Severe impairment of epithelial anti-<i>C. parvum</i> defense in the absence of TLR4 <i>in vitro</i> and TLR4-dependent production of NO in response to <i>C. parvum</i> infection.

<p>A and B, Infection dynamics in cultured H69 cells and cells stably expressing TLR4DN after initial exposure to the same amount of <i>C. parvum</i> sporozoites, as assessed by real-time PCR for parasite 18S (A) or fluorescent microscopy (<i>C. parvum</i> stained by an antibody in green and cell nuclei by DAPI in blue in B). C and D, Effect of <i>C. parvum</i> infection on the production of NO in cells. H69 and 603B cells were exposed to <i>C. parvum</i> for up to 48 h, followed by nitrite measurement (C). IEC4.1, HIBEpiC, SW480, Caco-2 cells and H69 cells stably expressing TLR4DN were exposed to <i>C. parvum</i> for 24 h followed by nitrite measurement (D). *, <i>p</i><0.05 vs non-infected cells (in A, C, and D). N.D. = not detectable. Bar = 1 µm.