Adaptive Immune Responses during Salmonella Infection.

The interaction betweenSalmonella and its host is complex and dynamic: the host mounts an immune defense against the pathogen, which in turn acts to reduce, evade, or exploit these responses to successfully colonize the host. Although the exact mechanisms mediating protective immunity are poorly understood, it is known that T cells are a critical component of immunity to Salmonella infection, and a robust T-cell response is required for both clearance of primary infection and resistance to subsequent challenge. B-cell functions, including but not limited to antibody production, are also required for generation of protective immunity. Additionally, interactions among host cells are essential. For example, antigen-presenting cells (including B cells) express cytokines that participate in CD4+ T cell activation and differentiation. Differentiated CD4+ T cells secrete cytokines that have both autocrine and paracrine functions, including recruitment and activation of phagocytes, and stimulation of B cell isotype class switching and affinity maturation. Multiple bacterium-directed mechanisms, including altered antigen expression and bioavailability and interference with antigen-presenting cell activation and function, combine to modify Salmonella's "pathogenic signature" in order to minimize its susceptibility to host immune surveillance. Therefore, a more complete understanding of adaptive immune responses may provide insights into pathogenic bacterial functions. Continued identification of adaptive immune targets will guide rational vaccine development, provide insights into host functions required to resist Salmonella infection, and correspondingly provide valuable reagents for defining the critical pathogenic capabilities of Salmonella that contribute to their success in causing acute and chronic infections.