Human T lymphocytes bind to germinal centers of human tonsils via integrin alpha4/VCAM-1 and LFA-1/ICAM-1 and -2

DOCK8 is essential for LFA-1-dependent positioning of T follicular helper cells in germinal centers

T follicular helper (Tfh) cell migration into germinal centers (GCs) is essential for the generation of GC B cells and antibody responses to T cell-dependent (TD) antigens. This process requires interactions between lymphocyte function-associated antigen 1 (LFA-1) on Tfh cells and ICAMs on B cells. The mechanisms underlying defective antibody responses to TD antigens in DOCK8 deficiency are incompletely understood. We show that mice selectively lacking DOCK8 in T cells had impaired IgG antibody responses to TD antigens, decreased GC size, and reduced numbers of GC B cells. However, they developed normal numbers of Tfh cells with intact capacity for driving B cell differentiation into a GC phenotype in vitro. Notably, migration of DOCK8-deficient T cells into GCs was defective. Following T cell receptor (TCR)/CD3 ligation, DOCK8-deficient T cells had impaired LFA-1 activation and reduced binding to ICAM-1. Our results therefore indicate that DOCK8 is important for LFA-1-dependent positioning of Tfh cells in GCs, and thereby the generation of GC B cells and IgG antibody responses to TD antigen.

Single-cell characterization and quantification of translation-competent viral reservoirs in treated and untreated HIV infection

The phenotypic characterization of the cells in which HIV persists during antiretroviral therapy (ART) remains technically challenging. We developed a simple flow cytometry-based assay to quantify and characterize infected cells producing HIV proteins during untreated and treated HIV infection. By combining two antibodies targeting the HIV capsid in a standard intracellular staining protocol, we demonstrate that p24-producing cells can be detected with high specificity and sensitivity in the blood from people living with HIV. In untreated individuals, the frequency of productively infected cells strongly correlated with plasma viral load. Infected cells preferentially displayed a transitional memory phenotype and were enriched in Th17, peripheral Tfh and regulatory T cells subsets. These cells also preferentially expressed activation markers (CD25, HLA-DR, Ki67), immune checkpoint molecules (PD-1, LAG-3, TIGIT, Tim-3) as well as the integrins α4β7 and α4β1. In virally suppressed individuals on ART, p24-producing cells were only detected upon stimulation (median frequency of 4.3 p24+ cells/10⁶ cells). These measures correlated with other assays assessing the size of the persistent reservoir including total and integrated HIV DNA, Tat/rev Induced Limiting Dilution Assay (TILDA) and quantitative viral outgrowth assay (QVOA). In ART-suppressed individuals, p24-producing cells preferentially displayed a transitional and effector memory phenotype, and expressed immune checkpoint molecules (PD-1, TIGIT) as well as the integrin α4β1. Remarkably, α4β1 was expressed by more than 70% of infected cells both in untreated and ART-suppressed individuals. Altogether, these results highlight a broad diversity in the phenotypes of HIV-infected cells in treated and untreated infection and suggest that strategies targeting multiple and phenotypically distinct cellular reservoirs will be needed to exert a significant impact on the size of the reservoir.

HIV persists in a small pool of infected CD4+ T cells during ART. A better characterization of these cells is a pre-requisite to the development of HIV eradication strategies. We developed a novel assay, named HIV-Flow, to simultaneously quantify and characterize reservoir cells in individuals receiving ART. With this assay, we found that a median of only 5 cells/million have the ability to produce the HIV protein Gag in individuals on suppressive ART. These frequencies correlated with other assays aimed at measuring HIV reservoirs. Importantly, we show that the HIV reservoir is phenotypically diverse, with numerous cell subsets contributing to the pool of persistently infected cells. Nonetheless, we identified several markers preferentially expressed at the surface or these rare reservoir cells, including immune checkpoint molecules and homing receptors. By combining these markers, we identified discrete cellular subsets highly enriched in HIV-infected cells. This novel assay will facilitate the identification of markers expressed by cellular HIV reservoirs.

Tissue Microenvironments in the Nasal Epithelium of Rainbow Trout (Oncorhynchus mykiss) Define Two Distinct CD8α+ Cell Populations and Establish Regional Immunity

Mucosal surfaces require balancing different physiological roles and immune functions. To effectively achieve multifunctionality, mucosal epithelia have evolved unique microenvironments that create unique regional immune responses without impairing other normal physiological functions. Whereas examples of regional immunity are known in other mucosal epithelia, to date, no immune microenvironments have been described in the nasal mucosa, a site where the complex functions of olfaction and immunity need to be orchestrated. In this study we identified the presence of CD8α⁺ cells in the rainbow trout (Oncorhynchus mykiss) nasal epithelium. Nasal CD8α⁺ cells display a distinct phenotype suggestive of CD8⁺ T cells with high integrin β₂ expression. Importantly, nasal CD8α⁺ cells are located in clusters at the mucosal tip of each olfactory lamella but scattered in the neuroepithelial region. The grouping of CD8α⁺ cells may be explained by the greater expression of CCL19, ICAM-1, and VCAM-1 in the mucosal tip compared with the neuroepithelium. Whereas viral Ag uptake occurred via both tip and lateral routes, tip-resident MHC class II⁺ cells are located significantly closer to the lumen of the nasal cavity than are their neuroepithelial counterparts, therefore having quicker access to invading pathogens. Our studies reveal compartmentalized mucosal immune responses within the nasal mucosa of a vertebrate species, a strategy that likely optimizes local immune responses while protecting olfactory sensory functions.

Novel pharmacological approaches for treatment of obstructive sleep apnea in children

INTRODUCTION

The lymphadenoid tissues in the upper airway are sparse and organized lympho-epithelial structures playing an important role against foreign pathogens, with the palatine tonsils being the major components of the lymphoid tissues contained in the Waldeyer's ring. Obstructive sleep apnea (OSA) has emerged as a very frequent condition in the pediatric age range that is associated with substantial neurobehavioral, cardiovascular and metabolic morbidities. Adenotonsillar hypertrophy is the major pathophysiological contributor to OSA occurrence in children.

AREAS COVERED

Here, the authors provide a systematic review and summary of some of the known histological and pathological features of human lymphadenoid tissues and their fundamental immunological functions, provide insights into the pathophysiology of pediatric OSA, particularly focusing on inflammatory pathways and the available outcomes associated with targeting such pathways with compounds such as corticosteroids and leukotriene modifiers. Furthermore, they present findings from an unbiased approach to discovery of therapeutic targets and formulate constructs toward putative future interventional approaches for this highly prevalent condition.

EXPERT OPINION

Surgical approaches for pediatric OSA may not be as effective as previously anticipated. Accordingly, expanded use of existing systemic or topical anti-inflammatory agents or development of novel compounds targeting selected immune cell populations underlying pathophysiological determinants of OSA is needed.

Differential expression of homing receptors and vascular addressins in tonsils and draining lymph nodes: Effect of Brucella infection in sheep

The differential expression of homing receptors (HR) and complementary vascular addressins was studied in T and B lymphocytes from ovine tonsils and draining lymph nodes (LN) in uninfected and Brucella melitensis-infected sheep. In uninfected sheep, CD4+CD25+ T cells expressed proportionally more L-selectin and beta1 integrin than beta7 integrin in pharyngeal and palatine tonsils and in parotid LN (PLN), retropharyngeal LN (RLN) and the peripheral prescapular LN (PSLN). In contrast, memory CD4+CD45RA- T cells expressed an equivalent proportion of the three HR in PLN and PSLN, whereas beta1 and beta7 integrins were proportionally more expressed than L-selectin in pharyngeal tonsil. beta7 integrin was proportionally more expressed than beta1 integrin or L-selectin in palatine tonsils, RLN and the mucosal mesenteric LN (MLN). beta1 integrin was proportionally more expressed in IgG+ and IgA+ cells than beta7 integrin and L-selectin in tonsils, PLN and RLN. The main endothelial addressin expressed on venules in both pharyngeal and palatine tonsils, the PLN and RLN, as well as in the PSLN, was the peripheral PNAd, while in the MLN it was MAdCAM-1. Conjunctival infection by Brucella resulted in an increase of CD4+CD25+ and CD4+CD45RA- T cell subsets, which was associated to modifications of HR expression. CD4+CD45RA- T cells expressed proportionally more beta1 and beta7 integrins than L-selectin in regional PLN and RLN, but also in PSLN. The infection induced an increase of IgG+ and IgA+ cell percentages expressing beta1 integrin in all LN, and also beta7 integrin in the RLN. PNAd continued to be expressed on venules of tonsils and draining LN after Brucella infection, and MAdCAM-1 was also weakly expressed on RLN venules. These results suggest that lymphocyte trafficking through tonsils and draining LN could involve L-selectin/PNAd interactions, as well as beta1 or beta7 integrin, possibly in interaction with VCAM-1 or MAdCAM-1. The homing of antigen-specific lymphocytes in these tissues could be modulated after conjunctival infection with Brucella, which induces the recruitment of lymphocytes that express both beta1 and/or beta7 integrin in regional and more distant LN.

Alpha6-integrin is expressed on germinal centre B cells and modifies growth of a B-cell line

The production of high-affinity antibodies requires diversification of the antibody repertoire by somatic hypermutation followed by selection of those B cells bearing the highest affinity antibodies. Whilst many surface molecules that mediate the cell-cell interactions required for germinal centre formation have been identified, little is known of the importance of interactions with components of the extracellular matrix, i.e. fibronectin, collagen and laminin. We demonstrate that the laminin-binding alpha6-integrin is expressed on germinal centre B cells and is induced during the in vitro activation of naïve splenic B cells. A laminin network is demonstrated within the germinal centre. Analysis of an alpha6-integrin-expressing mouse B-cell line, A20, demonstrates that this molecule is essential for binding to laminin, and that blocking by anti-alpha6-integrin immunoglobulin causes loss of adhesion associated with an increase in proliferation. There is no correlation with changes in BCL-6 or Blimp-1 expression, suggesting that alpha6-integrin does not play a role in differentiation.

Adenosine suppresses alpha(4)beta(7) integrin-mediated adhesion of T lymphocytes to colon adenocarcinoma cells

The interaction of T lymphocytes with tumor cells, a key step in the antitumor immune response, is suppressed by adenosine, a nucleoside produced at increased levels within the hypoxic tumor environment. We have explored the mechanism by which adenosine interferes with the lymphocyte:tumor cell interaction. The adhesion of anti-CD3-stimulated T cells to syngeneic MCA-38 mouse colon adenocarcinoma cells did not involve LFA-1 (alpha(L)beta(2)) or VLA-5 (alpha(5)beta(1)). However, antibodies against either lymphocyte alpha(4) or beta(7) (but not beta(1)) integrin subunits, or against VCAM-1 on the tumor cells, significantly suppressed adhesion, showing that the recognition of MCA-38 cells by T cells is strongly dependent upon the association of alpha(4)beta(7) on the effector cells with VCAM-1 on the tumor targets. This association is modulated by adenosine: The ability of adenosine to suppress T cell adhesion to MCA-38 cells was lost if alpha(4)beta(7) was functionally blocked with anti-alpha(4) antibodies (i) prior to or (ii) during the adhesion assay or if (iii) alpha(+)(4) cells were depleted from the T lymphocyte population. The binding of T cells to fibronectin through alpha(4)beta(1) was not suppressed by adenosine. We conclude that adenosine partially inhibits the interaction of T lymphocytes with tumor cells by blocking the function of integrin alpha(4)beta(7).

Inhibition of LFA-1/ICAM-1 and VLA-4/VCAM-1 as a therapeutic approach to inflammation and autoimmune diseases

This review focuses on providing insights into the structural basis and clinical relevance of LFA-1 and VLA-4 inhibition by peptides and small molecules as adhesion-based therapeutic strategies for inflammation and autoimmune diseases. Interactions of cell adhesion molecules (CAM) play central roles in mediating immune and inflammatory responses. Leukocyte function-associated antigen (LFA-1, alpha(L)beta(2), and CD11a/CD18) and very late antigen (VLA-4, alpha(4)beta(1), and CD49d/CD29) are members of integrin-type CAM that are predominantly involved in leukocyte trafficking and extravasation. LFA-1 is exclusively expressed on leukocytes and interacts with its ligands ICAM-1, -2, and -3 to promote a variety of homotypic and heterotypic cell adhesion events required for normal and pathologic functions of the immune systems. VLA-4 is expressed mainly on lymphocyte, monocytes, and eosinophils, but is not found on neutrophils. VLA-4 interacts with its ligands VCAM-1 and fibronectin (FN) CS1 during chronic inflammatory diseases, such as rheumatoid arthritis, asthma, psoriasis, transplant-rejection, and allergy. Blockade of LFA-1 and VLA-4 interactions with their ligands is a potential target for immunosuppression. LFA-1 and VLA-4 antagonists (antibodies, peptides, and small molecules) are being developed for controlling inflammation and autoimmune diseases. The therapeutic intervention of mostly mAb-based has been extensively studied. However, due to the challenging relative efficacy/safety ratio of mAb-based therapy application, especially in terms of systemic administration and immunogenic potential, strategic alternatives in the forms of peptide, peptide mimetic inhibitors, and small molecule non-peptide antagonists are being sought. Linear and cyclic peptides derived from the sequences of LFA-1, ICAM-1, ICAM-2, VCAM-1, and FN C1 have been shown to have inhibitory effects in vitro and in vivo. Finally, understanding the mechanism of LFA-1 and VLA-4 binding to their ligands has become a fundamental basis in developing therapeutic agents for inflammation and autoimmune diseases.

Inhibition of the adherence of T-lymphocytes to epithelial cells by a cyclic peptide derived from inserted domain of lymphocyte function-associated antigen-1

Tissue inflammation is characterized by aggravated leukocyte infiltration into the sites of inflammation. The mechanism requires the interactions of leukocyte adhesion-molecules and their ligands in the inflamed tissues. In this study, we demonstrate that a cyclic peptide cLAB.L [cyclol, 12-PenlTDGEATDSGC], derived from the "inserted" or I-domain of LFA-1 is able to inhibit the adherence of T-lymphocytes to the epithelial cell monolayers. This inhibition has been thought to involve the disruption of LFA-1/ICAM-1 interaction. The heterotypic adhesion of phorbol ester-activated Molt-3 cells and IFN-gamma-induced Caco-2 monolayers was inhibited upon treatment of the monolayers with monoclonal antibodies (MAbs) to adhesion molecules or with cLAB.L peptide. The adhesion can be inhibited by MAbs to ICAM-1, ICAM-2, and VCAM-1, and cLAB.L peptide in a concentration-dependent manner. However, none of the individual uses of these molecules led to a total inhibition. The inhibitory activity of cLAB.L is greatly reduced by low temperature and the absence of cell activation. Treatment of cLAB.L peptide may trigger an early event of apoptosis on activated but not on non-activated Molt-3 cells; no indication of peptide-induced apoptosis was found on Caco-2 cells. Taken together, data from this work suggest that cLAB.L may have applications to direct cell-targeted delivery during tissue inflammation.

Cell adhesion molecule expression in the sheep thymus

Cell adhesion molecules are potential regulating factors in both prethymic and intrathymic T cell development. An experimental challenge has been the development of a large animal model that facilitates in vivo studies of both intrathymic development and lymphocyte migration. To extend earlier studies of thymic development, we have developed a panel of monoclonal antibodies (mAb) to a variety of sheep cell adhesion molecules. Immunohistochemistry was used to define mAb reactivity and flow cytometry was used to quantify expression of cell adhesion molecules within the thymus. To facilitate flow cytometry definition of cortical thymocytes, mAbs were developed to the sheep CD1 antigen. Dual parameter flow cytometry provided a phenotypic characterization of cell adhesion molecule expression on both CD1(+) and CD1(-) sheep thymocyte populations. These studies demonstrated significantly enhanced cortical thymocyte expression of three cell adhesion molecules: beta1 integrin (CD29), ICAM-2 and LFA-3. The beta1 integrin cell adhesion molecule was also expressed at higher levels on CD1(+) thymocytes in post-natal lambs as compared to adult sheep. These studies of thymocyte membrane molecule expression should facilitate future investigations of sheep intrathymic development and T lymphocyte immigration.

Activated T lymphocytes bind in situ to stromal tissue of colon carcinoma but lack adhesion to tumor cells

It is not entirely clear which adhesion molecules are responsible for the site-directed traffic of T cells within the tumor microenvironment. The present study investigated whether colon carcinoma tissue and normal colon differ in the expression of functionally relevant molecules. In addition, we identified adhesion molecules involved in the binding of activated T cells onto colon carcinoma in situ. Malignant colon epithelium expressed few adhesion receptors, i.e. CD44 (HERMES), CD49b (integrin alpha2) and CD162 (PSGL-1), whereas the stromal compartment within colon carcinoma was positive for numerous binding molecules, e.g. CD44, CD49a (integrin alpha1), CD49e (integrin alpha5), CD51 (integrin alpha(v)), CD54 (ICAM-1), CD99 (MIC2) and CD162. Lymphocytes infiltrating tumor stroma contrasted with lymphocytes within normal colon interstitium by lacking CD28, CD154 (CD40L), CD56 (NCAM) and CD98 (4F2). Normal activated T cells bound to the lymphocyte-rich areas within the stroma of colon carcinoma using CD44, CD50 (ICAM-3), CD99, CD102 (ICAM-2) and CD162 on the T lymphocytes. We conclude that lymphocytes within colon carcinoma stroma may lack several functionally crucial cell surface molecules. We present a panel of adhesion molecules that could mediate the migration of activated T lymphocytes into the stroma of colon carcinoma.

The CD44-initiated pathway of T-cell extravasation uses VLA-4 but not LFA-1 for firm adhesion

Leukocytes extravasate from the blood in response to physiologic or pathologic demands by means of complementary ligand interactions between leukocytes and endothelial cells. The multistep model of leukocyte extravasation involves an initial transient interaction ("rolling" adhesion), followed by secondary (firm) adhesion. We recently showed that binding of CD44 on activated T lymphocytes to endothelial hyaluronan (HA) mediates a primary adhesive interaction under shear stress, permitting extravasation at sites of inflammation. The mechanism for subsequent firm adhesion has not been elucidated. Here we demonstrate that the integrin VLA-4 is used in secondary adhesion after CD44-mediated primary adhesion of human and mouse T cells in vitro, and by mouse T cells in an in vivo model. We show that clonal cell lines and polyclonally activated normal T cells roll under physiologic shear forces on hyaluronate and require VCAM-1, but not ICAM-1, as ligand for subsequent firm adhesion. This firm adhesion is also VLA-4 dependent, as shown by antibody inhibition. Moreover, in vivo short-term homing experiments in a model dependent on CD44 and HA demonstrate that superantigen-activated T cells require VLA-4, but not LFA-1, for entry into an inflamed peritoneal site. Thus, extravasation of activated T cells initiated by CD44 binding to HA depends upon VLA-4-mediated firm adhesion, which may explain the frequent association of these adhesion receptors with diverse chronic inflammatory processes.

Human Follicular Dendritic Cells Inhibit Superantigen-Induced T-Cell Proliferation by Distinct Mechanisms

Follicular dendritic cells (FDCs) reside within germinal centers of secondary lymphoid tissue where they play a critical role in antigen-driven immune responses. FDCs express numerous adhesion molecules that facilitate cellular interactions with B and T cells within the germinal center microenvironment. Although human FDCs have been shown to influence B-cell development, very little is known about the ability of FDCs to regulate T-cell responses. To investigate this functional aspect of FDCs, highly enriched preparations were isolated by magnetic cell separation using the FDC-restricted monoclonal antibody HJ2. We found that isolated human FDCs inhibited proliferation of both autologous and allogeneic T cells, and were dependent on the number of FDCs present. Inhibition by FDCs was observed using two serologically distinct superantigens at multiple concentrations (Staphylococcus enterotoxin A and B). In contrast, B cells failed to inhibit, and often augmented superantigen-induced T-cell proliferation. Antibody-blocking studies showed that CD54 and CD106 were involved in the ability of FDC to inhibit T-cell proliferative responses. When FDCs and T cells were separated by a semipermeable membrane, the inhibitory effect was partially abrogated, demonstrating that in addition to cell-cell interactions, a soluble factor(s) was also involved in the process. The addition of indomethicin to cultures improved the proliferative response in the presence of FDCs, indicating that inhibition was mediated, in part, by prostaglandins. These results indicate that FDCs regulate T-cell proliferation by two molecular mechanisms and that FDC:T-cell interactions may play a pivotal role in germinal center development.

Reduced Expression of Adhesion Molecules and Cell Signaling Receptors by Chronic Lymphocytic Leukemia Cells With 11q Deletion

Deletions in chromosome bands 11q22-q23 were recently shown to be one of the most frequent chromosome aberrations in B-cell chronic lymphocytic leukemia (B-CLL). Patients suffering from B-CLL with 11q deletion are characterized by extensive lymphadenopathy, rapid disease progression, and short survival times. Phenotypic and functional characteristics of B-CLL cells with 11q deletion that may help to explain the pathophysiology of this entity are yet unknown. In the present study, B-CLL cells with (n = 19) and without (n = 19) 11q deletion were analyzed for their expression of functionally relevant cell surface molecules (n = 57). B-CLL cells with 11q deletion carried significantly lower levels of the adhesion molecules CD11a/CD18 (integrin L/β2), CD11c/CD18 (integrin X/β2), CD31 (PECAM-1), CD48, and CD58 (LFA-3). Furthermore, B-CLL cells with 11q deletion expressed less the cell signaling receptors CD45 (leukocyte common antigen [LCA]), CD6, CD35 (complement receptor 1), and CD39. Reduced CD45 levels and low-level expression of CD49d correlated with decreased overall survival. B-CLL cells with or without 11q deletion did not differ in their growth fractions, expression levels of transcription factor NF-κB, or their response to mitogenic stimuli. Decreased levels of functionally relevant adhesion molecules and of cell signaling receptors may contribute to the pathogenesis of the subgroup of B-CLL characterized by 11q22-q23 deletion.

Reduced Expression of Adhesion Molecules and Cell Signaling Receptors by Chronic Lymphocytic Leukemia Cells With 11q Deletion

Deletions in chromosome bands 11q22-q23 were recently shown to be one of the most frequent chromosome aberrations in B-cell chronic lymphocytic leukemia (B-CLL). Patients suffering from B-CLL with 11q deletion are characterized by extensive lymphadenopathy, rapid disease progression, and short survival times. Phenotypic and functional characteristics of B-CLL cells with 11q deletion that may help to explain the pathophysiology of this entity are yet unknown. In the present study, B-CLL cells with (n = 19) and without (n = 19) 11q deletion were analyzed for their expression of functionally relevant cell surface molecules (n = 57). B-CLL cells with 11q deletion carried significantly lower levels of the adhesion molecules CD11a/CD18 (integrin L/β2), CD11c/CD18 (integrin X/β2), CD31 (PECAM-1), CD48, and CD58 (LFA-3). Furthermore, B-CLL cells with 11q deletion expressed less the cell signaling receptors CD45 (leukocyte common antigen [LCA]), CD6, CD35 (complement receptor 1), and CD39. Reduced CD45 levels and low-level expression of CD49d correlated with decreased overall survival. B-CLL cells with or without 11q deletion did not differ in their growth fractions, expression levels of transcription factor NF-κB, or their response to mitogenic stimuli. Decreased levels of functionally relevant adhesion molecules and of cell signaling receptors may contribute to the pathogenesis of the subgroup of B-CLL characterized by 11q22-q23 deletion.