Elevated Extracellular cGMP Produced after Exposure to Enterotoxigenic Escherichia coli (ETEC) Heat-Stable Toxin (ST) Induces Epithelial IL-33 Release and Alters Intestinal Immunity.

Enterotoxigenic Escherichia coli (ETEC) is a major diarrheal pathogen in children in low- to middle-income countries. Previous studies identify heat-stable enterotoxin (ST)-producing ETEC as a prevalent diarrheal pathogen in children younger than five. While many studies have evaluated the interaction of ETEC heat-labile enterotoxin (LT) with host epithelium and immunity, few investigations have attempted similar studies with ST. To further understand ST pathogenesis, we examined the impact of ST on cGMP localization, epithelial cell cytokine production, and antibody development following immunization. In addition to robust intracellular cGMP in T84 cells in the presence of phosphodiesterase inhibitors (PDEis) that prevent the breakdown of cyclic nucleotides, we found that prolonged ST intoxication induces extracellular cGMP accumulation in the presence or absence of PDEis. Further, ST intoxication induces luminal cGMP in vivo in mice, suggesting that secreted cGMP may have other cellular functions. Using RNAseq and qPCR, we demonstrate that ST intoxication, or treatment with the clinically-used ST-mimic linaclotide, alters inflammatory cytokine gene expression, including IL1-family member IL-33, which can also be induced by cell-permeable 8-Br-cGMP. Finally, when present during immunization, ST suppresses antibody induction to specific antigens. In conclusion, our studies indicate that ST modulates epithelial cell physiology and the interplay between the epithelial and immune compartments.