Increased production of intestinal immunoglobulins in Syntenin-1-deficient mice.

Syntenin-1 is an intracellular PDZ protein that binds multiple proteins and regulates protein trafficking, cancer metastasis, exosome production, synaptic formation, and IL-5 signaling. However, the functions of Syntenin-1 have not yet been clearly characterized in detail, especially in vivo. In this study, we generated a Syntenin-1 knock out (KO) mouse strain and analyzed the role(s) of Syntenin-1 in IL-5 signaling, because the direct interaction of Syntenin-1 with the cytoplasmic domain of the IL-5 receptor α subunit and the regulation of IL-5 signaling by Syntenin-1 have been reported. Unexpectedly, the number of IL-5-responding cells was normal and the levels of fecal immunoglobulins were rather higher in the Syntenin-1 KO mice. We also found that IgA and IgM production of splenic B cells stimulated in vitro was increased in Syntenin-1 KO mice. In addition, we showed that a distribution of intestinal microbial flora was influenced in Syntenin-1 KO mice. Our data indicate that Syntenin-1 negatively regulates the intestinal immunoglobulin production and has a function to maintain the intestinal homeostasis in vivo. The analysis of Syntenin-1 KO mice may provide novel information on not only mucosal immunity but also other functions of Syntenin-1 such as cancer metastasis and neural development.