Vertebrates harbor abundant lipopolysaccharide (LPS) in their gut microbiota. Alkaline phosphatases can dephosphorylate and detoxify the endotoxin component of LPS. Here, we show that expression of the zebrafish intestinal alkaline phosphatase (Iap), localized to the intestinal lumen brush border, is induced during establishment of the gut microbiota. Iap-deficient zebrafish are hypersensitive to LPS toxicity and exhibit the excessive intestinal neutrophil influx characteristic of wild-type zebrafish exposed to LPS. Both of these Iap mutant phenotypes are dependent on Myd88 and Tumor Necrosis Factor Receptor (Tnfr), proteins also involved in LPS sensitivity in mammals. When reared germ-free, the intestines of Iap-deficient zebrafish are devoid of neutrophils. Together, these findings demonstrate that the endogenous microbiota establish the normal homeostatic level of neutrophils in the zebrafish intestine through a process involving Iap, Myd88, and Tnfr. Thus, by preventing inflammatory responses, Iap plays a crucial role in promoting mucosal tolerance to resident gut bacteria.

All animals exist in intimate associations with microorganisms that play important roles in the hosts' normal development and tissue physiology. In vertebrates, the most populous and complex community of microbes resides in the digestive tract. Here, we describe the establishment of the gut microbiota and its role in digestive tract differentiation in the zebrafish model vertebrate, Danio rerio. We find that in the absence of the microbiota, the gut epithelium is arrested in aspects of its differentiation, as revealed by the lack of brush border intestinal alkaline phosphatase activity, the maintenance of immature patterns of glycan expression and a paucity of goblet and enteroendocrine cells. In addition, germ-free intestines fail to take up protein macromolecules in the distal intestine and exhibit faster motility. Reintroduction of a complex microbiota at later stages of development or mono-association of germ-free larvae with individual constituents of the microbiota reverses all of these germ-free phenotypes. Exposure of germ-free zebrafish to heat-killed preparations of the microbiota or bacterial lipopolysaccharide is sufficient to restore alkaline phosphatase activity but not mature patterns of Gal alpha1,3Gal containing glycans, indicating that the host perceives and responds to its associated microbiota by at least two distinct pathways.

SUMMARY Lymphocytes cross vascular boundaries via either disrupted tight junctions (TJs) or caveolae to induce tissue inflammation. In the central nervous system (CNS), Th17 lymphocytes cross the blood-brain barrier (BBB) prior to Th1 cells, yet this differential crossing is poorly understood. We have used intravital two-photon imaging of the spinal cord in wild-type and caveolae-deficient mice with fluorescently labeled endothelial TJs, to determine how TJ remodeling and caveolae regulate CNS entry of lymphocytes during the experimental autoimmune encephalomyelitis (EAE) model for multiple sclerosis. We find that dynamic TJ remodeling occurs early in EAE but does not depend upon caveolar transport. Moreover, Th1 but not Th17 lymphocytes are significantly reduced in the inflamed CNS of mice lacking caveolae. Therefore, TJ remodeling facilitates Th17 migration across the BBB, whereas caveolae promote Th1 entry into the CNS. Moroever, therapies that target both TJ degradation and caveolar transcytosis may limit lymphocyte infiltration during inflammation.

Compelling evidence points to immune cell infiltration as a critical component of successful immunotherapy. However, there are currently no clinically available, non-invasive methods capable of evaluating immune contexture prior to or during immunotherapy. In this study, we evaluate a T cell-specific PET agent, [18F]F-AraG, as an imaging biomarker predictive of response to checkpoint inhibitor therapy. We determined the specificity of the tracer for activated T cells in vitro and in a virally induced model of rhabdomyosarcoma. Of all immune cells tested, activated human CD8+ effector cells showed the highest accumulation of [18F]F-AraG. Isolation of lymphocytes from the rhabdomyosarcoma tumors showed that more than 80% of the intratumoral signal came from accumulation of [18F]F-AraG in immune cells, primarily CD8+ and CD4+. Longitudinal monitoring of MC38 tumor bearing mice undergoing anti-PD-1 treatment revealed differences in signal between PD-1 and isotype antibody-treated mice early into treatment. The differences in [18F]F-AraG signal were also apparent between responders and non-responders to anti-PD-1 therapy. Importantly, we found that the signal in the tumor draining lymph nodes provides key information about response to anti-PD-1 therapy. Overall, [18F]F-AraG has potential to serve as a much needed immunomonitoring clinical tool for timely evaluation of immunotherapy.

Crystallization of a catalytically important molecular sieve SAPO-34 was examined under dry gel conversion conditions including steam-assisted conversion (SAC) and vapor-phase transport (VPT). The progressive changes in the structure of solid gel phases were monitored by powder XRD, SEM, and several solid-state NMR techniques involving 31P, 27Al, 29Si, and 13C. The results suggest that the formation pathways under VPT and SAC appear to be similar: SAPO-34 crystallizes from a semicrystalline precursor with a layered structure held mainly by weak nonbonding interactions. AFM data indicate that the crystal growth mechanism is “birth and spread” and that the fast nucleation on the (001) crystal face likely results from simultaneous transformation of many small domains of precursor to SAPO-34 via cooperative bond breaking and reforming. 29Si NMR results suggest that Si incorporation occurs slowly via amorphous aluminosilicate species. These findings provide new physical insights into the formation of SAPO-34.