Given the role played by retinoic acid in influencing the Th1/Th2 balance 10, any local reduction in available RA through a decrease in the number of cells expressing ALDH enzymes may be a regulatory mechanism employed by the parasite to prevent host protective immunity, although the potential to produce retinoic acid is also decreased in nonparasitic models of colitis 16. Here, LDHA is linked to colitis.