Virulence mechanisms displayed by Salmonella to impair dendritic cell function

Dendritic cells (DCs) link innate and adaptive immunity by directly recognizing pathogen-associated molecular patterns (PAMPs) on bacteria. DCs can capture and degrade bacteria and present their antigens on MHC molecules to T cells. PAMP recognition promotes DC maturation, a phenotypic change that empowers them to prime naïve T cells. As a result, an adaptive immune response that specifically targets bacteria-derived antigens is initiated. Consequently, any impairment of DC function might contribute to bacterial survival and dissemination in the host. Therefore, the characterization of DC-bacteria interactions is required to understand the mechanisms used by virulent bacteria to avoid adaptive immunity. An example of a bacterial pathogen capable of interfering with DC function is Salmonella enterica serovar Typhimurium (S. Typhimurium), which causes a typhoid-like disease in mice. Virulent strains of S. Typhimurium are able to differentially modulate the entrance to DCs and avoid lysosomal degradation, to prevent antigen presentation on MHC molecules. These features of virulent S. Typhimurium are controlled by virulence factors encoded by Salmonella Pathogenicity Islands 1 and 2. Modulation of DC functions by the activity of these gene products is supported by several recent studies, which have shown that pathogenesis might depend on this attribute of virulent S. Typhimurium. Here we discuss recent data showing that several virulence factors from Salmonella are required to differentially modulate DC function and adaptive immunity in the host.