Molecular Mechanisms Used by Salmonella to Evade the Immune System

Human and animal pathogens are able to circumvent, at least temporarily, the sophisticated immune defenses of their hosts. Several serovars of the Gram-negative bacterium Salmonella enterica have been used as models for the study of pathogen-host interactions. In this review we discuss the strategies used by Salmonella to evade or manipulate three levels of host immune defenses: physical barriers, innate immunity and adaptive immunity. During its passage through the digestive system, Salmonella has to face the acidic pH of the stomach, bile and antimicrobial peptides in the intestine, as well as the competition with resident microbiota. After host cell invasion, Salmonella manipulates inflammatory pathways and the autophagy process. Finally, Salmonella evades the adaptive immune system by interacting with dendritic cells, and T and B lymphocytes. Mechanisms allowing the establishment of persistent infections are also discussed.