Hemodynamic response to intestinal pH stimulation measured with spectroscopic video imaging.

To investigate the relationship between the gut and skin (gut-skin axis), head skin hemodynamic responses to gut stimulation including the injection of acetic acid in nude mice were measured by spectroscopic video imaging, which was calculated using a modified Beer-Lambert formula. The relationship with blood proteins was also analyzed. The blood volume changes in three mice injected with acetic acid were highly reproducible in the mathematical model equation. Four proteins correlated with blood volume changes were all related to immunity. These results suggest that intestinal pH can alter the blood volume in the skin and induce immune-related responses.

Reactive granulopoiesis depends on T-cell production of IL-17A and neutropenia-associated alteration of gut microbiota.

Granulopoiesis in the bone marrow adjusts cellular output as demand for neutrophils changes. Reactive granulopoiesis is induced by profound neutropenia, but its mechanism remains to be clarified. We herein explored its mechanisms using mouse models of syngeneic hematopoietic stem cell transplantation (SCT) and 5-fluorouracil-induced neutropenia. After SCT, T cell production of IL-17A was up-regulated. Neutrophil recovery was significantly delayed in IL-17A-deficient or T cell-deficient RAG1-/- mice, and adoptive transfer of wild-type (WT) T cells facilitated neutrophil engraftment. Gut decontamination with oral antibiotics suppressed T cell production of IL-17A and impaired neutrophil recovery. Transplantation of fecal microbiota collected from neutropenic, not naive, mice promoted neutrophil recovery in these mice, suggesting that neutropenia-associated microbiota had a potential to stimulate reactive granulopoiesis. Our study uncovered a cross talk between gut microbiota and neutropenia after SCT and chemotherapy.

Expression and Localization of Paneth Cells and Their α-Defensins in the Small Intestine of Adult Mouse.

Paneth cells contribute to intestinal innate immunity by sensing bacteria and secreting α-defensin. In Institute of Cancer Research (ICR) mice, α-defensin termed cryptdin (Crp) in Paneth cells consists of six major isoforms, Crp1 to 6. Despite accumulating evidences that α-defensin functions in controlling the intestinal microbiota, topographical localization of Paneth cells in the small intestine in relation to functions of α-defensin remains to be determined. In this study, we examined the expression level of messenger RNA (mRNA) encoding six Crp-isoforms and Crp immunoreactivities using singly isolated crypts together with bactericidal activities of Paneth cell secretions from isolated crypts of duodenum, jejunum, and ileum. Here we showed that levels of Crp mRNAs in the single crypt ranged from 5 x 103 to 1 x 106 copies per 5 ng RNA. For each Crp isoform, the expression level in ileum was 4 to 50 times higher than that in duodenum and jejunum. Furthermore, immunohistochemical analysis of isolated crypts revealed that the average number of Paneth cell per crypt in the small intestine increased from proximal to distal, three to seven-fold, respectively. Both Crp1 and 4 expressed greater in ileal Paneth cells than those in duodenum or jejunum. Bactericidal activities in secretions of ileal Paneth cell exposed to bacteria were significantly higher than those of duodenum or jejunum. In germ-free mice, Crp expression in each site of the small intestine was attenuated and bactericidal activities released by ileal Paneth cells were decreased compared to those in conventional mice. Taken together, Paneth cells and their α-defensin in adult mouse appeared to be regulated topographically in innate immunity to control intestinal integrity.

Paneth cell α-defensin misfolding correlates with dysbiosis and ileitis in Crohn's disease model mice.

Crohn's disease (CD) is an intractable inflammatory bowel disease, and dysbiosis, disruption of the intestinal microbiota, is associated with CD pathophysiology. ER stress, disruption of ER homeostasis in Paneth cells of the small intestine, and α-defensin misfolding have been reported in CD patients. Because α-defensins regulate the composition of the intestinal microbiota, their misfolding may cause dysbiosis. However, whether ER stress, α-defensin misfolding, and dysbiosis contribute to the pathophysiology of CD remains unknown. Here, we show that abnormal Paneth cells with markers of ER stress appear in SAMP1/YitFc, a mouse model of CD, along with disease progression. Those mice secrete reduced-form α-defensins that lack disulfide bonds into the intestinal lumen, a condition not found in normal mice, and reduced-form α-defensins correlate with dysbiosis during disease progression. Moreover, administration of reduced-form α-defensins to wild-type mice induces the dysbiosis. These data provide novel insights into CD pathogenesis induced by dysbiosis resulting from Paneth cell α-defensin misfolding and they suggest further that Paneth cells may be potential therapeutic targets.