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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Thesis
  • Peer Reviewed
UC Davis Electronic Theses and Dissertations (2023)

Systemic Salmonella enterica infections are caused by serovars Typhi and Paratyphi, causing typhoid, and other serovars, which cause invasive non-typhodial Salmonellosis (iNTS). These infections cause about 200,000 deaths per year and thus are a large public health burden. Currently, the vaccines that are approved for typhoid are not given to individuals who live in endemic areas due to low efficacy and there are no approved vaccines for iNTS. Thus, an effective vaccine is desperately needed to combat these infections. How the host naturally protects itself from pathogens is required to make an effective vaccine. CD4 T cells are required for protection against systemic Salmonella. CD4 T cell memory is composed of three subsets: central, effector and tissue resident memory. Central memory T cells (TCM) circulate throughout the secondary lymphoid organs (SLOs) and blood while effector memory T cells (TEM) circulate throughout the SLOs, blood and non-lymphoid tissues (NLTs). Both TCM and TEM circulate the body looking for cognate antigen to be reactivated and therefore, together are termed circulating memory. The third subset tissue resident memory T cells (TRM) do not circulate and resides in previously infected tissues and become the front line of defense for subsequent infections. Previously, CD4 TRM in the liver has been shown to be required for complete protection against systemic Salmonella. Thus, to make an effective vaccine, this memory subset needs to be induced. However, how to induce the formation of CD4 TRM in the liver during vaccination is currently unknown. Previously, transcription factors have been shown to be important in the formation of CD8 TRM in a variety tissues and allow CD8 TRM to adapt and survive in the tissue microenvironments. In this study we demonstrate a novel way transcription factors impact TRM formation. T-bet acts upstream of CD4 TRM differentiation in tissues and T-bethi CD4 T cells express higher levels of LFA-1 which allow these TRM precursors to compete for the competitive liver niche where they can access signals in the liver microenvironment which will induce the CD4 T cells to become TRM. These TRM differentiation signals have previously been interrogated in CD8 TRM formation in a variety of tissues with inflammation and pro-inflammatory cytokines driving CD8 TRM formation. In this study we demonstrated that liver inflammation increases CD4 TRM formation in the liver with pro-inflammatory cytokines, IL-2 and IL-1 required for optimal CD4 TRM formation. Additionally, adding liver inflammation enhances the protection provided by Salmonella specific subunit vaccination which is partially protective. Thus, this study has demonstrated there are two phases in CD4 TRM formation in the liver. In the secondary lymphoid organs, CD4 T cell priming impacts T-bet expression and T-bethi CD4 T cells have a higher chance of accessing the liver niche by increased LFA-1 expression. Once in the liver microenvironment, liver inflammation, specifically IL-2 and IL-1, stimulated by Salmonella infection induces CD4 T cells to become TRM. This understanding of CD4 TRM formation can further be applied to vaccine design for systemic Salmonella infection and aid in combating this large public health burden.

    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2023)
    Hepatic CD4 tissue-resident memory T cells (TRM) are required for robust protection against Salmonella infection; however, the generation of this T cell population is poorly understood. To interrogate the contribution of inflammation, we developed a simple Salmonella-specific T cell transfer system that allowed direct visualization of hepatic TRM formation. Salmonella-specific (SM1) T cell receptor (TCR) transgenic CD4 T cells were activated in vitro and adoptively transferred into C57BL/6 mice while hepatic inflammation was induced by acetaminophen overdose or L. monocytogenes infection. In both model systems, hepatic CD4 TRM formation was accentuated by local tissue responses. Liver inflammation also enhanced the suboptimal protection provided by a subunit Salmonella vaccine which typically induces circulating memory CD4 T cells. To further elucidate the mechanism of CD4 TRM formation in response to liver inflammation, various cytokines were examined by RNAseq, bone marrow chimeras, and in vivo neutralization. Surprisingly, IL-2 and IL-1 were found to enhance CD4 TRM formation. Thus, local inflammatory mediators enhance CD4 TRM populations and can boost the protective immunity provided by a suboptimal vaccine. This knowledge will be foundational for the development of a more effective vaccine against invasive nontyphoidal salmonellosis (iNTS).
      Cover page: Optimal generation of hepatic tissue-resident memory CD4 T cells requires IL-1 and IL-2
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2022)
      Protective immune responses to Chlamydia infection within the female reproductive tract (FRT) are incompletely understood. MHC class II-restricted CD4 Th1 responses are believed to be vital for bacterial clearance due to their capacity to secrete IFN-γ, but an essential requirement for T-bet-expressing Th1 cells has yet to be demonstrated in the mouse model of Chlamydia infection. Here, we investigated the role of T-bet and IFN-γ in primary clearance of Chlamydia after FRT infection. Surprisingly, IFN-γ producing CD4 T cells from the FRT expressed low levels of T-bet throughout infection, suggesting that classical T-bet-expressing Th1 cells are inefficiently generated and therefore unlikely to participate in bacteria clearance. Furthermore, mice deficient in T-bet expression or with a CD4-specific T-bet deficiency cleared FRT infection similarly to wild-type controls. T-bet-deficient mice displayed significant skewing of FRT CD4 T cells towards Th17 responses, demonstrating that compensatory effector pathways are generated in the absence of Th1 cells. In marked contrast, IFN-γ-, and IFN-γR-deficient mice were able to reduce FRT bacterial burdens, but suffered systemic bacterial dissemination and 100% mortality. Together, these data demonstrate that IFN-γ signaling is essential to protect mice from fatal systemic disease, but that classical T-bet-expressing Th1 cells are non-essential for primary clearance within the FRT. Exploring the protective contribution of Th1 cells versus other CD4 effector lineages could provide important information for the generation of new Chlamydia vaccines.
        Cover page: Th1 cells are dispensable for primary clearance of Chlamydia from the female reproductive tract of mice
        • Article
        • Peer Reviewed
        UC Davis Previously Published Works (2023)
        CD4 tissue-resident memory T cells (TRMs) allow robust protection of barrier surfaces against pathogens. We investigated the role of T-bet in the formation of liver CD4 TRMs using mouse models. T-bet-deficient CD4 T cells did not efficiently form liver TRMs when compared with wild-type (WT). In addition, ectopic expression of T-bet enhanced the formation of liver CD4 TRMs, but only when in competition with WT CD4 T cells. Liver TRMs also expressed higher levels of CD18, which was T-bet dependent. The WT competitive advantage was blocked by Ab neutralization of CD18. Taken together, our data show that activated CD4 T cells compete for entry to liver niches via T-bet-induced expression of CD18, allowing TRM precursors to access subsequent hepatic maturation signals. These findings uncover an essential role for T-bet in liver TRM CD4 formation and suggest targeted enhancement of this pathway could increase the efficacy of vaccines that require hepatic TRMs.
          Cover page: Cutting Edge: Optimal Formation of Hepatic Tissue-Resident Memory CD4 T Cells Requires T-bet Regulation of CD18.
          • Article
          • Peer Reviewed
          UC Davis Previously Published Works (2021)
          Anatomical positioning of memory lymphocytes within barrier tissues accelerates secondary immune responses and is thought to be essential for protection at mucosal surfaces. However, it remains unclear whether resident memory in the female reproductive tract (FRT) is required for Chlamydial immunity. Here, we describe efficient generation of tissue-resident memory CD4 T cells and memory lymphocyte clusters within the FRT after vaginal infection with Chlamydia Despite robust establishment of localized memory lymphocytes within the FRT, naïve mice surgically joined to immune mice, or mice with only circulating immunity following intranasal immunization, were fully capable of resisting Chlamydia infection via the vaginal route. Blocking the rapid mobilization of circulating memory CD4 T cells to the FRT inhibited this protective response. These data demonstrate that secondary protection in the FRT can occur in the complete absence of tissue-resident immune cells. The ability to confer robust protection to barrier tissues via circulating immune memory provides an unexpected opportunity for vaccine development against infections of the FRT.
            Cover page: Circulating immunity protects the female reproductive tract from Chlamydia infection
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2024)
            Chlamydia vaccine approaches aspire to induce Th1 cells for optimal protection, despite the fact that there is no direct evidence demonstrating Th1-mediated Chlamydia clearance from the female reproductive tract (FRT). We recently reported that T-bet-deficient mice can resolve primary Chlamydia infection normally, undermining the potentially protective role of Th1 cells in Chlamydia immunity. Here, we show that T-bet-deficient mice develop robust Th17 responses and that mice deficient in Th17 cells exhibit delayed bacterial clearance, demonstrating that Chlamydia-specific Th17 cells represent an underappreciated protective population. Additionally, Th2-deficient mice competently clear cervicovaginal infection. Furthermore, we show that sensing of IFN-γ by non-hematopoietic cells is essential for Chlamydia immunity, yet bacterial clearance in the FRT does not require IFN-γ secretion by CD4 T cells. Despite the fact that Th1 cells are not necessary for Chlamydia clearance, protective immunity to Chlamydia is still dependent on MHC class-II-restricted CD4 T cells and IL-12p40. Together, these data point to IL-12p40-dependent CD4 effector maturation as essential for Chlamydia immunity, and Th17 cells to a lesser extent, yet neither Th1 nor Th2 cell development is critical. Future Chlamydia vaccination efforts will be more effective if they focus on induction of this protective CD4 T cell population.
              Cover page: Elimination of Chlamydia muridarum from the female reproductive tract is IL-12p40 dependent, but independent of Th1 and Th2 cells
              • Article
              • Peer Reviewed
              UC Davis Previously Published Works (2019)
              Salmonella infection can cause gastroenteritis in healthy individuals or a serious, systemic infection in immunocompromised patients and has a global impact. CD4 Th1 cells represent the main lymphocyte population that participates in bacterial clearance during both primary and secondary infections in mice of the H-2b haplotype. Previous studies have used congenic mice to examine the function of major histocompatibility complex (MHC) molecules in elimination of this pathogen from the host. In this study, we further characterized the ability of H-2b, H-2k, and H-2u molecules to influence adaptive immunity to Salmonella in MHC congenic mice. By depleting different cell populations during infection, we unexpectedly found that CD8 T cells, in addition to CD4 T cells, play a major role in accelerated clearance of bacteria from H-2k congenic hosts. Our data suggest that CD8 T cells accelerate clearance in some MHC congenic mouse strains and could therefore represent an unexpected contributor to the protective efficacy of Salmonella vaccines outside the typical studies in C57BL/6 mice.
                Cover page: Unexpected Role of CD8 T Cells in Accelerated Clearance of Salmonella enterica Serovar Typhimurium from H-2 Congenic mice
                • Article
                • Peer Reviewed
                UC Davis Previously Published Works (2024)
                In sub-Saharan Africa, multidrug-resistant non-typhoidal Salmonella serovars are a common cause of fatal bloodstream infection. Malnutrition is a predisposing factor, but the underlying mechanisms are unknown. Here we show that vitamin A deficiency, one of the most prevalent micronutrient deficits afflicting African children, increases susceptibility to disseminated non-typhoidal Salmonella disease in mice and impairs terminal neutrophil maturation. Immature neutrophils had reduced expression of Slc11a1, a gene that encodes a metal ion transporter generally thought to restrict pathogen growth in macrophages. Adoptive transfer of SLC11A1-proficient neutrophils, but not SLC11A1-deficient neutrophils, reduced systemic Salmonella burden in Slc11a1-/- mice or mice with vitamin A deficiency. Loss of terminal granulopoiesis regulator CCAAT/enhancer-binding protein ϵ (C/EBPϵ) also decreased neutrophil-mediated control of Salmonella, but not that mediated by peritoneal macrophages. Susceptibility to infection increased in Cebpe-/- Slc11a1+/+ mice compared with wild-type controls, in an Slc11a1-expression-dependent manner. These data suggest that SLC11A1 deficiency impairs Salmonella control in part by blunting neutrophil-mediated defence.
                  Cover page: Vitamin A deficiency impairs neutrophil-mediated control of Salmonella via SLC11A1 in mice
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