Immune responses to IAV infection and the roles of L-selectin and ADAM17 in lymphocyte homing

Influenza A virus (IAV) infection is a global public health burden causing up to 650,000 deaths per year. Yearly vaccination programmes and anti-viral drugs currently have limited benefits; therefore, research into IAV is fundamental. Leukocyte trafficking is a crucial process which orchestrates the immune response to infection to protect the host. It involves several homing molecules and receptors on both blood vessels and leukocytes. A key mediator of this process is the transmembrane glycoprotein L-selectin, which binds to vascular addressins on blood vessel endothelial cells. L-selectin classically mediates homing of naïve and central memory lymphocytes to lymph nodes via high endothelial venules (HEVs). Recent studies have found that L-selectin is essential for homing of activated CD8+ T cells to influenza-infected lungs and reduction in virus load. A disintegrin and metalloproteinase 17 (ADAM17) is the primary regulator of cell surface levels of L-selectin. Understanding the mechanisms that regulate these two proteins are central to comprehending recruitment of T cells to sites of IAV infection. This review summarises the immune response to IAV infection in humans and mice and discusses the roles of L-selectin and ADAM17 in T lymphocyte homing during IAV infectio

Understanding high endothelial venules: lessons for cancer immunology

High endothelial venules (HEVs) are blood vessels especially adapted for lymphocyte trafficking which are normally found in secondary lymphoid organs such as lymph nodes (LN) and Peyer's patches. It has long been known that HEVs develop in non-lymphoid organs during chronic inflammation driven by autoimmunity, infection or allografts. More recently, HEVs have been observed in solid, vascularized tumors and their presence correlated with reduced tumor size and improved patient outcome. It is proposed that newly formed HEV promote antitumor immunity by recruiting naive lymphocytes into the tumor, thus allowing the local generation of cancerous tissue-destroying lymphocytes. Understanding how HEVs develop and function are therefore important to unravel their role in human cancers. In LN, HEVs develop during embryonic and early post-natal life and are actively maintained by the LN microenvironment. Systemic blockade of lymphotoxin-β receptor leads to HEV de-differentiation, but the LN components that induce HEV differentiation have remained elusive. Recent elegant studies using gene-targeted mice have demonstrated clearly that triggering the lymphotoxin-β receptor in endothelial cells (EC) induces the differentiation of HEV and that CD11c+ dendritic cells play a crucial role in this process. It will be important to determine whether lymphotoxin-β receptor-dependent signaling in EC drives the development of HEV during tumorigenesis and which cells have HEV-inducer properties. This may reveal therapeutic approaches to promote HEV neogenesis and determine the impact of newly formed HEV on tumor immunity

Differential effects of hydrogen peroxide on indices of endothelial cell function

The responses of pig aortic endothelial cells to sublethal doses of potentially toxic stimuli were investigated by monitoring K+ efflux, prostaglandin production, and the release of cytoplasmic purines. Xanthine plus xanthine oxidase reversibly stimulated these three parameters of endothelial cell function at doses that were not cytotoxic, as measured by chromium release, adenine uptake, and vital dye exclusion. The effects of xanthine plus xanthine oxidase were inhibited by catalase but not by superoxide dismutase, suggesting that H2O2 was responsible. Reagent H2O2 also reversibly stimulated K+ efflux, prostaglandin production, and the release of purines. The threshold concentration of H2O2 for these effects was approximately 10 microM, which was at least 30-fold lower than that which caused cytotoxicity. In addition to the direct effect of H2O2 in stimulating prostaglandin production (PGI2 and PGE2), prior exposure of endothelial cells to lower doses of H2O2 (less than 0.1 microM) at high oxygen tension inhibited the subsequent stimulation of prostaglandin production by ATP, A23187, and H2O2 itself. We conclude that H2O2 has substantial effects on endothelial physiology at doses up to 3,000-fold lower than those which induce cytotoxicity

L-selectin is essential for delivery of activated CD8+ T cells to virus-infected organs for protective immunity

Cytotoxic CD8+ T lymphocytes play a critical role in the host response to infection by viruses. The ability to secrete cytotoxic chemicals and cytokines is considered pivotal for eliminating virus. Of equal importance is how effector CD8+ T cells home to virus-infected tissues. L-selectin has not been considered important for effector T cell homing, because levels are low on activated T cells. We report here that, although L-selectin expression is downregulated following T cell priming in lymph nodes, L-selectin is re-expressed on activated CD8+ T cells entering the bloodstream, and recruitment of activated CD8+ T cells from the bloodstream into virus-infected tissues is L-selectin dependent. Furthermore, L-selectin on effector CD8+ T cells confers protective immunity to two evolutionally distinct viruses, vaccinia and influenza, which infect mucosal and visceral organs, respectively. These results connect homing and a function of virus-specific CD8+ T cells to a single molecule, L-selectin

α6 integrins are required for Langerhans cell migration from the epidermis

Topical exposure of mice to chemical allergens results in the migration of epidermal Langerhans cells (LCs) from the skin and their accumulation as immunostimulatory dendritic cells (DCs) in draining lymph nodes. Epidermal cell–derived cytokines have been implicated in the maturation and migration of LCs, but the adhesion molecules that regulate LC migration have not been studied. We hypothesized that integrin-mediated interactions with extracellular matrix components of the skin and lymph node may regulate LC/DC migration. We found that α6 integrins and α4 integrins were differentially expressed by epidermal LCs and lymph node DCs. A majority of LCs (70%) expressed the α6 integrin subunit, whereas DCs did not express α6 integrins. In contrast, the α4 integrin subunit was expressed at high levels on DCs but at much lower levels on LCs. The anti-α6 integrin antibody, GoH3, which blocks binding to laminin, completely prevented the spontaneous migration of LCs from skin explants in vitro and the rapid migration of LCs from mouse ear skin induced after intradermal administration of TNF-α in vivo. GoH3 also reduced the accumulation of DCs in draining lymph nodes by a maximum of 70% after topical administration of the chemical allergen oxazolone. LCs remaining in the epidermis in the presence of GoH3 adopted a rounded morphology, rather than the interdigitating appearance typical of LCs in naive skin, suggesting that the cells had detached from neighboring keratinocytes and withdrawn cellular processes in preparation for migration, but were unable to leave the epidermis. The anti-α4 integrin antibody PS/2, which blocks binding to fibronectin, had no effect on LC migration from the epidermis either in vitro or in vivo, or on the accumulation of DCs in draining lymph nodes after oxazolone application. RGD-containing peptides were also without effect on LC migration from skin explants. These results identify an important role for α6 integrins in the migration of LC from the epidermis to the draining lymph node by regulating access across the epidermal basement membrane. In contrast, α4 integrins, or other integrin-dependent interactions with fibronectin that are mediated by the RGD recognition sequence, did not influence LC migration from the epidermis. In addition, α4 integrins did not affect the accumulation of LCs as DCs in draining lymph nodes

Measuring the incidence and reporting of violence against women and girls in liberia using the 'neighborhood method'

Background This paper reports on the use of a neighborhood method- to measure the nature and incidence of violence against women and girls in post-conflict Liberia. Methods The study population comprised females in Montserrado and Nimba counties. Study participants were randomly selected for interviews using multi-stage cluster sampling. 30 clusters of households were sampled in each county. Information on incidents of domestic violence and rape within the preceding 18 months was collected with regard to females of all ages in the respondent's household, and those of her four closest neighbors to make up the full sample. Findings Households in the sample contained 7015 females (1687 girls, 4586 women, 742 age missing) in Montserrado and 6632 (2070 girls, 4167 women, 95 age missing) in Nimba. In the previous 18 months 54.1% (CI 53.1-55.1) and 55.8% (CI 54.8-56.8) of females in Montserrado and Nimba respectively were indicated to have experienced non-sexual domestic abuse; 19.4% (CI 18.6-20.2) and 26.0% (CI 25.1-26.9) of females in Montserrado and Nimba respectively to have been raped outside of marriage; and 72.3% (CI 70.7-73.9) and 73.8% (CI 72.0-75.7) of married or separated women in Montserrado and Nimba respectively to have experienced marital rape. Husbands and boyfriends were reported as the perpetrators of the vast majority of reported violence. Strangers were reported to account for less than 2% of the perpetrators of rape in either county. Incidents were most commonly disclosed to other family members or to friends and neighbors, and less often to formal authorities such as the police, court or community leaders. Incidents were approaching fifty times more likely to be reported to police if perpetrated by strangers rather than intimate partners. Conclusions Violence against women and girls is widespread in the areas studied. Programming needs to address the fact that this violence is primarily occurring in the household, where most incidents go unreported outside the immediate family or social circle. Police and hospital reports severely under-represent these known perpetrators. Inter-interviewer variance and differences in reports for self and neighbors for some outcomes caution the precision and validity of some estimates. However, the potential utility of the neighborhood method for estimating prevalence rates with an accuracy suitable for programmatic purposes in conflict-affected and post-conflict settings is noted.sch_iih7pub4055pub

L-Selectin Shedding Does Not Regulate Constitutive T Cell Trafficking but Controls the Migration Pathways of Antigen-activated T Lymphocytes

L-Selectin mediates rolling of lymphocytes in high endothelial venules (HEVs) of peripheral lymph nodes (PLNs). Cross-linking of L-selectin causes proteolytic shedding of its ectodomain, the physiological significance of which is unknown. To determine whether L-selectin shedding regulates lymphocyte migration, a mutant form that resists shedding (LΔP-selectin) was engineered. Transgenic mice expressing either LΔP or wild-type (WT) L-selectin on T cells were crossed with L-selectin knockout (KO) mice. The cellularity and subset composition of secondary lymphoid organs did not differ between LΔP and WT mice, however, they were different from C57BL/6. Plasma levels of soluble L-selectin in LΔP mice were reduced to <5% of WT and C57BL/6 mice. The rolling properties of T lymphocytes from LΔP and WT mice on immobilized L-selectin ligands were similar. Furthermore, similar numbers of LΔP and WT T lymphocytes were recruited from the bloodstream into PLNs in mice, although LΔP T cells transmigrated HEVs more slowly. WT, but not LΔP-selectin, underwent rapid, metalloproteinase-dependent shedding after TCR engagement, and LΔP T cells retained the capacity to enter PLNs from the bloodstream. These results suggest that the ability to shed L-selectin is not required for T cell recirculation and homing to PLNs. However, L-selectin shedding from antigen-activated T cells prevents reentry into PLNs

Quantifying the limits of CAR T-cell delivery in mice and men

CAR (Chimeric Antigen Receptor) T cells have demonstrated clinical success for the treatment of multiple lymphomas and leukaemias, but not for various solid tumours, despite promising data from murine models. Lower effective CAR T-cell delivery rates to human solid tumours compared to haematological malignancies in humans and solid tumours in mice might partially explain these divergent outcomes. We used anatomical and physiological data for human and rodent circulatory systems to calculate the typical perfusion of healthy and tumour tissues, and estimated the upper limits of immune cell delivery rates across different organs, tumour types and species. Estimated maximum delivery rates were up to 10 000-fold greater in mice than humans yet reported CAR T-cell doses are typically only 10–100-fold lower in mice, suggesting that the effective delivery rates of CAR T cells into tumours in clinical trials are far lower than in corresponding mouse models. Estimated delivery rates were found to be consistent with published positron emission tomography data. Results suggest that higher effective human doses may be needed to drive efficacy comparable to mouse solid tumour models, and that lower doses should be tested in mice. We posit that quantitation of species and organ-specific delivery and homing of engineered T cells will be key to unlocking their potential for solid tumours