TYMSTR, a putative chemokine receptor selectively expressed in activated T cells, exhibits HIV-1 coreceptor function

Role of the CXCR6/CXCL16 axis in autoimmune diseases

The C-X-C motif ligand 16, or CXCL16, is a chemokine that belongs to the ELR - CXC subfamily. Its function is to bind to the chemokine receptor CXCR6, which is a G protein-coupled receptor with 7 transmembrane domains. The CXCR6/CXCL16 axis has been linked to the development of numerous autoimmune diseases and is connected to clinical parameters that reflect disease severity, activity, and prognosis in conditions such as multiple sclerosis, autoimmune hepatitis, rheumatoid arthritis, Crohn's disease, and psoriasis. CXCL16 is expressed in various immune cells, such as dendritic cells, monocytes, macrophages, and B cells. During autoimmune diseases, CXCL16 can facilitate the adhesion of immune cells like monocytes, T cells, NKT cells, and others to endothelial cells and dendritic cells. Additionally, sCXCL16 can regulate the migration of CXCR6-expressing leukocytes, which includes CD8⁺ T cells, CD4⁺ T cells, NK cells, constant natural killer T cells, plasma cells, and monocytes. Further investigation is required to comprehend the intricate interactions between chemokines and the pathogenesis of autoimmune diseases. It remains to be seen whether the CXCR6/CXCL16 axis represents a new target for the treatment of these conditions.

Autoantibodies against chemokines post-SARS-CoV-2 infection correlate with disease course

Infection with severe acute respiratory syndrome coronavirus 2 associates with diverse symptoms, which can persist for months. While antiviral antibodies are protective, those targeting interferons and other immune factors are associated with adverse coronavirus disease 2019 (COVID-19) outcomes. Here we discovered that antibodies against specific chemokines were omnipresent post-COVID-19, were associated with favorable disease outcome and negatively correlated with the development of long COVID at 1 yr post-infection. Chemokine antibodies were also present in HIV-1 infection and autoimmune disorders, but they targeted different chemokines compared with COVID-19. Monoclonal antibodies derived from COVID-19 convalescents that bound to the chemokine N-loop impaired cell migration. Given the role of chemokines in orchestrating immune cell trafficking, naturally arising chemokine antibodies may modulate the inflammatory response and thus bear therapeutic potential.

Anti-chemokine antibodies after SARS-CoV-2 infection correlate with favorable disease course

Infection by SARS-CoV-2 leads to diverse symptoms, which can persist for months. While antiviral antibodies are protective, those targeting interferons and other immune factors are associated with adverse COVID-19 outcomes. Instead, we discovered that antibodies against specific chemokines are omnipresent after COVID-19, associated with favorable disease, and predictive of lack of long COVID symptoms at one year post infection. Anti-chemokine antibodies are present also in HIV-1 infection and autoimmune disorders, but they target different chemokines than those in COVID-19. Monoclonal antibodies derived from COVID- 19 convalescents that bind to the chemokine N-loop impair cell migration. Given the role of chemokines in orchestrating immune cell trafficking, naturally arising anti-chemokine antibodies associated with favorable COVID-19 may be beneficial by modulating the inflammatory response and thus bear therapeutic potential.

One-Sentence Summary

Naturally arising anti-chemokine antibodies associate with favorable COVID-19 and predict lack of long COVID.

Chemokine-Driven Migration of Pro-Inflammatory CD4+ T Cells in CNS Autoimmune Disease

Pro-inflammatory CD4⁺ T helper (Th) cells drive the pathogenesis of many autoimmune conditions. Recent advances have modified views of the phenotype of pro-inflammatory Th cells in autoimmunity, extending the breadth of known Th cell subsets that operate as drivers of these responses. Heterogeneity and plasticity within Th1 and Th17 cells, and the discovery of subsets of Th cells dedicated to production of other pro-inflammatory cytokines such as GM-CSF have led to these advances. Here, we review recent progress in this area and focus specifically upon evidence for chemokine receptors that drive recruitment of these various pro-inflammatory Th cell subsets to sites of autoimmune inflammation in the CNS. We discuss expression of specific chemokine receptors by subsets of pro-inflammatory Th cells and highlight which receptors may be tractable targets of therapeutic interventions to limit pathogenic Th cell recruitment in autoimmunity.

Behavior of Chemokine Receptor 6 (CXCR6) in Complex with CXCL16 Soluble form Chemokine by Molecular Dynamic Simulations: General Protein‒Ligand Interaction Model and 3D-QSAR Studies of Synthetic Antagonists

The CXCR6‒CXCL16 axis is involved in several pathological processes, and its overexpression has been detected in different types of cancer, such as prostate, breast, ovary, and lung cancer, along with schwannomas, in which it promotes invasion and metastasis. Moreover, this axis is involved in atherosclerosis, type 1 diabetes, primary immune thrombocytopenia, vitiligo, and other autoimmune diseases, in which it is responsible for the infiltration of different immune system cells. The 3D structure of CXCR6 and CXCL16 has not been experimentally resolved; therefore, homology modeling and molecular dynamics simulations could be useful for the study of this signaling axis. In this work, a homology model of CXCR6 and a soluble form of CXCL16 (CXCR6‒CXCL16s) are reported to study the interactions between CXCR6 and CXCL16s through coarse-grained molecular dynamics (CG-MD) simulations. CG-MD simulations showed the two activation steps of CXCR6 through a decrease in the distance between the chemokine and the transmembrane region (TM) of CXCR6 and transmembrane rotational changes and polar interactions between transmembrane segments. The polar interactions between TM3, TM5, and TM6 are fundamental to functional conformation and the meta-active state of CXCR6. The interactions between D77-R280 and T243-TM7 could be related to the functional conformation of CXCR6; alternatively, the interaction between Q195-Q244 and N248 could be related to an inactive state due to the loss of this interaction, and an arginine cage broken in the presence of CXCL16s allows the meta-active state of CXCR6. A general protein‒ligand interaction supports the relevance of TM3‒TM5‒TM6 interactions, presenting three relevant pharmacophoric features: HAc (H-bond acceptor), HDn (H-bond donator), and Hph (hydrophobic), distributed around the space between extracellular loops (ECLs) and TMs. The HDn feature is close to TM3 and TM6; likewise, the HAc and Hph features are close to ECL1 and ECL2 and could block the rotation and interactions between TM3‒TM6 and the interactions of CXCL16s with the ECLs. Tridimensional quantitative structure-activity relationships (3D-QSAR) models show that the positive steric (VdW) and electrostatic fields coincide with the steric and positive electrostatic region of the exo-azabicyclo[3.3.1]nonane scaffold in the best pIC50 ligands. This substructure is close to the E274 residue and therefore relevant to the activity of CXCR6. These data could help with the design of new molecules that inhibit chemokine binding or antagonize the receptor based on the activation mechanism of CXCR6 and provoke a decrease in chemotaxis caused by the CXCR6‒CXCL16 axis.

A Disintegrin and Metalloproteinase-Control Elements in Infectious Diseases

Despite recent advances in treatment strategies, infectious diseases are still under the leading causes of death worldwide. Although the activation of the inflammatory cascade is one prerequisite of defense, persistent and exuberant immune response, however, may lead to chronicity of inflammation predisposing to a temporal or permanent tissue damage not only of the site of infection but also among different body organs. The initial response to invading pathogens is mediated by the recognition through various pattern-recognition receptors along with cellular engulfment resulting in a coordinated release of soluble effector molecules and cytokines aiming to terminate the external stimuli. Members of the ‘a disintegrin and metalloproteinase’ (ADAM) family have the capability to proteolytically cleave transmembrane molecules close to the plasma membrane, a process called ectodomain shedding. In fact, in infectious diseases dysregulation of numerous ADAM substrates such as junction molecules (e.g., E-cadherin, VE-cadherin, JAM-A), adhesion molecules (e.g., ICAM-1, VCAM-1, L-selectin), and chemokines and cytokines (e.g., CXCL16, TNF-α) has been observed. The alpha-cleavage by ADAM proteases represents a rate limiting step for downstream regulated intramembrane proteolysis (RIPing) of several substrates, which influence cellular differentiation, cell signaling pathways and immune modulation. Both the substrates mentioned above and RIPing crucially contribute to a systematic damage in cardiovascular, endocrine, and/or gastrointestinal systems. This review will summarize the current knowledge of ADAM function and the subsequent RIPing in infectious diseases (e.g., pathogen recognition and clearance) and discuss the potential long-term effect on pathophysiological changes such as cardiovascular diseases.

CXCL16 Stimulates Antigen-Induced MAIT Cell Accumulation but Trafficking During Lung Infection Is CXCR6-Independent

Mucosa-associated invariant T (MAIT) cells are a unique T cell subset that contributes to protective immunity against microbial pathogens, but little is known about the role of chemokines in recruiting MAIT cells to the site of infection. Pulmonary infection with Francisella tularensis live vaccine strain (LVS) stimulates the accrual of large numbers of MAIT cells in the lungs of mice. Using this infection model, we find that MAIT cells are predominantly CXCR6⁺ but do not require CXCR6 for accumulation in the lungs. However, CXCR6 does contribute to long-term retention of MAIT cells in the airway lumen after clearance of the infection. We also find that MAIT cells are not recruited from secondary lymphoid organs and largely proliferate in situ in the lungs after infection. Nevertheless, the only known ligand for CXCR6, CXCL16, is sufficient to drive MAIT cell accumulation in the lungs in the absence of infection when administered in combination with the MAIT cell antigen 5-OP-RU. Overall, this new data advances the understanding of mechanisms that facilitate MAIT cell accumulation and retention in the lungs.

Evolutionary analysis of chemokine CXCL16 and its receptor CXCR6 in murine rodents

The chemokine CXCL16 and its receptor CXCR6 are implicated in various physiological and pathological processes in cooperative and/or stand-alone fashions. Despite the significance of rodent animal models in elucidating the function and clinical relevance of the chemokine and its receptor, the evolutionary characterization of these molecules remains deficient for this taxon to a certain extent. In this study, we implemented a comparison of synonymous and nonsynonymous variation rates in combination with the maximum likelihood (ML) analysis and Tajima's test to evaluate the interspecific and intraspecific evolutions of CXCL16 and CXCR6 in murine rodents. Our results indicate that adaptive selection has frequently contributed to genetic diversity of both CXCL16 and CXCR6 in the murine lineage that is asynchronous with a relative dependence between these genes. This signature is radically different from the lineage-specific and concordant adaptive diversity of the primate homologues of these genes, which was reported in a previous study. The diversity identified in the present study shed further light on molecular strategies against the challenges towards CXCL16 and CXCR6.

CXCR6-Deficiency Improves the Control of Pulmonary Mycobacterium tuberculosis and Influenza Infection Independent of T-Lymphocyte Recruitment to the Lungs

T-lymphocytes are critical for protection against respiratory infections, such as Mycobacterium tuberculosis and influenza virus, with chemokine receptors playing an important role in directing these cells to the lungs. CXCR6 is expressed by activated T-lymphocytes and its ligand, CXCL16, is constitutively expressed by the bronchial epithelia, suggesting a role in T-lymphocyte recruitment and retention. However, it is unknown whether CXCR6 is required in responses to pulmonary infection, particularly on CD4⁺ T-lymphocytes. Analysis of CXCR6-reporter mice revealed that in naïve mice, lung leukocyte expression of CXCR6 was largely restricted to a small population of T-lymphocytes, but this population was highly upregulated after either infection. Nevertheless, pulmonary infection of CXCR6-deficient mice with M. tuberculosis or recombinant influenza A virus expressing P25 peptide (rIAV-P25), an I-A^b-restricted epitope from the immunodominant mycobacterial antigen, Ag85B, demonstrated that the receptor was redundant for recruitment of T-lymphocytes to the lungs. Interestingly, CXCR6-deficiency resulted in reduced bacterial burden in the lungs 6 weeks after M. tuberculosis infection, and reduced weight loss after rIAV-P25 infection compared to wild type controls. This was paradoxically associated with a decrease in Th1-cytokine responses in the lung parenchyma. Adoptive transfer of P25-specific CXCR6-deficient T-lymphocytes into WT mice revealed that this functional change in Th1-cytokine production was not due to a T-lymphocyte intrinsic mechanism. Moreover, there was no reduction in the number or function of CD4⁺ and CD8⁺ tissue resident memory cells in the lungs of CXCR6-deficient mice. Although CXCR6 was not required for T-lymphocyte recruitment or retention in the lungs, CXCR6 influenced the kinetics of the inflammatory response so that deficiency led to increased host control of M. tuberculosis and influenza virus.

Genetic diversification of chemokine CXCL16 and its receptor CXCR6 in primates

Chemokine CXCL16 and its receptor CXCR6 are associated with a series of physiological and pathological processes in cooperative and stand-alone fashions. To shed insight into their versatile nature, we studied genetic variations of CXCL16 and CXCR6 in primates. Evolutionary analyses revealed that these genes underwent a similar evolutionary fate. Both genes experienced adaptive diversification with the phylogenetic division of cercopithecoids (Old World monkeys) and hominoids (humans, great apes, and gibbons) from their common ancestor. In contrast, they were conserved in the periods preceding and following the dividing process. In terms of the adaptive diversification between cercopithecoids and hominoids, the adaptive genetic changes have occurred in the mucin-like and chemokine domains of CXCL16 and the N-terminus and transmembrane helixes of CXCR6. In combination with currently available structural and functional information for CXCL16 and CXCR6, the parallels between the evolutionary footprints and the co-occurrence of adaptive diversification at some evolutionary stage suggest that interplay could exist between the diversification-related amino acid sites, or between the domains on which the identified sites are located, in physiological processes such as chemotaxis and/or cell adhesion.

The roles of serum CXCL16 in circulating Tregs and gastrointestinal stromal tumor cells

Gastrointestinal stromal tumors (GIST) are the most common sarcomas of the digestive system. Abnormal expression of CXCL16 and its sole receptor, CXCR6, has been demonstrated in many cancers. However, no studies have shown the relationship between CXCL16 or CXCR6 expression and GIST. In this study, we detected CXCL16 and CXCR6 expression in GIST patient samples by using immunohistochemistry analysis and Western blot analysis. Serum CXCL16 level was determined by using enzyme-linked immunosorbent assay. Circulating Tregs were isolated by using flow cytometry. MTT assay, cell cycle assay, and transwell assay were used to test the effects of recombinant CXCL16 on Tregs and GIST cells in vitro. The levels of CXCL16 and CXCR6 protein were higher in cancer tissues than in normal tissues. Serum CXCL16 level and circulating Tregs were higher in GIST patients than that in the healthy volunteers. CXCL16, CXCR6, serum CXCL16, and circulating Tregs were significantly associated with a decreased survival time of patients. Relative to control cells, high concentration recombinant CXCL16 treated Tregs and GIST cells exhibited lower proliferation and mobility rates as assessed by MTT assay and transwell assay, respectively. Taken together, CXCL16 was observed to mediate the inhibitory effects in Tregs and GIST cells, and these involved suppression of the MEK/ERK signaling pathway.

Role of Bone Marrow-Derived Fibroblasts in Renal Fibrosis

Renal fibrosis represents a common pathway leading to progression of chronic kidney disease. Renal interstitial fibrosis is characterized by extensive fibroblast activation and excessive production and deposition of extracellular matrix (ECM), which leads to progressive loss of kidney function. There is no effective therapy available clinically to halt or even reverse renal fibrosis. Although activated fibroblasts/myofibroblasts are responsible for the excessive production and deposition of ECM, their origin remains controversial. Recent evidence suggests that bone marrow-derived fibroblast precursors contribute significantly to the pathogenesis of renal fibrosis. Understanding the molecular signaling mechanisms underlying the recruitment and activation of the bone marrow-derived fibroblast precursors will lead to novel therapy for the treatment of chronic kidney disease. In this review, we summarize recent advances in our understanding of the recruitment and activation of bone marrow-derived fibroblast precursors in the kidney and the development of renal fibrosis and highlights new insights that may lead to novel therapies to prevent or reverse the development of renal fibrosis.

Selectivity in the Use of Gi/o Proteins Is Determined by the DRF Motif in CXCR6 and Is Cell-Type Specific

CXCR6, the receptor for CXCL16, is expressed on multiple cell types and can be a coreceptor for human immunodeficiency virus 1. Except for CXCR6, all human chemokine receptors contain the D(3.49)R(3.50)Y(3.51) sequence, and all but two contain A(3.53) at the cytoplasmic terminus of the third transmembrane helix (H3C), a region within class A G protein-coupled receptors that contacts G proteins. In CXCR6, H3C contains D(3.49)R(3.50)F(3.51)I(3.52)V(3.53) at positions 126-130. We investigated the importance and interdependence of the canonical D126 and the noncanonical F128 and V130 in CXCR6 by mutating D126 to Y, F128 to Y, and V130 to A singly and in combination. For comparison, we mutated the analogous positions D142, Y144, and A146 to Y, F, and V, respectively, in CCR6, a related receptor containing the canonical sequences. Mutants were analyzed in both human embryonic kidney 293T and Jurkat E6-1 cells. Our data show that for CXCR6 and/or CCR6, mutations in H3C can affect both receptor signaling and chemokine binding; noncanonical H3C sequences are functionally linked, with dual changes mitigating the effects of single mutations; mutations in H3C that compromise receptor activity show selective defects in the use of individual Gi/o proteins; and the effects of mutations in H3C on receptor function and selectivity in Gi/o protein use can be cell-type specific. Our findings indicate that the ability of CXCR6 to make promiscuous use of the available Gi/o proteins is exquisitely dependent on sequences within the H3C and suggest that the native sequence allows for preservation of this function across different cellular environments.

Prognostic impact of CXCL16 and CXCR6 in non-small cell lung cancer: combined high CXCL16 expression in tumor stroma and cancer cells yields improved survival

Background

The chemokine CXCL16 and its receptor CXCR6 are expressed by a variety of immune cells and have been shown to influence angiogenesis. The expression of CXCR6 and CXCL16 has been examined in numerous human cancers; however no studies have yet investigated their influence on prognosis in non-small cell lung cancer (NSCLC). We aimed to explore their prognostic significance in NSCLC, in addition to examining associations with previously investigated markers.

Methods

Resected tumor tissue from 335 consecutive unselected stage I-IIIA NSCLC patients (1990–2005) were collected. Immunohistochemistry was used to evaluate the expression of CXCR6 and CXCL16 on tissue microarrays. In vitro, NSCLC cells (NCI-H460, A549 cells) were transfected with CXCL16 siRNA to examine effects on proliferation.

Results

In univariate analysis, ↑ stromal cell CXCL16 expression was a significant positive prognostic factor (P = 0.016). CXCR6 was expressed in cancer cells, but did not show any prognostic impact. In the multivariate analysis, combined ↑cancer, and ↑stromal cell CXCL16 expression was an independent positive prognostic factor when compared to ↓stromal and ↓cancer cell expression (HR: 0.42; 95 % CI: 0.20–0.88; P = 0.022). Knockdown of CXCL16 by siRNA resulted in accelerated proliferation of NSCLC cell lines.

Conclusion

We have shown that combined ↑cancer and ↑stromal cell CXCL16 expression is an independent positive prognostic factor in NSCLC. Further studies are warranted to elucidate the biological mechanism underlying this finding.

Regulation of NKT Cell Localization in Homeostasis and Infection

Natural killer T (NKT) cells are a specialized subset of T lymphocytes that regulate immune responses in the context of autoimmunity, cancer, and microbial infection. Lipid antigens derived from bacteria, parasites, and fungi can be presented by CD1d molecules and recognized by the canonical T cell receptors on NKT cells. Alternatively, NKT cells can be activated through recognition of self-lipids and/or pro-inflammatory cytokines generated during infection. Unlike conventional T cells, only a small subset of NKT cells traffic through the lymph nodes under homeostatic conditions, with the largest NKT cell populations localizing to the liver, lungs, spleen, and bone marrow. This is thought to be mediated by differences in chemokine receptor expression profiles. However, the impact of infection on the tissue localization and function of NKT remains largely unstudied. This review focuses on the mechanisms mediating the establishment of peripheral NKT cell populations during homeostasis and how tissue localization of NKT cells is affected during infection.

The function of the chemokine receptor CXCR6 in the T cell response of mice against Listeria monocytogenes

The chemokine receptor CXCR6 is expressed on different T cell subsets and up-regulated following T cell activation. CXCR6 has been implicated in the localization of cells to the liver due to the constitutive expression of its ligand CXCL16 on liver sinusoidal endothelial cells. Here, we analyzed the role of CXCR6 in CD8+ T cell responses to infection of mice with Listeria monocytogenes. CD8+ T cells responding to listerial antigens acquired high expression levels of CXCR6. However, deficiency of mice in CXCR6 did not impair control of the L. monocytogenes infection. CXCR6-deficient mice were able to generate listeria-specific CD4+ and CD8+ T cell responses and showed accumulation of T cells in the infected liver. In transfer assays, we detected reduced accumulation of listeria-specific CXCR6-deficient CD8+ T cells in the liver at early time points post infection. Though, CXCR6 was dispensable at later time points of the CD8+ T cell response. When transferred CD8+ T cells were followed for extended time periods, we observed a decline in CXCR6-deficient CD8+ T cells. The manifestation of this cell loss depended on the tissue analyzed. In conclusion, our results demonstrate that CXCR6 is not required for the formation of a T cell response to L. monocytogenes and for the accumulation of T cells in the infected liver but CXCR6 appears to influence long-term survival and tissue distribution of activated cells.

International Union of Basic and Clinical Pharmacology. [corrected]. LXXXIX. Update on the extended family of chemokine receptors and introducing a new nomenclature for atypical chemokine receptors

Sixteen years ago, the Nomenclature Committee of the International Union of Pharmacology approved a system for naming human seven-transmembrane (7TM) G protein-coupled chemokine receptors, the large family of leukocyte chemoattractant receptors that regulates immune system development and function, in large part by mediating leukocyte trafficking. This was announced in Pharmacological Reviews in a major overview of the first decade of research in this field [Murphy PM, Baggiolini M, Charo IF, Hébert CA, Horuk R, Matsushima K, Miller LH, Oppenheim JJ, and Power CA (2000) Pharmacol Rev 52:145-176]. Since then, several new receptors have been discovered, and major advances have been made for the others in many areas, including structural biology, signal transduction mechanisms, biology, and pharmacology. New and diverse roles have been identified in infection, immunity, inflammation, development, cancer, and other areas. The first two drugs acting at chemokine receptors have been approved by the U.S. Food and Drug Administration (FDA), maraviroc targeting CCR5 in human immunodeficiency virus (HIV)/AIDS, and plerixafor targeting CXCR4 for stem cell mobilization for transplantation in cancer, and other candidates are now undergoing pivotal clinical trials for diverse disease indications. In addition, a subfamily of atypical chemokine receptors has emerged that may signal through arrestins instead of G proteins to act as chemokine scavengers, and many microbial and invertebrate G protein-coupled chemokine receptors and soluble chemokine-binding proteins have been described. Here, we review this extended family of chemokine receptors and chemokine-binding proteins at the basic, translational, and clinical levels, including an update on drug development. We also introduce a new nomenclature for atypical chemokine receptors with the stem ACKR (atypical chemokine receptor) approved by the Nomenclature Committee of the International Union of Pharmacology and the Human Genome Nomenclature Committee.

The eye: A window to the soul of the immune system

The eye is considered as an immune privileged site, and with good reason. It has evolved a variety of molecular and cellular mechanisms that limit immune responses to preserve vision. For example, the cornea is mainly protected from autoimmunity by the lack of blood and lymphatic vessels, whereas the retina-blood barrier is maintained in an immunosuppressive state by the retinal pigment epithelium. However, there are several scenarios in which immune privilege is altered and the eye becomes susceptible to immune attack. In this review, we highlight the role of the immune system in two clinical conditions that affect the anterior and posterior segments of the eye: corneal transplantation and age-related macular degeneration. Interestingly, crosstalk between the innate and adaptive immune systems is critical in both acute and chronic inflammatory responses in the eye, with T cells playing a central role in combination with neutrophils and macrophages. In addition, we emphasize the advantage of using the eye as a model for in vivo longitudinal imaging of the immune system in action. Through this technique, it has been possible to identify functionally distinct intra-graft motility patterns of responding T cells, as well as the importance of chemokine signaling in situ for T cell activation. The detailed study of ocular autoimmunity could provide novel therapeutic strategies for blinding diseases while also providing more general information on acute versus chronic inflammation.

Role of T cell recruitment and chemokine-regulated intra-graft T cell motility patterns in corneal allograft rejection

Keratoplasty is the primary treatment to cure blindness due to corneal opacification. However, immune-mediated rejection remains the leading cause of keratoplasty failure. Here, we utilize an in vivo imaging approach to monitor, track, and characterize in real-time the recruitment of GFP-labeled allo-specific activated (Bonzo) T cells during corneal allograft rejection. We show that the recruitment of effector T cells to the site of transplantation determined the fate of corneal allografts, and that local intra-graft production of CCL5 and CXCL9/10 regulated motility patterns of effector T cells in situ, and correlated with allograft rejection. We also show that different motility patterns associate with distinct in vivo phenotypes (round, elongated, and ruffled) of graft-infiltrating effector T cells with varying proportions during progression of rejection. The ruffled phenotype was characteristic of activated effectors T cells and predominated during ongoing rejection, which associated with significantly increased T cell dynamics within the allografts. Importantly, CCR5/CXCR3 blockade decreased the motility, size, and number of infiltrating T cells and significantly prolonged allograft survival. Our findings indicate that chemokines produced locally within corneal allografts play an important role in the in situ activation and dynamic behavior of infiltrating effector T cells, and may guide targeted interventions to promote graft survival.

CXCL16 recruits bone marrow-derived fibroblast precursors in renal fibrosis

Although fibroblasts are responsible for the production and deposition of extracellular matrix in renal fibrosis, their origin is controversial. Circulating fibroblast precursors may contribute to the pathogenesis of renal fibrosis, but the signaling mechanisms underlying the recruitment of bone marrow-derived fibroblast precursors into the kidney in response to injury are incompletely understood. Here, in the unilateral ureteral obstruction model of renal fibrosis, tubular epithelial cells upregulated the chemokine CXCL16 in obstructed kidneys, and circulating fibroblast precursors expressed the CXCL16 receptor, CXCR6. Compared with wild-type mice, CXCL16-knockout mice accumulated significantly fewer bone marrow-derived fibroblast precursors in obstructed kidneys. CXCL16-knockout mice also exhibited significantly fewer CD45-, collagen I-, and CXCR6-triple-positive fibroblast precursors in injured kidneys. Furthermore, targeted deletion of CXCL16 inhibited myofibroblast activation, reduced collagen deposition, and suppressed expression of collagen I and fibronectin. In conclusion, CXCL16 contributes to the pathogenesis of renal fibrosis by recruiting bone marrow-derived fibroblast precursors.

Expression and regulation of the chemokine CXCL16 in Crohn's disease and models of intestinal inflammation

BACKGROUND

CXCL16 mediates adhesion and phagocytosis of both Gram-negative and Gram-positive bacteria and is a strong chemoattractant for CXCR6+ T cells. In this study, we determined the so far unknown expression and signal transduction of the novel CXCL16-CXCR6 chemokine-ligand receptor system in intestinal inflammation in vivo and in vitro.

METHODS

CXCL16 mRNA was measured by quantitative PCR in human colonic biopsies of patients with Crohn's disease (CD) as well as in the TNFΔARE mouse model of ileitis and in murine cytomegalovirus (MCMV)-induced colitis. CXCL16 serum levels were analyzed by ELISA. CXCL16-induced signal transduction was analyzed in intestinal epithelial cells with phospho-specific antibodies for mitogen-activated protein (MAP) kinases and Akt.

RESULTS

We found an inverse expression pattern of CXCL16 and CXCR6, with highest CXCL16 mRNA expression in the proximal murine small intestine and the highest CXCR6 mRNA expression in the distal colon. CXCL16 and CXCR6 mRNA were expressed in colorectal cancer (CRC)-derived intestinal epithelial cell (IEC) lines. CRC-expressed CXCR6 was functional, as demonstrated by CXCL16-induced MAP kinase and Akt activation. Intestinal CXCL16 expression was elevated in the TNFΔARE mouse model of ileitis and in MCMV-induced colitis (P < 0.05) and in the sera and colons of patients with CD (P < 0.05), where its expression correlated highly with CXCR6 and IL-8 levels (r = 0.85 and 0.89, respectively).

CONCLUSIONS

CRC-derived IECs express the functional CXCL16 receptor CXCR6. CXCL16 mRNA and protein expression is up-regulated in intestinal inflammation in vitro and in CD patients, suggesting an important role for this chemokine in intestinal inflammation.

Two-photon laser scanning microscopy imaging of intact spinal cord and cerebral cortex reveals requirement for CXCR6 and neuroinflammation in immune cell infiltration of cortical injury sites

The mouse spinal cord is an important site for autoimmune and injury models. Skull thinning surgery provides a minimally invasive window for microscopy of the mouse cerebral cortex, but there are no parallel methods for the spinal cord. We introduce a novel, facile and inexpensive method for two-photon laser scanning microscopy of the intact spinal cord in the mouse by taking advantage of the naturally accessible intervertebral space. These are powerful methods when combined with gene-targeted mice in which endogenous immune cells are labeled with green fluorescent protein (GFP). We first demonstrate that generation of the intervertebral window does not elicit a reaction of GFP(+) microglial cells in CX3CR1(gfp/+) mice. We next demonstrate a distinct rostrocaudal migration of GFP(+) immune cells in the spinal cord of CXCR6(gfp/+) mice during active experimental autoimmune encephalomyelitis (EAE). Interestingly, infiltration of the cerebral cortex by GFP(+) cells in these mice required three conditions: EAE induction, cortical injury and expression of CXCR6 on immune cells.

Virus entry via the alternative coreceptors CCR3 and FPRL1 differs by human immunodeficiency virus type 1 subtype

Human immunodeficiency virus type 1 (HIV-1) infects target cells by binding to CD4 and a chemokine receptor, most commonly CCR5. CXCR4 is a frequent alternative coreceptor (CoR) in subtype B and D HIV-1 infection, but the importance of many other alternative CoRs remains elusive. We have analyzed HIV-1 envelope (Env) proteins from 66 individuals infected with the major subtypes of HIV-1 to determine if virus entry into highly permissive NP-2 cell lines expressing most known alternative CoRs differed by HIV-1 subtype. We also performed linear regression analysis to determine if virus entry via the major CoR CCR5 correlated with use of any alternative CoR and if this correlation differed by subtype. Virus pseudotyped with subtype B Env showed robust entry via CCR3 that was highly correlated with CCR5 entry efficiency. By contrast, viruses pseudotyped with subtype A and C Env proteins were able to use the recently described alternative CoR FPRL1 more efficiently than CCR3, and use of FPRL1 was correlated with CCR5 entry. Subtype D Env was unable to use either CCR3 or FPRL1 efficiently, a unique pattern of alternative CoR use. These results suggest that each subtype of circulating HIV-1 may be subject to somewhat different selective pressures for Env-mediated entry into target cells and suggest that CCR3 may be used as a surrogate CoR by subtype B while FPRL1 may be used as a surrogate CoR by subtypes A and C. These data may provide insight into development of resistance to CCR5-targeted entry inhibitors and alternative entry pathways for each HIV-1 subtype.

Genotype-phenotype analysis of the CXCL16 p.Ala181Val polymorphism in inflammatory bowel disease

To identify if genetic determinants of CXCL16 modulate the susceptibility and phenotype of inflammatory bowel diseases (IBD), we analyzed genomic DNA from 574 individuals (365 IBD patients, 209 healthy controls) for the CXCL16 p.Ala181Val polymorphism. In this study, we demonstrate that in Crohn's disease (CD), the CXCL16 p.Ala181Val polymorphism is not a disease susceptibility gene but associated with younger age at disease onset (p=0.016) and higher frequency of ileal involvement (p=0.024; OR 2.17; 95% CI 1.12-4.21) in ValVal carriers compared to a higher frequency of colonic involvement in AlaAla carriers (p=0.009; OR 2.60; CI 1.29-5.25). Carriers of at least one Val allele and one CARD15/NOD2 variant had a higher incidence of a stricturing and penetrating phenotype (p=0.030, OR 4.04, CI 1.27-12.84) and of stenoses (p=0.014; OR 3.97; CI 1.38-11.40) than patients carrying NOD2 variants only, suggesting that this polymorphism contributes to a severe disease phenotype in CD.

CXCR6 is expressed on T cells in both T helper type 1 (Th1) inflammation and allergen-induced Th2 lung inflammation but is only a weak mediator of chemotaxis

Numerous chemokine receptors are increased in number on T cells in inflamed tissues. Our objective was to examine CXCR6 expression on lymphocytes during immune and inflammatory reactions and its potential for mediating T-cell recruitment. The cDNA for rat CXCR6 was cloned and monoclonal antibodies (mAbs) to CXCR6 were developed. CXCR6 was present on 4-6% of CD4 and CD8 T cells in blood, normal lymph nodes (LNs) and the spleen, primarily on memory T cells. In vitro antigen re-stimulation of LN T cells from animals with autoimmune arthritis and experimental autoimmune encephalomyelitis (EAE) increased the proportion of CXCR6(+) T cells to 35-50% and anti-T-cell receptor (TCR) activation to 60-80%. In vivo, after antigen challenge of LNs there was only a small increase in CXCR6(+) T cells on the lymphoblasts in the LNs, and a much higher percentage of T cells were CXCR6(+) in virus-induced peritoneal exudates (approximately 47%) and in allergen-induced lung inflammation (33%). Chemotaxis of CXCR6-expressing inflammatory T cells to CXCL16 was poor, but that to CXCL10 was robust. We conclude that few T cells in normal and antigen-challenged LNs are CXCR6(+), whereas a high proportion of in vitro activated T cells and T cells from inflammatory sites are CXCR6(+), but these cells migrate poorly to CXCL16. This suggests that CXCR6 may contribute to T-cell positioning and activation, rather than recruitment. CXCR6 is also expressed on T cells not only in T helper type 1 (Th1) inflammation (arthritis and EAE) but also, as shown here, in Th2 inflammation, where it is increased after allergen challenge.

Medulloblastomas Derived fromCxcr6Mutant Mice Respond to Treatment with a Smoothened Inhibitor

The sonic hedgehog (Shh) pathway is activated in approximately 30% of human medulloblastoma resulting in increased expression of downstream target genes. In about half of these cases, this has been shown to be a consequence of mutations in regulatory genes within the pathway, including Ptc1, Smo, and Sufu. However, for some tumors, no mutations have been detected in known pathway genes. This suggests that either mutations in other genes promote tumorigenesis or that epigenetic alterations increase pathway activity in these tumors. Here, we report that 3% to 4% of mice lacking either one or both functional copies of Cxcr6 develop medulloblastoma. Although CXCR6 is not known to be involved in Shh signaling, tumors derived from Cxcr6 mutant mice expressed Shh pathway target genes including Gli1, Gli2, Ptc2, and Sfrp1, indicating elevated pathway activity. Interestingly, the level of Ptc1 expression was decreased in tumor cells although two normal copies of Ptc1 were retained. This implies that reduced CXCR6 function leads to suppression of Ptc1 thereby increasing Smoothened function and promoting tumorigenesis. We used a direct transplant model to test the sensitivity of medulloblastoma arising in Cxcr6 mutant mice to a small-molecule inhibitor of Smoothened (HhAntag). We found that transplanted tumors were dramatically inhibited in mice treated for only 4 days with HhAntag. These findings suggest that HhAntag may be effective against tumors lacking mutations in known Shh pathway genes.

Genetics of resistance to HIV infection: Role of co-receptors and co-receptor ligands

Susceptibility to HIV infection and AIDS progression is variable among individuals and populations, and in part genetically determined. Genetic variants of genes encoding HIV co-receptors and their chemokine ligands have been described, and some of these variants were associated with resistance to HIV infection and/or disease progression. We review here the reported data regarding the variants of the CCR5, CCR2, CX3CR1, MIP-1alpha/CCL3, MIP-1beta/CCL4, RANTES/CCL5 and SDF-1/CXCL12 genes. The Delta32 deletion mutant of CCR5, resulting in a non-functional receptor not reaching the cell surface, is unambiguously associated with strong, although incomplete, resistance to HIV infection for homozygotes, and retarded progression for heterozygotes. Specific haplotypes encompassing the CCR5 and CCR2 loci, and the copy number of the CCL3L1 gene, have also been convincingly correlated with delayed progression. For other gene variants, involving CXCL12/SDF-1 and CX3CR1, conclusive evidence for their relevance in the frame of HIV susceptibility is still lacking.

TLR4-NOX4-AP-1 signaling mediates lipopolysaccharide-induced CXCR6 expression in human aortic smooth muscle cells

CXCL16 is a transmembrane non-ELR CXC chemokine that signals via CXCR6 to induce aortic smooth muscle cell (ASMC) proliferation. While bacterial lipopolysaccharide (LPS) has been shown to stimulate CXCL16 expression in SMC, its effects on CXCR6 are not known. Here, we demonstrate that LPS upregulates CXCR6 mRNA, protein, and surface expression in human ASMC. Inhibition of TLR4 with neutralizing antibodies or specific siRNA interference blocked LPS-mediated CXCR6 expression. LPS stimulated both AP-1 (c-Fos, c-Jun) and NF-kappaB (p50 and p65) activation, but only inhibition of AP-1 attenuated LPS-induced CXCR6 expression. Using dominant negative expression vectors and siRNA interference, we demonstrate that LPS induces AP-1 activation via MyD88, TRAF6, ERK1/2, and JNK signaling pathways. Furthermore, the flavoprotein inhibitor diphenyleniodonium chloride significantly attenuated LPS-mediated AP-1-dependent CXCR6 expression, as did inhibition of NOX4 NADPH oxidase by siRNA. Finally, CXCR6 knockdown inhibited CXCL16-induced ASMC proliferation. These results demonstrate that LPS-TLR4-NOX4-AP-1 signaling can induce CXCR6 expression in ASMC, and suggest that the CXCL16-CXCR6 axis may be an important proinflammatory pathway in the pathogenesis of atherosclerosis.

Evolution of cell recognition by viruses: a source of biological novelty with medical implications

The picture beginning to form from genome analyses of viruses, unicellular organisms, and multicellular organisms is that viruses have shared functional modules with cells. A process of coevolution has probably involved exchanges of genetic information between cells and viruses for long evolutionary periods. From this point of view present-day viruses show flexibility in receptor usage and a capacity to alter through mutation their receptor recognition specificity. It is possible that for the complex DNA viruses, due to a likely limited tolerance to generalized high mutation rates, modifications in receptor specificity will be less frequent than for RNA viruses, albeit with similar biological consequences once they occur. It is found that different receptors, or allelic forms of one receptor, may be used with different efficiency and receptor affinities are probably modified by mutation and selection. Receptor abundance and its affinity for a virus may modulate not only the efficiency of infection, but also the capacity of the virus to diffuse toward other sites of the organism. The chapter concludes that receptors may be shared by different, unrelated viruses and that one virus may use several receptors and may expand its receptor specificity in ways that, at present, are largely unpredictable.

Genetic influence of CXCR6 chemokine receptor alleles on PCP-mediated AIDS progression among African Americans

CXCR6 is a chemokine receptor and the primary coreceptor in SIV infection. A single nucleotide polymorphism 1469G-->A, results in a nonconservative change in codon 3 (CXCR6-E3K) of the N-terminus of the coreceptor. To investigate the relation between the chemokine receptor CXCR6 genotype and progression to Pneumocystis carinii pneumonia (PCP) and from PCP to death, we clinically assessed and genotyped 805 individuals from an African-American injection drug-using cohort in Baltimore, MD, USA, for this CXCR6-E3K polymorphism. The allele frequency of CXCR6-3K was high (44%) in African Americans and rare in European Americans (f<1%). Although time to AIDS and PCP was similar for all CXCR6 genotypes, the median survival time from PCP to death for the CXCR6-3E/E and CXCR6-3E/K genotype was 1.5 years compared to 3.1 years for the CXCR6-K/K genotype. Individuals homozygous or heterozygous for the CXCR6-3E allele were 5.6 times more likely to die a PCP-mediated AIDS-related death than were individuals homozygous for CXCR6-3K. This study shows an association between CXCR6 genotype and progression from PCP to death among African-Americans with HIV. We suggest that CXCR6 may play a role in late-stage HIV-1 infection and may alter the progression to death after initial infection with PCP.

Down-regulation of cell surface CXCR6 expression during T cell activation is predominantly mediated by calcineurin

CXCR6, the receptor for the membrane-anchored chemokine, CXCL16, is expressed on a subset of CCR5-bearing memory T cells, and may play a role in recruiting these cells to sites of inflammation. Here, we set out to determine the effect of T cell activation on CXCR6 expression. Highly purified human peripheral blood T cells were cultured for 7-8 days in presence of IL-2 (400 U/ml) to enhance CXCR6 expression. Overnight stimulation with anti-CD3 mAb+anti-CD28 mAb, which resulted in CD69 induction and cytokine (IL-2 and IFN-gamma) production, reduced cell surface expression of CXCR6 by 85% and that of CCR5 by 76%. The Ca(2+) ionophore, ionomycin (125-500 ng/ml), also markedly diminished CXCR6 expression (85%), but without inducing CD69 expression or cytokine production, and reduced CCR5 expression by only 40%. In contrast, the phorbol esters, PdBu or PMA had little effect on CXCR6 expression (23% reduction) but induced CD69 expression and caused a profound down-regulation (92%) of CCR5 expression. Moreover, CCR7, whose expression was low on CXCR6(+) T cells, was little affected by any of these modes of activation. The down-regulation of CXCR6 expression induced by CD3/CD28 activation was blocked by the broad kinase inhibitor, staurosporine, and by the src kinase inhibitor, PP2, but not by the MEK1 inhibitor, U0106. Most interestingly, the calcineurin inhibitor, FK506, consistently inhibited CD3/CD28-induced CXCR6 down-regulation. FK506 also blocked the decrease of CXCR6 expression caused by ionomycin, whereas staurosporine or PP2 had no effect on this decrease. Altogether, these data indicate that CXCR6 expression is down-regulated, independent of CCR5 or CD69 expression and of cytokine induction, by T cell activation signals that involve predominantly the Ca(2+)-dependent calcineurin pathway.

The leukocyte cytoskeleton in cell migration and immune interactions

Leukocyte migration is crucial during the development of the immune system and in the responses to infection, inflammation, and tumor rejection. The migratory behavior of leukocytes under physiological and pathological conditions as well as the extracellular cues and intracellular machinery that control and guide migration have been studied thoroughly. The cytoskeleton of leukocytes is extremely versatile, bearing characteristic features that enable these cells to migrate under conditions of flow through narrow spaces and onto target tissues. What makes the cytoskeleton machinery so extraordinary is not so much its molecular composition, but its flexibility which allows it to display a unique combination of responses to the extracellular medium and a rapid regulation of the architecture of its components. This review focuses on the cytoskeleton of the leukocyte. Its molecular components and the regulation of their assembly and organization are discussed. Furthermore, it highlights aspects of the regulation of the leukocyte cytoskeleton that confer flexibility to these cells in order to perform their specific tasks. Finally, different subcellular structures such as the immunological synapse, the uropod of migrating leukocytes, and the phagosome displayed by phagocytic cells are discussed in detail. The relationship of the leukocyte with its environment occurs through different kinds of receptors that interact with ligands that are soluble, fixed on the membrane of other cells, or immobilized on the extracellular matrix. The impact of receptor-ligand binding on the functional responses and the rearrangement of the cytoskeleton is also examined.

Mother-to-child transmission of HIV-1: the role of HIV-1 variability and the placental barrier

The acquired immunodeficiency syndrome (AIDS), which is caused by the human immunodeficiency virus (HIV), was first described in the United States of America in 1981 [1]. The worldwide spread of HIV has soon been recognized and AIDS has become one of the most alarming infectious diseases of our days. Its impact has been tremendous, high morbidity and mortality has caused a reversal of socioeconomic gains previously recorded in several developing countries, especially those in Sub-Saharan Africa [2]. Epidemiological data about the HIV and AIDS pandemic are updated by the Joint United Nation Programme on HIV/AIDS, UNAIDS (http://www.unaids.org). Their latest report from December 2000 states that in year 2000 approximately 5.3 million people have become newly infected with HIV, of which 2.2 were women and 600,000 children younger than 15 years of age. The estimated number of people living with HIV/AIDS globally is 36.1 million, of which 16.4 million are women and 1.4 million are children younger than 15 years of age. Approximately 25.3 million (70%) of these HIV infected people live in Sub-Saharan Africa, 5.8 million in South- and South-East Asia (15%), and 1.4 million in Latin-America (5%). During year 2000, 3 million people died of AIDS (1.3 million women and 500,000 children younger than 15 years of age). This means that an estimated total of 21.8 million persons have died of AIDS since the beginning of the epidemic, including 4.3 million children younger than 15 years of age.

HIV type 1 chemokine receptor usage in mother-to-child transmission

To investigate the role of the HIV-1 phenotype in mother-to-child HIV-1 transmission, we evaluated coreceptor usage and replication kinetics in chemokine receptor-expressing U87MG.CD4 cells of primary isolates from 32 HIV-1-infected mothers of Italian origin, none under preventive antiretroviral therapy, and from their infected infants. Five of 15 mothers of infected children and 2 of 17 mothers of uninfected children harbored viruses able to use CXCR4 as coreceptor. However, all isolates used CCR5, alone or in association with CXCR4. The replicative capacity in coreceptor-expressing cells of the viral isolates did not differ between the two groups of mothers. All mothers with an R5 virus transmitted a virus with the same coreceptor usage, whereas those four with a multitropic virus transmitted such a virus in one case. Although the presence of a mixed viral population was documented in the mothers, we did not observe transmission solely of X4 viruses. Interestingly, the only child infected with a multitropic virus carried a defective CCR5 allele. Analysis of the env V3 region of the provirus from this child revealed infection with multiple viral variants with a predominance of R5-type over X4-type sequences. These findings show that CCR5 usage of a viral isolate is not a discriminating risk factor for vertical transmission. Furthermore, X4 viruses can be transmitted to the newborn, although less frequently. In particular, we document the transmission of multiple viral variants with different coreceptor usage in a Delta32 CCR5 heterozygous child, and demonstrate that the heterozygous genotype per se does not contribute to the restriction of R5-type virus spread.

Expression cloning of the STRL33/BONZO/TYMSTRligand reveals elements of CC, CXC, and CX3C chemokines

STRL33/BONZO/TYMSTR is an orphan chemokine and HIV/SIV coreceptor receptor that is expressed on activated T lymphocytes. We describe an expression cloning strategy whereby we isolated a novel chemokine, which we name CXCL16. CXCL16 is an alpha (CXC) chemokine but also has characteristics of CC chemokines and a structure similar to fractalkine (neurotactin) in having a transmembrane region and a chemokine domain suspended by a mucin-like stalk. A recombinant version of CXCL16 fails to mediate chemotaxis to all known chemokine receptor transfectants tested but does mediate robust chemotaxis, high affinity binding, and calcium mobilization to Bonzo receptor transfectants, indicating that this is a unique receptor ligand interaction. In vitro polarized T cell subsets including Th1, Th2, and Tr1 cells express functional Bonzo, suggesting expression of this receptor in chronic inflammation, which we further verified by demonstration of CXCL16-mediated migration of tonsil-derived CD4(+) T lymphocytes. CXCL16 is expressed on the surface of APCs including subsets of CD19(+) B cells and CD14(+) monocyte/macrophages, and functional CXCL16 is also shed from macrophages. The combination of unique structural features of both Bonzo and CXCL16 suggest that this interaction may represent a new class of ligands for this receptor family. Additionally, this chemokine might play a unique dual role of attracting activated lymphocyte subsets during inflammation as well as facilitating immune responses via cell-cell contact.

HIV type 1 molecular clones able to use the Bonzo/STRL-33 coreceptor for virus entry

We describe the cloning of env genes from the mother-infant HIV-1 isolate pair P6-v3 and M6-v3. These viruses are unusual in that they can use the coreceptor Bonzo/STRL33 as well as CCR5 and, in the case of M6, CXCR4, to enter transfected cell lines in vitro. The phenotype of the parental isolates is generally reflected by the properties of the cloned env genes, when these are used in an Env-complementation assay of virus entry. Chimeric viruses were also made that contain the env genes of P6-v3 and M6-v3 inserted into the background of the infectious molecular clone, HIV-1 NL4-3. Some of the chimeric viruses derived from HIV1 P6-v3 were able to use Bonzo for entry into transfected cell lines, albeit to a lesser extent than they could use CCR5. There are some indications that one of these chimeric viruses, P6-v3-22-1, can use a coreceptor other than CCR5, perhaps Bonzo, to enter mitogen-stimulated PBMC, although only weakly. However, formal proof that this virus can use Bonzo in primary cells has not been obtained. The P6-v3-22-1 chimeric virus was unable to infect CD4-negative, placental cell lines, in the presence or absence of soluble CD4. Env sequence analysis revealed several differences among viruses with different tropisms, most notably a four amino acid deletion in the central region of the V3 loop that distinguishes the R5 virus P6-v3-25-4 from the R5, Bonzo virus P6-v3-22-1.

Lymphocyte traffic control by chemokines

In contrast to the remarkable chemokine responses of phagocytes and monocytes that were documented early on, lymphocytes have been considered for a long time to be poor targets for chemokine action. This view has changed dramatically with the discovery that peripheral blood T cells need to be activated before they can migrate in response to inflammatory chemokines. These chemokines do not act on the bulk of resting T cells that are in circulation. The identification of a new group of chemokines that selects resting, as opposed to effector, T and B cells was very exciting. These inflammation-unrelated chemokines affect transendothelial migration and localization of progenitor and mature lymphocytes in lymphoid and nonlymphoid tissues. Here, we summarize the current view of chemokine-mediated lymphocyte traffic and focus on the molecular mechanisms by which T cell responses to chemokines are modulated. Recent developments in this area justify the hypothesis that the distinct migration patterns of lymphocytes throughout their life cycle--that is, during lymphopoiesis, antigen-dependent priming, inflammation and immune surveillance--are finely tuned by changing sets of chemokines that are selective for developmentally regulated chemokine receptors. Thus, the chemokine system assures that cell traffic during inflammatory responses occurs in the proper spatial and temporal fashion and disturbance of this system, therefore, can lead to inflammatory disease.

Donor- and ligand-dependent differences in C-C chemokine receptor 5 reexpression

N-terminal modifications of the chemokine RANTES bind to C-C chemokine receptor 5 (CCR5) and block human immunodeficiency virus type 1 (HIV-1) infection with greater efficacy than native RANTES. Modified RANTES compounds induce rapid CCR5 internalization and much slower receptor reexpression than native RANTES, suggesting that receptor sequestration is one mode of anti-HIV activity. The rates of CCR5 internalization and reexpression were compared using the potent n-nonanoyl (NNY)-RANTES derivative and CD4(+) T cells derived from donors with different CCR5 gene polymorphisms. NNY-RANTES caused even more rapid receptor internalization and slower reexpression than aminooxypentane (AOP)-RANTES. Polymorphisms in the promoter and coding regions of CCR5 significantly affected the receptor reexpression rate after exposure of cells to NNY-RANTES. These observations may be relevant for understanding the protective effects of different CCR5 genotypes against HIV-1 disease progression.

Positive and negative aspects of the human immunodeficiency virus protease: development of inhibitors versus its role in AIDS pathogenesis

In this review we summarize multiple aspects of the human immunodeficiency virus (HIV) protease from both structural and functional viewpoints. After an introductory overview, we provide an up-to-date status report on protease inhibitors (PI). This proceeds from a discussion of PI structural design, to how PI are optimally utilized in highly active antiretroviral triple therapy (one PI along with two reverse transcriptase inhibitors), the emergence of PI resistance, and the natural role of secretory leukocyte PI. Then we switch to another focus: the interaction of HIV protease with other genes in acute and persistent infection, which in turn may have an effect on AIDS pathogenesis. We conclude with a discussion on future directions in HIV treatment, involving multiple-target anti-HIV therapy, vaccine development, and novel reactivation-inhibitory reagents.

A transmembrane CXC chemokine is a ligand for HIV-coreceptor Bonzo

We describe a protein with the hallmarks of a chemokine, designated CXCL16, that is made by dendritic cells (DCs) in lymphoid organ T cell zones and by cells in the splenic red pulp. CXCL16 contains a transmembrane domain and both membrane-bound and soluble forms are produced. Naïve CD8 T cells, natural killer T cells and a subset of memory CD4 T cells bind CXCL16, and activated T cells migrated chemotactically to the soluble chemokine. By expression cloning, Bonzo (also known as STRL33 and TYMSTR) was identified as a CXCL16 receptor. CXCL16 may function in promoting interactions between DCs and CD8 T cells and in guiding T cell movements in the splenic red pulp. CXCL16 was also found in the thymic medulla and in some nonlymphoid tissues, indicating roles in thymocyte development and effector T cell trafficking.

The primate lentiviral receptor Bonzo/STRL33 is coordinately regulated with CCR5 and its expression pattern is conserved between human and mouse

Chemokines play necessary and important roles in regulating the trafficking of lymphocytes to intra- or interlymphoid tissues as well as to sites of inflammation. The complex migratory patterns of lymphoid lineage cells is governed by subset-specific expression of chemokine receptors and their access to specific ligands. Several chemokine receptors and chemokine receptor-like orphan receptors also serve, in conjunction with CD4, as coreceptors for infection by human and simian immunodeficiency viruses (HIV and SIV). Here we show that the expression pattern of Bonzo/STRL33, an orphan SIV/HIV coreceptor, is highly restricted to the memory subset of T cells and is up-regulated upon stimulation of these cells with IL-2 or IL-15. Both the pattern and the regulation of Bonzo expression closely paralleled that of CC family chemokine receptors CCR5 or CCR6 and inversely correlated with CXCR4 expression. However, in striking contrast to CCR5, Bonzo expression was not down-modulated by PMA or mitogen stimulation of T cells. Targeted replacement of the Bonzo gene with a gene encoding green fluorescent protein in mice revealed that the expression and cytokine regulation of mouse Bonzo are comparable to those of its human counterpart. The similar expression and regulation patterns of Bonzo and the HIV coreceptor CCR5 may have implications for understanding the role of HIV/SIV receptors in viral evolution and pathogenesis.

Use of inhibitors to evaluate coreceptor usage by simian and simian/human immunodeficiency viruses and human immunodeficiency virus type 2 in primary cells

We have used coreceptor-targeted inhibitors to investigate which coreceptors are used by human immunodeficiency virus type 1 (HIV-1), simian immunodeficiency viruses (SIV), and human immunodeficiency virus type 2 (HIV-2) to enter peripheral blood mononuclear cells (PBMC). The inhibitors are TAK-779, which is specific for CCR5 and CCR2, aminooxypentane-RANTES, which blocks entry via CCR5 and CCR3, and AMD3100, which targets CXCR4. We found that for all the HIV-1 isolates and all but one of the HIV-2 isolates tested, the only relevant coreceptors were CCR5 and CXCR4. However, one HIV-2 isolate replicated in human PBMC even in the presence of TAK-779 and AMD3100, suggesting that it might use an undefined, alternative coreceptor that is expressed in the cells of some individuals. SIV(mac)239 and SIV(mac)251 (from macaques) were also able to use an alternative coreceptor to enter PBMC from some, but not all, human and macaque donors. The replication in human PBMC of SIV(rcm) (from a red-capped mangabey), a virus which uses CCR2 but not CCR5 for entry, was blocked by TAK-779, suggesting that CCR2 is indeed the paramount coreceptor for this virus in primary cells.

The immunodeficiency virus coreceptor, Bonzo/STRL33/TYMSTR, is expressed by macaque and human skin- and blood-derived dendritic cells

Dendritic cells (DCs) have been shown to be important in the replication of human and simian immunodeficiency viruses (HIV and SIV, respectively) in vivo and in vitro. DCs express CD4 and several chemokine receptors, such as CCR5 and CXCR4, which are important for viral entry. In vivo, DCs are abundant at body surfaces, where they might be one of the first cells that encounter naturally transmitted virus. Furthermore, DCs pulsed with HIV or SIV in vitro can efficiently transmit virus to T cells, thereby propagating vigorous viral replication. Reports have implicated Bonzo/STRL33/TYMSTR to be an additional alternative coreceptor for HIV and especially SIV infection. However, at present there are no reports regarding the expression of Bonzo/STRL33/TYMSTR by human or macaque DCs. Here we demonstrate the presence of Bonzo/STRL33/TYMSTR transcripts in rhesus macaque and human skin-derived DCs, in immature and mature blood monocyte-derived DCs, and in T cells from both skin and blood. Therefore, Bonzo/STRL33/TYMSTR is expressed in DCs and T cells that can play a role in the transmission of immunodeficiency viruses.

Simian immunodeficiency virus utilizes human and sooty mangabey but not rhesus macaque STRL33 for efficient entry

It has been established that many simian immunodeficiency virus (SIV) isolates utilize the orphan receptors GPR15 and STRL33 about as efficiently as the chemokine receptor CCR5 for entry into target cells. Most studies were performed, however, with coreceptors of human origin. We found that SIV from captive rhesus macaques (SIVmac) can utilize both human and simian CCR5 and GPR15 with comparable efficiencies. Strikingly, however, only human STRL33 (huSTRL33), not rhesus macaque STRL33 (rhSTRL33), functioned efficiently as an entry cofactor for a variety of isolates of SIVmac and SIV from sooty mangabeys. A single amino acid substitution of S30R in huSTRL33 impaired coreceptor activity, and the reverse change in rhSTRL33 greatly increased coreceptor activity. In comparison, species-specific sequence variations in N-terminal tyrosines in STRL33 had only moderate effects on SIV entry. These results show that a serine residue located just outside of the cellular membrane in the N terminus of STRL33 is critical for SIV coreceptor function. Interestingly, STRL33 derived from sooty mangabeys, a natural host of SIV, also contained a serine at the corresponding position and was used efficiently as an entry cofactor. These results suggest that STRL33 is not a relevant coreceptor in the SIV/macaque model but may play a role in SIV replication and transmission in naturally infected sooty mangabeys.