Ontogenetic regulation of leukocyte recruitment in mouse yolk sac vessels.

In adult mammals, leukocyte recruitment follows a well-defined cascade of adhesion events enabling leukocytes to leave the circulatory system and transmigrate into tissue. Currently, it is unclear whether leukocyte recruitment proceeds in a similar fashion during fetal development. Considering the fact that the incidence of neonatal sepsis increases dramatically with decreasing gestational age in humans, we hypothesized that leukocyte recruitment may be acquired only late during fetal ontogeny. To test this, we developed a fetal intravital microscopy model in pregnant mice and, using LysEGFP (neutrophil reporter) mice, investigated leukocyte recruitment during fetal development. We show that fetal blood neutrophils acquire the ability to roll and adhere on inflamed yolk sac vessels during late fetal development, whereas at earlier embryonic stages (before day E15), rolling and adhesion were essentially absent. Accordingly, flow chamber experiments showed that fetal EGFP(+) blood cells underwent efficient adhesion only when they were harvested on or after E15. Fluorescence-activated cell sorter analysis on EGFP(+) fetal blood cells revealed that surface expression of CXCR2 and less pronounced P-selectin glycoprotein ligand-1 (PSGL-1) begin to increase only late in fetal life. Taken together, our findings demonstrate that inflammation-induced leukocyte recruitment is ontogenetically regulated and enables efficient neutrophil trafficking only during late fetal life.

Oral pretreatment with recombinant human lactoferrin limits trauma-hemorrhagic shock-induced gut injury and the biological activity of mesenteric lymph.

BACKGROUND: Lactoferrin (LF) is a pleiotropic glycoprotein that is found in bodily secretions and is postulated to enhance the gastrointestinal barrier and promote mucosal immunity. Thus, the ability of talactoferrin, an oral recombinant form of human LF, to limit gut injury and the production of biologically active gut-derived products was tested using a rat model of trauma-hemorrhagic shock (T/HS). METHODS: Male rats were orally dosed with vehicle or talactoferrin (1000 mg/kg, every day) for 5 d before being subjected to T/HS or trauma-sham shock (T/SS). Subsequently, rats were subjected to a laparotomy (trauma) and hemorrhagic shock (mean arterial pressure, 30-35 mm Hg × 90 min) or to T/SS, followed by resuscitation with their shed blood. Before inducing shock, the mesenteric lymphatic duct was catheterized for collection of mesenteric lymph. Four hours after the end of the shock or sham-shock period, rats were sacrificed, a segment of the distal ileum was collected for morphologic analysis, and lymph samples were processed and frozen. Subsequently, lymph samples were tested in several pharmacodynamic assays, including endothelial cell permeability, neutrophil respiratory burst activity, and red blood cell (RBC) deformability. Total white blood cell counts in lymph samples were also quantified. RESULTS: Pretreatment with talactoferrin reduced the incidence of T/HS-induced morphologic injury of ileum to T/SS levels. Post-T/HS lymph from vehicle-treated rats increased endothelial monolayer permeability and neutrophil priming for an augmented respiratory burst, and induced loss of RBC deformability, compared with T/SS groups. Talactoferrin pretreatment significantly reduced the biological activity of T/HS lymph on respiratory burst activity and RBC deformability, but had no effect on the lymph cell count or endothelial cell permeability. CONCLUSIONS: These results provide a proof of principle that prophylactic dosing of oral talactoferrin can potentially protect the gut in a T/HS model and limit the production of biologically active factors in rat gastrointestinal tissue subjected to ischemia-reperfusion-type injuries.

A novel endothelial L-selectin ligand activity in lymph node medulla that is regulated by alpha(1,3)-fucosyltransferase-IV.

Lymphocytes home to peripheral lymph nodes (PLNs) via high endothelial venules (HEVs) in the subcortex and incrementally larger collecting venules in the medulla. HEVs express ligands for L-selectin, which mediates lymphocyte rolling. L-selectin counterreceptors in HEVs are recognized by mAb MECA-79, a surrogate marker for molecularly heterogeneous glycans termed peripheral node addressin. By contrast, we find that medullary venules express L-selectin ligands not recognized by MECA-79. Both L-selectin ligands must be fucosylated by alpha(1,3)-fucosyltransferase (FucT)-IV or FucT-VII as rolling is absent in FucT-IV+VII(-/-) mice. Intravital microscopy experiments revealed that MECA-79-reactive ligands depend primarily on FucT-VII, whereas MECA-79-independent medullary L-selectin ligands are regulated by FucT-IV. Expression levels of both enzymes paralleled these anatomical distinctions. The relative mRNA level of FucT-IV was higher in medullary venules than in HEVs, whereas FucT-VII was most prominent in HEVs and weak in medullary venules. Thus, two distinct L-selectin ligands are segmentally confined to contiguous microvascular domains in PLNs. Although MECA-79-reactive species predominate in HEVs, medullary venules express another ligand that is spatially, antigenically, and biosynthetically unique. Physiologic relevance for this novel activity in medullary microvessels is suggested by the finding that L-selectin-dependent T cell homing to PLNs was partly insensitive to MECA-79 inhibition.

Discovery of potent 3,5-diphenyl-1,2,4-oxadiazole sphingosine-1-phosphate-1 (S1P1) receptor agonists with exceptional selectivity against S1P2 and S1P3.

A class of 3,5-diphenyl-1,2,4-oxadiazole based compounds have been identified as potent sphingosine-1-phosphate-1 (S1P1) receptor agonists with minimal affinity for the S1P2 and S1P3 receptor subtypes. Analogue 26 (S1P1 IC50 = 0.6 nM) has an excellent pharmacokinetics profile in the rat and dog and is efficacious in a rat skin transplant model, indicating that S1P3 receptor agonism is not a component of immunosuppressive efficacy.

Sphingosine-1-phosphate agonists increase macrophage homing, lymphocyte contacts, and endothelial junctional complex formation in murine lymph nodes.

The sphingosine-1-phosphate (S1P) receptor agonist, phosphorylated FTY720 (FTY-P), causes lymphopenia, lymphocyte sequestration in mesenteric lymph nodes (MLNs), and immunosuppression. Using multiple techniques to analyze MLN cells harvested from mice treated with S1P receptor agonists, we saw a redistribution of lymphocytes out of nodal sinuses and an expansion of follicles. Although changes in circulating monocytes were not observed with overnight exposure to FTY720, we saw a significant increase in S1P receptor 1 (S1P1)-expressing CD68+ macrophages in subcapsular sinuses of FTY-P-treated MLNs. This was confirmed by quantitative analysis of F4/80+ cells in MLN suspensions. The sinus volume and number of S1P1-positive cells within sinuses were also increased by FTY-P. High endothelial venules and lymphatic endothelium expressed high levels of S1P1, and treatment with FTY-P resulted in intense staining and colocalization of CD31, beta-catenin, and zona occludens 1 in junctions between sinus cells. Transmission electron microscopy showed that FTY-P greatly reduced lymphocyte microvilli and increased cell-cell contacts in the parenchyma. Immunoelectron microscopy revealed that intranodal lymphocytes lacked surface expression of S1P1, whereas S1P1 was evident on the surface and within the cytoplasm of macrophages, endothelial cells, and stromal cells. This subcellular pattern of intranodal receptor distribution was unchanged by treatment with FTY-P. We conclude that S1P1 agonists have profound effects on macrophages and endothelial cells, in addition to inducing lymphopenia.

Total body irradiation causes profound changes in endothelial traffic molecules for hematopoietic progenitor cell recruitment to bone marrow.

Nonirradiated bone marrow (BM) venules and sinusoids in murine skull support hematopoietic progenitor cell (HPC) rolling through constitutively expressed endothelial (P- and E-) selectins and VCAM-1. Using intravital microscopy, we tested whether host conditioning with total body irradiation (TBI) changes the molecular mechanisms by which murine HPCs from fetal livers (FL) interact with BM endothelial cells. Although a high dose of TBI did not affect the overall frequency of HPC rolling in BM microvessels, the underlying molecular mechanisms differed from those in nonirradiated BM. TBI induced VCAM-1 up-regulation in BM microvessels, whereas P-selectin expression was reduced and the low baseline level of E-selectin remained unchanged. Only the administration of anti-VCAM-1, but not anti-P- or -E-selectin monoclonal antibodies, decreased FL HPC rolling. Rolling was frequently followed by firm arrest (sticking), even in nonirradiated BM microvessels in which sticking was entirely pertussis toxin-insensitive-that is, Galpha(i)-coupled signaling events (eg, through chemokines) were apparently not required. TBI increased the frequency of sticking FL HPC. This irradiation-induced additional sticking was reversed when FL HPCs were pretreated with pertussis toxin, suggesting that TBI induced elevated expression of a Galpha(i)-protein-coupled chemotactic signal in the BM. This chemoattractant was probably distinct from SDF-1alpha because, unlike adult HPCs, FL HPCs (day 11 of gestation) responded poorly to SDF-1alpha in vitro. These results demonstrate that TBI induces profound changes in the expression of endothelial traffic molecules in the BM, and they indicate that FL HPCs can home to the BM in the absence of SDF-1alpha and other Galpha(i)-protein-coupled signals.

Lethal neonatal and severe late infantile forms of carnitine palmitoyltransferase II deficiency associated with compound heterozygosity for different protein truncation mutations.

We describe a lethal neonatal form of carnitine palmitoyltransferase II (CPT II) deficiency with compound heterozygosity for 2 truncation mutations (Q413fs and 109AGC --> GCAGC). A new phenotype for a severe late infantile form of CPT II deficiency with hypoglycemia is associated with compound heterozygosity for the severe Q413fs mutation and a mild point mutation (P50H).

Sphingosine-1-phosphate receptor agonism impairs the efficiency of the local immune response by altering trafficking of naive and antigen-activated CD4+ T cells.

FTY720 (2-amino-[2-(4-octylphenyl) ethyl]-1,3-propanediol hydrochloride) is an immunosuppressive agent that inhibits allograft rejection. We recently demonstrated that FTY-phosphate, the active metabolite of FTY720, acts as a full agonist for sphingosine-1-phosphate (S1P) receptors. Furthermore, activation of S1P receptors with their natural ligand, S1P, as well as pharmacological ligands leads to lymphopenia, probably due to sequestration of lymphocytes in secondary lymphoid organs. In the present study we used a local Ag-challenged mouse model to examine the effects of FTY720 on T cell activation in the draining lymph node (DLN) and on the release of activated T cells to the peripheral blood compartment. We showed that the number of Ag-activated CD4(+) T cells in the DLN after injection of Ag and CFA into a footpad was dramatically reduced after FTY720 treatment. However, T cell proliferation, both in vitro and in vivo, was not impaired by FTY720. Our results suggest that the reduced efficiency of T cell responses in the DLN in response to a local Ag is probably due to a defective recirculation of naive T cells caused by FTY720 treatment. Furthermore, we found that the numbers of naive and Ag-activated CD4(+) T cells in the peripheral blood of Ag-challenged mice were equally reduced with FTY720 treatment, suggesting that both T cell subsets are sequestered in the DLNs. Thus, FTY720 induces immunosuppression through inhibition of both the recirculation of naive T cells and the release of Ag-activated T cells from the DLN to lymph and to the blood compartment.