Naturally Occurring Altered Peptide Ligands Control Salmonella-Specific CD4+ T Cell Proliferation, IFN-γ Production, and Protective Potency

Abstract

T cell activation required for host defense against infection is an intricately regulated and precisely controlled process. Although in vitro studies indicate that three distinct stimulatory signals are required for T cell activation, the precise contribution of each signal in regulating T cell proliferation and differentiation after in vivo infection is unknown. In this study, altered peptide ligands (APLs) derived from the protective Salmonella-specific FliC Ag and CD4+ T cells specific for the immune-dominant FliC431–439 peptide within this Ag were used to determine how changes in TCR stimulation impact CD4+ T cell proliferation, differentiation, and protective potency. To explore the prevalence and potential use of altered TCR stimulation by bacterial pathogens, naturally occurring APLs containing single amino acid substitutions in putative TCR contact residues within the FliC431–439 peptide were identified and used for stimulation under both noninfection and infection conditions. On the basis of this analysis, naturally-occurring APLs that prime proliferation of FliC-specific CD4+ T cells either more potently or less potently compared with the wild-type FliC431–439 peptide were identified. Remarkably, despite these differences in proliferation, all of the APLs primed reduced IFN-γ production by FliC431–439-specific CD4+ T cells after stimulation in vivo. Moreover, after expression of the parental FliC431–439 peptide or each APL in recombinant Listeria monocytogenes, only CD4+ T cells stimulated with the wild-type FliC431–439 peptide conferred significant protection against challenge with virulent Salmonella. These results reveal important and unanticipated roles for TCR stimulation in controlling pathogen-specific CD4+ T cell proliferation, differentiation, and protective potency.

Selective culling of high avidity antigen-specific CD4+ T cells after virulent Salmonella infection

“…22 To establish if the short-lived nature of adoptively transferred FliC-specific CD4 + T cells was unique to Salmonella infection, we also compared the expansion and contraction kinetics of these cells after infection with recombinant L. monocytogenes engineered to express the FliC 427-441 peptide (Lm-FliC) as an endogenous antigen. 33 By contrast to the near complete elimination of these cells that occurs after Salmonella infection, FliC-specific CD45.1 + CD4 + cells primed by Lm-FliC were maintained, and by day 21 after infection were found at $ 5% levels compared with day 5 (Fig. 1).…”

“…3a). 27,33 Compared with Lm-FliC infection alone, co-infection using either wild-type or DFliC Salmonella each with Lm-FliC primed similar levels of FliC-specific CD4 + T-cell expansion on day 5 after infection ( Fig. 3a).…”

“…31 Recombinant Listeria monocytogenes (Lm) that are attenuated because of targeted defects in actA (required for intracellular and intercellular spread) and engineered to express the FliC 427)441 (Lm-FliC) or 2W1S 52-68 (Lm-2W1S) peptides as L. monocytogenes endogenous antigens have each been described previously. 32,33 For L. monocytogenes infection, each strain was grown in brain-heart infusion medium supplemented with chloramphenicol (20 lg/ml) at 37°, washed and diluted with sterile saline, and injected intravenously (5 · 10 6 colony-forming units in 200 ll per mouse).…”

Igg Subclasses Targeting the Flagella of Salmonella Enterica Serovar Typhimurium Can Mediate Phagocytosis and Bacterial Killing

“…In addition, the efficient intracellular bacterial killing by phagocytic cells is critical to containment of the infection which could lead to a faster resolution of the disease. Other studies have also illustrated a role for flagella in T-cell immunity and its association with protection in mice [31,34,52,53].…”

Cutting Edge: Bcl6-Interacting Corepressor Contributes to Germinal Center T Follicular Helper Cell Formation and B Cell Helper Function

“…Mice were infected intravenously with 10 7 actA-deficient Listeria monocytogenes (Lm) bacteria expressing FliC peptide RFNSAITNLGN (12) or 2W peptide EAWGALANWAVDSA fused to chicken ovalbumin (13), or immunized by i.p. injection of 200 μl of 0.6 ug of 2W peptide conjugated to 25 μg of PE (2W-PE) emulsified in CFA (Sigma).…”