Intestinal immune response to human Cryptosporidium sp. infection.

摘要

Cryptosporidium is an obligate intracellular protozoan parasite that is a major cause of diarrheal illness worldwide. Cryptosporidium primarily infects the distal small intestine. Immunocompetent hosts control and eliminate the infection, which typically causes acute, self-limited watery diarrhea lasting 5 to 10 days. However, in patients with defects in cellular immune responses (e.g., AIDS, malnutrition, or defects in the CD40-CD154 system), Cryptosporidium frequently causes persistent or chronic diarrhea and may also involve the biliary tract (40). In malnourished children, persistent diarrhea is associated with increased susceptibility to recurrent diarrheal episodes, which can lead to death or chronic nutritional and cognitive sequelae (1, 9, 33). Thus, the host immune response plays a critical role in the control of human cryptosporidiosis. Although extensive studies with various animal models have provided important insight into the host immune response towards Cryptosporidium parvum , the ability of these models to explain the human immune response is limited. The clinical picture in rodents differs from that in humans, as mice do not get diarrhea after infection. Nonhuman primates, although probably the best in vivo model to mimic human disease, are difficult to work with, expensive, and not widely available. Cryptosporidium hominis , the pathogen causing most human cryptosporidiosis, infects only humans and gnotobiotic pigs, thus limiting data from animal models. Most importantly, comparison of animal and human data has shown that the immune response towards Cryptosporidium in humans differs significantly from that in animals; for example, in mice gamma interferon (IFN-gamma ) production seems to be associated with the innate and primary immune responses (35, 47), whereas in humans it is most probably associated with the memory response towards the parasite (93). Conducting studies to elucidate human mucosal immune responses is difficult.