Living in the danger zone: innate immunity to Salmonella.

Phagocytic cells, including macrophages, neutrophils and dendritic cells, are critical components of the innate immune response to bacterial pathogens such as Salmonella typhimurium. These cells can have several roles during the early stage of an infection including controlling bacterial replication and producing cytokines and chemokines that activate and recruit additional cells. Macrophages, neutrophils and dendritic cells increase in number early after oral Salmonella infection and produce cytokines important in host survival such as tumor necrosis factor alpha (TNF-alpha). All three phagocytic cell types also harbor bacteria during infection. Natural killer cells, natural killer T cells and T cell receptor alpha beta T cells also respond rapidly to infection and are early sources of interferon-gamma during infection with Salmonella. Studies using infection models with Salmonella are providing a picture of the innate response to bacteria and insight into the role of defined cell types and cytokines important in the transition from innate to adaptive immunity.