The neonatal Fc receptor for IgG (FcRn) plays a major role in regulating host IgG levels and transporting IgG and associated antigens across polarized epithelial barriers. Selective expression of FcRn in the epithelium is shown here to be associated with secretion of IgG into the lumen that allows for defense against an epithelium-associated pathogen (Citrobacter rodentium). This pathway of host resistance to a bacterial pathogen as mediated by FcRn involves retrieval of bacterial antigens from the lumen and initiation of adaptive immune responses in regional lymphoid structures. Epithelial-associated FcRn, through its ability to secrete and absorb IgG, may thus integrate luminal antigen encounters with systemic immune compartments and as such provide essential host defense and immunoregulatory functions at the mucosal surfaces.
Masaru Yoshida, Kanna Kobayashi, Timothy T. Kuo, Lynn Bry, Jonathan N. Glickman, Steven M. Claypool, Arthur Kaser, Takashi Nagaishi, Darren E. Higgins, Emiko Mizoguchi, Yoshio Wakatsuki, Derry C. Roopenian, Atsushi Mizoguchi, Wayne I. Lencer, Richard S. Blumberg
Salivary nitrate from dietary or endogenous sources is reduced to nitrite by oral bacteria. In the acidic stomach, nitrite is further reduced to NO and related compounds, which have potential biological activity. We used an in vivo rat model as a bioassay to test effects of human saliva on gastric mucosal blood flow and mucus thickness. Gastric mucosal blood flow and mucus thickness were measured after topical administration of human saliva in HCl. The saliva was collected either after fasting (low in nitrite) or after ingestion of sodium nitrate (high in nitrite). In additional experiments, saliva was exchanged for sodium nitrite at different doses. Mucosal blood flow was increased after luminal application of nitrite-rich saliva, whereas fasting saliva had no effects. Also, mucus thickness increased in response to nitrite-rich saliva. The effects of nitrite-rich saliva were similar to those of topically applied sodium nitrite. Nitrite-mediated effects were associated with generation of NO and S-nitrosothiols. In addition, pretreatment with an inhibitor of guanylyl cyclase markedly inhibited nitrite-mediated effects on blood flow. We conclude that nitrite-containing human saliva given luminally increases gastric mucosal blood flow and mucus thickness in the rat. These effects are likely mediated through nonenzymatic generation of NO via activation of guanylyl cyclase. This supports a gastroprotective role of salivary nitrate/nitrite.
Håkan Björne, Joel Petersson, Mia Phillipson, Eddie Weitzberg, Lena Holm, Jon O. Lundberg