Rallying the Troops: Innate Mucosal Responses to Enteric Pathogens

The mucosal surfaces of the gastrointestinal tract are constantly exposed to large quantities of commensal microbes and enteric pathogens. Highly sophisticated innate immune mechanisms are in place to recognize and prevent the establishment of infections with such pathogens. At the same time, immune responses to commensals are being donwregulated resulting in a phenomen called oral tolerance. In turn, enteric pathogens have developed a variety of mechanisms to counter the immune response including novel colonization strategies and the production of virulence factors that can downregulate recognition and elimination by the innate immune system. This review focuses on enteric infections in large animals and describes the complex interplay between the host's innate immune system and pathogenic bacteria such as Escherichia coli, Salmonella spp., Campylobacter jejuni, Yersinia spp. and Shigella spp.