Regulation of host epithelial responses to Cryptosporidium infection by microRNAs.

Cryptosporidium species infect the gastrointestinal epithelium and other mucosal surfaces of vertebrate hosts. Epithelial cells provide the first line of defence against Cryptosporidium infection and play a critical role in the initiation, regulation and resolution of both innate and adaptive immune reactions. Host miRNAs in mammalian cells have been shown to play crucial roles in cellular responses to infection by diverse pathogens, including viruses, parasites and bacteria. Given the absence of RNAi machinery in Cryptosporidium, lack of miRNA expression in the parasite and minimal invasion nature of infection, Cryptosporidium infection provides an ideal model for exploring miRNA-mediated epithelial cell defence, relevant to infection of mucosal epithelial cells by pathogens in general. Increasing evidence supports that miRNAs may modulate many stages of epithelial responses following Cryptosporidium infection, including activation of the intracellular signalling pathways, production of antimicrobial molecules, expression of cytokines/chemokines, release of epithelial cell-derived exosomes and feedback regulation of immune homeostasis. On the other hand, this parasite may have developed strategies to modulate host miRNA-mediated cellular function for immune evasion. In this review, we will summarize the recent advances on miRNA regulation of epithelial responses to Cryptosporidium infection, with an emphasis on host defence and parasite immune evasion.