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

L-selectin controls trafficking of chronic lymphocytic leukemia cells in lymph node high endothelial venules in vivo

B-cell chronic lymphocytic leukemia (CLL) is the most common leukemia in adults. Lymph nodes (LNs) are sites of malignant proliferation and LN enlargement is associated with poor prognosis in the clinics. The LN microenvironment is believed to favor disease progression by promoting CLL cell growth and drug resistance. A better understanding of the mechanisms regulating trafficking of CLL cells to LNs is thus urgently needed. Here, we studied the first step of CLL cell migration to LNs, their interaction with high endothelial venules (HEVs), specialized blood vessels for lymphocyte extravasation in lymphoid organs. We observed that the density of HEV blood vessels was increased in CLL LNs and that CD20(+) CLL cells accumulated within HEV pockets, suggesting intense trafficking. We used intravital imaging to visualize the behavior of human CLL cells within the mouse LN microcirculation, and discovered that CLL cells bind to HEVs in vivo via a multistep adhesion cascade, which involves rolling, sticking, and crawling of the leukemic cells on the endothelium. Functional analyses revealed that the lymphocyte homing receptor L-selectin (CD62L) is the key factor controlling the binding of CLL cells to HEV walls in vivo. Interestingly, L-selectin expression was decreased on CLL cells from patients treated with idelalisib, a phosphoinositide-3-kinase δ inhibitor recently approved for CLL therapy. Interference with L-selectin-mediated trafficking in HEVs could represent a novel strategy to block dissemination of CLL cells to LNs and increase the efficacy of conventional therapy.

The role of novel and known extracellular matrix and adhesion molecules in the homeostatic and regenerative bone marrow microenvironment

Maintenance of haematopoietic stem cells and differentiation of committed progenitors occurs in highly specialized niches. The interactions of haematopoietic stem and progenitor cells (HSPCs) with cells, growth factors and extracellular matrix (ECM) components of the bone marrow (BM) microenvironment control homeostasis of HSPCs. We only start to understand the complexity of the haematopoietic niche(s) that comprises endosteal, arterial, sinusoidal, mesenchymal and neuronal components. These distinct niches produce a broad range of soluble factors and adhesion molecules that modulate HSPC fate during normal hematopoiesis and BM regeneration. Adhesive interactions between HSPCs and the microenvironment will influence their localization and differentiation potential. In this review we highlight the current understanding of the functional role of ECM- and adhesion (regulating) molecules in the haematopoietic niche during homeostatic and regenerative hematopoiesis. This knowledge may lead to the improvement of current cellular therapies and more efficient development of future cellular products.

Absence of both Sos-1 and Sos-2 in peripheral CD4(+) T cells leads to PI3K pathway activation and defects in migration

Sos-1 and Sos-2 are ubiquitously expressed Ras-guanine exchange factors involved in Erk-MAP kinase pathway activation. Using mice lacking genes encoding Sos-1 and Sos-2, we evaluated the role of these proteins in peripheral T-cell signaling and function. Our results confirmed that TCR-mediated Erk activation in peripheral CD4(+) T cells does not depend on Sos-1 and Sos-2, although IL-2-mediated Erk activation does. Unexpectedly, however, we show an increase in AKT phosphorylation in Sos-1/2dKO CD4(+) T cells upon TCR and IL-2 stimulation. Activation of AKT was likely a consequence of increased recruitment of PI3K to Grb2 upon TCR and/or IL-2 stimulation in Sos-1/2dKO CD4(+) T cells. The increased activity of the PI3K/AKT pathway led to downregulation of the surface receptor CD62L in Sos-1/2dKO T cells and a subsequent impairment in T-cell migration.

HIV-1 Nef and Vpu Interfere with L-Selectin (CD62L) Cell Surface Expression To Inhibit Adhesion and Signaling in Infected CD4+ T Lymphocytes

Leukocyte recirculation between blood and lymphoid tissues is required for the generation and maintenance of immune responses against pathogens and is crucially controlled by the L-selectin (CD62L) leukocyte homing receptor. CD62L has adhesion and signaling functions and initiates the capture and rolling on the vascular endothelium of cells entering peripheral lymph nodes. This study reveals that CD62L is strongly downregulated on primary CD4(+) T lymphocytes upon infection with human immunodeficiency virus type 1 (HIV-1). Reduced cell surface CD62L expression was attributable to the Nef and Vpu viral proteins and not due to increased shedding via matrix metalloproteases. Both Nef and Vpu associated with and sequestered CD62L in perinuclear compartments, thereby impeding CD62L transport to the plasma membrane. In addition, Nef decreased total CD62L protein levels. Importantly, infection with wild-type, but not Nef- and Vpu-deficient, HIV-1 inhibited the capacity of primary CD4(+) T lymphocytes to adhere to immobilized fibronectin in response to CD62L ligation. Moreover, HIV-1 infection impaired the signaling pathways and costimulatory signals triggered in primary CD4(+) T cells by CD62L ligation. We propose that HIV-1 dysregulates CD62L expression to interfere with the trafficking and activation of infected T cells. Altogether, this novel HIV-1 function could contribute to virus dissemination and evasion of host immune responses.

IMPORTANCE

L-selectin (CD62L) is an adhesion molecule that mediates the first steps of leukocyte homing to peripheral lymph nodes, thus crucially controlling the initiation and maintenance of immune responses to pathogens. Here, we report that CD62L is downmodulated on the surfaces of HIV-1-infected T cells through the activities of two viral proteins, Nef and Vpu, that prevent newly synthesized CD62L molecules from reaching the plasma membrane. We provide evidence that CD62L downregulation on HIV-1-infected primary T cells results in impaired adhesion and signaling functions upon CD62L triggering. Removal of cell surface CD62L may predictably keep HIV-1-infected cells away from lymph nodes, the privileged sites of both viral replication and immune response activation, with important consequences, such as systemic viral spread and evasion of host immune surveillance. Altogether, we propose that Nef- and Vpu-mediated subversion of CD62L function could represent a novel determinant of HIV-1 pathogenesis.

L-selectin shedding is activated specifically within transmigrating pseudopods of monocytes to regulate cell polarity in vitro

L-selectin is a cell adhesion molecule that tethers free-flowing leukocytes from the blood to luminal vessel walls, facilitating the initial stages of their emigration from the circulation toward an extravascular inflammatory insult. Following shear-resistant adhesion to the vessel wall, L-selectin has frequently been reported to be rapidly cleaved from the plasma membrane (known as ectodomain shedding), with little knowledge of the timing or functional consequence of this event. Using advanced imaging techniques, we observe L-selectin shedding occurring exclusively as primary human monocytes actively engage in transendothelial migration (TEM). Moreover, the shedding was localized to transmigrating pseudopods within the subendothelial space. By capturing monocytes in midtransmigration, we could monitor the subcellular distribution of L-selectin and better understand how ectodomain shedding might contribute to TEM. Mechanistically, L-selectin loses association with calmodulin (CaM; a negative regulator of shedding) specifically within transmigrating pseudopods. In contrast, L-selectin/CaM interaction remained intact in nontransmigrated regions of monocytes. We show phosphorylation of L-selectin at Ser 364 is critical for CaM dissociation, which is also restricted to the transmigrating pseudopod. Pharmacological or genetic inhibition of L-selectin shedding significantly increased pseudopodial extensions in transmigrating monocytes, which potentiated invasive behavior during TEM and prevented the establishment of front/back polarity for directional migration persistence once TEM was complete. We conclude that L-selectin shedding directly regulates polarity in transmigrated monocytes, which affirms an active role for this molecule in driving later stages of the multistep adhesion cascade.

Regulation of leucocyte homeostasis in the circulation

The functions of blood cells extend well beyond the immune functions of leucocytes or the respiratory and hemostatic functions of erythrocytes and platelets. Seen as a whole, the bloodstream is in charge of nurturing and protecting all organs by carrying a mixture of cell populations in transit from one organ to another. To optimize these functions, evolution has provided blood and the vascular system that carries it with various mechanisms that ensure the appropriate influx and egress of cells into and from the circulation where and when needed. How this homeostatic control of blood is achieved has been the object of study for over a century, and although the major mechanisms that govern it are now fairly well understood, several new concepts and mediators have recently emerged that emphasize the dynamism of this liquid tissue. Here we review old and new concepts that relate to the maintenance and regulation of leucocyte homeostasis in blood and briefly discuss the mechanisms for platelets and red blood cells.

Increased expression of L-selectin (CD62L) in high-grade urothelial carcinoma: A potential marker for metastatic disease

INTRODUCTION

L-Selectin (CD62L) is a vascular adhesion molecule constitutively expressed on leukocytes with a primary function of directing leukocyte migration and homing of lymphocytes to lymph nodes. In a gene expression microarray study comparing laser-captured microdissected high-grade muscle-invasive bladder cancer (MIBC) without prior treatment and low-grade bladder cancer (LGBC) human samples, we found CD62L to be the highest differentially expressed gene. We sought to examine the differential expression of CD62L in MIBCs and its clinical relevance.

METHODS

Unfixed fresh and formalin-fixed paraffin-embedded human bladder cancer specimens and serum samples were obtained from the University of Connecticut Health Center tumor bank. Tumor cells were isolated from frozen tumor tissue sections by laser-captured microdissected followed by RNA isolation. Quantitative polymerase chain reaction was used to validate the level of CD62L transcripts. Immunohistochemistry and enzyme-linked immunosorbent assay were performed to evaluate the CD62L protein localization and expression level. Flow cytometry was used to identify the relative number of cells expressing CD62L in fresh tumor tissue. In silico studies were performed using the Oncomine database.

RESULTS

Immunostaining showed a uniformly higher expression of CD62L in MIBC specimens vs. LGBCs specimens. Further, CD62L localization was seen in foci of metastatic tumor cells in lymph node specimens from patients with high-grade MIBC and known nodal involvement. Up-regulated expression of CD62L was also observed by flow cytometric analysis of freshly isolated tumor cells from biopsies of high-grade cancers vs. LGBC specimens. Circulating CD62L levels were also found to be higher in serum samples from patients with high-grade metastatic vs. high-grade nonmetastatic MIBC. In addition, in silico analysis of Oncomine Microarray Database showed a significant correlation between CD62L expression and tumor aggressiveness and clinical outcomes.

CONCLUSION

These data confirm the expression of CD62L on urothelial carcinoma cells and suggest that CD62L may serve as biomarker to predict the presence of or risk for developing metastatic disease in patients with bladder cancer.

Regulation of T-cell activation and migration by the kinase TBK1 during neuroinflammation

Development of an immune or autoimmune response involves T-cell activation in lymphoid organs and subsequent migration to peripheral tissues. Here we show that T-cell-specific ablation of the kinase TBK1 promotes T-cell activation but causes retention of effector T cells in the draining lymph node in a neuroinflammatory autoimmunity model, experimental autoimmune encephalomyelitis (EAE). At older ages, the T-cell-conditional TBK1-knockout mice also spontaneously accumulate T cells with activated phenotype. TBK1 controls the activation of AKT and its downstream kinase mTORC1 by a mechanism involving TBK1-stimulated AKT ubiquitination and degradation. The deregulated AKT-mTORC1 signalling in turn contributes to enhanced T-cell activation and impaired effector T-cell egress from draining lymph nodes. Treatment of mice with a small-molecule inhibitor of TBK1 inhibits EAE induction. These results suggest a role for TBK1 in regulating T-cell migration and establish TBK1 as a regulator of the AKT-mTORC1 signalling axis.

T cells that are activated by self-antigens in the periphery can migrate into the brain causing neuroinflammatory disease. Here the authors show that TBK1 is necessary for activated T-cell egress from the lymph node, and blocking TBK1 ameliorates autoimmunity in a mouse model of multiple sclerosis.

Revisiting the role of B cells in skin immune surveillance

Whereas our understanding of the skin immune system has increased exponentially in recent years, the role of B cells in cutaneous immunity remains poorly defined. Recent studies have revealed the presence of B cells within lymphocytic infiltrates in chronic inflammatory skin diseases and cutaneous malignancies including melanoma, and have examined their functional significance in these settings. We review these findings and discuss them in the context of the current understanding of the role of B cells in normal skin physiology, as well as in both animal and human models of skin pathology. We integrate these findings into a model of cutaneous immunity wherein crosstalk between B cells and other skin-resident immune cells plays a central role in skin immune homeostasis.

Deficiency of both L-selectin and ICAM-1 exacerbates imiquimod-induced psoriasis-like skin inflammation through increased infiltration of antigen presenting cells

To assess the role of inter-cellular adhesion molecule (ICAM)-1 and L-selectin in psoriasis pathogenic process, we examined the psoriasiform skin inflammation triggered by imiquimod, a toll-like receptor 7/8 agonist, in mice lacking ICAM-1 (ICAM-1(-/-)), L-selectin (L-selectin(-/-)), or both (L-selectin/ICAM-1(-/-)). Disease severity was significantly reduced in ICAM-1(-/-) and L-selectin(-/-) mice compared with wild type mice, while it was exacerbated in L-selectin/ICAM-1(-/-) mice. Cutaneous interleukin (IL)-17A, IL-23, and tumor necrosis factor (TNF)-α expression was increased in L-selectin/ICAM-1(-/-) mice compared with wild type mice. Furthermore, only L-selectin/ICAM-1(-/-) mice was refractory to anti-TNF-α antibody treatment. The skin lesion from L-selectin/ICAM-1(-/-) mice showed augmented E-selectin expression compared with ICAM-1(-/-) and L-selectin(-/-) mice, and augmented E-selectin ligand-1 expression compared with wild type mice. The current study demonstrates that although ICAM-1 and L-selectin regulate psoriasiform inflammation, deleting both L-selectin and ICAM-1 simultaneously would rather induce refractory skin inflammation, due to compensatory up-regulation of other adhesion molecules.

Time course of lewisite-induced skin lesions and inflammatory response in the SKH-1 hairless mouse model

Data on the toxicity of lewisite (L), a vesicant chemical warfare agent, are scarce and conflicting, and the use of the specific antidote is not without drawbacks. This study was designed to evaluate if the SKH-1 hairless mouse model was suitable to study the L-induced skin injuries. We studied the progression of lesions following exposure to L vapors for 21 days using paraclinical parameters (color, transepidermal water loss (TEWL), and biomechanical measurements), histological assessments, and biochemical indexes of inflammation. Some data were also obtained over 27 weeks. The development of lesions was similar to that reported in other models. The TEWL parameter appeared to be the most appropriate index to follow their progression. Histological analysis showed inflammatory cell infiltration and microvesications at day 1 and a complete wound closure by day 21. Biochemical studies indicated a deregulation of the levels of several cytokines and receptors involved in inflammation. An increase in the quantity of pro-matrix metalloproteinases 2 and 9 was shown as observed in other models. This suggests that the SKH-1 mouse model is relevant for the investigation of the physiopathological process of skin lesions induced by L and to screen new treatment candidates.

Saikosaponin D isolated from Bupleurum falcatum inhibits selectin-mediated cell adhesion

Three saikosaponins were isolated from the MeOH extract of the roots of Bupleurum falcatum L.: saikosaponins B3 (1); B4 (2); and D (3). Of the three, compound 3 inhibited the interaction of selectins (E, L, and P) and THP-1 cells with IC₅₀ values of 1.8, 3.0 and 4.3 µM, respectively. Also, the aglycone structure 4 of compound 3 showed moderate inhibitory activity on L-selectin-mediated cell adhesion. From these results, we suspect that compound 3 isolated from Bupleurum falcatum roots would be a good candidate for therapeutic strategies to treat inflammation.

Time course of skin features and inflammatory biomarkers after liquid sulfur mustard exposure in SKH-1 hairless mice

Sulfur mustard (SM) is a strong bifunctional alkylating agent that produces severe tissue injuries characterized by erythema, edema, subepidermal blisters and a delayed inflammatory response after cutaneous exposure. However, despite its long history, SM remains a threat because of the lack of effective medical countermeasures as the molecular mechanisms of these events remain unclear. This limited number of therapeutic options results in part of an absence of appropriate animal models. We propose here to use SKH-1 hairless mouse as the appropriate model for the design of therapeutic strategies against SM-induced skin toxicity. In the present study particular emphasis was placed on histopathological changes associated with inflammatory responses after topical exposure of dorsal skin to three different doses of SM (0.6, 6 and 60mg/kg) corresponding to a superficial, a second-degree and a third-degree burn. Firstly, clinical evaluation of SM-induced skin lesions using non invasive bioengineering methods showed that erythema and impairment of skin barrier increased in a dose-dependent manner. Histological evaluation of skin sections exposed to SM revealed that the time to onset and the severity of symptoms including disorganization of epidermal basal cells, number of pyknotic nuclei, activation of mast cells and neutrophils dermal invasion were dose-dependent. These histopathological changes were associated with a dose- and time-dependent increase in expression of specific mRNA for inflammatory mediators such as interleukins (IL1β and IL6), tumor necrosis factor (TNF)-α, cycloxygenase-2 (COX-2), macrophage inflammatory proteins (MIP-1α, MIP-2 and MIP-1αR) and keratinocyte chemoattractant (KC also called CXCL1) as well as adhesion molecules (L-selectin and vascular cell adhesion molecule (VCAM)) and growth factor (granulocyte colony-stimulating factor (Csf3)). A dose-dependent increase was also noted after SM exposure for mRNA of matrix metalloproteinases (MMP9) and laminin-γ2 which are associated with SM-induced blisters formation. Taken together, our results show that SM-induced skin histopathological changes related to inflammation is similar in SKH-1 hairless mice and humans. SKH-1 mouse is thus a reliable animal model for investigating the SM-induced skin toxicity and to develop efficient treatment against SM-induced inflammatory skin lesions.

A crucial role of L-selectin in C protein-induced experimental polymyositis in mice

OBJECTIVE

To investigate the role of adhesion molecules in C protein-induced myositis (CIM), a murine model of polymyositis (PM).

METHODS

CIM was induced in wild-type mice, L-selectin-deficient (L-selectin(-/-) ) mice, intercellular adhesion molecule 1 (ICAM-1)-deficient (ICAM-1(-/-) ) mice, and mice deficient in both L-selectin and ICAM-1 (L-selectin(-/-) ICAM-1(-/-) mice). Myositis severity, inflammatory cell infiltration, and messenger RNA expression in the inflamed muscles were analyzed. The effect of dendritic polyglycerol sulfate, a synthetic inhibitor that suppresses the function of L-selectin and endothelial P-selectin, was also examined.

RESULTS

L-selectin(-/-) mice and L-selectin(-/-) ICAM-1(-/-) mice developed significantly less severe myositis compared to wild-type mice, while ICAM-1 deficiency did not inhibit the development of myositis. L-selectin(-/-) mice that received wild-type T cells developed myositis. Treatment with dendritic polyglycerol sulfate significantly diminished the severity of myositis in wild-type mice compared to treatment with control.

CONCLUSION

These data indicate that L-selectin plays a major role in the development of CIM, whereas ICAM-1 plays a lesser role, if any, in the development of CIM. L-selectin-targeted therapy may be a candidate for the treatment of PM.

L-selectin deficiency decreases aortic B1a and Breg subsets and promotes atherosclerosis

There is a significant recruitment of leucocytes into aortas during atherogenesis. L-selectin regulates leucocyte migration into secondary lymphoid and peripheral tissues and was proposed to play a role in leucocyte homing into aortas. Here, we determine the role of L-selectin in atherosclerosis. L-selectin-deficient Apoe-/- (Sell-/-Apoe-/-) mice had a 74% increase in plaque burden compared to Apoe-/- mice fed a chow diet for 50 weeks. Elevated atherosclerosis was accompanied by increased aortic leucocyte content, but a 50% reduction in aortic B cells despite elevated B cell counts in the blood. Follicular B cells represented 65%, whereas B1a and regulatory B cells (Breg) comprised 5% of aortic B cells. B1a and Breg cell subsets were reduced in Sell-/-Apoe-/- aortas with accompanied two-fold decrease in aortic T15 antibody and 1.2-fold decrease of interleukin-10 (IL-10) levels. L-selectin was required for B1 cell homing to the atherosclerotic aorta, as demonstrated by a 1.5-fold decrease in the migration of Sell-/-Apoe-/- vs Apoe-/- cells. Notably, we found a 1.6-fold increase in CD68hi macrophages in Sell-/-Apoe-/- compared to Apoe-/- aortas, despite comparable blood monocyte numbers and L-selectin-dependent aortic homing. L-selectin had no effect on neutrophil migration into aorta, but led to elevated blood neutrophil numbers, suggesting a potential involvement of neutrophils in atherogenesis of Sell-/-Apoe-/- mice. Thus, L-selectin deficiency increases peripheral blood neutrophil and lymphocyte numbers, decreases aortic B1a and Breg populations, T15 antibody and IL-10 levels, and increases aortic macrophage content of Sell-/-Apoe-/- mice. Altogether, these data provide evidence for an overall atheroprotective role of L-selectin.

Defining the functional boundaries of the murine α1,3-fucosyltransferase Fut7 reveals a remarkably compact locus

Fut7 encodes an α1,3-fucosyltransferase critical for biosynthesis of glycan ligands for all three selectins. Consistent with this function, Fut7 expression is limited to hematopoietic cells and high endothelial cells which express selectin ligands. Mechanisms that govern Fut7 expression are poorly defined. To begin to understand the molecular genetic basis for transcriptional regulation of Fut7, a transgenic, gain-of-function, genetic complementation approach in mice was used to define the "functional boundaries" of the murine Fut7 locus, defined here as any uninterupted stretch of genomic DNA that contains all cis-acting genetic elements essential for accurate physiologic expression. A 12.7-kb contiguous genomic interval, which lies completely between the highly conserved flanking Npdc1 and Abca2 loci on chromosome 2 and which contains the complete transcriptional unit plus ∼7.4 kb upstream of the transcriptional start site and ∼2 kb downstream of the transcriptional termination and polyadenylation sites, was used as a transgene (Tg) on a Fut7 null background. Tg+ mice exhibited restoration of Fut7 gene expression and physiologic levels of selectin ligand expression and function on neutrophils, activated T cells, and high endothelial cells and corrected the functional defects in these cells found in Fut7 null mice without leading to detectable expression of Fut7 in normally non-expressing tissues. These results demonstrate that all genetic information essential for appropriate and selective expression of Fut7 in diverse cell types and in response to distinct developmental signals is contained within this comparatively small genetic region.

T-bet and Eomes instruct the development of two distinct natural killer cell lineages in the liver and in the bone marrow

Trail(+)DX5(-)Eomes(-) natural killer (NK) cells arise in the mouse fetal liver and persist in the adult liver. Their relationships with Trail(-)DX5(+) NK cells remain controversial. We generated a novel Eomes-GFP reporter murine model to address this question. We found that Eomes(-) NK cells are not precursors of classical Eomes(+) NK cells but rather constitute a distinct lineage of innate lymphoid cells. Eomes(-) NK cells are strictly dependent on both T-bet and IL-15, similarly to NKT cells. We observed that, in the liver, expression of T-bet in progenitors represses Eomes expression and the development of Eomes(+) NK cells. Reciprocally, the bone marrow (BM) microenvironment restricts T-bet expression in developing NK cells. Ectopic expression of T-bet forces the development of Eomes(-) NK cells, demonstrating that repression of T-bet is essential for the development of Eomes(+) NK cells. Gene profile analyses show that Eomes(-) NK cells share part of their transcriptional program with NKT cells, including genes involved in liver homing and NK cell receptors. Moreover, Eomes(-) NK cells produce a broad range of cytokines, including IL-2 and TNF in vitro and in vivo, during immune responses against vaccinia virus. Thus, mutually exclusive expression of T-bet and Eomes drives the development of different NK cell lineages with complementary functions.

Analysis of L-selectin-mediated cellular interactions under flow conditions

Lymphocyte homing is mediated by a specific interaction between L-selectin expressed on lymphocytes and its ligands expressed on high endothelial venules (HEVs) in lymph nodes under physiological flow conditions. In this chapter, two methods for detecting L-selectin-mediated cellular interactions under shear stress mimicking physiological flow conditions are described. First, a modified Stamper-Woodruff cell-binding assay using leukocytes labeled with a fluorescent orange dye, CMTMR, is introduced. In this method, leukocytes are allowed to bind to frozen lymph node sections under shear stress and their binding to HEVs can be clearly visualized by fluorescence microscopy. Second, a parallel flow chamber assay is described. In this assay, leukocytes are allowed to roll on L-selectin ligand-expressing cells under various levels of shear stress and their adhesive interactions are recorded by a video camera equipped with an inverted microscope. These methods can be applied to determine the effects of various agents that might affect L-selectin-mediated lymphocyte homing and recruitment.

Understanding the biology of ex vivo-expanded CD8 T cells for adoptive cell therapy: role of CD62L

CD62L governs the circulation of CD8(+) T cells between lymph nodes and peripheral tissues, whereby the expression of CD62L by CD8(+) T cells promotes their recirculation through lymph nodes. As such, CD62L participates in the fate of adoptively transferred CD8(+) T cells and may control their effectiveness for cancer immunotherapy, including settings in which host preconditioning results in the acute lymphopenia-induced proliferation of the transferred cells. Indeed, previous studies correlated CD62L expression by donor CD8(+) cells with the success rate of adoptive cell therapy (ACT). Here, we analyzed the functions and fate of ex vivo-activated, tumor-specific CD62L(-/-) CD8(+) T cells in a mouse melanoma model for ACT. Unexpectedly, we observed that CD62L(-/-) CD8(+) T cells were functionally indistinguishable from CD62L(+/+) CD8(+) T cells, i.e., both greatly expanded in cyclophosphamide preconditioned animals, controlled subcutaneously and hematogenously spreading tumors, and generated anti-tumor-specific CD8(+) T cell memory. Moreover, even in hosts with rudimentary secondary lymphoid organs (LT(-/-) animals), CD8(+) T cells with and without CD62L expanded equivalently to those adoptively transferred into wild-type animals. These results put into question the utility of CD62L as a predictive biomarker for the efficacy of ex vivo-expanded T cells after ACT in lymphopenic conditions and also offer new insights into the homing, engraftment, and memory generation of adoptively transferred ex vivo-activated CD8(+) T cells.

Roles of T cell-associated L-selectin and β7 integrins during induction and regulation of chronic colitis

BACKGROUND

L-selectin (CD62L) and β(7) integrins are important for trafficking of naive T cells under steady-state conditions. The objectives of this study were to dissect the requirements for T cell-associated CD62L and β(7) integrins during initiation, progression, and regulation of chronic colitis.

METHODS

Using the T-cell transfer model, we compared colitogenic potential between T cells lacking one or both of these molecules with wild-type T cells. To assess trafficking of cells to the secondary lymphoid tissue and the gut, we performed co-homing experiments.

RESULTS

Adoptive transfer of wild-type, CD62L(-/-) or β(7)(-/-) single-deficient T cells induced moderate to severe disease with slightly different kinetics. However, transfer of CD62L(-/-) β(7)(-/-) double-deficient (DKO) T cells produced significantly attenuated gut inflammation, which correlated with fewer T cells and reduced levels of proinflammatory cytokines in the colon lamina propria. Our subsequent experiments established that lack of colitogenic potential of these cells was due to inability of DKO T cells to home to the secondary lymphoid tissue. Furthermore, homing of in vitro-generated effector DKO T cells to the inflamed intestine was significantly impaired. Lastly, DKO regulatory T cells were ineffective at suppressing colitis induced by wild-type T cells.

CONCLUSIONS

We established that T cells can use either CD62L(-/-) or β(7)(-/-) integrins to induce chronic colitis, but lack of both abrogates their colitogenic potential. Effector T cells critically rely on β(7) integrin during their recruitment to the inflamed intestinal mucosa. Finally, regulation of intestinal inflammation by regulatory T cells requires one or both of these adhesion molecules.

Enhanced expression of the soluble form of E-selectin attenuates progression of lupus nephritis and vasculitis in MRL/lpr mice

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that causes inflammatory tissue damage, including lupus nephritis and vasculitis. Local generation of adhesion molecules and expression of their ligands on inflammatory cells appears to contribute to the progression of SLE. We found significantly increased E-selectin expression in the glomeruli and renal interstitial microvasculature of MRL/MpJ-lpr/lpr (MRL/lpr) lupus model mice. This was accompanied with infiltration of inflammatory cells, especially macrophages and CD8(+) T cells. Similarly, in 21 patients with proliferative lupus nephritis, there was a significant correlation between renal E-selectin levels and macrophage and CD8(+) T cell infiltration in the affected kidneys. By contrast, in transgenic MRL/lpr mice exhibiting elevated levels of circulating soluble E-selectin (sE-selectin) protein, which competitively inhibits E- and P-selectin-mediated extravasation of inflammatory cells, the progression of lupus nephritis and vasculitis was significantly suppressed and survival was significantly prolonged. This improvement was accompanied by significant reductions in renal infiltration by macrophages and CD8(+) T cells. These results suggest that E-selectin plays a crucial role in lupus nephritis and vasculitis by mediating renal infiltration of inflammatory cells, and that because it inhibits this process, sE-selectin could potentially serve as an effective treatment for lupus nephritis and vasculitis.

The impact of KLF2 modulation on the transcriptional program and function of CD8 T cells

Krüppel-like factor 2 (KLF2) is a transcription factor that is highly expressed in quiescent T lymphocytes and downregulated in effector T cells. We now show that antigen receptor engagement downregulates KLF2 expression in a graded response determined by the affinity of T cell antigen receptor (TCR) ligand and the integrated activation of protein kinase B and the MAP kinases ERK1/2. The present study explores the importance of KLF2 downregulation and reveals that the loss of KLF2 controls a select portion of the CD8 effector T cell transcriptional program. In particular, KLF2 loss is required for CD8 T cells to express the inflammatory chemokine receptor CXCR3 and for maximum clonal expansion of T cells. KLF2 thus negatively controls the ability of CD8 T cells to respond to the CXCR3 ligand CXCL10. Strikingly, the KLF2 threshold for restraining expression of CXCR3 is very low and quite distinct to the KLF2 threshold for restraining T cell proliferation. KLF2 is thus an analogue (tunable) not a digital (on/off) cellular switch where the magnitude of KLF2 expression differentially modifies the T cell responses.

The PSGL-1-L-selectin signaling complex regulates neutrophil adhesion under flow

Neutrophils are recruited from the blood to sites of inflammation, where they contribute to immune defense but may also cause tissue damage. During inflammation, neutrophils roll along the microvascular endothelium before arresting and transmigrating. Arrest requires conformational activation of the integrin lymphocyte function-associated antigen 1 (LFA-1), which can be induced by selectin engagement. Here, we demonstrate that a subset of P-selectin glycoprotein ligand-1 (PSGL-1) molecules is constitutively associated with L-selectin. Although this association does not require the known lectin-like interaction between L-selectin and PSGL-1, the signaling output is dependent on this interaction and the cytoplasmic tail of L-selectin. The PSGL-1-L-selectin complex signals through Src family kinases, ITAM domain-containing adaptor proteins, and other kinases to ultimately result in LFA-1 activation. The PSGL-1-L-selectin complex-induced signaling effects on neutrophil slow rolling and recruitment in vivo demonstrate the functional importance of this pathway. We conclude that this is a signaling complex specialized for sensing adhesion under flow.

ICAM-1 deficiency exacerbates sarcoid-like granulomatosis induced by Propionibacterium acnes through impaired IL-10 production by regulatory T cells

Propionibacterium acnes has been implicated as one of the suggested causative antigens for sarcoidosis, a systemic granulomatous disease. By injecting heat-killed P. acnes into the dorsal skin of C57BL/6J mice on days 1, 3, 5, and 14, sarcoid-like granulomatosis was induced in skin and lungs of these mice on day 28. To clarify the role of cell adhesion molecules in cutaneous sarcoidosis, we induced sarcoid-like granulomatosis in mice deficient of intercellular adhesion molecule (ICAM)-1, L-selectin, P-selectin, or E-selectin via repeated P. acnes injection. Histopathologic analysis revealed that granuloma formation was aggravated in the skin and lungs of ICAM-1-deficient mice compared with wild-type mice. Within skin granulomas of ICAM-1-deficient mice, P. acnes immunization up-regulated mRNA expression of tumor necrosis factor-α, although it failed to induce IL-10 mRNA expression in contrast to wild-type mice. Infiltration of regulatory T cells into skin granuloma was similar between wild-type mice and ICAM-1-deficient mice. P. acnes immunization induced IL-10 production by CD4(+)CD25(+)Foxp3(+) regulatory T cells in lymph nodes of wild-type mice in vivo, which was absent in regulatory T cells of ICAM-1-deficient mice. Our results indicate that ICAM-1 is imperative for inducing regulatory T cells to produce IL-10 in vivo, which would prevent granuloma formation.

Activated T cell trans-endothelial migration relies on myosin-IIA contractility for squeezing the cell nucleus through endothelial cell barriers

Following activation, T cells are released from lymph nodes to traffic via the blood to effector sites. The re-entry of these activated T cells into tissues represents a critical step for them to carry out local effector functions. Here we have assessed defects in effector T cells that are acutely depleted in Myosin-IIA (MyoIIA) and show a T cell intrinsic requirement for this motor to facilitate the diapedesis step of extravasation. We show that MyoIIA accumulates at the rear of T cells undergoing trans-endothelial migration. T cells can extend protrusions and project a substantial portion of their cytoplasm through the endothelial wall in the absence of MyoIIA. However, this motor protein plays a crucial role in allowing T cells to complete the movement of their relatively rigid nucleus through the endothelial junctions. In vivo, this defect manifests as poor entry into lymph nodes, tumors and into the spinal cord, during tissue-specific autoimmunity, but not the spleen. This suggests that therapeutic targeting of this molecule may allow for differential attenuation of tissue-specific inflammatory responses.

Vascular endothelial growth factor receptor inhibitor SU5416 suppresses lymphocyte generation and immune responses in mice by increasing plasma corticosterone

Inhibitors of vascular endothelial growth factor and its receptors (VEGFRs) are attractive therapeutic candidates for cancer treatment. One such small molecule VEGFR inhibitor, SU5416, limits angiogenesis in vivo and is widely used for investigating VEGFR signaling in tumor pathophysiology. Herein, we describe novel actions of SU5416 on the immune system. Treatment of mice with SU5416 for 3 days induced significant reductions in size and cellularity of peripheral lymph nodes. Interestingly, SU5416 did not affect initial lymphocyte localization to peripheral lymph nodes but did reduce lymphocyte accumulation during long-term migration assays. Treatment with SU5416 also induced severe loss of double-positive thymocytes resulting in thymic atrophy and a reduction in peripheral B cells. Furthermore, immune responses following immunization were reduced in mice treated with SU5416. Findings of thymic atrophy and reduced weight gain during SU5416 treatment suggested elevated corticosterone levels. Indeed, a significant 5-fold increase in serum corticosterone was found 4 hours after treatment with SU5416. Importantly, adrenalectomy negated the effects of SU5416 treatment on primary immune tissues, and partial reversal of SU5416-induced changes was observed following blockade of glucocorticoid receptors. SU5416 has been reported to inhibit the activation of latent transforming growth factor (TGF)-β, a cytokine involved in the regulation of glucocorticoid release by the adrenal glands. Interestingly, treatment with a TGF-β receptor inhibitor, showed a similar phenotype as SU5416 treatment, including elevated serum corticosterone levels and thymic atrophy. Therefore, these results suggest that SU5416 induces glucocorticoid release directly from the adrenal glands, possibly by inhibition of TGF-β activation.

Sindbis viral vectors transiently deliver tumor-associated antigens to lymph nodes and elicit diversified antitumor CD8+ T-cell immunity

Tumors are theoretically capable of eliciting an antitumor immune response, but are often poorly immunogenic. Oncolytic viruses (OVs) have recently emerged as a promising strategy for the immunogenic delivery of tumor-associated antigens (TAAs) to cancer patients. However, safe and effective OV/TAA therapies have not yet been established. We have previously demonstrated that vectors based on Sindbis virus (SV) can inhibit tumor growth and activate the innate immune system in mice. Here, we demonstrate that SV vectors carrying a TAA generate a dramatically enhanced therapeutic effect in mice bearing subcutaneous, intraperitoneal, and lung cancers. Notably, SV/TAA efficacy was not dependent on tumor cell targeting, but was characterized by the transient expression of TAAs in lymph nodes draining the injection site. Early T-cell activation at this site was followed by a robust influx of NKG2D expressing antigen-specific cytotoxic CD8+ T cells into the tumor site, subsequently leading to the generation of long-lasting memory T cells which conferred protection against rechallenge with TAA-positive as well as TAA-negative tumor cells. By combining in vivo imaging, flow cytometry, cytotoxicity/cytokine assays, and tetramer analysis, we investigated the relationship between these events and propose a model for CD8+ T-cell activation during SV/TAA therapy.

Reshaping of T-lymphocyte compartment in adult prepubertaly ovariectomised rats: a putative role for progesterone deficiency

This study explores the role of ovarian hormones in the phenotypic shaping of peripheral T-cell pool over the reproductive lifespan of rats. For this purpose, 2-month-old prepubertally ovariectomised (Ox) rats, showing oestrogen and progesterone deficiency, and 11-month-old Ox rats, exhibiting only progesterone deficiency, were examined for thymus output, and cellularity and composition of major TCRαβ+ peripheral blood lymphocyte (PBL) and splenocyte subsets. Although ovariectomy increased thymic output in both 2- and 11-month-old rats, the count of both CD4+ and CD8+ PBLs and splenocytes increased only in the former. In the blood and spleen of 11-month-old Ox rats only the count of CD8+ cells increased. Although ovariectomy affected the total CD4+ count in none of the examined compartments from the 11-month-old rats, it increased CD4+FoxP3+ PBL and splenocyte relative proportions over those in the age-matched controls. The age-related differences in the cellularity and the major subset composition in Ox rats were linked to the differences in the ovarian steroid hormone levels registered in 2- and 11-month-old rats. The administration of progesterone to Ox rats during the seven days before the sacrificing confirmed contribution of this hormone deficiency to the ovariectomy-induced changes in the TCRαβ+ PBL and splenocyte pool from 11-month-old rats. The expansion of the CD8+ splenocyte subset in the 11-month-old Ox rats reflected increases in cellularity of memory and, particularly, naïve cells. This was due to greater thymic output of CD8+ cells and homeostatic proliferation than apoptosis in 11-month-old Ox rats when compared with age-matched sham-Ox control rats. The homeostatic changes within CD8+ splenocyte pool from 11-month-old Ox rats, most likely, reflected the enhanced splenic IL-7 and TGF-β mRNA expression. Overall, in adult female rats, circulating oestrogen and progesterone provide maintenance of T-cell counts, a diversity of T-cell repertoire, and the main T-cell subset composition in the periphery. Progesterone deficiency affects mainly the CD8+ lymphocyte compartment through increasing thymic CD8+ cell export and upsetting homeostatic regulation within the CD8+ splenocyte pool. These alterations were reversible through progesterone supplementation.

CD62L as a therapeutic target in chronic lymphocytic leukemia

PURPOSE

Despite advances in the treatment of chronic lymphocytic leukemia (CLL), the disease remains incurable with standard therapies and relapse is inevitable. A growing body of evidence indicates that alterations in the adhesion properties of neoplastic cells play a pivotal role in the development and progression of CLL.

EXPERIMENTAL DESIGN

The expression of 71 cell surface molecules was examined on CLL peripheral blood mononuclear cells (PBMCs) over 3 weeks in culture. The most highly upregulated marker, CD62L, was examined further for expression on CD5(+)/CD19(+) CLL cells in vitro and in lymph node and bone marrow biopsies. The prosurvival role of CD62L was examined using a functional blocking antibody and therapeutic potential evaluated by comparison with current chemotherapy agents.

RESULTS

Blocking CD62L resulted in apoptosis of CLL cells but not PBMCs from healthy donors suggesting a novel role for CD62L in CLL cell survival. The beneficial effect of coculturing CLL cells with bone marrow stromal cells or endothelial cells does not protect CLL cells from anti-CD62L-related toxicity. Moreover, combining fludarabine or mafosfamide with the anti-CD62L in vitro produced an additive effect both with and without stromal cells.

CONCLUSION

This is the first reported data showing that blocking the activation and homing marker, CD62L, regulates CLL cell survival in vitro. These data also suggest that therapeutic antibodies against CD62L may provide additional clinical benefit to patients with CLL receiving current standard chemotherapy protocols.

Virus-associated activation of innate immunity induces rapid disruption of Peyer's patches in mice

Early in the course of infection, detection of pathogen-associated molecular patterns by innate immune receptors can shape the subsequent adaptive immune response. Here we investigate the influence of virus-associated innate immune activation on lymphocyte distribution in secondary lymphoid organs. We show for the first time that virus infection of mice induces rapid disruption of the Peyer's patches but not of other secondary lymphoid organs. The observed effect was not dependent on an active infectious process, but due to innate immune activation and could be mimicked by virus-associated molecular patterns such as the synthetic double-stranded RNA poly(I:C). Profound histomorphologic changes in Peyer's patches were associated with depletion of organ cellularity, most prominent among the B-cell subset. We demonstrate that the disruption is entirely dependent on type I interferon (IFN). At the cellular level, we show that virus-associated immune activation by IFN-α blocks B-cell trafficking to the Peyer's patches by downregulating expression of the homing molecule α4β7-integrin. In summary, our data identify a mechanism that results in type I IFN-dependent rapid but reversible disruption of intestinal lymphoid organs during systemic viral immune activation. We propose that such rerouted lymphocyte trafficking may impact the development of B-cell immunity to systemic viral pathogens.

Overlapping roles for endothelial selectins in murine hematopoietic stem/progenitor cell homing to bone marrow

Selectins are carbohydrate-binding adhesion molecules that are critically involved in leukocyte recognition of endothelium. The endothelial selectins have been implicated in homing of hematopoietic stem and progenitor cells (HSPCs) to the bone marrow (BM) during bone marrow transplant (BMT), but the precise roles of individual selectins in this process have never been defined. BMT of lethally irradiated mice lacking both endothelial selectins (E/P KO) with limiting numbers of wild type BM cells rescued significantly fewer E/P KO than WT recipients, but higher numbers of transplanted WT cells rescued E/P KOs in a dose-dependent fashion. Short-term homing assays confirmed a substantial defect in HSPC homing to BM in E/P KO mice. In contrast, BMT of E-selectin null or P-selectin null mice at limiting cell number uniformly rescued greater than 95% of the transplanted animals. Consistent with these functional results, flow cytometric analysis revealed both E-selectin ligands and P-selectin ligands on distinct subsets of HSPC. These results demonstrate overlapping functions for the endothelial selectins in HSPC homing to BM in the setting of BMT, and define a novel aspect of HSPC heterogeneity linked to selectin ligand expression.

Calmodulin adopts an extended conformation when interacting with L-selectin in membranes

Calmodulin, an intracellular calcium-binding protein, is thought to regulate ectodomain shedding of many membrane proteins, but the underlying molecular mechanism has remained unclear. Basing on a solution structure of calcium-loaded calmodulin in complex with a L-selectin fragment that contains a portion of its transmembrane domain, Gifford et al. (University of Calgary) recently suggested that calmodulin regulates L-selectin shedding by binding directly to a portion of the L-selectin transmembrane domain in a compact conformation. Using fluorescently labeled calmodulin, we show however that calmodulin adopts a distinctly different and much more extended conformation when it binds to the CLS peptide (i.e. the entire transmembrane and cytoplasmic domains of L-selectin) reconstituted in the phosphatidylcholine liposome with micromolar dissociation constant and in a calcium-independent manner. Calmodulin adopts a similarly extended conformation in a ternary complex with the N-terminal FERM domain of moesin and CLS reconstituted in the phospholipid liposome that mimics the native membrane environment. These results indicate that calmodulin does not bind directly to the transmembrane domain of L-selectin. Understanding the association of calmodulin with L-selectin helps to shed light on the mechanisms underlying regulation of ectodomain shedding.

Neutrophil recruitment and function in health and inflammation

Neutrophils have traditionally been thought of as simple foot soldiers of the innate immune system with a restricted set of pro-inflammatory functions. More recently, it has become apparent that neutrophils are, in fact, complex cells capable of a vast array of specialized functions. Although neutrophils are undoubtedly major effectors of acute inflammation, several lines of evidence indicate that they also contribute to chronic inflammatory conditions and adaptive immune responses. Here, we discuss the key features of the life of a neutrophil, from its release from bone marrow to its death. We discuss the possible existence of different neutrophil subsets and their putative anti-inflammatory roles. We focus on how neutrophils are recruited to infected or injured tissues and describe differences in neutrophil recruitment between different tissues. Finally, we explain the mechanisms that are used by neutrophils to promote protective or pathological immune responses at different sites.

L-selectin shedding by NSAIDs: old friends in new dresses

The recruitment of leukocytes to sites of inflammation requires the highly organized interplay of cell adhesion molecules on both leukocytes and inflamed endothelial cells, and disrupting the interaction of these molecules may compromise efficient recruitment of immune cells. Non-steroidal anti-inflammatory drugs inhibit inflammatory responses by several mechanisms including inhibition of prostaglandin synthesis and decreasing the expression of cell surface adhesion molecules. A report by Herrera-Garcia et al. [Eur. J. Immunol. 2013. 43: 55-64] in this issue of the European Journal of Immunology shows that the non-steroidal anti-inflammatory drug N-phenylanthranilic acid (N-Ph) causes L-selectin to be shed from the leukocyte plasma membrane and that this process in turn causes a decrease in leukocyte recruitment during inflammation in vivo. This finding may lead to novel approaches using N-Ph in the control of inflammatory processes as discussed in this Commentary.

CD62L is critical for maturation and accumulation of murine hepatic NK cells in response to viral infection

NK cells play critical roles in the first line of defense against viruses and other pathogens. However, the factors that control NK cell recruitment into local sites to exert effector functions during viral infection remain poorly understood. In this study, we found that murine NK cells in various organs could be divided into CD62L(-) and CD62L(+) subsets, the latter of which were less abundant in the liver and exhibited a relatively mature NK cell phenotype and a stronger cytotoxic function. Moreover, NK cells acquired CD62L expression after birth, and the frequency of CD62L(+) NK cells gradually increased during postnatal development. In models of polyinosinic-polycytidylic acid administration and adenovirus infection in vivo, CD62L(+) NK cell frequency and absolute numbers in the liver rapidly and markedly increased as a result of the augmented differentiation of CD62L(-) to CD62L(+) NK cells and recruitment of peripheral mature NK cells to the liver. However, blocking CD62L prior to administering viral stimuli in vivo abolished viral stimulation-induced NK cell accumulation and maturation in the liver. Collectively, these data suggest that CD62L marks a mature NK cell subset, as well as affects the magnitude of the local NK cell response to viral infection.

KSGal6ST generates galactose-6-O-sulfate in high endothelial venules but does not contribute to L-selectin-dependent lymphocyte homing

The addition of sulfate to glycan structures can regulate their ability to serve as ligands for glycan-binding proteins. Although sulfate groups present on the monosaccharides glucosamine, uronate, N-acetylglucosamine and N-acetylgalactosamine are recognized by defined receptors that mediate important functions, the functional significance of galactose-6-O-sulfate (Gal6S) is not known. However, in vitro studies using synthetic glycans and sulfotransferase overexpression implicate Gal6S as a binding determinant for the lymphocyte homing receptor, L-selectin. Only two sulfotransferases have been shown to generate Gal6S, namely keratan sulfate galactose 6-O-sulfotransferase (KSGal6ST) and chondroitin 6-O-sulfotransferase-1 (C6ST-1). In the present study, we use mice deficient in KSGal6ST and C6ST-1 to test whether Gal6S contributes to ligand recognition by L-selectin in vivo. First, we establish that KSGal6ST is selectively expressed in high endothelial venules (HEVs) in lymph nodes and Peyer's patches. We also determine by mass spectrometry that KSGal6ST generates Gal6S on several classes of O-glycans in peripheral lymph nodes. Furthermore, KSGal6ST, but not C6ST-1, is required for the generation of the Gal6S-containing glycan, 6,6'-disulfo-3'sLN (Siaα2→3[6S]Galβ1→4[6S]GlcNAc) or a closely related structure in lymph node HEVs. Nevertheless, L-selectin-dependent short-term homing of lymphocytes is normal in KSGal6ST-deficient mice, indicating that the Gal6S-containing structures we detected do not contribute to L-selectin ligand recognition in this setting. These results refine our understanding of the biological ligands for L-selectin and introduce a mouse model for investigating the functions of Gal6S in other contexts.

Exogenous application of hydrogen sulfide donor attenuates inflammatory reactions through the L-selectin-involved pathway in the cutaneous reverse passive Arthus reaction

H2S has been highlighted recently as an endogenous, gaseous signaling molecule, especially in inflammations. The deposition of IC induces an acute inflammatory response with tissue injury. To assess the roles of H2S in the IC-induced diseases, the cutaneous, reverse passive Arthus reaction was conducted using NaHS as a H2S donor. Furthermore, we conducted similar experiments using selectin(-/-) mice to determine the involvement of selectin molecules in the H2S-mediated pathway. Exogenous application of NaHS dramatically attenuated inflammatory reactions in WT mice associated with Arthus reaction. Namely, mRNA expressions of TNF-α, IFN-γ, and neutrophil numbers were reduced significantly in the lesional skins of NaHS-treated WT mice relative to untreated ones. NaHS treatment significantly reduced these three parameters in the lesional skins of E- and P-selectin(-/-) mice but not in those of L-selectin(-/-) mice. Quite similar results were obtained in the blocking study using WT mice injected with mAb to E-, P-, and L-selectin. Our results indicated that the exogenous application of NaHS attenuates inflammatory responses in reverse passive Arthus reaction through a L-selectin-involved pathway but not through E- or P-selectin pathways.

Transient PKCα shuttling to the immunological synapse is governed by (DGK)ζ and regulates L-selectin shedding

Considerable evidence indicates that diacylglycerol (DAG) generation at the immunological synapse (IS) determines T cell functions by regulating the duration and amplitude of Ras/ERK signals. The exact mechanism by which DAG regulates Ras/ERK activation downstream of the T cell receptor (TCR) nonetheless remains poorly understood. Here we characterize PKCα as a previously unrecognized component of the machinery that translates cell receptor occupancy into Ras/ERK-propagated signals. We show transient translocation of PKCα to the IS, mediated by DAG generation at the contact area. Diacylglycerol kinase (DGK)ζ negatively regulated PKCα translocation kinetics, whereas PKCα activity limited its own persistence at the IS. Coordinated activation of DGKζ and PKCα in response to antigen recognition regulated the amplitude and duration of Ras/ERK activation; this in turn mediated early processes of T cell surface proteolysis such as L-selectin shedding. Analysis of DGKζ-deficient mice further showed that increased DAG signaling is translated to downstream elements of this pathway, as reflected by enhanced PKCα-dependent L-selectin shedding. We propose that early activation of a DAG/PKCα axis contributes to the mechanisms by which antigen affinity translates into TCR biological responses.

Recruitment of monocytes/macrophages in different tumor microenvironments

After emigration from the bone marrow into the peripheral blood, monocytes enter tissues and differentiate into macrophages. Monocytes/macrophages have many roles in immune regulation, angiogenesis, and tumor metastasis and invasion. In addition, studies have revealed that these cells are essential to tumor progression. Recently, an accumulation of evidence has indicated that macrophages in distinct regions of tumor masses have distinct origins. For instance, classical monocytes appear to be a major source of macrophages in tumor epithelial, perivascular, and hypoxic regions. In contrast, non-classical monocytes are an important source of macrophages in the tumor perivascular region. During the past century, it has been demonstrated that several chemoattractants can regulate the recruitment of monocytes/macrophages to tumor sites. Despite the importance of monocytes/macrophages in tumor progression, there had been, until recently, no efforts to summarize receptor-ligand pairs between tumor-derived chemokines and corresponding receptors in monocytes in different microenvironments. In this review, we present a cohesive view of the distinct expression patterns of chemokine receptors in two different monocyte subsets (classical and non-classical monocytes) and describe their roles in monocyte/macrophage recruitment into distinct tumor microenvironments. This review provides insight into the behavior of monocytes/macrophages in different tumor microenvironments.

The molecular basis of leukocyte recruitment and its deficiencies

The innate immune system responds to inflammation, infection and injury by recruiting neutrophils and other leukocytes. These cells are able to leave the intravascular compartment in a process called leukocyte recruitment. This process involves several distinct steps: selectin-mediated rolling, firm adhesion via integrins, postarrest modifications including adhesion strengthening and leukocyte crawling and finally transmigration into tissue. Genetic defects affecting the different steps of the cascade can result in severe impairment in leukocyte recruitment. So far, three leukocyte adhesion deficiencies (LAD I-III) have been described in humans. These LADs are rare autosomal recessive inherited disorders and, although clinically distinct, exhibit several common features including recurrent bacterial infections and leukocytosis. In LAD-I, mutations within the β2-integrin gene result in a severe defect in β2 integrin-mediated firm leukocyte adhesion. Defects in the posttranslational fucosylation of selectin ligands dramatically reduce leukocyte rolling and lead to LAD-II. Finally, LAD-III, also known as LAD-I variant, is caused by impaired integrin activation due to mutations within the kindlin-3 gene. This review provides an overview on the molecular basis of leukocyte adhesion and its deficiencies.

FOXO1 Up-Regulates Human L-selectin Expression Through Binding to a Consensus FOXO1 Motif

L-selectin plays important roles in lymphocyte homing and leukocyte rolling. Mounting evidence shows that it is involved in many disease entities including diabetes, ischemia/reperfusion injuries, inflammatory diseases, and tumor metastasis. Regulation of L-selectin at protein level has been well characterized. However, the regulation of human L-selectin transcription remains largely unknown. To address transcriptional regulation of L-selectin, we cloned 1088 bp 5' of the start codon ATG. Luciferase analysis of the serial 5' deletion mutants located the core promoter region at -288/-1. A major transcription initiation site was mapped at -115 by 5'RACE. Transcription factors Sp1, Ets1, Mzf1, Klf2, and Irf1 bind to and transactivate the L-selectin promoter. Significantly, FOXO1 binds to a FOXO1 motif, CCCTTTGG, at -87/-80, and transactivates the L-selectin promoter in a dose-dependent manner. Over-expression of a constitutive-active FOXO1 increased the endogenous L-selectin expression in Jurkat cells. We conclude that FOXO1 regulates L-selectin expression through targeting its promoter.

L-selectin and skin damage in systemic sclerosis

BACKGROUND

L-selectin ligands are induced on the endothelium of inflammatory sites. L-selectin expression on neutrophils and monocytes may mediate the primary adhesion of these cells at sites of inflammation by mediating the leukocyte-leukocyte interactions that facilitate their recruitment. L-selectin retains functional activity in its soluble form. Levels of soluble L-selectin have been reported as both elevated and lowered in patients with systemic sclerosis (SSc). This preliminary study seeks to discern amongst these disparate results and to discover whether there is an association between L-selectin concentrations in plasma and skin damage in SSc patients.

METHODOLOGY AND PRINCIPAL FINDINGS

Nineteen cases with limited systemic sclerosis (lSSc) and 11 cases with diffuse systemic sclerosis (dSSc) were compared on a pairwise basis to age- and sex-matched controls. Criteria of the American College of Rheumatology were used to diagnose SSc. Skin involvement was assessed using the modified Rodnan skin score (mRSS). We find no association between mRSS and plasma L-selectin concentration in lSSc cases (p = 0.9944) but a statistically significant negative correlation in dSSc cases (R(2) = 73.11 per cent, p = 0.0008). The interpretation of the slope for dSSc cases is that for each increase of 100 ng/ml in soluble L-selectin concentration, the mRSS drops 4.22 (95 per cent CI: 2.29, 6.16). There was also a highly statistically significant negative correlation between sL-selectin and disease activity (p = 0.0007) and severity (p = 0.0007) in dSSc cases but not in lSSc cases (p = 0.2596, p = 0.7575, respectively).

CONCLUSIONS AND SIGNIFICANCE

No effective treatments exist for skin damage in SSc patients. Nor is there a laboratory alternative to the modified Rodnan skin score as is the case for other organs within the body. Modulation of circulating L-selectin is a promising target for reducing skin damage in dSSc patients. Plasma levels of soluble L-selectin could serve as an outcome measure for dSSc patients in clinical trials.

Optical projection tomography reveals dynamics of HEV growth after immunization with protein plus CFA and features shared with HEVs in acute autoinflammatory lymphadenopathy

The vascular–stromal compartment of lymph nodes is important for lymph node function, and high endothelial venules (HEVs) play a critical role in controlling the entry of recirculating lymphocytes. In autoimmune and autoinflammatory diseases, lymph node swelling is often accompanied by apparent HEV expansion and, potentially, targeting HEV expansion could be used therapeutically to limit autoimmunity. In previous studies using mostly flow cytometry analysis, we defined three differentially regulated phases of lymph node vascular–stromal growth: initiation, expansion, and the re-establishment of vascular quiescence and stabilization. In this study, we use optical projection tomography to better understand the morphologic aspects of HEV growth upon immunization with ovalbumin/CFA (OVA/CFA). We find HEV elongation as well as modest arborization during the initiation phase, increased arborization during the expansion phase, and, finally, vessel narrowing during the re-establishment of vascular quiescence and stabilization. We also examine acutely enlarged autoinflammatory lymph nodes induced by regulatory T cell depletion and show that HEVs are expanded and morphologically similar to the expanded HEVs in OVA/CFA-stimulated lymph nodes. These results reinforce the idea of differentially regulated, distinct phases of vascular–stromal growth after immunization and suggest that insights gained from studying immunization-induced lymph node vascular growth may help to understand how the lymph node vascular–stromal compartment could be therapeutically targeted in autoimmune and autoinflammatory diseases.

IL-7Rα and L-selectin, but not CD103 or CD34, are required for murine peanut-induced anaphylaxis

Background

Allergy to peanuts results in severe anaphylactic responses in affected individuals, and has dramatic effects on society and public policy. Despite the health impacts of peanut-induced anaphylaxis (PIA), relatively little is known about immune mechanisms underlying the disease. Using a mouse model of PIA, we evaluated mice with deletions in four distinct immune molecules (IL7Rα, L-selectin, CD34, CD103), for perturbed responses.

Methods

PIA was induced by intragastric sensitization with peanut antigen and cholera toxin adjuvant, followed by intraperitoneal challenge with crude peanut extract (CPE). Disease outcome was assessed by monitoring body temperature, clinical symptoms, and serum histamine levels. Resistant mice were evaluated for total and antigen specific serum IgE, as well as susceptibility to passive systemic anaphylaxis.

Results

PIA responses were dramatically reduced in IL7Rα^−/− and L-selectin^−/− mice, despite normal peanut-specific IgE production and susceptibility to passive systemic anaphylaxis. In contrast, CD34^−/− and CD103^−/− mice exhibited robust PIA responses, indistinguishable from wild type controls.

Conclusions

Loss of L-selectin or IL7Rα function is sufficient to impair PIA, while CD34 or CD103 ablation has no effect on disease severity. More broadly, our findings suggest that future food allergy interventions should focus on disrupting sensitization to food allergens and limiting antigen-specific late-phase responses. Conversely, therapies targeting immune cell migration following antigen challenge are unlikely to have significant benefits, particularly considering the rapid kinetics of PIA.

Human suppressive neutrophils CD16bright/CD62Ldim exhibit decreased adhesion

Neutrophils are essential effector cells in host defense against invading pathogens. Regulation of adhesion, migration, and chemotactic processes is important in the homing and activation of these cells. We recently described three distinct subsets of circulating human neutrophils in peripheral blood during acute systemic inflammation. One subset, CD16(bright)/CD62L(dim), has immune suppressive characteristics because it can inhibit T-cell proliferation. The other two subsets consist of banded CD16(dim)/CD62L(bright) and phenotypically mature (normal) CD16(bright)/CD62L(bright) neutrophils. The current study was designed to determine the adhesion characteristics of these different neutrophil subsets. Analysis of adhesion to activated endothelium under flow conditions revealed that CD16(bright)/CD62L(dim) neutrophils adhered less compared with CD16(bright)/CD62L(bright) and CD16(dim)/CD62L(bright) neutrophils. This decrease in binding capacity could be mimicked in the other neutrophil subsets by blocking L-selectin. Chemotaxis of CD16(bright)/CD62L(dim) neutrophils to the end-target chemoattractant N-formylmethionine-leucine-phenylalanine was lower compared with that for the CD16(dim)/CD62L(bright) neutrophil subset, whereas chemotaxis to cell-derived chemoattractant CXCL8 was comparable. Our data indicate that capture on endothelium under flow conditions, a key mechanism necessary for extravasation, of CD16(bright)/CD62L(dim) neutrophils to inflammatory sites is attenuated, which may facilitate migration of these cells to other tissue localizations. Modulation of this process is a potential target to manipulate inflammation because potentiation of this immune suppression might aid in anti-inflammatory therapy.

T cell factor-1 and β-catenin control the development of memory-like CD8 thymocytes

Innate memory-like CD8 thymocytes develop and acquire effector function during maturation in the absence of encounter with Ags. In this study, we demonstrate that enhanced function of transcription factors T cell factor (TCF)-1 and β-catenin regulate the frequency of promyelocytic leukemia zinc finger (PLZF)-expressing, IL-4-producing thymocytes that promote the generation of eomesodermin-expressing memory-like CD8 thymocytes in trans. In contrast, TCF1-deficient mice do not have PLZF-expressing thymocytes and eomesodermin-expressing memory-like CD8 thymocytes. Generation of TCF1 and β-catenin-dependent memory-like CD8 thymocytes is non-cell-intrinsic and requires the expression of IL-4 and IL-4R. CD8 memory-like thymocytes migrate to the peripheral lymphoid organs, and the memory-like CD8 T cells rapidly produce IFN-γ. Thus, TCF1 and β-catenin regulate the generation of PLZF-expressing thymocytes and thereby facilitate the generation of memory-like CD8 T cells in the thymus.