Remodeling of the epithelial barrier during Cryptosporidium parvum infection in neonatal calves.

Cryptosporidiosis is a common disease in neonatal calves that compromises animal welfare and causes substantial economic losses. Opportunistic secondary infections with bacterial and viral pathogens are frequently observed and may be facilitated by impairment of the intestinal epithelial barrier. This study aimed to assess the abundance and localization of key barrier components, i.e., claudins (CLDN), occludin (OCLN) and mucus producing goblet cells in neonatal calves infected with C. parvum compared with healthy controls. Male Holstein-Friesian calves were orally infected with 2 × 107C. parvum oocysts on the first day of life (N = 5) or administered water as healthy controls (N = 4). After one week, the calves were sacrificed, and jejunum epithelium was collected for RT-qPCR, Western blot analysis, and immunofluorescence staining. Infected calves showed increased mRNA expression of CLDN3 and 4 (p < 0.05), whereas no differences in protein abundance were detected. Immunofluorescence staining revealed stable localization of CLDN1 and OCLN at the enterocyte membrane, whereas CLDN3 appeared to accumulate intracellularly and at the apical membrane 7 days post infection, suggesting endocytosis and subsequent redistribution during the course of infection. In addition, infected calves had significantly fewer goblet cells in jejunal villi than healthy controls, which may have been compensated by an approximately five-fold increased MUCIN (MUC) 2 gene expression (p < 0.05). In conclusion, our findings indicate remodeling of the epithelial barrier in response to C. parvum infection. The increased expression and altered localization of CLDN3, together with reduced goblet cell numbers and elevated MUC2 expression, suggest a compensatory response aimed at restoring barrier integrity.