A potential role for interleukin‐18 in inhibition of the development of Cryptosporidium parvum

Summary Accumulating evidence suggests that intestinal epithelial cells (IECs) constitutively express the immunoregulatory cytokine interleukin (IL)‐18. IECs also serve as the host cell for the intracellular parasitic protozoan Cryptosporidium parvum. In the present study, C. parvum infection of a human enterocyte cell‐line HCT‐8 resulted in increased expression of IL‐18 mRNA as measured by quantitative reverse transcription–polymerase chain reaction (RT‐PCR). IL‐18 protein was detected in control uninfected cells and following infection there was increased expression as measured by enzyme‐linked immunosorbent assay (ELISA). Gene expression revealed the presence of the IL‐18 receptor subunits not only in cell‐lines but also in freshly isolated IECs, suggesting that IL‐18‐mediated signalling events may contribute to epithelial host defence during infection. Recombinant IL‐18 inhibited intracellular development of the parasite in HCT‐8 and HT‐29 cells. Increased expression of bactericidal antibiotic peptides LL‐37 and α‐defensin 2 by IL‐18 in HCT‐8 and HT‐29 cells may represent one mode of action by which this pluripotent cytokine aids in limiting the development of intracellular pathogens such as C. parvum in the gastrointestinal tract.