Lymphocyte homing and leukocyte rolling and migration are impaired in L-selectin-deficient mice

Memory-like CD8+ T cells generated during homeostatic proliferation defer to antigen-experienced memory cells

Naive T cells proliferate in response to lymphopenia and acquire the phenotypic and functional qualities of memory T cells, providing enhanced protection against infection. How well memory-like T cells generated during lymphopenia-induced homeostatic proliferation (HP)-memory differentiate into secondary memory cells and compete with Ag-experienced true-memory cells is unknown. We found that CD8(+) HP-memory T cells generated robust responses upon infection and produced a secondary memory population comparable to true-memory cells in the absence of competition. However, when true-memory and HP-memory T cells competed during infection, HP-memory cells contributed less to the effector population, contracted earlier, and formed fewer secondary memory cells. Furthermore, HP- and true-memory cells demonstrated distinct chemokine receptor expression and localization within the spleen during infection, indicating differential access to signals necessary for secondary memory formation. Thus, HP-memory T cells provide protection without compromising the true-memory population. Differences in HP- and true-memory T cells may reveal the basis of competition for limited resources within the memory-T cell compartment.

KLF2 transcription-factor deficiency in T cells results in unrestrained cytokine production and upregulation of bystander chemokine receptors

The transcription factor KLF2 regulates T cell trafficking by promoting expression of the lipid-binding receptor S1P(1) and the selectin CD62L. Recently, it was proposed that KLF2 also represses the expression of chemokine receptors. We confirmed the upregulation of the chemokine receptor CXCR3 on KLF2-deficient T cells. However, we showed that this was a cell-nonautonomous effect, as revealed by CXCR3 upregulation on wild-type bystander cells in mixed bone-marrow chimeras with KLF2-deficient cells. Furthermore, KLF2-deficient T cells overproduced IL-4, leading to the upregulation of CXCR3 through an IL-4-receptor- and eomesodermin-dependent pathway. Consistent with the increased IL-4 production, we found high concentrations of serum IgE in mice with T cell-specific KLF2 deficiency. Our findings support a model where KLF2 regulates T cell trafficking by direct regulation of S1P(1) and CD62L and restrains spontaneous cytokine production in naive T cells.

Myeloid-derived suppressor cells down-regulate L-selectin expression on CD4+ and CD8+ T cells

Effective cell-mediated antitumor immunity requires the activation of tumor-reactive T cells and the trafficking of activated T cells to tumor sites. These processes involve the extravasation of lymphocytes from the blood and lymphatics, and their homing to lymph nodes and tumors. L-selectin (CD62L) is an important molecule in these processes. It directs naive lymphocytes to peripheral lymph nodes where they become activated and it traffics naive lymphocytes to inflammatory environments, such as tumors. Individuals with advanced cancer are immune suppressed due to myeloid-derived suppressor cells (MDSC), a population of immature myeloid cells that accumulate to high levels in response to tumor-secreted and proinflammatory factors. We now demonstrate that the reduction in T cell levels of L-selectin that is commonly seen in individuals with cancer inversely correlates with MDSC levels. Three lines of evidence demonstrate that MDSC directly down-regulate L-selectin on naive T cells: 1) naive T cells cocultured with tumor-induced MDSC have reduced L-selectin; 2) T cells in tumor-free aged mice with elevated levels of MDSC have reduced L-selectin, and 3) peritoneal exudate T cells of tumor-free mice treated with plasminogen activator urokinase to elevate MDSC have reduced levels of L-selectin. MDSC are likely to down-regulate L-selectin through their plasma membrane expression of ADAM17 (a disintegrin and metalloproteinase domain 17), an enzyme that cleaves the ectodomain of L-selectin. Therefore, MDSC down-regulate L-selectin levels on naive T cells, decreasing their ability to home to sites where they would be activated. This is another mechanism by which MDSC inhibit antitumor immunity.

Secretory phospholipase A2-IID is an effector molecule of CD4+CD25+ regulatory T cells

Suppression by natural CD4(+)CD25(+) regulatory T cells (Tregs) is one mechanism by which tolerance is maintained. However, the way in which Tregs mediate suppression is not well understood. Here, we show that secreted phospholipase A2 (sPLA2)-IID is selectively produced by Tregs. sPLA2-IID is a potent mediator of Treg function, because it strongly suppressed proliferation of CD4(+) and CD8(+) T cells in vitro and in vivo in a manner independent of its catalytic activity. Furthermore, sPLA2-IID promoted the differentiation of Tregs, presumably via attenuating signaling through the PI3K/Akt/mammalian target of rapamycin pathway. Importantly, administration of a sPLA2-IID-Fc fusion protein inhibited disease development in murine models of colitis and multiple sclerosis, suggesting that sPLA2-IID's immunosuppressive function might be exploited therapeutically.

Low zone tolerance requires ICAM-1 expression to limit contact hypersensitivity elicitation

Painting subsensitizing doses of contact sensitizers on skin (low-dose tolerization) induces antigen (Ag)-specific tolerance, known as low zone tolerance (LZT), which has been experimentally demonstrated by the inhibition of contact hypersensitivity (CHS). Although LZT resulted from the inhibition of the sensitization phase, the effects on the effector/elicitation phase remain unknown. L-selectin and ICAM-1 regulate leukocyte influx into inflamed tissues during the elicitation phase of CHS. LZT was investigated in mice lacking either L-selectin or ICAM-1 to evaluate the roles these leukocyte receptors play in LZT during the elicitation phase. Low-dose tolerization effectively suppressed CHS in wild-type and L-selectin-deficient mice, but not in ICAM-1-deficient mice. Low-dose-tolerized ICAM-1-deficient splenocytes effectively suppressed the elicitation phase in naive wild-type recipients. Sensitized ICAM-1-deficient splenocytes showed normal proliferative responses to the sensitizing Ag and generated normal CHS in wild-type recipients. Thus, ICAM-1 deficiency did not affect sensitization. LZT was associated with a lack of ICAM-1 upregulation after elicitation, suggesting a potentially mechanistic role for ICAM-1. The blockade of IL-10, a possible mediator of LZT, produced by hapten-specific suppressor cells, abrogated LZT and restored ICAM-1 upregulation. These results indicate that low-dose tolerization controls CHS by abrogating ICAM-1 upregulation during the elicitation phase.

Intracellular bacterial vectors that induce CD8(+) T cells with similar cytolytic abilities but disparate memory phenotypes provide contrasting tumor protection

Induction of a functional CD8(+) T-cell response is the important criterion for cancer vaccines, and it is unclear whether acute or chronic live vectors are better suited for cancer antigen delivery. We have evaluated the tumor protective ability of two recombinant vectors, Listeria monocytogenes (LM) and Salmonella typhimurium (ST), both expressing ovalbumin (OVA). Although both vectors induced a similar OVA-specific CD8(+) T-cell response in the long term, LM-OVA induced mainly central-phenotype (T(CM), CD44(high)CD62L(high)), whereas ST-OVA induced mainly effector-phenotype (T(EM), CD44(high)CD62L(low)) cells. Both vectors induced functional OVA-specific CD8(+) T cells that expressed IFN-gamma and killed targets specifically in vivo. However, only LM-OVA-vaccinated mice were protected against B16-OVA tumors. This correlated to the ability of CD8(+) T cells generated against LM-OVA, but not against ST-OVA, to produce interleukin 2 and exhibit profound homeostatic and antigen-induced proliferation in vivo. Furthermore, adoptive transfer of memory CD8(+) T cells generated against LM-OVA (but not against ST-OVA) into recipient mice resulted in their trafficking to tumor-draining lymph nodes conferring protection. Although cytotoxicity and IFN-gamma production are considered to be the principal functions of memory CD8(+) T cells, the vaccine delivery strategy may also influence memory CD8(+) T-cell quality, and ability to proliferate and traffic to tumors. Thus, for efficacy, cancer vaccines should be selected for their ability to induce self-renewing memory CD8(+) T cells (CD44(high)IL-7Ralpha(high)CD62L(high)) besides their effector functions.

Gender differences in abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) comprise the tenth leading cause of death in Caucasian males 65 to 74 years of age and accounted for nearly 16,000 deaths overall in 2000. Therefore, understanding the pathophysiology of AAAs is an important undertaking. Clinically, multiple risk factors are associated with the development of AAAs, including increasing age, positive smoking history, and hypertension. Male gender is also a well-established risk factor for the development of an AAA, with a 4:1 male to female ratio. The reason for this gender disparity is unknown. The pathogenesis of AAAs formation is complex and multifactorial. Histologically, AAAs are characterized by early chemokine-driven leukocyte infiltration into the aortic wall. Subsequent destruction of elastin and collagen in the media and adventitia ensues owing to excessive local production of matrix-degrading enzymes and is accompanied by smooth muscle cell loss and thinning of the aortic wall. At present, no medical therapies are available to treat patients with aortic aneurysms, using only the crude measurement of aortic diameter as a threshold for which patients must undergo life-threatening and costly surgery. Defining the early mechanisms underlying gender-related differences in AAA formation is critical as understanding differences in disease patterns based on gender may allow us to develop new translational approaches to the prevention and treatment of patients with aortic aneurysms.

Establishment of experimental eosinophilic vasculitis by IgE-mediated cutaneous reverse passive arthus reaction

Prominent eosinophil infiltration is a characteristic of some forms of vasculitis, such as Churg-Strauss syndrome, also known as allergic granulomatous vasculitis. In the current study, we established a mouse model of cutaneous eosinophilic vasculitis by the cutaneous reverse passive Arthus reaction using IgE injection instead of IgG. Wild-type C57BL/6 mice were injected with IgE anti-trinitrophenyl antibodies, followed immediately by intravenous administration of trinitrophenyl bovine serum albumin. IgE-mediated immune complex challenge induced substantial hemorrhage with marked infiltration of eosinophils in which neutrophils, mast cells, and macrophages were also mixed. This finding contrasted remarkably with the neutrophil-dominant infiltration pattern in IgG-mediated immune complex challenge. In the lesion, the expression level of monocyte chemotactic protein-3 was increased, and anti-monocyte chemotactic protein-3 treatment resulted in a significant but incomplete blockade of eosinophil recruitment. Furthermore, mice lacking E-selectin, P-selectin, L-selectin, or intercellular adhesion molecule-1, as well as wild-type mice that received anti-vascular cell adhesion molecule-1-blocking antibodies were assessed for the IgE-mediated Arthus reaction. After 24 hours, the loss of P-selectin resulted in a significant reduction in eosinophil accumulation compared with both wild-type mice and other mouse mutants. Collectively, the Fc class of immunoglobulins, which forms these immune complexes, critically determines the disease manifestation of vasculitis. The IgE-mediated cutaneous reverse passive Arthus reaction may serve as an experimental model for cutaneous eosinophilic infiltration in vasculitis as well as in other diseases.

NAD+ and ATP released from injured cells induce P2X7-dependent shedding of CD62L and externalization of phosphatidylserine by murine T cells

Extracellular NAD(+) and ATP trigger the shedding of CD62L and the externalization of phosphatidylserine on murine T cells. These events depend on the P2X(7) ion channel. Although ATP acts as a soluble ligand to activate P2X(7), gating of P2X(7) by NAD(+) requires ecto-ADP-ribosyltransferase ART2.2-catalyzed transfer of the ADP-ribose moiety from NAD(+) onto Arg125 of P2X(7). Steady-state concentrations of NAD(+) and ATP in extracellular compartments are highly regulated and usually are well below the threshold required for activating P2X(7). The goal of this study was to identify possible endogenous sources of these nucleotides. We show that lysis of erythrocytes releases sufficient levels of NAD(+) and ATP to induce activation of P2X(7). Dilution of erythrocyte lysates or incubation of lysates at 37 degrees C revealed that signaling by ATP fades more rapidly than that by NAD(+). We further show that the routine preparation of primary lymph node and spleen cells induces the release of NAD(+) in sufficient concentrations for ART2.2 to ADP-ribosylate P2X(7), even at 4 degrees C. Gating of P2X(7) occurs when T cells are returned to 37 degrees C, rapidly inducing CD62L-shedding and PS-externalization by a substantial fraction of the cells. The "spontaneous" activation of P2X(7) during preparation of primary T cells could be prevented by i.v. injection of either the surrogate ART substrate etheno-NAD or ART2.2-inhibitory single domain Abs 10 min before sacrificing mice.

Differential effect of human herpesvirus 6A on cell division and apoptosis among naive and central and effector memory CD4+ and CD8+ T-cell subsets

The immune responses of naive and different memory subsets of CD4(+) and CD8(+) T cells to human herpesvirus 6 (HHV-6) have not been previously investigated. We show that HHV-6A induces cell division, as measured by 5,6-carboxyfluorescein succinimidyl ester dye and flow cytometry, predominantly in two populations of effector memory CD4(+) and CD8(+) T cells (T(EM) and T(EMRA)); naïve (T(N)) and central memory (T(CM)) CD4(+) and CD8(+) T cells showed almost no cell division. In contrast, HHV-6A induced apoptosis primarily in T(N) and T(CM) CD4(+) and CD8(+) T cells, whereas T(EM) and T(EMRA) CD4(+) and CD8(+) T cells were resistant to HHV-6A-induced apoptosis. HHV-6A-induced apoptosis was associated with activation of caspase-8, caspase-9, and caspase-3, suggesting the involvement of death receptor and mitochondrial signaling pathways. In addition, HHV-6A induced secretion of interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-alpha), IL-8, and gamma interferon by peripheral blood mononuclear cells; TNF-alpha secretion was observed exclusively from CCR7(+) (T(N) plus T(CM)) CD4(+) T cells. These data show that HHV-6 differentially influences the functions of naïve T cells and different subsets of memory CD4(+) and CD8(+) T cells, which in part may be due to differential susceptibility to HHV-6A-induced apoptosis.

Natural killer cells require selectins for suppression of subcutaneous tumors

Natural killer (NK) cells recognize and destroy cancer cells through a variety of mechanisms. They may also modulate the adaptive immune response to cancer by interacting with dendritic cells and T cells. Although NK cells play an important role in tumor suppression, little is known about the mechanisms of their recruitment to tumors. Previously it has been shown that subcutaneous tumor growth is enhanced in mice lacking selectins, a family of cell adhesion molecules that mediate the first step of immune cell entry into tissue from the blood. Here we show that NK cell recruitment to tumors is defective in selectin-deficient mice. In vivo NK cell depletion, either pharmacologic or genetic, leads to enhanced subcutaneous tumor growth, similar to the phenotype observed in the selectin-deficient animals. We also show that although NK cells from selectin-deficient mice appear developmentally normal and are functional in in vitro assays, their in vivo function is impaired. This study reveals a role for selectins in NK cell recruitment to tumors and in regulation of effective tumor immunity.

Polymorphism in ICAM-1, PECAM-1, E-selectin, and L-selectin genes in Tunisian patients with inflammatory bowel disease

BACKGROUND

Ulcerative colitis (UC) and Crohn's disease (CD) are chronic intestinal disorders characterized by immune dysregulation and leukocytes recruitment into gastrointestinal tract. Cell adhesion molecules (CAM) mediate the extravasation of leukocytes and their accumulation in inflamed intestinal mucosa. Recently, CAM genes have been implicated in determining susceptibility to UC and CD. We investigate seven mutations in CAM: G241R and K469E in ICAM-1, V125L in PECAM-1, G98T, S128R, and L554F in E-selectin and F206L in L-selectin in 197 Tunisian patients (73 with UC and 124 with CD) and 194 controls. These polymorphisms were detected by polymerase chain reaction sequence-specific primers and restriction enzyme analysis.

RESULTS

A significant increase in allele frequencies of 206L of L-selectin and the associated genotype F/L was observed in both patients with UC and CD compared with controls. Subgroup analysis showed that the L206 allele and F/L206 genotype frequencies were significantly increased in UC patients with left-sided type; whereas, the F/L206 genotype was significant in CD patients with ileocolonic location and stricturing behavior compared with controls. No significant differences in allele or genotype frequencies were observed for ICAM-1 K469E, E-selectin, and PECAM-1 polymorphisms between UC patients, CD patients, and controls.

CONCLUSION

We found an association of inflammatory bowel disease with allele L206 of L-selectin gene, whereas genotype L/F was associated with a subgroup of UC (left-sided type) and CD patients with more extensive location of disease and stricturing behavior. However, further studies are needed to confirm our findings.

Foxo1 links homing and survival of naive T cells by regulating L-selectin, CCR7 and interleukin 7 receptor

Foxo transcription factors have a conserved role in the adaptation of cells and organisms to nutrient and growth factor availability. Here we show that Foxo1 has a crucial, nonredundant role in T cells. In naive T cells, Foxo1 controlled the expression of the adhesion molecule L-selectin, the chemokine receptor CCR7 and the transcription factor Klf2, and its deletion was sufficient to alter lymphocyte trafficking. Furthermore, Foxo1 deficiency resulted in a severe defect in interleukin 7 receptor alpha-chain (IL-7Ralpha) expression associated with its ability to bind an Il7r enhancer. Finally, growth factor withdrawal induced a Foxo1-dependent increase in Sell, Klf2 and Il7r expression. These data suggest that Foxo1 regulates the homeostasis and life span of naive T cells by sensing growth factor availability and regulating homing and survival signals.

Requirement of L-selectin for gammadelta T lymphocyte activation and migration during allergic pleurisy: co-relation with eosinophil accumulation

Intra-thoracic antigenic challenge (ovalbumin, 12.5 microg/cavity) led to increased numbers of gammadelta T lymphocytes in pleural cavities, blood and thoracic lymph nodes in sensitized mice within 48 h. Part of these cells expressed CD62L, which increased on gammadelta T cell surfaces obtained from lymph nodes after ovalbumin (OVA) challenge. Selectin blockade by fucoidan pre-treatment (10 mg/kg, i.v.) impaired in vivo increase in CD25(+) and c-fos(+) gammadelta T cell numbers in lymph nodes, indicating a role for selectins on gammadelta T lymphocyte activation and proliferation. In vivo selectin blockade by fucoidan or alpha-CD62L mAb (200 microg/mice, i.p.) also inhibited OVA-induced gammadelta T cell accumulation in pleural cavities. Confirming the direct effect of CD62L on gammadelta T cell transmigration, the migration of i.v. adoptively-transferred CFSE-labeled gammadelta T lymphocytes into pleural cavities of challenged recipient mice was impaired by fucoidan ex vivo treatment. It is noteworthy that eosinophil influx was also impaired in those mice, indicating that reduced eosinophil migration by CD62L in vivo blockade depended on gammadelta T cell migration via CD62L molecules. Accordingly, pleural gammadelta T lymphocytes from fucoidan-treated mice presented reduced OVA-induced IL-5 and CCL11 production. Supporting these data, the depletion of Vgamma4 T lymphocytes, which are pulmonary gammadelta T cells, decreased OVA-induced eosinophil influx into allergic site. Such results demonstrate that CD62L is crucial for the activation of gammadelta T cells in lymph nodes, for their migration into inflamed tissue and for the modulation of eosinophil influx during allergic response.

CD19 regulates the development of bleomycin-induced pulmonary fibrosis in a mouse model

OBJECTIVE

The contribution of CD19 and B lymphocytes to pulmonary fibrosis is controversial. The aim of this study was to address the role of CD19 during the development of pulmonary fibrosis.

METHODS

Mice lacking or overexpressing the B cell surface molecule CD19, which is known as a positive regulator of B cell activation, were used in a model of bleomycin-induced pulmonary fibrosis. Ten or sixteen days after intratracheal injection of bleomycin, lung sections from mice were evaluated by histologic analysis. Seven days after instillation, the total leukocyte count and the number of B cells in bronchoalveolar lavage fluid (BALF) were determined, using a hemocytometer and flow cytometry. Bleomycin was also administered into selectin-deficient or intercellular adhesion molecule 1-deficient mouse strains. The level of CXCR3 expression on B cells was determined by flow cytometry.

RESULTS

CD19 deficiency significantly reduced susceptibility to intratracheal bleomycin challenge on day 16, while CD19 overexpression augmented fibrosis even on day 10. Furthermore, the survival rate and number of B cells in BALF also correlated with CD19 expression levels. The accumulation of B cells in BALF was dependent on CD19 levels, whereas there was no association with the levels of selectins or intercellular adhesion molecule 1. Additionally, CXCR3 was up-regulated in BALF B cells, while it was rarely expressed on circulating B cells. Furthermore, CD19 signaling facilitated B cell CXCR3 up-regulation in response to stimulation in vitro.

CONCLUSION

These results suggest that CD19 signaling is associated with the development of pulmonary fibrosis by controlling B cell infiltration into lung tissue, which may be associated with CXCR3 up-regulation.

The N-glycolyl form of mouse sialyl Lewis X is recognized by selectins but not by HECA-452 and FH6 antibodies that were raised against human cells

E-, P- and L-selectins critically function in lymphocyte recirculation and recruiting leukocytes to inflammatory sites. MECA-79 antibody inhibits L-selectin-mediated lymphocyte adhesion in several species and does not require sialic acid in its epitope. Many other antibodies, however, recognize human selectin ligands expressing N-acetylneuraminic acid but not mouse selectin ligands expressing N-glycolylneuraminic acid, suggesting that difference in sialic acid in sialyl Lewis X leads to differential reactivity. We found that HECA-452 and FH6 monoclonal antibodies bind Chinese hamster ovary (CHO) cells expressing N-acetylneuraminyl Lewis X oligosaccharide but not its N-glycolyl form. Moreover, synthetic N-acetylneuraminyl Lewis X oligosaccharide but not its N-glycolyl oligosaccharide inhibited HECA-452 and FH6 binding. By contrast, E-, P- and L-selectin bound to CHO cells regardless of whether they express N-acetyl or N-glycolyl form of sialyl Lewis X, showing that selectins have a broader recognition capacity than HECA-452 and FH-6 anti-sialyl Lewis x antibodies.

Leukocyte adhesion molecules in animal models of inflammatory bowel disease

The dysregulated recruitment of leukocytes into the intestine is required for the initiation and maintenance of inflammatory bowel disease (IBD). Several families of molecules regulate the influx of these cells into sites of inflammation. Interference with some of these molecules has already shown efficacy in the clinics and antibodies that target the molecules involved have been approved by the FDA for use in Crohn's disease (CD), multiple sclerosis (i.e., natalizumab), and psoriasis (i.e., efalizumab). Here, we discuss basic aspects of the different families of relevant molecules and compile a large body of preclinical studies that supported the targeting of specific steps of the leukocyte adhesion cascade for therapeutic purposes in colitis and in novel models of CD-like ileitis.

Specific immunosuppression with inducible Foxp3-transduced polyclonal T cells

Forkhead box p3 (Foxp3)-expressing regulatory T cells are key mediators of peripheral tolerance suppressing undesirable immune responses. Ectopic expression of Foxp3 confers regulatory T cell phenotype to conventional T cells, lending itself to therapeutic use in the prevention of autoimmunity and transplant rejection. Here, we show that adoptive transfer of polyclonal, wild-type T cells transduced with an inducible form of Foxp3 (iFoxp3) can be used to suppress immune responses on demand. In contrast to Foxp3-transduced cells, iFoxp3-transduced cells home "correctly" into secondary lymphoid organs, where they expand and participate in immune responses. Upon induction of iFoxp3, the cells assume regulatory T cell phenotype and start to suppress the response they initially partook in without causing systemic immunosuppression. We used this approach to suppress collagen-induced arthritis, in which conventional Foxp3-transduced cells failed to show any effect. This provides us with a generally applicable strategy to specifically halt immune responses on demand without prior knowledge of the antigens involved.

Analysis of Adhesion Molecules Involved in Leukocyte Homing into the Basolateral Pockets of Mouse Peyer's Patch M Cells

The basolateral membranes of intestinal M cells are invaginated to form large intraepithelial "pockets" that are populated by specific sub-sets of mucosal leukocytes, including CD4+ T cells, memory and naïve B cells, and occasional dendritic cells. The adhesion molecules involved in leukocyte trafficking and/or retention within this unique immunological niche are unknown. In this study, we used immunofluorescence microscopy and a battery of monoclonal antibodies to identify the adhesion molecules expressed by leukocytes situated within the intracellular pockets of mouse Peyer's patch (PP) M cells. M cell associated leukocytes (MAL) consistently stained positive for integrin alpha4beta7, and integrin LFA-1 (CD11a/CD18), but were rarely positive for L-selectin (CD62L) or the mucosal integrin alphaEbeta7. However, neither the alpha4beta7 ligands MadCAM-1 or VCAM-1, nor the LFA-1 ligand ICAM-1, were detected on M cell basolateral membranes. To determine whether integrins alpha4beta7 or LFA-1 play a functional role leukocyte homing to M cell pockets, we examined M cells in mice deficient in integrin beta7 or CD11a/CD18. Although PP from CD18 or integrin beta7 mice were reduced in number and size as compared to age-matched controls, we identified M cells in both strains of mice. However, mice lacking CD18 (but not integrin beta7) had significantly fewer leukocytes within M cell pockets as compared to control animals, suggesting LFA-1 (but not alpha4beta7) may contribute, in part, to leukocyte trafficking into and/or retention within this unique immunological niche.

An L-selectin ligand distinct from P-selectin glycoprotein ligand-1 is expressed on endothelial cells and promotes neutrophil rolling in inflammation

Neutrophils recruited from the blood are key players in the innate immune response. Selectins play critical roles in neutrophil recruitment by mediating their tethering and rolling in inflamed venules. While the roles of P- and E-selectin in this process are well established, the mechanisms of L-selectin-mediated neutrophil recruitment remain elusive. One proposal is that tethering is mediated by L-selectin on flowing neutrophils interacting with P-selectin glycoprotein ligand-1 (PSGL-1) on adherent neutrophils. To clarify whether L-selectin-mediated neutrophil recruitment depends entirely on PSGL-1, we examined the impact of L-selectin deficiency in mice with a PSGL-1-deficient background. L-selectin and PSGL-1 double-knockout mice exhibited a higher increase in their peripheral blood neutrophil count and a worse defect in neutrophil recruitment into the inflamed peritoneum than PSGL-1-deficient mice. Intravital microscopy of inflamed cremaster muscle venules showed that L-selectindeficiency or antibody blockade of L-selectin reduced the residual leukocyte rolling in PSGL-1-deficient mice. Flow cytometric analyses showed that the endothelial cells from the cremaster muscle bound L-selectin in a PSGL-1-independent manner. These results provide evidence for the existence of an L-selectin ligand distinct from PSGL-1 in inflammation and indicate that such a ligand is expressed on endothelial cells, promoting neutrophil rolling in vivo.

Cell adhesion antagonists: therapeutic potential in asthma and chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) and asthma are inflammatory diseases of the lung where a hallmark feature is excessive leukocyte infiltration that leads to tissue injury. Cell adhesion molecules (e.g. selectins and integrins) play a key role in cell trafficking, and in the lung they regulate leukocyte extravasation, migration within the interstitium, cellular activation, and tissue retention. All selectin family members (including L-selectin, P-selectin, and E-selectin) and many of the beta1 and beta2 integrins appear to be important therapeutic targets, as numerous animal studies have demonstrated essential roles for these cell adhesion molecules in lung inflammation. Not surprisingly, these families of adhesion molecules have been under intense investigation by the pharmaceutical industry for the development of novel therapeutics. Integrins are validated drug targets, as drugs that antagonize integrin alphaIIbbeta3 (e.g. abciximab), integrin alphaLbeta2 (efalizumab), and integrin alpha4beta1 (natalizumab) are currently US FDA-approved for acute coronary syndromes, psoriasis, and multiple sclerosis, respectively. However, none has been approved for indications related to asthma or COPD. Here, we provide an overview of roles played by selectins and integrins in lung inflammation. We also describe recent clinical results (both failures and successes) in developing adhesion molecule antagonists, with specific emphasis on those targets that may have potential benefit in asthma and COPD. Early clinical trials using selectin and integrin antagonists have met with limited success. However, recent positive phase II clinical trials with a small-molecule selectin antagonist (bimosiamose) and a small-molecule integrin alpha4beta1 antagonist (valategrast [R411]), have generated enthusiastic anticipation that novel strategies to treat asthma and COPD may be forthcoming.

The absence of lymphoid CD8+ dendritic cell maturation in L-selectin-/- respiratory compartment attenuates antiviral immunity

Intratracheal instillation of L-selectin-deficient (L-Sel(-/-)) mice with an adenovirus 2 (Ad2) vector resulted in the lack of respiratory Ad2- or beta-galactosidase-specific CTLs with concomitant long-lived beta-galactosidase transgene expression in the lungs. The absence of Ag-specific CTLs was attributed to a deficiency in lymphoid CD11c(+)CD8(+) dendritic cells (DCs) in the lower respiratory lymph nodes (LRLNs). To enable L-Sel(-/-) CTL activity, cell-sorted L-Sel(-/-)CD8(+) T cells were cocultured with cell-sorted L-Sel(+/+)CD8(+) or CD8(-) DCs or L-Sel(-/-)CD8(-) DCs. Only the CD8(+) DCs restored CTL activity; L-Sel(-/-)CD8(-) DCs failed to support L-Sel(+/+) CTLs because these remained immature, lacking the ability to express costimulatory molecules CD40, CD80, or CD86. Although no lung CD8(+) DCs were detected, the DC environment remained suppressive in L-Sel(-/-) mice evident by the lack of CTL responses following adenoviral challenge with OVA in recipient L-Sel(-/-) adoptively transferred with OT-1 CD8(+) T cells. To assess whether the L-Sel(-/-)CD8(-) DCs could be induced into maturity, microbial stimulation studies were performed showing the failure of L-Sel(-/-) LRLN to make matured DCs. When L-Sel(-/-) mice were subjected in vivo to microbial activation before Ad2 vector dosing, CTL activity was restored stimulating the renewed presence of LRLN CD8(+) DCs in L-Sel(-/-) mice. These studies show that impairment of L-Sel(-/-) DC maturation results in insufficient mature DCs that require microbial activation to restore increases in respiratory CD8(+) DCs to support CTL responses.

Nonmucosal alphavirus vaccination stimulates a mucosal inductive environment in the peripheral draining lymph node

The strongest mucosal immune responses are induced following mucosal Ag delivery and processing in the mucosal lymphoid tissues, and much is known regarding the immunological parameters which regulate immune induction via this pathway. Recently, experimental systems have been identified in which mucosal immune responses are induced following nonmucosal Ag delivery. One such system, footpad delivery of Venezuelan equine encephalitis virus replicon particles (VRP), led to the local production of IgA Abs directed against both expressed and codelivered Ags at multiple mucosal surfaces in mice. In contrast to the mucosal delivery pathway, little is known regarding the lymphoid structures and immunological components that are responsible for mucosal immune induction following nonmucosal delivery. In this study, we have used footpad delivery of VRP to probe the constituents of this alternative pathway for mucosal immune induction. Following nonmucosal VRP delivery, J chain-containing, polymeric IgA Abs were detected in the peripheral draining lymph node (DLN), at a time before IgA detection at mucosal surfaces. Further analysis of the VRP DLN revealed up-regulated alpha4beta7 integrin expression on DLN B cells, expression of mucosal addressin cell adhesion molecule 1 on the DLN high endothelia venules, and production of IL-6 and CC chemokines, all characteristics of mucosal lymphoid tissues. Taken together, these results implicate the peripheral DLN as an integral component of an alternative pathway for mucosal immune induction. A further understanding of the critical immunological and viral components of this pathway may significantly improve both our knowledge of viral-induced immunity and the efficacy of viral-based vaccines.

Leukocyte trafficking in a mouse model for leukocyte adhesion deficiency II/congenital disorder of glycosylation IIc

Leukocyte adhesion deficiency II (LAD II), also known as congenital disorder of glycosylation IIc (CDG-IIc), is a human disease in which a defective GDP-fucose transporter (SLC35C1) causes developmental defects and an immunodeficiency that is based on the lack of fucosylated selectin ligands. Since the study of in vivo leukocyte trafficking in patients with LAD II is experimentally limited, we analyzed this process in mice deficient for Slc35c1. We found that E-, L-, and P-selectin-dependent leukocyte rolling in cremaster muscle venules was virtually absent. This was accompanied by a strong but not complete decrease in firm leukocyte adhesion. Moreover, neutrophil migration to the inflamed peritoneum was strongly reduced by 89%. Previous reports showed surprisingly normal lymphocyte functions in LAD II, which indicated sufficient lymphocyte trafficking to secondary lymphoid organs. We now found that while lymphocyte homing to lymph nodes was reduced to 1% to 2% in Slc35c1(-/-) mice, trafficking to the spleen was completely normal. In accordance with this, we found a defect in the humoral response to a T cell-dependent antigen in lymph nodes but not in the spleen. Taken together, Slc35c1(-/-) mice show strongly defective leukocyte trafficking but normal lymphocyte homing to the spleen, which may explain normal lymphocyte functions in LAD II.

CD73-generated adenosine restricts lymphocyte migration into draining lymph nodes

After an inflammatory stimulus, lymphocyte migration into draining lymph nodes increases dramatically to facilitate the encounter of naive T cells with Ag-loaded dendritic cells. In this study, we show that CD73 (ecto-5'-nucleotidase) plays an important role in regulating this process. CD73 produces adenosine from AMP and is expressed on high endothelial venules (HEV) and subsets of lymphocytes. Cd73(-/-) mice have normal sized lymphoid organs in the steady state, but approximately 1.5-fold larger draining lymph nodes and 2.5-fold increased rates of L-selectin-dependent lymphocyte migration from the blood through HEV compared with wild-type mice 24 h after LPS administration. Migration rates of cd73(+/+) and cd73(-/-) lymphocytes into lymph nodes of wild-type mice are equal, suggesting that it is CD73 on HEV that regulates lymphocyte migration into draining lymph nodes. The A(2B) receptor is a likely target of CD73-generated adenosine, because it is the only adenosine receptor expressed on the HEV-like cell line KOP2.16 and it is up-regulated by TNF-alpha. Furthermore, increased lymphocyte migration into draining lymph nodes of cd73(-/-) mice is largely normalized by pretreatment with the selective A(2B) receptor agonist BAY 60-6583. Adenosine receptor signaling to restrict lymphocyte migration across HEV may be an important mechanism to control the magnitude of an inflammatory response.

T lymphocyte migration to lymph nodes is maintained during homeostatic proliferation

The immune system maintains appropriate cell numbers through regulation of cell proliferation and death. Normal tissue distribution of lymphocytes is maintained through expression of specific adhesion molecules and chemokine receptors such as L-selectin and CCR7, respectively. Lymphocyte insufficiency or lymphopenia induces homeostatic proliferation of existing lymphocytes to increase cell numbers. Interestingly, homeostatic proliferation of T lymphocytes induces a phenotypic change from naïve- to memory-type cell. Naïve T cells recirculate between blood and lymphoid tissues whereas memory T cells migrate to nonlymphoid sites such as skin and gut. To assess effects of homeostatic proliferation on migratory ability of T cells, a murine model of lymphopenia-induced homeostatic proliferation was used. Carboxyfluorescein diacetate, succinimidyl ester-labeled wild-type splenocytes were adoptively transferred into recombination activation gene-1-deficient mice and analyzed by flow cytometry, in vitro chemotactic and in vivo migration assays, and immunofluorescence microscopy. Homeostatically proliferated T cells acquired a mixed memory-type CD44high L-selectinhigh CCR7low phenotype. Consistent with this, chemotaxis to secondary lymphoid tissue chemokine in vitro was reduced by 22%-34%. By contrast, no differences were found for migration or entry into lymph nodes during in vivo migration assays. Therefore, T lymphocytes that have undergone homeostatic proliferation recirculate using mechanisms similar to naïve T cells.

Effect of tumour necrosis factor-alpha receptor 1 genetic deletion on carrageenan-induced acute inflammation: a comparison with etanercept

In the present study, we used tumour necrosis factor-alpha receptor 1 knock-out mice (TNF-alphaR1KO) to evaluate an in vivo role of TNF-alphaR1 on the pathogenesis of inflammatory diseases. We used a murine model of carrageenan-induced acute inflammation (pleurisy), a preclinical model of airway inflammation. The data proved that TNF-alphaR1KO were resistant to carrageenan-induced acute inflammation compared with TNF-alpha wild-type mice. TNF-alphaR1KO showed a significant reduction in accumulation of pleural exudate and in the number of inflammatory cells, in lung infiltration of polymorphonuclear leucocytes and lipid peroxidation and showed a decreased production of nitrite/nitrate in pleural exudates. Furthermore, the intensity and degree of the adhesion molecule intercellular adhesion molecule-1 and P-selectin, Fas ligand (FasL), inducible nitric oxide sythase and nitrotyrosine determined by immunohistochemical analysis were reduced markedly in lung tissues from TNF-alphaR1KO at 4 h and 24 h after carrageenan injection. Moreover, TNF-alpha and interleukin-1beta concentrations were reduced in inflamed areas and in pleural exudates from TNF-alphaR1KO. To support the results generated using pleural inflammation, carrageenan-induced paw oedema models were also performed. In order to elucidate whether the observed anti-inflammatory effects were related to the inhibition of TNF-alpha, we also investigated the effect of etanercept, a TNF-alpha soluble receptor construct, on carrageenan-induced pleurisy. The treatment with etanercept (5 mg/kg subcutaneously 2 h before the carrageenan injection) reduces markedly both laboratory and histological signs of carrageenan-induced pleurisy. Our results showed that administration of etanercept resulted in the same outcome as that of deletion of the TNF-alphaR1 receptor, adding a new insight to TNF-alpha as an excellent target by therapeutic applications.

Phosphatidylinositol-3-OH kinase and nutrient-sensing mTOR pathways control T lymphocyte trafficking

Phosphatidylinositol-3-OH kinase (PI(3)K) and the nutrient sensor mTOR are evolutionarily conserved regulators of cell metabolism. Here we show that PI(3)K and mTOR determined the repertoire of adhesion and chemokine receptors expressed by T lymphocytes. The key lymph node-homing receptors CD62L (L-selectin) and CCR7 were highly expressed on naive T lymphocytes but were downregulated after immune activation. CD62L downregulation occurred through ectodomain proteolysis and suppression of gene transcription. The p110delta subunit of PI(3)K controlled CD62L proteolysis through mitogen-activated protein kinases, whereas control of CD62L transcription by p110delta was mediated by mTOR through regulation of the transcription factor KLF2. PI(3)K-mTOR nutrient-sensing pathways also determined expression of the chemokine receptor CCR7 and regulated lymphocyte trafficking in vivo. Hence, lymphocytes use PI(3)K and mTOR to match metabolism and trafficking.

Murine models of immunodeficiency and autoimmune disease

Genetically determined murine immunodeficiency states are useful for understanding the function of specific immune-system genes and cellpopulations. In addition, certain immunodeficient strains may be exploited as hosts for foreign tumors or immune cells. The more commonly used immunodeficiency models are described in this appendix. Not included are strains better known for primary neurological or neuromuscular abnormalities or for defective osteoclast function. Many of the recently described immune-deficient "knockout" strains are described, including cytokine and cytokine receptor knockout strains. The most widely studied murine strains for autoimmune disease and experimental autoreactivity are also listed.

Selective regulation of CD8 effector T cell migration by the p110 gamma isoform of phosphatidylinositol 3-kinase

Chemokine-mediated T cell migration is essential to an optimal immune response. The p110gamma isoform of PI3K is activated by G protein-coupled receptors and regulates neutrophil and macrophage chemotaxis. We used p110gamma-deficient mice to examine the role of p110gamma in CD8 T cell migration and activation in response to viral challenge. Naive CD8 T cell migration in response to CCL21 in vitro and trafficking into secondary lymphoid organs in vivo was unaffected by the loss of p110gamma. Furthermore, loss of p110gamma did not affect CD8 T cell proliferation and effector cell differentiation in vitro in response to anti-CD3 stimulation or in vivo in response to vaccinia virus (VV) challenge. However, there was reduced migration of p110gamma knockout (p110gamma(-/-)) CD8 effector T cells into the peritoneum following i.p. challenge with VV. The role of p110gamma in CD8 effector T cell migration was intrinsic to T cells, as p110gamma(-/-) CD8 effector T cells exhibited impaired migration into the inflamed peritoneum following secondary transfer into wild-type recipients. In addition, p110gamma(-/-) CD8 effector T cells exhibited impaired migration in vitro in response to inflammatory chemoattractants. Although wild-type mice efficiently cleared VV at high viral doses, infection of p110gamma knockout mice resulted in visible illness and death less than a week after infection. Thus, p110gamma is dispensable for constitutive migration of naive CD8 T cells and subsequent activation and differentiation into effector CD8 T cells, but plays a central role in the migration of effector CD8 T cells into inflammatory sites.

No detectable endothelial- or leukocyte-derived L-selectin ligand activity on the endothelium in inflamed cremaster muscle venules

L-selectin is important in mediating leukocyte recruitment in inflammation. The role of L-selectin was for long believed to be influenced by an inducible endothelial ligand; however, L-selectin ligand activity was recently shown to be mediated by leukocytic P-selectin glycoprotein ligand 1 (PSGL-1). Still, it is unknown whether PSGL-1 is deposited on the endothelium or whether leukocyte fragments or leukocytic uropods are presented on the venular surface. Moreover, it is unclear whether ligands for L-selectin other than PSGL-1 are present in inflammation. Overall, this has complicated understanding of the mechanisms that guide recruitment of inflammatory cells. Here, I used intravital microscopy on mouse cremaster muscle venules to show that L-selectin influences leukocyte rolling in inflammation exclusively by mediating L-selectin/PSGL-1-dependent, secondary capture to rolling and adherent leukocytes. I show that leukocyte primary capture in inflammation is mediated almost entirely by P-selectin, whereas the capacity of E-selectin to mediate capture appears to be minimal. In parallel, primary capture remaining after function inhibition of P-selectin is not decreased by blockage or absence of L-selectin. Rolling along the endothelium in venules following a number of inflammatory treatments was abolished by simultaneous blockage of P-selectin, E-selectin, and VCAM-1, indicating that there is no additional adhesive pathway involving L-selectin or any other molecule that can mediate leukocyte rolling in inflamed cremaster muscle venules in response to the used stimuli. Moreover, in vivo staining failed to detect any L-selectin ligand activity on the endothelium. These data demonstrate that expression of L-selectin on leukocytes is insufficient for mediating rolling and efficient recruitment of leukocytes in inflammation.

The highway code of T cell trafficking

Coordinated migratory events are required for the development of effective and regulated immunity. Naïve T lymphocytes are programmed to recirculate predominantly in secondary lymphoid tissue by non-specific stimuli. In contrast, primed T cells must identify specific sites of antigen location in non-lymphoid tissue to exert targeted effector responses. Following priming, T cells acquire the ability to establish molecular interactions mediated by tissue-selective integrins and chemokine receptors (homing receptors) that allow their access to specific organs, such as the skin and the gut. Recent studies have shown that an additional level of specificity is provided by the induction of specific T cell migration into the tissue following recognition of antigen displayed by the endothelium. In addition, co-stimulatory signals (such as those induced by CD28 and CTLA-4 molecules) have been shown not only to regulate T cell activation and differentiation, but also to orchestrate the anatomy of the ensuing T cell response.

Crotoxin alters lymphocyte distribution in rats: Involvement of adhesion molecules and lipoxygenase-derived mediators

Crotoxin is the main neurotoxic component of Crotalus durissus terrificus snake venom and modulates immune and inflammatory responses, interfering with the activity of leukocytes. In the present work, the effects of crotoxin on the number of blood and lymphatic leukocytes and on lymph nodes and spleen lymphocytes population were investigated. The toxin s.c. administered to male Wistar rats, decreases the number of lymphocytes in blood and lymph circulation and increases the content of B and T-lymphocytes in lymph nodes. These effects were detected 1-2h after treatment. The crotoxin molecule is composed of two subunits, an acidic non-toxic polypeptide, named crotapotin and a toxic basic phospholipase A(2) (PLA(2)). PLA(2), but not crotapotin, decreased the number of circulating blood and lymph lymphocytes. Crotoxin promotes leukocyte adherence to endothelial cells of blood microcirculation and to lymph node high endothelial venules, which might contribute to the drop in the number of circulating lymphocytes. Crotoxin increases expression of the adhesion molecule LFA-1 in lymphocytes. The changes in the expression of the adhesion molecule might contribute, at least in part, for the increased leukocyte adhesion to endothelium. Zileuton, a 5-lipoxygenase inhibitor, blocked the decrease in the number of circulating leukocytes induced by crotoxin and also abolished the changes observed in leukocyte-endothelial interactions, suggesting the involvement of lipoxygenase-derived mediators in the effects of the toxin.

Effects of donor T-cell trafficking and priming site on graft-versus-host disease induction by naive and memory phenotype CD4 T cells

Graft-versus-host disease (GVHD) remains a major cause of morbidity and mortality in allogeneic stem cell transplantation. Effector memory T cells (T(EM)) do not cause GVHD but engraft and mount immune responses, including graft-versus-tumor effects. One potential explanation for the inability of T(EM) to cause GVHD is that T(EM) lack CD62L and CCR7, which are instrumental in directing naive T cells (T(N)) to lymph nodes (LN) and Peyer patches (PP), putative sites of GVHD initiation. Thus T(EM) should be relatively excluded from LN and PP, possibly explaining their inability to cause GVHD. We tested this hypothesis using T cells deficient in CD62L or CCR7, transplant recipients lacking PNAd ligands for CD62L, and recipients without LN and PP or LN, PP, and spleen. Surprisingly, CD62L and CCR7 were not required for T(N)-mediated GVHD. Moreover, in multiple strain pairings, GVHD developed in recipients that lacked LN and PP. Mild GVHD could even be induced in mice lacking all major secondary lymphoid tissues (SLT). Conversely, enforced constitutive expression of CD62L on T(EM) did not endow them with the ability to cause GVHD. Taken together, these data argue against the hypothesis that T(EM) fail to induce GVHD because of inefficient trafficking to LN and PP.

CD95-mediated apoptosis in naïve, central and effector memory subsets of CD4+ and CD8+ T cells in aged humans

Aging is associated with a decrease in naïve (T(N)) and central memory (T(CM)), and an accumulation of effector memory (T(EM) and T(EMRA)) T cell subsets. Previously, we have demonstrated an increased sensitivity of T(N) and T(CM) CD4+ and CD8+ T cells in aging to TNF-alpha-induced apoptosis. In this investigation, we examined whether similar differential sensitivity is applicable to CD95-mediated apoptosis. We show that T(N) and T(CM) CD4+ and CD8+ T cells from aged subjects are significantly more sensitive to CD95-mediated apoptosis. Increased apoptosis is associated with increased activation of caspase-8 and caspase-3. Both caspase-8 and caspase-3 inhibitors blocked CD95-mediated apoptosis and activation of caspase-8 and caspase-3 in T(N) and T(CM) CD4+ and CD8+ T cells. No significant difference was observed in apoptosis or in activation of caspase-8 and caspase-3 in T(EM) and T(EMRA) CD4+ and CD8+ T cells between young and aged subjects; both populations were relatively and comparably resistant to CD95-mediated apoptosis and caspase activation. No correlation was observed between the sensitivity/resistance of any of the subsets of CD4+ or CD8+T cells to CD95-mediated apoptosis and the expression of CD95. Our data suggest that increased CD95-mediated apoptosis of T(N) and T(CM) CD8+ and CD4+ T cells may play a role in their decline in human aging.

S1P1 receptor signaling overrides retention mediated by G alpha i-coupled receptors to promote T cell egress

The mechanism by which sphingosine-1-phosphate receptor-1 (S1P1) acts to promote lymphocyte egress from lymphoid organs is not defined. Here, we showed that CCR7-deficient T cells left lymph nodes more rapidly than wild-type cells did, whereas CCR7-overexpressing cells were retained for longer. After treatment with FTY720, an agonist that causes downmodulation of lymphocyte S1P1, CCR7-deficient T cells were less effectively retained than wild-type T cells. Moreover, treatment with pertussis toxin to inactivate signaling via G alpha i-protein-coupled receptors restored egress competence to S1P1-deficient lymphocytes. We also found that T cell accumulation in lymph node cortical sinusoids required intrinsic S1P1 expression and was antagonized by CCR7. These findings suggest a model where S1P1 acts in the lymphocyte to promote lymph node egress by overcoming retention signals mediated by CCR7 and additional G alpha i-coupled receptors. Furthermore, by simultaneously upregulating S1P1 and downregulating CCR7, T cells that have divided multiple times switch to a state favoring egress over retention.

Initiation of protein O glycosylation by the polypeptide GalNAcT-1 in vascular biology and humoral immunity

Core-type protein O glycosylation is initiated by polypeptide N-acetylgalactosamine (GalNAc) transferase (ppGalNAcT) activity and produces the covalent linkage of serine and threonine residues of proteins. More than a dozen ppGalNAcTs operate within multicellular organisms, and they differ with respect to expression patterns and substrate selectivity. These distinctive features imply that each ppGalNAcT may differentially modulate regulatory processes in animal development, physiology, and perhaps disease. We found that ppGalNAcT-1 plays key roles in cell and glycoprotein selective functions that modulate the hematopoietic system. Loss of ppGalNAcT-1 activity in the mouse results in a bleeding disorder which tracks with reduced plasma levels of blood coagulation factors V, VII, VIII, IX, X, and XII. ppGalNAcT-1 further supports leukocyte trafficking and residency in normal homeostatic physiology as well as during inflammatory responses, in part by providing a scaffold for the synthesis of selectin ligands expressed by neutrophils and endothelial cells of peripheral lymph nodes. Animals lacking ppGalNAcT-1 are also markedly impaired in immunoglobulin G production, coincident with increased germinal center B-cell apoptosis and reduced levels of plasma B cells. These findings reveal that the initiation of protein O glycosylation by ppGalNAcT-1 provides a distinctive repertoire of advantageous functions that support vascular responses and humoral immunity.

Importance of donor- and recipient-derived selectins in cardiac allograft rejection

The selectins expressed on activated endothelial cells (E- and P-selectin), leukocytes (L-selectin), and platelets (P-selectin) play crucial roles in the rolling and tethering of leukocytes. We explored the importance of donor and recipient selectins in acute and chronic cardiac allograft rejection using mice deficient in all three selectins (ELP-/-). In BALB/c recipients, survival of fully allomismatched hearts from ELP-/- C57BL/6 donors was almost double that of wild-type grafts. In ELP-/- cardiac allografts, mononuclear cell infiltration and vasculitis of intramyocardial coronary arteries were significantly reduced. Interestingly, ELP-/- grafts were rejected similarly in both the presence and the absence of recipient selectins, and both wild-type and ELP-/- recipients promptly rejected wild-type hearts. Alternative adhesive molecules such as alpha4beta7 integrin may compensate for the lack of selectins and may mediate rejection in ELP-/- recipients. Chronic rejection was evaluated in a major histocompatibility complex (MHC) class II mismatch model using C57BL/6.C-H2(bm12) mice. While lack of selectins in recipients did not offer protection against chronic rejection, luminal stenosis of coronary arteries in ELP-/- grafts was markedly diminished. In conclusion, donor-derived selectins contribute to the development of both acute and chronic cardiac allograft rejection, and targeting donor selectins may open novel therapeutic approaches in clinical transplantation.

Triiodothyronine modulates differential homing of recent thymic emigrants to peripheral lymphoid organs

The functioning of the immune system partially relies on T-cell exportation from the thymus, the major site of T-cell differentiation. Although the molecular mechanisms governing this process begin to be elucidated, it is not clear if thyroid hormones can alter the homing of recent thymic emigrants (RTE) to peripheral lymphoid organs. Herein, we investigated whether triiodothyronine (T(3)) could influence the homing of thymus-derived T cells. For that we used intrathymic injection of T(3) in combination with fluorescein isothiocyanate (FITC) to trace, 16 h later, FITC(+) cells, termed RTE, in peripheral lymphoid organs. We observed that T(3) stimulated thymocyte export, increasing the frequency of CD4(+) RTE and CD8(+) RTE in the subcutaneous and mesenteric lymph nodes. By contrast, the relative numbers of CD4(+) RTE in the spleen were decreased. T(3) also changed the differential distribution pattern of CD4(+) RTE, and to a lesser extent CD8(+) RTE in the peripheral lymphoid organs. Moreover, the expression of extracellular matrix (ECM) components, such as laminin and fibronectin, which are known to be involved in T-cell migration, increased in the lymph nodes but not in the spleen following intrathymic T(3) treatment. In conclusion, our data correspond to the first demonstration that in vivo treatment with thyroid hormone stimulates thymic T-cell homing and T-cell distribution in peripheral lymphoid organs.

Recirculating CD4 memory T cells mount rapid secondary responses without major contributions from follicular CD4 effectors and B cells

For weeks after primary immunization with thymus-dependent antigens the responding lymph nodes contain effector CD4 T cells in T zones and germinal centers as well as recirculating memory T cells. Conversely, remote nodes, not exposed to antigen, only receive recirculating memory cells. We assessed whether lymph nodes with follicular effector CD4 T cells in addition to recirculating memory CD4 T cells mount a more rapid secondary response than nodes that only contain recirculating memory cells. Also, the extent to which T cell frequency governs accelerated CD4 T cell recall responses was tested. For this, secondary antibody responses to a superantigen, where the frequency of responding T cells is not increased at the time of challenge, were compared with those to conventional protein antigens. With both types of antigens similar accelerated responses were elicited in the node draining the site of primary immunization and in the contralateral node, not previously exposed to antigen. Thus recirculating memory cells are fully capable of mounting accelerated secondary responses, without the assistance of CD4 effector T cells, and accelerated memory responses are not solely dependent on higher T cell frequencies. Accelerated memory CD4 T cell responses were also seen in B cell-deficient mice.

S1P1 receptor expression regulates emergence of NKT cells in peripheral tissues

The S1P1 receptor, on the surface of lymphocytes and endothelial cells, regulates the unique trafficking behavior of certain lymphocyte populations. We have examined whether the S1P1 receptor also dictates the distinctive tissue distribution of V alpha14-J alpha18 natural killer T (NKT) cells, whose trafficking pattern is not well understood. Mice (TCS1P1 KO) were established with a conditional deletion of the S1P1 receptor in thymocytes that included precursors of NKT cells. Within the thymus, NKT cells were found at normal or increased levels, indicating that S1P1 receptor expression was dispensable for NKT cell development. However, substantially reduced numbers of NKT cells were detected in the peripheral tissues of the TCS1P1 KO mice. Short-term S1P1 deletion after NKT cells had established residence in the periphery did not substantially alter their distribution in tissues, except for a partial decrease in the spleen. FTY720, a S1P1 receptor ligand that has potent effects on the trafficking of conventional T cells, did not alter the preexisting distribution of NKT cells within peripheral tissues of wild-type mice. Our results indicate that the S1P1 receptor expression on NKT cells is dispensable for development within thymus but is essential for the establishment of their tissue residency in the periphery.

Differential sensitivity of naïve and subsets of memory CD4+ and CD8+ T cells to hydrogen peroxide-induced apoptosis

CD4+ and CD8+ memory T cells are identified into central and effector memory subsets, which are characterized by distinct homing patterns and functions. In this investigation, we show that naïve and central memory CD4+ and CD8+ T cells are sensitive to hydrogen peroxide (H2O2)-induced apoptosis, whereas effector memory CD4+ and CD8+ T cells are relatively resistant to H2O2-induced apoptosis. Apoptosis in naïve and central memory CD4+ and CD8+ is associated with the release of cytochrome c and activation of caspase-9 and caspase-3, upregulation of Bax and voltage-dependent anion channel (VDAC) expression, and decreased intracellular glutathione (GSH). In vitro GSH and a superoxide dismutase mimetic Mn(III) tetrakis (1-methyl-4-pyridyl) porphyrin inhibited H2O2-induced apoptosis in both naïve and central memory CD4+ and CD8+ T cells. Furthermore, VDAC inhibitor 4,4'-diisothiocynostilbene-2,2'-disulfonic acid blocked H2O2-induced apoptosis. These data demonstrate that H2O2 induces apoptosis preferentially in human naïve and central memory CD4+ and CD8+ T cells via the mitochondrial pathway by regulating intracellular GSH and the expression of Bax and VDAC.