 mice were transferred to CD45.2+ C57BL/6 mice and Rag2−/− mice. Results Immunized lung CD4+ T cells were increased equivalently in both C57BL/6 mice and Cxcr6−/− mice, demonstrating that CXCR6 was dispensable for the formation of lung CD4+ T cells. Splenic CD4+ T cells were > 95% depleted with anti-GK1.5 mAb. In contrast, < 5% of vaccine elicited lung CD4+ T cells were depleted despite being well coated by the antibody, strongly suggesting that these cells are TRM cells. Additionally, using an adoptive transfer model, we found that lung CD4+ T cells preferentially homed to lung compared to splenic CD4+ T cells. We next performed single-cell RNAseq on these cells and elucidated several unique adhesion molecules such as Embigin, Ramp1, Lgals1, and Thy1 besides Cxcr6. Conclusions These data support that vaccine strategies can be developed by targeting a unique feature of tissue-resident memory CD4+ T cells in lungs.

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