ABSTRACT
Innate immunity serves as an early sensor of infection and also activates evolutionarily conserved antimicrobial killing mechanisms that might curb the reproduction of invading microorganisms until the adaptive immune response becomes functional. Epithelial cells are the only cells known to be infected by Cryptosporidium in vivo. Microarray analyses of 12,600 genes in a human enterocyte cell line infected with C. parvum showed that 223 were regulated by the parasite, including some involved in immune responses. Intestinal epithelial cells are capable of producing antimicrobial peptides that can kill bacteria or parasites by disrupting their cell membranes. In addition, some peptides such as ß-defensins have been shown to play a role in the development of adaptive immune responses. Natural killer cells are non-T, non-B lymphocytes that play a major role in the innate immune response against intracellular infection by viruses, bacteria, and parasites, and also tumor cells.
