Mucosal Immune Responses to Escherichia coli and Salmonella Infections

The best-characterized mucosa-associated lymphoid tissue (MALT), and also the most relevant for this review, is the gastrointestinal-associated lymphoid tissue (GALT). The review reviews our understanding of the importance of mucosal immune responses in resisting infections caused by E. coli and Salmonella spp. It focuses on the major human E. coli infections and discusses whether antigen-specific mucosal immune responses are important for resistance against primary infection or reinfection by pathogenic E. coli. It analyzes human data on mucosal immunity against E. coli, a growing body of data of mucosal responses in food production animals and other natural hosts of E. coli, and more recent experimental studies in mice carrying defined deletions in genes encoding specific immunological effectors, to show that there may be considerable conservation of the effective host mucosal immune response against this pathogen. The species Salmonella enterica contains a number of serovars that include pathogens of both humans and animals; these bacteria are frequently host specific and may cause different diseases in different hosts. Ingestion of various Salmonella serovars, such as Typhimurium, results in localized infections of the small intestine leading to gastroenteritis in humans, whereas ingestion of serovar Typhi results in systemic infection and enteric fever. Serovar Typhi infects only humans, and the review discusses the mucosal immune responses against serovar Typhi, focusing on the responses in humans and in the mouse typhoid fever model.