ABSTRACT
In immunocompetent individuals, non-typhoidal Salmonella serovars (NTS) are associated with gastroenteritis, however, there is currently an epidemic of NTS bloodstream infections in sub-Saharan Africa. Plasmodium falciparum malaria is an important risk factor for invasive NTS bloodstream in African children. Here we investigated whether a live, attenuated Salmonella vaccine could be protective in mice, in the setting of concurrent malaria. Surprisingly, mice acutely infected with the nonlethal malaria parasite Plasmodium yoelii 17XNL exhibited a profound loss of protective immunity to NTS, but vaccine-mediated protection was restored after resolution of malaria. Absence of protective immunity during acute malaria correlated with maintenance of antibodies to NTS, but a marked reduction in effector capability of Salmonella-specific CD4 and CD8 T cells. Further, increased expression of the inhibitory molecule PD1 was identified on memory CD4 T cells induced by vaccination. Blockade of IL-10 restored protection against S. Typhimurium, without restoring CD4 T cell effector function. Simultaneous blockade of CTLA-4, LAG3, and PDL1 restored IFN-γ production by vaccine-induced memory CD4 T cells but was not sufficient to restore protection. Together, these data demonstrate that malaria parasite infection induces a temporary loss of an established adaptive immune response via multiple mechanisms, and suggest that in the setting of acute malaria, protection against NTS mediated by live vaccines may be interrupted.
Subject(s)
Immune Tolerance , Malaria/complications , Malaria/immunology , Salmonella Infections, Animal/complications , Salmonella Infections, Animal/immunology , Salmonella Vaccines/immunology , Animals , Antibodies, Bacterial/blood , Bacteremia/complications , Bacteremia/immunology , CD4-Positive T-Lymphocytes/immunology , CD8-Positive T-Lymphocytes/immunology , Disease Models, Animal , Female , Mice, Inbred C57BL , Mice, Inbred CBA , Vaccines, Attenuated/immunologyABSTRACT
CD4(+) T cells and B cells are both essential for acquired immunity to Salmonella infection. It is well established that Salmonella inhibit host CD4(+) T-cell responses, but a corresponding inhibitory effect on B cells is less well defined. Here, we utilize an Ag tetramer and pull-down enrichment strategy to directly visualize OVA-specific B cells in mice, as they respond to infection with Salmonella-OVA. Surprisingly, OVA-specific B-cell expansion and germinal center formation was not detected until bacteria were cleared from the host. Furthermore, Salmonella infection also actively inhibited both B- and T-cell responses to the same coinjected Ag but this did not require the presence of iNOS. The Salmonella Pathogenicity Island 2 (SPI2) locus has been shown to be responsible for inhibition of Salmonella-specific CD4(+) T-cell responses, and an examination of SPI2-deficient bacteria demonstrated a recovery in B-cell expansion in infected mice. Together, these data suggest that Salmonella can simultaneously inhibit host B- and T-cell responses using SPI2-dependent mechanisms.
Subject(s)
B-Lymphocytes/immunology , Bacterial Proteins/genetics , CD4-Positive T-Lymphocytes/immunology , Germinal Center/immunology , Membrane Proteins/genetics , Salmonella typhimurium/immunology , Animals , B-Lymphocytes/microbiology , B-Lymphocytes/pathology , Bacterial Proteins/immunology , CD4-Positive T-Lymphocytes/microbiology , CD4-Positive T-Lymphocytes/pathology , Cell Proliferation , Clone Cells , Flow Cytometry/methods , Gene Expression , Germinal Center/microbiology , Germinal Center/pathology , Host-Pathogen Interactions , Immunization , Immunophenotyping , Lipopolysaccharides/administration & dosage , Membrane Proteins/deficiency , Membrane Proteins/immunology , Mice , Mice, Inbred C57BL , Mice, Knockout , Nitric Oxide Synthase Type II/genetics , Nitric Oxide Synthase Type II/immunology , Ovalbumin/administration & dosage , Ovalbumin/chemistry , Ovalbumin/immunology , Time FactorsABSTRACT
Typhoid fever and nontyphoidal bacteremia caused by Salmonella remain critical human health problems. B cells are required for protective immunity to Salmonella, but the mechanism of protection remains unclear. In this study, we immunized wild-type, B cell-deficient, Ab-deficient, and class-switched Ab-deficient mice with attenuated Salmonella and examined protection against secondary infection. As expected, wild-type mice were protected and B cell-deficient mice succumbed to secondary infection. Interestingly, mice with B cells but lacking secreted Ab or class-switched Ab had little deficiency in resistance to Salmonella infection. The susceptibility of B cell-deficient mice correlated with marked reductions in CD4 T cell IFN-γ production after secondary infection. Taken together, these data suggest that the primary role of B cells in acquired immunity to Salmonella is via the development of protective T cell immunity.
Subject(s)
Antibodies, Bacterial/biosynthesis , B-Lymphocyte Subsets/immunology , B-Lymphocyte Subsets/microbiology , Salmonella Infections/prevention & control , Salmonella typhimurium/immunology , Animals , B-Lymphocyte Subsets/metabolism , Immunity, Cellular , Mice , Mice, Inbred BALB C , Mice, Knockout , Mice, Transgenic , Salmonella Infections/immunology , Salmonella Infections/pathology , Salmonella typhimurium/pathogenicity , Th1 Cells/immunology , Th1 Cells/microbiology , Virulence/immunologyABSTRACT
Despite the importance of Salmonella infections in human and animal health, the target antigens of Salmonella-specific immunity remain poorly defined. We have previously shown evidence for antibody-mediating protection against invasive Salmonellosis in mice and African children. To generate an overview of antibody targeting in systemic Salmonellosis, a Salmonella proteomic array containing over 2,700 proteins was constructed and probed with immune sera from Salmonella-infected mice and humans. Analysis of multiple inbred mouse strains identified 117 antigens recognized by systemic antibody responses in murine Salmonellosis. Importantly, many of these antigens were independently identified as target antigens using sera from Malawian children with Salmonella bacteremia, validating the study of the murine model. Furthermore, vaccination with SseB, the most prominent antigenic target in Malawian children, provided mice with significant protection against Salmonella infection. Together, these data uncover an overlapping immune signature of disseminated Salmonellosis in mice and humans and provide a foundation for the generation of a protective subunit vaccine.
Subject(s)
Salmonella Infections, Animal/immunology , Salmonella Infections/immunology , Animals , Antibody Formation/immunology , Antigens, Bacterial/immunology , Bacterial Proteins/immunology , Blood Bactericidal Activity , Child , Child, Preschool , Convalescence , Female , Humans , Infant , Infant, Newborn , Malawi , Male , Mice , Mice, Inbred Strains , Protein Array Analysis , Reproducibility of Results , Salmonella Infections/blood , Vaccination , Vaccines, Attenuated/immunology , Vaccines, Subunit/immunologyABSTRACT
Typhoid fever is a persistent infection caused by host-adapted Salmonella strains adept at circumventing immune-mediated host defences. Given the importance of T cells in protection, the culling of activated CD4+ T cells after primary infection has been proposed as a potential immune evasion strategy used by this pathogen. We demonstrate that the purging of activated antigen-specific CD4+ T cells after virulent Salmonella infection requires SPI-2 encoded virulence determinants, and is not restricted only to cells with specificity to Salmonella-expressed antigens, but extends to CD4+ T cells primed to expand by co-infection with recombinant Listeria monocytogenes. Unexpectedly, however, the loss of activated CD4+ T cells during Salmonella infection demonstrated using a monoclonal population of adoptively transferred CD4+ T cells was not reproduced among the endogenous repertoire of antigen-specific CD4+ T cells identified with MHC class II tetramer. Analysis of T-cell receptor variable segment usage revealed the selective loss and reciprocal enrichment of defined CD4+ T-cell subsets after Salmonella co-infection that is associated with the purging of antigen-specific cells with the highest intensity of tetramer staining. Hence, virulent Salmonella triggers the selective culling of high avidity activated CD4+ T-cell subsets, which re-shapes the repertoire of antigen-specific T cells that persist later after infection.
Subject(s)
Antigens, Bacterial/immunology , Bacterial Proteins/immunology , CD4-Positive T-Lymphocytes/immunology , Lymphocyte Activation , Membrane Proteins/immunology , Salmonella Infections, Animal/immunology , Salmonella , Adoptive Transfer , Animals , Coinfection , Female , Listeria monocytogenes/genetics , Listeriosis/immunology , Major Histocompatibility Complex/immunology , Male , Mice , Mice, Inbred C57BL , T-Lymphocyte Subsets/immunologyABSTRACT
Systemic Salmonella infection commonly induces prolonged splenomegaly in murine or human hosts. Although this increase in splenic cellularity is often assumed to be due to the recruitment and expansion of leukocytes, the actual cause of splenomegaly remains unclear. We monitored spleen cell populations during Salmonella infection and found that the most prominent increase is found in the erythroid compartment. At the peak of infection, the majority of spleen cells are immature CD71(-)Ter119(+) reticulocytes, indicating that massive erythropoiesis occurs in response to Salmonella infection. Indeed, this increase in RBC precursors corresponded with marked elevation of serum erythropoietin (EPO). Furthermore, the increase in RBC precursors and EPO production required innate immune signaling mediated by Myd88/TRIF. Neutralization of EPO substantially reduced the immature RBC population in the spleen and allowed a modest increase in host control of infection. These data indicate that early innate immunity to Salmonella initiates marked splenic erythropoiesis and may hinder bacterial clearance.