GDNF and infection: Figure 4B to F show that confluent Caco-2 cell monolayers stimulated with GSNO (80 μM) for 24 h had significantly higher ZO-1 fluorescence intensity than untreated cells (P < 0.001), together suggesting that GSNO contributes to maintaining the intestinal epithelial barrier during rotavirus infection and increases the appearance of ZO-1 protein. Infection of Caco-2 cell monolayers without addition of extracullular GDNF did not increase ZO-1 expression, as determined by immunofluorescence (Fig. S4).