CD4 + -T-Cell Responses Generated during Murine Salmonella enterica Serovar Typhimurium Infection Are Directed towards Multiple Epitopes within the Natural Antigen FliC

Abstract

ABSTRACT The flagellar filament protein FliC is a natural antigen recognized by memory CD4 + T cells recovered from Salmonella enterica serovar Typhimurium-infected humans and mice. To further investigate T-cell responses to FliC, we derived FliC-specific CD4 + -T-cell clones from mice of two different haplotypes following oral S. enterica serovar Typhimurium infection. Using C-terminal truncations of MalE-FliC recombinant fusion proteins, we mapped antigenic activity to four different regions of FliC; three of the four epitope-containing regions were present in both FliC and the alternate flagellin subunit FljB. We determined that two novel FliC epitopes were also present in flagellins from several gram-negative enteric bacterial species: E k -restricted FliC 80-94 (amino acids 80 to 94) and A b -restricted FliC 455-469. Further mapping confirmed the presence of two previously identified FliC epitopes: A k -restricted FliC 339-350 and A b -restricted FliC 428-442. Therefore, like the recognition site of the innate immune receptor Toll-like receptor 5, three of four FliC epitopes recognized by CD4 + T cells colocalize in the D0/D1 domains of FliC. Salmonella -infected macrophages and dendritic cells stimulated epitope-specific CD4 + -T-cell proliferation; infected dendritic cells also activated T cells to produce gamma interferon. These data demonstrate that Salmonella infection generates murine CD4 + -T-cell responses to multiple epitopes in the natural antigen FliC and that recognition of infected phagocytes by FliC-specific CD4 + T cells triggers effector functions known to be essential for protective immunity. Together, these data suggest that FliC-specific CD4 + T cells may contribute to cell-mediated host defenses against Salmonella .