Mucosal physical and chemical innate barriers: Lessons from microbial evasion strategies

• The human intestinal epithelium constitutes a host protective barrier.
• Mucus and antimicrobial factors control resident and transient bacterial populations.
• Homeostasis is subverted by crosstalks between enteric pathogens and mucosal tissues.

The innate immune system has evolved since millions of years under a selective pressure. Among the different host mechanisms selected and conserved as a first line of defense, the gastrointestinal mucus layer constitutes an efficient physical and chemical barrier against invading microbes. Mucin glycoproteins and antimicrobial peptides are the major components of the mucus barrier, and evidences prove that they form an effective protection against most microbes. However, successful pathogens have evolved evasion strategies to circumvent this defense barrier. Here, we discuss the interactions between pathogens, mucins, and antimicrobial peptides, and the mechanisms that pathogens have developed to evade the innate defense systems of the intestinal mucosal barrier.