Infection-induced type I interferons critically modulate the homeostasis and function of CD8+ naïve T cells

Naïve T (Tn) cells require two homeostatic signals for long-term survival: tonic T cell receptor:self-peptide-MHC contact and IL-7 stimulation. However, how microbial exposure impacts Tn homeostasis is still unclear. Here we show that infections can lead to the expansion of a subpopulation of long-lived, Ly6C+ CD8+ Tn cells with accelerated effector function. Mechanistically, mono-infection with West Nile virus transiently, and polymicrobial exposure persistently, enhances Ly6C expression selectively on CD5hiCD8+ cells, which in the case of polyinfection translates into a numerical CD8+ Tn cell increase in the lymph nodes. This conversion and expansion of Ly6C+ Tn cells depends on IFN-I, which upregulates MHC class I expression and enhances tonic TCR signaling in differentiating Tn cells. Moreover, for Ly6C+CD8+ Tn cells, IFN-I-mediated signals optimize their homing to secondary sites, extend their lifespan, and enhance their effector differentiation and antibacterial function, particularly for low-affinity clones. Our results thus uncover significant regulation of Tn homeostasis and function via infection-driven IFN-I, with potential implications for immunotherapy.

CD5+MYC+ predicts worse prognosis in diffuse large B-cell lymphoma

The dual expression of CD5 and MYC protein (DECM) on B-lymphocytes may arise at a specific stage of de novo diffuse large B-cell lymphoma (DLBCL). This study retrospectively reviewed 210 patients with de novo DLBCL at the Affiliated Hospital of Jiangnan University between 2006 and 2017. DECM was significantly correlated with a worse prognosis than that in either the CD5⁺ or MYC⁺ or CD5^-MYC^- patients. Furthermore, patients with DECM showed a similar outcome to MYC⁺BCL2⁺ lymphoma patients who have extremely poor survival rates. Multivariate analysis demonstrated that DECM was a significant independent predictor for overall survival (P < .0001) and progression-free survival (P < .0001) in DLBCL. DLBCL patients with DECM showed significantly inferior clinical outcomes compared to the CD5⁺, MYC⁺ or CD5^-MYC^- patients. Combinational therapeutic modalities might be a candidate approach to improve the prognosis of these patients.

Pharmacodynamic assessment of ex-vivo canine T-lymphocyte proliferation: Responses to dexamethasone, cyclosporine, mycophenolic acid, and the active metabolite of leflunomide

A lack of understanding of specific immune defects underlying canine immune-mediated diseases hampers optimal therapy. Failure to tailor treatment to an individual's immune abnormality can result in lack of efficacy, secondary complications, added expense, and drug-potentiated adverse effects. We adopted a small-volume whole-blood flow cytometric assay to determine the effect of immunosuppressant drugs on T-lymphocyte proliferation. Using healthy dogs in this proof-of-principle study, we hypothesized that there would be dose-dependent suppression of T-lymphocyte proliferation in response to dexamethasone, cyclosporine, mycophenolic acid, and the active metabolite of leflunomide (A77 1726). Whole blood was collected from 6 healthy pet dogs and incubated for 4 d with or without the mitogens concanavalin A and lipopolysaccharide and with increasing concentrations of immunosuppressant. Samples were subsequently stained with viability dye and with antibodies against the pan-T-lymphocyte marker CD5 and the cell proliferation marker Ki67. Percentages of proliferating T-lymphocytes were determined by flow cytometry, and the 50% inhibitory concentration (IC₅₀) was calculated. Inhibition of T-lymphocyte proliferation by the panel of immunosuppressants was shown to be dose-dependent, with marked variability among the dogs. The mean IC₅₀ was 394.8 ± 871 (standard deviation) μM for dexamethasone, 18.89 ± 36.2 ng/mL for cyclosporine, 106.3 ± 157.7 nM for mycophenolic acid, and 3.746 ± 6.8 μM for A77 1726. These results support the use of this assay for detecting the efficacy of individual immunosuppressants used to diminish T-lymphocyte proliferation. In future, the assay may be applied to pet dogs with spontaneous immune-mediated disease to help tailor individual treatment.

CD5 on dendritic cells regulates CD4+ and CD8+ T cell activation and induction of immune responses

The role of CD5 as a regulator of T cell signaling and tolerance is well recognized. Recent data show expression of CD5 on different subtypes of human dendritic cells, however its functional relevance in modulating DC mediated responses remains poorly understood. In this study, we show CD5 is expressed on CD11c+ DC from murine thymus, lymph node, spleen, skin and lung. Although the development of DC subpopulations in CD5-/- mice was normal, CD5-deficient DC produced significantly higher levels of IL-12 than wild type DC in response to LPS. CD5-/- DC, in comparison to CD5+/+ DC, enhanced the activation of CD4+ and CD8+ T cells in vitro and in vivo and induced significantly higher production of IL-2 and IFN-gamma by T cells. Consequently, CD5-/- DC were significantly more potent than wild type DC in the induction of anti-tumor immunity and contact hypersensitivity responses in mice. Restoration of CD5 expression in CD5-/- DC reduced IL-12 production and inhibited their capacity to stimulate T cells. Collectively, these data demonstrate that the specific expression of CD5 on DC inhibits the production of inflammatory cytokines and has a regulatory effect on their activity to stimulate T cells and induce immune responses. This study reveals a previously unrecognized regulatory role for CD5 on DC and provides novel insights into mechanisms for DC biology in immune responses.

Antibody-mediated targeting of cleavage-specific OPN-T cell interactions

T cells are crucial players in obesity-mediated adipose tissue inflammation. We hypothesized that osteopontin (OPN), an inflammatory protein with enhanced activity when proteolytically cleaved, affects the number of viable T cells in adipose tissue and assessed inhibition of the interaction between T cells and thrombin and matrix metalloproteinases-cleaved OPN using antibodies and postimmune sera. Gene expression of T cell markers in adipose tissue from wild-type (wt) and Spp1-/- (OPN deficient) mice was analyzed after 16 weeks of high fat diet (HFD) or low fat diet (LFD) feeding. CD3, CD8 and OPN gene expression in omental adipose tissue from individuals with obesity was measured. OPN-T cell interactions were assessed with a fluorescence-based adhesion assay and blocked with antibodies targeting OPN. Comparison of T cell gene expression in adipose tissue from wt and Spp1-/- mice showed that OPN affected the number of T cells while in humans, levels of OPN correlated with T cell markers in omental adipose tissue. The interaction between T cells and cleaved OPN was blocked by postimmune sera following OPN peptide vaccinations and with monoclonal antibodies. In conclusion, levels of OPN affected the number of T cells in obesity and antibodies against cleaved OPN antagonize OPN-T cell interactions.

The ectodomains of the lymphocyte scavenger receptors CD5 and CD6 interact with tegumental antigens from Echinococcus granulosus sensu lato and protect mice against secondary cystic echinococcosis

Background

Scavenger Receptors (SRs) from the host’s innate immune system are known to bind multiple ligands to promote the removal of non-self or altered-self targets. CD5 and CD6 are two highly homologous class I SRs mainly expressed on all T cells and the B1a cell subset, and involved in the fine tuning of activation and differentiation signals delivered by the antigen-specific receptors (TCR and BCR, respectively), to which they physically associate. Additionally, CD5 and CD6 have been shown to interact with and sense the presence of conserved pathogen-associated structures from bacteria, fungi and/or viruses.

Methodology/Principal findings

We report herein the interaction of CD5 and CD6 lymphocyte surface receptors with Echinococcus granulosus sensu lato (s.l.). Binding studies show that both soluble and membrane-bound forms of CD5 and CD6 bind to intact viable protoscoleces from E. granulosus s.l. through recognition of metaperiodate-resistant tegumental components. Proteomic analyses allowed identification of thioredoxin peroxidase for CD5, and peptidyl-prolyl cis-trans isomerase (cyclophilin) and endophilin B1 (antigen P-29) for CD6, as their potential interactors. Further in vitro assays demonstrate that membrane-bound or soluble CD5 and CD6 forms differentially modulate the pro- and anti-inflammatory cytokine release induced following peritoneal cells exposure to E. granulosus s.l. tegumental components. Importantly, prophylactic infusion of soluble CD5 or CD6 significantly ameliorated the infection outcome in the mouse model of secondary cystic echinococcosis.

Conclusions/Significance

Taken together, the results expand the pathogen binding properties of CD5 and CD6 and provide novel evidence for their therapeutic potential in human cystic echinococcosis.

Scavenger Receptors (SRs) are constituents of host’s innate immune system able to sense and remove altered-self and/or pathogen components. Data on their interaction with helminth parasites is scarce. In this work, we describe that CD5 and CD6 -two lymphoid SRs previously reported to interact with conserved structures from bacteria, fungi and viruses- recognize tegumental components in the cestode parasite Echinococcus granulosus sensu lato (s.l.). Moreover, both receptors differentially modulate the cytokine release by host cells exposed to E. granulosus s.l. tegumental components. Importantly, the infusion of soluble forms of CD5 or CD6 improve infection outcomes in a murine model of secondary cystic echinococcosis. In summary, our results expand the pathogen binding properties of CD5 and CD6 and suggest their therapeutic potential against helminth infections.

T Cell Calcium Signaling Regulation by the Co-Receptor CD5

Calcium influx is critical for T cell effector function and fate. T cells are activated when T cell receptors (TCRs) engage peptides presented by antigen-presenting cells (APC), causing an increase of intracellular calcium (Ca2+) concentration. Co-receptors stabilize interactions between the TCR and its ligand, the peptide-major histocompatibility complex (pMHC), and enhance Ca2+ signaling and T cell activation. Conversely, some co-receptors can dampen Ca2+ signaling and inhibit T cell activation. Immune checkpoint therapies block inhibitory co-receptors, such as cytotoxic T-lymphocyte associated antigen 4 (CTLA-4) and programmed death 1 (PD-1), to increase T cell Ca2+ signaling and promote T cell survival. Similar to CTLA-4 and PD-1, the co-receptor CD5 has been known to act as a negative regulator of T cell activation and to alter Ca2+ signaling and T cell function. Though much is known about the role of CD5 in B cells, recent research has expanded our understanding of CD5 function in T cells. Here we review these recent findings and discuss how our improved understanding of CD5 Ca2+ signaling regulation could be useful for basic and clinical research.

Human Blood CD1c+ Dendritic Cells Encompass CD5high and CD5low Subsets That Differ Significantly in Phenotype, Gene Expression, and Functions

There are three major dendritic cell (DC) subsets in both humans and mice, that is, plasmacytoid DCs and two types of conventional DCs (cDCs), cDC1s and cDC2s. cDC2s are important for polarizing CD4+ naive T cells into different subsets, including Th1, Th2, Th17, Th22, and regulatory T cells. In mice, cDC2s can be further divided into phenotypically and functionally distinct subgroups. However, subsets of human cDC2s have not been reported. In the present study, we showed that human blood CD1c+ cDCs (cDC2s) can be further separated into two subpopulations according to their CD5 expression status. Comparative transcriptome analyses showed that the CD5high DCs expressed higher levels of cDC2-specific genes, including IFN regulatory factor 4, which is essential for the cDC2 development and its migration to lymph nodes. In contrast, CD5low DCs preferentially expressed monocyte-related genes, including the lineage-specific transcription factor MAFB. Furthermore, compared with the CD5low subpopulation, the CD5high subpopulation showed stronger migration toward CCL21 and overrepresentation among migratory DCs in lymph nodes. Additionally, the CD5high DCs induced naive T cell proliferation more potently than did the CD5low DCs. Moreover, CD5high DCs induced higher levels of IL-10-, IL-22-, and IL-4-producing T cell formation, whereas CD5low DCs induced higher levels of IFN-γ-producing T cell formation. Thus, we show that human blood CD1c+ cDC2s encompass two subsets that differ significantly in phenotype, that is, gene expression and functions. We propose that these two subsets of human cDC2s could potentially play contrasting roles in immunity or tolerance.

The Role of Regulatory B Cell-Like Malignant Cells and Treg Cells in the Mouse Model of BCL1 Tumor Dormancy

Cancer dormancy is a clinical state in which residual tumor cells persist for long periods of time but do not cause detectable disease. In the mouse B cell lymphoma model (BCL1), dormancy can be induced and maintained by immunizing mice with a soluble form of the IgM expressed on the surface of the tumor cells. Immunization induces an anti-idiotype antibody response that maintains dormancy. Mice with dormant tumor have low numbers of BCL1 cells in their spleens that divide and are killed at the same rate. When the anti-Id antibodies wane, the tumor cells grow rapidly and kill the host. Spleens from tumor-bearing mice contain both effector (CD4⁺ and CD8⁺) and regulatory T cells (T_regs). In other tumor models, it has been reported that T_regs promote tumor progression by preventing effector cells from killing the tumor. In this report, we demonstrate that the tumor site with rapidly dividing BCL1 cells has fewer T_regs than the tumor site harboring dormant BCL1 cells. In both cases, the T_regs were equally suppressive in vitro. In spleens from mice with actively growing tumor, CD8⁺ but not CD4⁺ T cells were virtually absent. In vitro analysis demonstrated a tumor-mediated elimination of CD8⁺ T cells that was contact dependent and involved the caspase-3 pathway. Most importantly, we found that the BCL1 cells expressed characteristics of B10 regulatory B cells, i.e., they were CD1d^hiCD5⁺ and secreted high levels of IL-10. These BCL1 tumor cells can inhibit anti-tumor immune responses by depleting CD8⁺ effector T cells.

Dynamic variation of CD5 surface expression levels within individual chronic lymphocytic leukemia clones

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of clonally derived mature CD5^high B cells; however, the cellular origin of CLL is still unknown. Patients with CLL also harbor variable numbers of CD5^low B cells, but the clonal relationship of these cells to the bulk disease is unknown and can have important implications for monitoring, treating, and understanding the biology of CLL. Here, we use B-cell receptors (BCRs) as molecular barcodes to first show by single-cell BCR sequencing that the great majority of CD5^low B cells in the blood of CLL patients are clonally related to CD5^high CLL B cells. We investigate whether CD5 state switching was likely to occur continuously as a common event or as a rare event in CLL by tracking somatic BCR mutations in bulk CLL B cells and using them to reconstruct the phylogenetic relationships and evolutionary history of the CLL in four patients. Using statistical methods, we show that there is no parsimonious route from a single or low number of CD5^low switch events to the CD5^high population, but rather, large-scale and/or dynamic switching between these CD5 states is the most likely explanation. The overlapping BCR repertoires between CD5^high and CD5^low cells from CLL patient peripheral blood reveal that CLL exists in a continuum of CD5 expression. The major proportion of CD5^low B cells in patients are leukemic, thus identifying CD5^low B cells as an important component of CLL, with implications for CLL pathogenesis, clinical monitoring, and the development of anti-CD5-directed therapies.

Analysis of ancestral and functionally relevant CD5 variants in systemic lupus erythematosus patients

Objective

CD5 plays a crucial role in autoimmunity and is a well-established genetic risk factor of developing RA. Recently, evidence of positive selection has been provided for the CD5 Pro224-Val471 haplotype in East Asian populations. The aim of the present work was to further analyze the functional relevance of non-synonymous CD5 polymorphisms conforming the ancestral and the newly derived haplotypes (Pro224-Ala471 and Pro224-Val471, respectively) as well as to investigate the potential role of CD5 on the development of SLE and/or SLE nephritis.

Methods

The CD5 SNPs rs2241002 (C/T; Pro224Leu) and rs2229177 (C/T; Ala471Val) were genotyped using TaqMan allelic discrimination assays in a total of 1,324 controls and 681 SLE patients of Spanish origin. In vitro analysis of CD3-mediated T cell proliferative and cytokine response profiles of healthy volunteers homozygous for the above mentioned CD5 haplotypes were also analyzed.

Results

T-cell proliferation and cytokine release were significantly increased showing a bias towards to a Th2 profile after CD3 cross-linking of peripheral mononuclear cells from healthy individuals homozygous for the ancestral Pro224-Ala471 (CC) haplotype, compared to the more recently derived Pro224-Val471 (CT). The same allelic combination was statistically associated with Lupus nephritis.

Conclusion

The ancestral Ala471 CD5 allele confers lymphocyte hyper-responsiveness to TCR/CD3 cross-linking and is associated with nephritis in SLE patients.

CD5 enhances Th17-cell differentiation by regulating IFN-γ response and RORγt localization

Mechanisms that modulate the generation of Th17 cells are incompletely understood. We report that the activation of casein kinase 2 (CK2) by CD5 is essential for the efficient generation of Th17 cells in vitro and in vivo. In our study, the CD5-CK2 signaling pathway enhanced TCR-induced activation of AKT and promoted the differentiation of Th17 cells by two independent mechanisms: inhibition of glycogen synthase kinase 3 (GSK3) and activation of mTOR. Genetic ablation of the CD5-CK2 signaling pathway attenuated TCR-induced AKT activation and consequently increased activity of GSK3 in Th17 cells. This resulted in increased sensitivity of Th17 cells to IFN-γ-mediated inhibition. In the absence of CD5-CK2 signaling, we observed decreased activity of S6K and attenuated nuclear translocation of RORγt (ROR is retinoic acid receptor related orphan receptor). These results reveal a novel and essential function of the CD5-CK2 signaling pathway and GSK3-IFN-γ axis in regulating Th-cell differentiation and provide a possible means to dampen Th17-type responses in autoimmune diseases.

Transgenic expression of soluble human CD5 enhances experimentally-induced autoimmune and anti-tumoral immune responses

CD5 is a lymphoid-specific transmembrane glycoprotein constitutively expressed on thymocytes and mature T and B1a lymphocytes. Current data support the view that CD5 is a negative regulator of antigen-specific receptor-mediated signaling in these cells, and that this would likely be achieved through interaction with CD5 ligand/s (CD5L) of still undefined nature expressed on immune or accessory cells. To determine the functional consequence of loss of CD5/CD5L interaction in vivo, a new transgenic mouse line was generated (shCD5EμTg), expressing a circulating soluble form of human CD5 (shCD5) as a decoy to impair membrane-bound CD5 function. These shCD5EμTg mice showed an enhanced response to autologous antigens, as deduced from the presentation of more severe forms of experimentally inducible autoimmune disease (collagen-induced arthritis, CIA; and experimental autoimmune encephalitis, EAE), as well as an increased anti-tumoral response in non-orthotopic cancer models (B16 melanoma). This enhancement of the immune response was in agreement with the finding of significantly reduced proportions of spleen and lymph node Treg cells (CD4+CD25+FoxP3+), and of peritoneal IL-10-producing and CD5+ B cells, as well as an increased proportion of spleen NKT cells in shCD5EμTg mice. Similar changes in lymphocyte subpopulations were observed in wild-type mice following repeated administration of exogenous recombinant shCD5 protein. These data reveal the relevant role played by CD5/CD5L interactions on the homeostasis of some functionally relevant lymphocyte subpopulations and the modulation of immune responses to autologous antigens.

Down-regulation of CD5 expression on activated CD8+ T cells in familial hemophagocytic lymphohistiocytosis with perforin gene mutations

Hemophagocytic lymphohistiocytosis (HLH) is characterized by uncontrolled activation of T cells and macrophages with overproduction of cytokines. Familial HLH type 2 (FHL2) is the most common form of primary HLH and is caused by mutations in PRF1. We have recently described a significant increase in the subpopulation of CD8(+) T cells with clonal expansion and CD5 down-regulation in Epstein-Barr virus associated-HLH, which represented a valuable tool for its diagnosis. However, this unusual phenotype of CD8(+) T cells has not been investigated fully in patients with FHL2. We performed immunophenotypic analysis of peripheral blood and measured serum pro-inflammatory cytokines in five patients with FHL2. All patients showed significantly increased subpopulations of activated CD8(+) T cells with down-regulation of CD5, which were negligible among normal controls. Analysis of T-cell receptor Vβ repertoire suggested the reactive and oligoclonal expansion of these cells. The proportion of the subset declined after successful treatment concomitant with reduction in the serum levels of cytokines in all patients except one who continued to have a high proportion of the subset and died. These findings suggest that down-regulation of CD5 on activated CD8(+) T cells may serve as a useful marker of dysregulated T cell activation and proliferation in FHL2.

Differential expression of candidate virus receptors in human T lymphocytes prone or resistant to infection with patient-derived hepatitis C virus

Accumulated evidence implies that hepatitis C virus (HCV) infects not only the liver but also the immune system. A lymphocyte-specific CD5 molecule was recently identified as essential for infection of T cells with native, patient-derived HCV. To assess whether the proposed hepatocyte receptors may also contribute to HCV lymphotropism, expression of scavenger receptor-class B type 1 (SR-B1), claudin-1 (CLDN-1), claudin-6 (CLDN-6), occludin (OCLN), CD5 and CD81 was examined by real-time RT-PCR and the respective proteins quantified by immunoblotting in HCV-prone and resistant T cell lines, peripheral blood mononuclear cells (PBMC), primary T cells and their subsets, and compared to hepatoma Huh7.5 and HepG2 cells. SR-B1 protein was found in T and hepatoma cell lines but not in PBMC or primary T lymphocytes, CLDN-1 in HCV-resistant PM1 T cell line and hepatoma cells only, while CLDN-6 equally in the cells investigated. OCLN protein occurred in HCV-susceptible Molt4 and Jurkat T cells and its traces in primary T cells, but not in PBMC. CD5 was displayed by HCV-prone T cell lines, primary T cells and PBMC, but not by non-susceptible T and hepatoma cell lines, while CD81 in all cell types except HepG2. Knocking-down OCLN in virus-prone T cell line inhibited HCV infection, while de novo infection downregulated OCLN and CD81, and upregulated CD5 without modifying SR-B1 expression. Overall, while no association between SR-B1, CLDN-1 or CLDN-6 and the susceptibility to HCV was found, CD5 and CD81 expression coincided with virus lymphotropism and that of OCLN with permissiveness of T cell lines but unlikely primary T cells. This study narrowed the range of factors potentially utilized by HCV to infect T lymphocytes amongst those uncovered using laboratory HCV and Huh7.5 cells. Together with the demonstrated role for CD5 in HCV lymphotropism, the findings indicate that virus utilizes different molecules to enter hepatocytes and lymphocytes.

T cell-positive selection uses self-ligand binding strength to optimize repertoire recognition of foreign antigens

Developing T cells express diverse antigen receptors whose specificities are not prematched to the foreign antigens they eventually encounter. Past experiments have revealed that thymocytes must productively signal in response to self antigens to mature and enter the peripheral T cell pool (positive selection), but how this process enhances effective mature T cell responses to foreign antigen is not fully understood. Here we have documented an unsuspected connection between thymic recognition events and foreign antigen-driven T cell responses. We find that the strength of self-reactivity is a clone-specific property unexpectedly directly related to the strength of T cell receptor (TCR) binding to presented foreign antigen. T cells with receptors showing stronger interaction with self dominate in responses to infections and accumulate in aging individuals, revealing that positive selection contributes to effective immunity by skewing the mature TCR repertoire toward highly effective recognition of pathogens that pose a danger to the host.

CD81 interacts with the T cell receptor to suppress signaling

CD81 (TAPA-1) is a ubiquitously expressed tetraspanin protein identified as a component of the B lymphocyte receptor (BCR) and as a receptor for the Hepatitis C Virus. In an effort to identify trans-membrane proteins that interact with the T-cell antigen receptor (TCR), we performed a membrane yeast two hybrid screen and identified CD81 as an interactor of the CD3delta subunit of the TCR. We found that in the absence of CD81, in thymocytes from knockout mice, TCR engagement resulted in stronger signals. These results were recapitulated in T cell lines that express low levels of CD81 through shRNA mediated silencing. Increased signaling did not result from alterations in the levels of TCR on the surface of T lymphocytes. Although CD81 is not essential for normal T lymphocyte development, it plays an important role in regulating TCR and possibly pre-TCR signal transduction by controlling the strength of signaling. CD81 dependent alterations in thymocyte signaling are evident in increased CD5 expression on CD81 deficient double positive (DP) thymocytes. We conclude that CD81 interacts with the T cell receptor to suppress signaling.

c-Cbl mediated ubiquitylation and regulation of cell surface exposure of CD5

Downregulation of cell surface receptors is an important process aimed at attenuation or termination of receptor signaling. c-Cbl role in the process is thought to be initial ubiquitylation of the receptors targeted for degradation and assembly of internalization complexes consisting of several other proteins. c-Cbl seems to be present during the whole process of vesicle sorting after internalization. However, there are very few receptor molecules so far like EGFR being proven to be regulated by c-Cbl. It is known that a level of CD5 on mouse c-Cbl-/- thymocytes is upregulated in comparison to wild type cells. The mechanism leading to the upregulation is unknown. We show that CD5 is ubiquitylated in Jurkat-TAg cells and in mouse thymocytes and that the ubiquitylation is c-Cbl dependent. We also show that amount of CD5 associated with lysosomal marker LAMP-1 after stimulation is significantly lower in c-Cbl-/- thymocytes. CD5 mRNA level did not differ significantly between c-Cbl-/- and wild type thymocytes. We conclude that CD5 is ubiquitylated; the ubiquitylation is mediated by c-Cbl; CD5 level on a T lymphocyte cell surface is regulated by ubiquitylation and targeting to lysosomes.

CD5 plays an inhibitory role in the suppressive function of murine CD4(+) CD25(+) T(reg) cells

A subset of CD4(+) T cells, the CD4(+) CD25(+) regulatory T (T(reg)) cells in the lymphoid organs and peripheral blood are known to possess suppressive function. Previous in vitro and in vivo studies have indicated that T cell receptor (TCR) signal is required for development of such 'natural regulatory (T(reg)) cells' and for activation of the effector function of CD4(+) CD25(+) regulatory T cells. CD5 is a cell surface molecule present on all T cells and a subtype of B lymphocytes, the B-1 cells, primarily localized to coelomic cavities, Peyer's patches, tonsils and spleen. CD5 acts as a negative regulator of T cell and B cell signaling via recruitment of SHP-1. Here, we demonstrate that T(reg) cells obtained from CD5(-/-) mice are more potent than those from wild type mice in suppressing the in vitro cell proliferation of anti-CD3 stimulated CD4(+) CD25(-) responder T cells. This phenomenon was cell contact and GITR dependent. Lack of CD5 expression on T(reg) cells (from spleen, lymph node and thymus) did not affect the intracellular levels of Foxp3. However, CD5(-/-) T(reg) thymocytes were able to elicit a higher Ca(2+) response to TCR + co-stimulatory signals than the wild type cells. CD5(-/-) mice expressed more Foxp3 mRNA in the colon than wild type mice, and additionally, the severity of the dextran sulfate sodium (DSS)-induced colitis in CD5(-/-) mice was less than the wild type strain. We suggest that manipulation of CD5 expression or the downstream signaling components of CD4(+) CD25(+) T(reg) cells as a potential strategy for therapeutic intervention in cases of auto-immune disorders.

Three-dimensional solution structure and conformational plasticity of the N-terminal scavenger receptor cysteine-rich domain of human CD5

The lymphocyte receptor CD5 influences cell activation by modifying the strength of the intracellular response initiated by antigen engagement. Regulation through CD5 involves the interaction of one or more of its three scavenger receptor cysteine-rich domains present in the extracellular region. Here, we present the 3D solution structure of a non-glycosylated double mutant of the N-terminal domain of human CD5 expressed in Escherichia coli (eCD5d1m), which has enhanced solubility compared to the non-glycosylated wild-type (eCD5d1). In common with a glycosylated form expressed in Pichia pastoris, the [(15)N,(1)H]-correlation spectra of both eCD5d1 and eCD5d1m exhibit non-uniform temperature-dependent signal intensities, indicating extensive conformational fluctuations on the micro-millisecond timescale. Although approximately one half of the signals expected for the domain are absent at 298 K, essentially complete resonance assignments and a solution structure could be obtained at 318 K. Because of the sparse nature of the experimental restraint data and the potentially important contribution of conformational exchange to the nuclear Overhauser effect peak intensity, we applied inferential structure determination to calculate the eCD5d1m structure. The inferential structure determination ensemble has similar features to that obtained by traditional simulated annealing methods, but displays superior definition and structural quality. The eCD5d1m structure is similar to other members of the scavenger receptor cysteine-rich superfamily, but the position of the lone alpha helix differs due to interactions with the unique N-terminal region of the domain. The availability of an experimentally tractable form of CD5d1, together with its 3D structure, provides new tools for further investigation of its function within intact CD5.

Optimization of a DNA vaccine against SARS

Severe acute respiratory syndrome coronavirus (SARS-CoV) first appeared in Southern China in November 2002, and then quickly spread to 33 countries on five continents along international air travel routes. Although the SARS epidemic has been contained, there is a clear need for a safe and effective vaccine should an outbreak of a SARS-CoV infection reappear in human population. In this study, we tested four DNA-vaccine constructs: (1) pLL70, containing cDNA for the SARS-CoV spike (S) gene; (2) pcDNA-SS, containing codon-optimized S gene for SARS-CoV S protein (residues 12-1255) fused with a leader sequence derived from the human CD5 gene; (3) pcDNA-St, containing the gene encoding the N-portion of the codon-optimized S gene (residues 12-532) with the CD5 leader sequence; (4) pcDNA-St-VP22C, containing the gene encoding the N-portion of the codon-optimized S protein with the CD5 leader sequence fused with the C-terminal 138 amino acids of the bovine herpesvirus-1 (BHV-1) major tegument protein VP22. Each of these plasmids was intradermally administered to C57BL/6 mice in three separate immunizations. Analysis of humoral and cellular immune responses in immunized mice demonstrated that pcDNA-SS and pcDNA-St-VP22C are the most immunogenic SARS vaccine candidates.

Natural phosphorylation of CD5 in chronic lymphocytic leukemia B cells and analysis of CD5-regulated genes in a B cell line suggest a role for CD5 in malignant phenotype

Chronic lymphocytic leukemia (CLL) results in the accumulation of B cells, presumably reflecting the selection of malignant cell precursors with Ag combined with complex alterations in protein activity. Repeated BCR stimulation of normal B cells leads to anergy and CD5 expression, both of which are features of CLL. Because CD5 is phosphorylated on tyrosine following BCR engagement and negatively regulates BCR signaling in normal B cells, we investigated its phosphorylation status and found it to be naturally phosphorylated on tyrosine but not on serine residues in CLL samples. To analyze the role of CD5, we established a B cell line in which CD5 is phosphorylated. Gene profiling of vector vs CD5-transfected B cells pointed out gene groups whose expression was enhanced: Apoptosis inhibitors (BCL2), NF-kappaB (RELB, BCL3), Wnt, TGFbeta, VEGF, MAPKs, Stats, cytokines, chemokines (IL-10, IL-10R, IL-2R, CCL-3, CCL-4, and CCR7), TLR-9, and the surface Ags CD52, CD54, CD70, and CD72. Most of these gene groups are strongly expressed in CLL B cells as compared with normal B cells. Unexpectedly, metabolic pathways, namely cholesterol synthesis and adipogenesis, are also enhanced by CD5. Conversely, CD5 inhibited genes involved in RNA splicing and processing, ribosome biogenesis, proteasome, and CD80 and CD86 Ags, whose expression is low in CLL. Comparison of CD5- vs tailless CD5-transfected cells further demonstrated the role of CD5 phosphorylation in the regulation of selected genes. These results support a model where CLL cells are chronically stimulated, leading to CD5 activation and cell survival. In addition to CD5 itself, we point to several CD5-induced genes as potential therapeutic targets.

Presenilins regulate alphabeta T cell development by modulating TCR signaling

TCRαβ signaling is crucial for the maturation of CD4 and CD8 T cells, but the role of the Notch signaling pathway in this process is poorly understood. Genes encoding Presenilin (PS) 1/2 were deleted to prevent activation of the multiple Notch receptors expressed by developing thymocytes. PS1/2 knockout thymocyte precursors inefficiently generate CD4 T cells, a phenotype that is most pronounced when thymocytes bear a single major histocompatibility complex (MHC) class II–restricted T cell receptor (TCR). Diminished T cell production correlated with evidence of impaired TCR signaling, and could be rescued by manipulations that enhance MHC recognition. Although Notch appears to directly regulate binary fate decisions in many systems, these findings suggest a model in which PS-dependent Notch signaling influences positive selection and the development of αβ T cells by modifying TCR signal transduction.

CD5-positive mucosa-associated lymphoid tissue (MALT) lymphoma of ocular adnexal origin: usefulness of fluorescence in situ hybridization for distinction between mantle cell lymphoma and MALT lymphoma

Extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue type (MALT lymphoma) usually lacks CD5 expression. Herein is described two cases of CD5-positive MALT lymphoma of ocular adnexal origin. The differential diagnosis between CD5-positive MALT lymphoma and mantle cell lymphoma (MCL), notably cyclin D1-negative MCL, was difficult because both cases consisted histologically of small to medium-sized cells with diffuse or vaguely nodular growth pattern, and the neoplastic cells were positive for CD5 and negative for cyclin D1. Somatic mutation analysis of the immunoglobulin heavy chain variable region (VH) gene in case 1 found a relatively higher mutation frequency (5.0%), which was not definitive to rule out MCL. Interphase fluorescence in situ hybridization (FISH) on paraffin-embedded section using IgH/cyclin D1 (CCND1) probe showed that in both cases there was no molecular evidence of t(11;14), finally leading to the diagnosis of CD5-positive MALT lymphoma. Although the present two patients had no recurrence over 34 months after initial diagnosis, careful observation is needed because the clinicopathological significance of MALT lymphoma with this rare phenotype remains obscure.

GATA3 controls the expression of CD5 and the T cell receptor during CD4 T cell lineage development

The transcription factor GATA3 is essential at multiple stages of T cell development, including the earliest double-negative stages, beta-selection and CD4 single-positive thymocytes. Here, we show that in CD2-GATA3 transgenic mice, with enforced GATA3 expression driven by the CD2 promoter, thymocytes have reduced levels of CD5, which is a negative regulator of TCR signaling participating in TCR repertoire fine-tuning. Reduction of CD5 expression was most prominent in CD4(+)CD8(+) double-positive (DP) cells and was associated with increased levels of the transcription factor E2A. Conversely, GATA3-deficient DP thymocytes showed consistently higher CD5 levels and defective TCR up-regulation during their development towards the CD4(lo)CD8(lo) subpopulation. CD2-GATA3 transgenic mice carrying the MHC class II-restricted TCR DO11.10 also manifested decreased CD5 levels. As in these TCR-transgenic mice reduced CD5 expression cannot result from an effect of GATA3 on repertoire selection, we conclude that enforced GATA3 interferes with the developmentally regulated increase of CD5 levels. Enforced GATA3 expression in DO11.10 transgenic mice was also accompanied by enhanced TCR expression during CD4 positive selection. Because GATA3 is induced by TCR signaling in DP thymocytes, our findings indicate that GATA3 establishes a positive feedback loop that increases TCR surface expression in developing CD4 lineage cells.

Expression, purification and crystallization of human CD5 domain III, a nano-scale crystallization example

The human lymphocyte receptor CD5, a key regulator of immune responses, is involved in the modulation of antigen specific receptor-mediated T cell activation and differentiation signals. CD5 is a membrane glycoprotein which belongs to the group B scavenger receptor cysteine-rich (SRCR) superfamily for which no structural information is available. The most conserved membrane-proximal SRCR domain of CD5 (domain III) has been expressed in HEK-EBNA-293 cells. Although the yield of the purified protein was at the level of micrograms, well diffracting crystals have been obtained. The crystals belong to a tetragonal space group P4(1)22 or P4(3)22. They contain two molecules per asymmetric unit and diffracted to 2.5A resolution using synchrotron radiation. The strategy shown here to produce, isolate and crystallize CD5 domain III can be used for other mammalian proteins difficult to produce for structural or other biophysical studies.

Intravascular large B-cell lymphoma (IVLBCL): a clinicopathologic study of 96 cases with special reference to the immunophenotypic heterogeneity of CD5

Intravascular large B-cell lymphoma (IVLBCL) is pathologically distinct with a broad clinical spectrum and immunophenotypic heterogeneity. A series of 96 patients with IVLBCL (median age, 67 years; range, 41-85 years; 50 men) was reviewed. Anemia/thrombocytopenia (84%), hepatosplenomegaly (77%), B symptoms (76%), bone marrow involvement (75%), and hemophagocytosis (61%) were frequently observed. The International Prognostic Index score was high or high-intermediate in 92%. For 62 patients receiving anthracycline-based chemotherapies, median survival was 13 months. CD5, CD10, Bcl-6, MUM1, and Bcl-2 were positive in 38%, 13%, 26%, 95%, and 91% of tumors, respectively. All 59 CD10- IVLBCL cases examined were nongerminal center B-cell type because they lacked the Bcl-6+MUM1- immunophenotype. CD5 positivity was associated with a higher prevalence of marrow/blood involvement and thrombocytopenia and a lower frequency of neurologic abnormalities among patients with CD10-IVLBCL. Compared with 97 cases of de novo CD5+CD10-diffuse LBCL, 31 cases of CD5+CD10-IVLBCL exhibited higher frequencies of poor prognostic parameters, except age. Multivariate analysis in IVLBCL revealed that a lack of anthracycline-based chemotherapies (P<.001, hazard ratio [HR]: 9.256), age older than 60 years (P=.012, HR: 2.459), and thrombocytopenia less than 100x10(9)/L (P=.012, HR: 2.427) were independently unfavorable prognostic factors; CD5 positivity was not. Beyond immunophenotypic diversity, IVLBCL constitutes a unique group with aggressive behavior.

Chronic lymphocytic leukaemia profiled for prognosis using a fluorescence in situ hybridisation panel

A panel of fluorescence in situ hybridisation (FISH) probes was used on 894 cases to target chromosome 11q, 13q, 17p deletions (del), trisomy 12 (+12) in all and 6q deletion in 59. Chronic lymphocytic leukaemia (CLL) immunophenotype (CD5 and CD19 with CD23) was found in 509 cases (average age 67.7 years, 319 males and 190 females). Among the 509 CLL cases 349 (68.6%) had FISH (4-probe panel) abnormalities: 160 del 13q [45.8% (122-del 13q, 18-biallelic del 13q, 20-monoallelic/biallelic del 13q)], 71 tri 12 (20.3%), 17 del ATM (5%), 12 del p53 (3.4%) and 89 > or = 2 FISH abnormalities (25.5%). Of 151/509 cases karyotyped, 108 were normal and 43 (43/151 = 28.5%) abnormal. Del 6q was found in 1/59 (1.6%) FISH cases and in 6/151 (4%) karyotypes. In 14 CD23 negative cases IGH/BCL1 FISH detected t(11;14) and was confirmed to be mantle cell lymphoma. Multiple probes/panels that included IGH probe were ordered for 57 CLL cases, 11 had an IGH rearrangement with an unidentified partner. This study favours the inclusion of del 6q and IGH probes in the CLL panel. The FISH panel could also serve to monitor 13q deletion for secondary changes with adverse prognosis. Understanding prognosis in specific types of 13q deletion would enhance outcome prediction.

Characterization of the human CD5 endogenous retrovirus-E in B lymphocytes

All T lymphocytes and some B lymphocytes express CD5. This coreceptor is encoded by one gene that consists of 11 exons. We have previously described a B cell-specific alternative exon 1, leading to the synthesis of a protein, devoid of leader peptide, and, therefore, retained in the cytoplasm. The novel exon 1 originates from a human endogenous retrovirus (HERV) at a time interval between the divergence of New World monkeys from Old World monkeys, and prior to the divergence of humans from Old World monkeys. Based on sequence similarity to gamma-retroviruses, it was categorized as class I: based on the specificity of its primer binding site, it was allotted to the subclass E, and based on its location within the cd5 gene, named HERV-E.CD5. Alternative transcripts were detected in lymphoid organs including fetal liver (not adult liver), more particularly in CD5-negative cell surface B-1b than in CD5-positive cell surface B-1a, and not at all in B-2 cells. By alignment of 5' long terminal repeats, HERV-E.CD5 was distinguished from similar proviruses. This could be central to the regulation of membrane expression of CD5 in human B lymphocytes, and, thereby, to the strength of the B-cell antigen receptor signaling.

An alternative exon 1 of the CD5 gene regulates CD5 expression in human B lymphocytes

T lymphocytes and a subpopulation of B lymphocytes express the CD5 coreceptor. Its functional importance is evident from the multiple levels and developmental stages of the regulation of its expression. We here report the discovery of a novel regulatory exon upstream of the noncoding region of the CD5 gene in humans. This alternate exon 1 is designated E1B (with the conventional exon 1 renamed E1A) and was shown to regulate the expression of CD5. E1B-containing transcripts existed exclusively in B lymphocytes and encoded a protein that was truncated and retained intracellularly. As a consequence, the amount of E1A-containing transcripts was down-regulated and the membrane CD5 expression was diminished in the presence of E1B-containing transcripts. High levels of E1A transcripts were found in chronic lymphocytic leukemia, and there were no E1A transcripts in 697 pre-B cells, which have no membrane CD5. Introduction of E1B into Jurkat cells reduced their membrane expression of CD5, and sequence analysis revealed that the E1B motif is a defective human endogenous retrovirus. A balance between the 2 alternative exons 1 might be central to the regulation of membrane CD5 in human B cells, and, through CD5-associated SH2-containing phosphatase 1, to the modulation of B-cell antigen receptor-transduced signals.

Polymorphism in the CD5 gene promoter in B-cell chronic lymphocytic leukemia and mantle cell lymphoma

Despite the low incidence of microsatellite instability (MSI) in lymphoid malignant neoplasms, it has been reported that the CD5 promoter MSI was relatively frequent among B-cell chronic lymphoproliferative disorders. We studied the presence of MSI in the CD5 promoter in 134 cases of B-cell chronic lymphocytic leukemia (B-CLL) and 47 of mantle cell lymphoma (MCL) by comparing the pattern of microsatellite repeats on autologous germline and tumor DNA samples. Microsatellite alterations were not observed in any case. However, the allele distribution of this polymorphism showed a higher frequency of the 18 CA allele (0.585) in MCL cases (P = .026; odds ratio [OR], 1.75; 95% confidence interval [CI], 1.07-2.87) and of the 19 CA allele (0.179) in B-CLL cases (P = .005; OR, 2.26; 95% CI, 1.27-4.01) compared with control cases (0.442 and 0.087, respectively). This suggests that although MSI seems not to be involved in the pathogenesis of these 2 lymphoid malignant neoplasms, the polymorphic CD5 promoter is associated with increased susceptibility to these disorders.

Stable expression of the extracellular domains of rabbit recombinant CD5: development and characterization of polyclonal and monoclonal antibodies

Previous studies in our laboratory suggested that there was positive selection of B cells during early development in the appendix of normal and V(H) mutant (ali/ali) rabbits. Preferential expansion and survival of B lymphocytes was affected by the Ig V(H) frameworks 1 and 3 sequences expressed on the cell surface. We demonstrated a specific interaction between rabbit CD5 and the V region of rabbit heavy chains and suggested that CD5 is a potential selecting ligand for B-cell surface immunoglobulin framework region sequences. To further investigate the role of CD5 in rabbit B-cell selection and survival we prepared recombinant constructs and obtained stable expression of the three scavenger receptor cysteine-rich (SRCR) extracellular domains of rabbit CD5. Here we describe the production and purification of this expressed recombinant CD5 protein, polyclonal antibody obtained by immunization of a goat and initial production and characterization of specific mAbs against peptides selected from each sequenced SRCR domain.

Suppression of immune system genes by methylprednisolone in exacerbations of multiple sclerosis. Preliminary results

Acute relapses of multiple sclerosis (MS) are treated with intravenous methylprednisolone (IVMP), which speeds recovery from exacerbation. It is known that IVMP suppresses the immunological activation which occurs during an acute attack of MS. However, the specific target genes affected by this therapy remain obscure. A cDNA microarray for 448 genes was used to identify the target genes in IVMP therapy. Total RNA was isolated from peripheral blood mononuclear cells derived from six MS patients immediately before and after completion of therapy. IVMP significantly reduced mRNA levels for T-cell-specific transcription factor 7 (p=0.02), T-cell-specific protein-tyrosine kinase (p=0.02), T-cell surface glycoprotein CD5 (p=0.05) and interferon-stimulated gene factor 3 gamma subunit (p=0.04). Significantly increased expression was found for eosinophil-derived neurotoxin (p=0.05). The suppression of expression of genes associated with T-cell differentiation and antigen-specific T-cell activation detected in this study may contribute to the beneficial effect of MP in relapses of MS.

Cytogenetic features of de novo CD5-positive diffuse large B-cell lymphoma: Chromosome aberrations affecting 8p21 and 11q13 constitute major subgroups with different overall survival

De novo CD5-positive diffuse large B-cell lymphoma (CD5(+)DLBCL) is regarded as a different clinicopathological entity from CD5-negative DLBCL (CD5(-)DLBCL) and mantle cell lymphoma (MCL). Because only a few published cytogenetic studies of de novo CD5(+)DLBCL are available, we investigated chromosomal changes in 23 Japanese patients who had de novo CD5(+)DLBCL. A characteristic of cytogenetic abnormalities in de novo CD5(+)DLBCL was a high incidence of chromosomal aberrations affecting 8p21 and 11q13. Major chromosomal breakpoints were concentrated at 8p21, 11q13, and 3q27. Patients with 8p21 aberrations showed aggressive clinical features, including advanced stage of disease, elevated serum LDH level, poor performance status, and an inferior survival curve compared with patients who had 11q13 changes (P = .043). Chromosomal abnormalities of both 8p21 and 11q13 were not observed in the same patient, and each abnormality showed different chromosomal gains and losses. These results indicate that de novo CD5(+)DLBCL may occur in previously unidentified subgroups that differ in their chromosomal abnormalities. The conflicting results of previous studies on prognosis may thus be explained in part by the differences in chromosomal changes.

Mechanisms of Peritoneal B-1a Cells Accumulation Induced by Murine Lupus Susceptibility LocusSle2

The abundance of B-1a cells found in the peritoneal cavity of mice is under genetic control. The lupus-prone mouse New Zealand Black and New Zealand White (NZB x NZW)F(1) and its derivative NZM2410 are among the strains with the highest numbers of peritoneal B1-a cells. We have previously identified an NZM2410 genetic locus, Sle2, which is associated with the production of large numbers of B-1a cells. In this paper, we examined the mechanisms responsible for this phenotype by comparing congenic C57BL/6 mice with or without Sle2. Fetal livers generated more B-1a cells in B6.Sle2 mice, providing them with a greater starting number of B-1a cells early in life. Sle2-expressing B1-a cells proliferated significantly more in vivo than their B6 counterparts, and reciprocal adoptive transfers showed that this phenotype is intrinsic to Sle2 peritoneal B cells. The rate of apoptosis detected was significantly lower in B6.Sle2 peritoneal cavity B-1a cells than in B6, with or without exogenous B cell receptor cross-linking. Increased proliferation and decreased apoptosis did not affect Sle2 peritoneal B-2 cells. In addition, a significant number of peritoneal cavity B-1a cells were recovered in lethally irradiated B6.Sle2 mice reconstituted with B6.Igh(a) bone marrow, showing radiation resistance in Sle2 B-1a cells or its precursors. Finally, B6.Sle2 adult bone marrow and spleen were a significant source of peritoneal B-1a cells when transferred into B6.Rag2(-/-) mice. This suggests that peritoneal B-1a cells are replenished throughout the animal life span in B6.Sle2 mice. These results show that Sle2 regulates the size of the B-1a cell compartment at multiple developmental checkpoints.

Transcriptional Regulation of Human CD5: Important Role of Ets Transcription Factors in CD5 Expression in T Cells

CD5 is a surface receptor constitutively expressed on thymocytes and mature T and B-1a cells. CD5 expression is tightly regulated during T and B cell development and activation processes. In this study we shown that the constitutive expression of CD5 on human T cells correlates with the presence of a DNase I-hypersensitive (DH) site at the 5'-flanking region of CD5. Human CD5 is a TATA-less gene for which 5'-RACE analysis shows multiple transcriptional start sites, the most frequent of which locates within an initiator sequence. Luciferase reporter assays indicate that a 282-bp region upstream of the initiation ATG displays full promoter activity in human T cells. Two conserved Ets-binding sites (at positions -239 and -185) were identified as functionally relevant to CD5 expression by site-directed mutagenesis, EMSAs, and cotransfection experiments. A possible contribution of Sp1 (-115 and -95), c-Myb (-177), and AP-1-like (-151) motifs was also detected. Further DH site analyses revealed an inducible DH site 10 kb upstream of the human CD5 gene in both T and B CD5(+) cells. Interestingly, a 140-bp sequence showing high homology with a murine inducible enhancer is found within that site. The data presented indicate that the 5'-flanking region of human CD5 is transcriptionally active in T cells, and that Ets transcription factors in conjunction with other regulatory elements are responsible for constitutive and tissue-specific CD5 expression.

Reduced expression of chemokine receptors on peripheral blood lymphocytes in patients with hepatocellular carcinoma

OBJECTIVES

Hepatocellular carcinoma (HCC) is a rapidly progressive malignancy. Chemokine receptors are important mediators of lymphocyte migration in cancer. This study evaluated expression of chemokine receptors on lymphocytes of HCC patients.

METHODS

Chemokine receptor expression on peripheral blood lymphocytes (PBL) was determined by flow cytometry and RT-PCR. Tumor infiltrating lymphocytes (TIL) and adjacent nontumor liver infiltrating lymphocytes (NIL) were also studied.

RESULTS

The expressions of CCR5, CCR6, and CXCR3 on PBL were significantly reduced in HCC patients compared with normal controls, which occurred concurrently with increased expression of the chemokine receptors in TIL and NIL. Reduced expression of CXCR3 on PBL correlated with large tumor size and advanced tumor stage. The reduced chemokine receptor expression was consistent with the reduced mRNA levels and intracellular protein levels in PBL. HCC patients exhibited lower proportions of CD4(+) and CD8(+) T cells with CCR5, CCR6, and CXCR3 expression on PBL, which occurred concurrently with the increased expression of these chemokine receptors on TIL and NIL. The reduced CCR6 and CXCR3 expression on PBL correlated with the reduced memory phenotype in circulation and increased memory phenotype in liver. Furthermore, CCR5-expressing memory T cells were increased in liver compartment compared with circulation.

CONCLUSION

This study demonstrated that reduced chemokine receptor expression on PBL was concurrent with increased chemokine receptor expression on both TIL and NIL in HCC. The results demonstrated the role of chemokine receptors in recruitment of lymphocytes from peripheral blood to HCC. The findings have important implications in understanding of immunopathogenesis of HCC.

The E47 transcription factor negatively regulates CD5 expression during thymocyte development

The expression of CD5 increases progressively as thymocytes mature. We have shown that CD5 expression is controlled by a tissue-specific regulatory promoter located upstream of the CD5 translation start sites. Deletion of this regulatory promoter, which contains three potential transcription factor binding sites (CCAAT, kappa E2, and ets) reduces the promoter activity to basal level. Of these sites, only ets proved essential for CD5 expression in T cell lines. Here, we introduce a role for the E47 transcription factor and the CD5 promoter kappa E2 site in regulating CD5 expression during thymocyte development. Using T cell lines, we show that (i) mutation of the kappa E2 site in the CD5 regulatory promoter results in a significant elevation of CD5 promoter activity; (ii) the E47 transcription factor binds to the kappa E2 site; and (iii) overexpression of E47 inhibits CD5 expression. We then show, in high-dimensional fluorescence-activated cell sorting studies with primary thymocytes at successive developmental stages, that (i) intracellular E47 levels decrease as surface CD5 expression increases; (ii) E47 expression is down-regulated and CD5 expression is correspondingly up-regulated in DN3 thymocytes in RAG-2-deficient mice injected with anti-CD3 to mimic pre-T cell receptor stimulation; and (iii) E47 expression is down-regulated and CD5 expression is up-regulated when double positive thymocytes are stimulated in vitro with anti-CD3. Based on these data, we propose that E47 negatively regulates CD5 expression by interacting with the kappa E2 site in the CD5 regulatory promoter and that decreases in E47 in response to developmental signals are critical to the progressive increase in CD5 expression as thymocytes mature.

Analysis of chromosomal imbalances in de novo CD5-positive diffuse large-B-cell lymphoma detected by comparative genomic hybridization

We recently demonstrated that the prognosis for de novo CD5-positive (CD5+) diffuse large-B-cell lymphoma (DLBCL) is markedly worse than that for CD5-negative (CD5-) DLBCL. Our findings also suggested that on the basis of its clinical features CD5+ DLBCL may constitute a unique disease category. However, the genetic basis for these two categories has not been established. Therefore, we performed comparative genomic hybridization analysis (CGH) of 26 cases of CD5+ DLBCL and 44 cases of CD5- DLBCL. Several identical changes in CD5+ and CD5- DLBCLs were found, such as gains of 3q, 9p, 12q, 13q, and 18q and losses of 1p, 6q, 17p, and 19p. However, distinct differences between the two categories were also detected. These included gains of 11q21-q24 (P=0.032) and 16p (P=0.005) in CD5+ DLBCL, and loss of 16p (P=0.028) in CD5- DLBCL. A comparison with results reported for mantle cell lymphoma, chronic lymphocytic leukemia, and Richter's syndrome demonstrated that the CGH pattern of CD5+ DLBCL was markedly different. This indicates that CD5+ DLBCL constitutes a disease category distinct from that of CD5- DLBCL and other CD5+ malignancies.

B Cell receptor directs the activation of NFAT and NF-κB via distinct molecular mechanisms

BCR engagement initiates intracellular calcium ([Ca2+]i) mobilization which is critical for the activation of multiple transcription factors including NF-kappaB and NFAT. Previously, we showed that Bruton's tyrosine kinase (BTK)-deficient (btk-/-) B cells, which display a modestly reduced calcium response to BCR crosslinking, do not activate NF-kappaB. Here we show that BTK is also essential for the activation of NFAT following BCR engagement. Pharmacological mobilization of [Ca2+]i in BTK-deficient DT40 B cells (DT40.BTK) does not rescue BCR directed activation of NF-kappaB and only partially that of NFAT, suggesting existence of additional BTK-signaling pathways in this process. Therefore, we investigated a requirement for BTK in the production of diacylglycerol (DAG). We found that DT40.BTK B cells do not produce DAG in response to BCR engagement. Pharmacological inhibition of PKC isozymes and Ras revealed that the BCR-induced activation of NF-kappaB requires conventional PKCbeta, whereas that of NFAT may involve non-conventional PKCdelta and Ras pathways. Consistent with an essential role for BTK in the regulation of NFAT, B cells from btk-/- mice display defective expression of CD5, a gene under the control of NFAT. Together, these results suggest that BCR employs distinct BTK-dependent molecular mechanisms to regulate the activation of NF-kappaB versus NFAT.

CD5, an important regulator of lymphocyte selection and immune tolerance

The CD5 coreceptor is a cysteine-rich scavenger receptor family glycoprotein that is expressed constitutively on all T cells and a subset of B cells (B I a B cells). It is now generally accepted that the biologic role of CD5 is to regulate intracellular strength induced by antigen receptors in both T and B cells. However, at present it is unclear if this coreceptor's effect on antigen receptor signaling is primarily costimulatory or inhibitory since support for both exists. Our studies focus on understanding the physiologic role of CD5 in the context of regulation of antigen receptor activation, B and T cell selection, and generation/maintenance of immune tolerance. In this overview, I discuss studies using experimental models of lymphocyte selection and tolerance showing that CD5 plays a key role in B and T cell selection as well as generation and maintenance of tolerance. I and others, reviewed here, now provide clear evidence that CD5 is a key regulator of immune tolerance and that alterations of its activity can promote development of autoreactivity.

Involvement of avidity for major histocompatibility complex in homeostasis of naive and memory T cells

The requirements for survival and self-renewal of peripheral T cells and the nature of mechanisms controlling the size of the naive and memory pool are not completely understood. Here, we examine the involvement of the major histocompatibility complex (MHC) in survival and homeostatic expansion of naive and memory T cells. We show that the homeostatic behavior of naive T cell receptor (TCR)-transgenic T cells can be deduced by the expression levels of TCR and CD5, a negative regulator of TCR signaling. Both these factors determine the strength of TCR stimulation by MHC-derived signals. We further show that, similarly to naive T cells, MHC-derived signals influence the homeostatic expansion capacity of memory T cells under lymphopenic conditions. In contrast to naive T cells, however, memory T cells can reach a homeostatic equilibrium, in which survival/self-renewal of each clone is dissociated from their avidity for MHC-derived signals.

Microarray reveals differences in both tumors and vascular specific gene expression in de novo CD5+ and CD5- diffuse large B-cell lymphomas

Malignant lymphoma is a heterogeneous disease with different clinical features. Among diffuse large B-cell lymphomas (DLBCLs), a unique subtype has been identified recently based on cell surface marker CD5 and clinicopathological features. These de novo CD5(+) DLBCLs account for approximately 10% of all of the DLBCLs and have poorer prognosis. To additionally understand this subtype of DLBCLs at the molecular level and to find genes that are differentially expressed in de novo CD5(+) DLBCLs, CD5(-) DLBCLs, and mantle cell lymphomas, which also have poor prognosis, we performed gene expression profiling using cDNA microarray technology. Data from a total of 9 samples of CD5(-) DLBCLs, 11 samples of de novo CD5(+) DLBCLs, and 10 samples of mantle cell lymphomas were acquired. A series of genes were identified that distinguish these three types of lymphomas. Among DLBCL cases, integrin beta1 and/or CD36 adhesion molecules were overexpressed in most cases of CD5(+) DLBCL. An immunohistochemical confirmation study revealed that integrin beta1 was expressed on lymphoma cells, which may account for the high extranodal involvement and poor prognosis of CD5(+) DLBCLs. In contrast, CD36 was overexpressed on vascular endothelia in CD5(+) DLBCLs, although there was no difference in vascularity detected by von Wilbrand factor antibody between CD5(+) and CD5(-) DLBCLs. Those results suggest that CD5(+) and CD5(-) DLBCLs have different gene expression signatures in both tumor cells and their vascular systems.

Two phenotypically distinct subsets of spleen dendritic cells in rats exhibit different cytokine production and T cell stimulatory activity

We recently reported that splenic dendritic cells (DC) in rats can be separated into CD4(+) and CD4(-) subsets and that the CD4(-) subset exhibited a natural cytotoxic activity in vitro against tumor cells. Moreover, a recent report suggests that CD4(-) DC could have tolerogenic properties in vivo. In this study, we have analyzed the phenotype and in vitro T cell stimulatory activity of freshly isolated splenic DC subsets. Unlike the CD4(-) subset, CD4(+) splenic DC expressed CD5, CD90, and signal regulatory protein alpha molecules. Both fresh CD4(-) and CD4(+) DC displayed an immature phenotype, although CD4(+) cells constitutively expressed moderate levels of CD80. The half-life of the CD4(-), but not CD4(+) DC in vitro was extremely short but cells could be rescued from death by CD40 ligand, IL-3, or GM-CSF. The CD4(-) DC produced large amounts of the proinflammatory cytokines IL-12 and TNF-alpha and induced Th1 responses in allogeneic CD4(+) T cells, whereas the CD4(+) DC produced low amounts of IL-12 and no TNF-alpha, but induced Th1 and Th2 responses. As compared with the CD4(+) DC that strongly stimulated the proliferation of purified CD8(+) T cells, the CD4(-) DC exhibited a poor CD8(+) T cell stimulatory capacity that was substantially increased by CD40 stimulation. Therefore, as previously shown in mice and humans, we have identified the existence of a high IL-12-producing DC subset in the rat that induces Th1 responses. The fact that both the CD4(+) and CD4(-) DC subsets produced low amounts of IFN-alpha upon viral infection suggests that they are not related to plasmacytoid DC.

CD5- mantle cell lymphoma

Mantle cell lymphoma (MCL) typically expresses B-cell antigens and CD5 and overexpresses bcl-1 protein. However, unusual cases of bcl-1+ and CD5-MCL have been observed, posing a practical challenge for correct diagnosis and management. We identified 25 cases (48 samples) of bcl-1+ and CD5- lymphoma. CD5 expression was assessed by flow cytometric analysis alone (1 case), immunohistochemical analysis alone (17 cases), or dual flow cytometric/immunohistochemical methods (7 cases). The morphologic features were consistent with MCL with centrocytic cytomorphology in 20 cases and blastic variant in 5 cases. The t(11;14) was confirmed in 8 of 11 cases by fluorescence in situ hybridization of paraffin-embedded tissue. Cytogenetic analysis revealed the t(11;14) within a complex karyotype in 2 additional cases. These data show that MCL may lack CD5 expression. Evaluation of bcl-1 expression by immunohistochemical analysis or molecular genetics may be indicated if MCL is suspected clinically or morphologically despite a lack of CD5 expression.

Origins and functions of B-1 cells with notes on the role of CD5

Whether B-1a (CD5+) cells are a distinct lineage derived from committed fetal/neonatal precursors or arise from follicular B-2 cells in response to BCR ligation and other, unknown signals remains controversial. Recent evidence indicates that B-1a cells can derive from adult precursors expressing an appropriate specificity when the (self-) antigen is present. Antibody specificity determines whether a B cell expressing immunoglobulin transgenes has a B-2, B-1a or marginal zone (MZ) phenotype. MZ cells share many phenotypic characteristics of B-1 cells and, like them, appear to develop in response to T independent type 2 antigens. Because fetal-derived B cell progenitors fail to express terminal deoxynucleotidyl transferase (TdT) and for other reasons, they are likely to express a repertoire that allows selection into the B-1a population. As it is selected by self-antigen, the B-1 repertoire tends to be autoreactive. This potentially dangerous repertoire is also useful, as B-1 cells are essential for resistance to several pathogens and they play an important role in mucosal immunity. The CD5 molecule can function as a negative regulator of BCR signaling that may help prevent inappropriate activation of autoreactive B-1a cells.

CD2 physically associates with CD5 in rat T lymphocytes with the involvement of both extracellular and intracellular domains

T lymphocytes can be activated and induced to proliferate through stimulation of the CD2 glycoprotein with functional combinations of CD2 antibodies. However, this mechanism of signal transduction via CD2 is still not fully understood. We have investigated which molecules on the T cell surface preferentially associate in Cis with CD2 and may regulate its signaling properties. Though a quantification method we found that CD5 represents the antigen capable of co-precipitating a larger proportion of CD2. Using co-capping assays and immunoprecipitations from cell lysates, we show that an association between CD2 and CD5 can be found in rat thymocytes, T lymphocytes and in a thymoma cell line. Possibly, this interaction is a direct one, since CD2 and CD5 transiently expressed in Cos7 cells co-precipitate each other. Furthermore, using CD2 chimeric proteins containing different domains of CD2, expressed in Cos7 cells as well as in stably transfected Jurkat cells, we show that the interaction between CD2 and CD5 is held at both the intra- and extracellular levels, but does not involve the transmembrane domain. The fact that both the extracellular and the cytoplasmic domains of CD2 interact with CD5 suggests a specific and tight association between the two molecules, possibly relevant for the fine-tuning of signal transduction in T lymphocytes.