ABSTRACT
All animals, vertebrate or invertebrate, face the challenge of combating pathogens while maintaining a tolerant relationship with symbiotic microorganisms. Tolerance to symbiotes is not a static or inert interaction but, rather, requires continuous active regulation; the frontlines for these interactions are the mucosal surfaces. A fundamental question is whether or not specialized immune cells or organs have evolved in all animals to cope with the unique problems of mucosal defense, or whether specialized mucosal immunity is unique to vertebrates such as mammals. With regard to the mucosal immune system, invertebrates continue to shed light on the conserved interactions between the microbiota and the intestinal immune system. Mosquito C-type lectins regulate antimicrobial peptide expression, coat bacterial surfaces, and contribute to the maintenance of the gut microbiota in a similar manner to vertebrate mucosal immunoglobulins. Organized mucosal lymphoid structures were traditionally thought to be an immune innovation of endotherms.
