The overarching research goals of the lab are directed toward understanding important host and microbial mechanisms that instruct the development of pathogen-specific effector, memory, and protective T-cell immunity after infection with intracellular bacteria.
As our primary model, we use murine infection with Salmonella enterica Serovar typhimurium. Salmonellae are naturally acquired by the oral route and invade early after infection from the intestinal lumen through M-cells into the Peyer’s Patches. Afterward, Salmonella disseminates systemically to colonize peripheral tissues (e.g., the spleen). Protective host defenses initiate in the gut and later at peripheral sites where ultimately a combination of innate (macrophages) and humoral (B-cells, antibody) and cellular (T-cells) immunity work in concert to resolve infection. The production of the cytokine IFNγ throughout the host response (Th1-type) is absolutely required for protective immunity.
Bacteria that infect via the enteral route encounter a qualitatively different environment than pathogens that colonize through parenteral routes. Salmonella must navigate through and may take advantage of the unique immunobiology of the gut mucosa in order to efficiently colonize and establish infection. In addition, the gut mucosal immune system has evolved several mechanisms that serve to maintain immune homeostasis under a continuous onslaught of potential inflammatory and immunogenic exposure from nominal food antigens and the enormous biomass of the commensal microbiota. It is in this complex environment, that host defenses must distinguish “friend or foe”. Understanding mechanisms in this environment, under homeostatic or dysregulated states, that influence the development ofSalmonella-specific CD4+ T-cells is one goal of our research.
An additional area of research aims to understand the compartmentalization of host defenses as Salmonella effectively exists as a mucosal and at later times a systemic pathogen. For instance, Salmonellae that colonize the gut and those that subsequently transition to colonize peripheral sites have different antigenic mosaics (e.g., flagellin expression). Recognizing the host and microbial differences in these compartments, we aim to determine the relative importance of CD4+ T-cells primed in the mucosa versus T-cells primed at systemic sites for overall host protective immunity. After activation, lymphocytes are instructed to progress through several possible fates and T-cells develop into an effector (TEFF) and/or memory (TCM and TEM) T-cell subsets, each with unique and important properties for immunity. CD4+ T-cells are further classified by their mucosal or peripheral imprinting status based on the expression of specific molecules on the T-cell surface. In particular, the integrin α4β7 is highly expressed on T-cells activated/imprinted in Peyer’s Patches and α4β7 mediates T-cell migration to the gut. Using flow cytometry and multiple cellular immunological techniques, we aim to isolate several populations of Salmonella-specific T-cells based on their memory and imprinting phenotypes to determine the functional roles of each subset towards protective host defense against oral Salmonella infection.
Another research theme in the lab focuses on membrane vesicles (MVs): discrete spherical nano-assemblies produced from the outer membrane by Gram-negative bacteria. Although described in the literature for decades, the mechanism of production and MV function(s) have only begun to be clarified. In preliminary studies using Salmonella, we demonstrated MVs have potent adjuvant and immunogenic properties for pathogen-specific humoral and cell-mediated host defense stimulation in vivo. After vaccination, MVs induce protective immunity in mice against subsequent live Salmonella challenge, unlike that reported for heat-inactivated bacteria. In a partly translational research approach, we aim to determine the immunogenic and proinflammatory properties of MVs that promote the induction protective immunity. In one approach to accomplish this goal, we will determine the capacity of MVs to activate dendritic cells (DCs), the critical antigen presenting cell for inducing host adaptive immunity in vivo. In addition, we will determine the immunogenic potential of MVs produced by Salmonella using in vivo immunization models as well as in vitro proteomic techniques.