Patterns of expression, membrane localization, and effects of ectopic expression suggest a function for MS4a4B, a CD20 homolog in Th1 T cells

LMD: Cluster-Independent Multiscale Marker Identification in Single-cell RNA-seq Data

Identifying accurate cell markers in single-cell RNA-seq data is crucial for understanding cellular diversity and function. Localized Marker Detector (LMD) is a novel tool to identify "localized genes" - genes exclusively expressed in groups of highly similar cells - thereby characterizing cellular diversity in a multi-resolution and fine-grained manner. LMD constructs a cell-cell affinity graph, diffuses the gene expression value across the cell graph, and assigns a score to each gene based on its diffusion dynamics. LMD's candidate markers can be grouped into functional gene modules, which accurately reflect cell types, subtypes, and other sources of variation such as cell cycle status. We apply LMD to mouse bone marrow and hair follicle dermal condensate datasets, where LMD facilitates cross-sample comparisons, identifying shared and sample-specific gene signatures and novel cell populations without requiring batch effect correction or integration methods. Furthermore, we assessed the performance of LMD across nine single-cell RNA sequencing datasets, compared it with six other methods aimed at achieving similar objectives, and found that LMD outperforms the other methods evaluated.

Autoimmunity-associated allele of tyrosine phosphatase gene PTPN22 enhances anti-viral immunity

The 1858C>T allele of the tyrosine phosphatase PTPN22 is present in 5-10% of the North American population and is strongly associated with numerous autoimmune diseases. Although research has been done to define how this allele potentiates autoimmunity, the influence PTPN22 and its pro-autoimmune allele has in anti-viral immunity remains poorly defined. Here, we use single cell RNA-sequencing and functional studies to interrogate the impact of this pro-autoimmune allele on anti-viral immunity during Lymphocytic Choriomeningitis Virus clone 13 (LCMV-cl13) infection. Mice homozygous for this allele (PEP-619WW) clear the LCMV-cl13 virus whereas wildtype (PEP-WT) mice cannot. This is associated with enhanced anti-viral CD4 T cell responses and a more immunostimulatory CD8α- cDC phenotype. Adoptive transfer studies demonstrated that PEP-619WW enhanced anti-viral CD4 T cell function through virus-specific CD4 T cell intrinsic and extrinsic mechanisms. Taken together, our data show that the pro-autoimmune allele of Ptpn22 drives a beneficial anti-viral immune response thereby preventing what is normally a chronic virus infection.

Aberrant pro-inflammatory responses of CD20+ T cells in experimental arthritis

CD20+ T cells comprise a highly inflammatory subset implicated in autoimmunity, including rheumatoid arthritis (RA). We sought to characterize the CD20+ T cell subset in the murine collagen-induced arthritis (CIA) model of RA and investigate the phenotype and functional relevance of CD3+CD20+ T cells in the lymph nodes and arthritic joints using flow cytometry and immunohistochemistry. We demonstrate that CD3+CD4+CD20+ and CD3+CD8+CD20+ T cells are expanded in the draining lymph nodes of CIA mice, produce increased levels of pro-inflammatory cytokines and are less susceptible to regulation by regulatory T cells. Notably, CD3+CD4+CD20+ and CD3+CD8+CD20+ T cells are enriched with CXCR5+PD-1+ T follicular helper cells and CXCR5-PD-1+ peripheral T helper cells, subsets of T cells implicated in promoting B-cell responses and antibody production within pathologically inflamed non-lymphoid tissues in RA. Our findings suggest CD20+ T cells are associated with inflammatory responses and may exacerbate pathology by promoting inflammatory B-cell responses.

CD3+CD20+ T cells and their roles in human diseases

CD3⁺CD20⁺ T cells are a population of CD3⁺ T cells co-expressing CD20 that make up to ∼3-5% of the CD3⁺ T-cell compartment in the peripheral blood of human beings. In healthy individuals, CD3⁺CD20⁺ T cells are heterogeneous for containing a lower proportion of CD4⁺ cells, but produce higher levels of IL-17A and/or IFN-γ than those of CD3⁺CD20^- T cells. Recently, emerging studies have shown a pathogenic behavior of CD3⁺CD20⁺ T cells in autoimmune diseases and CD20⁺ T-cell malignancies, and patients with the diseases may benefit from anti-CD20 immunotherapy to deplete these cells. However, CD3⁺CD20⁺ T cells may also play a protective role in ovarian cancer and HIV infection for their strong propensity to IFN-γ production. In this review, we will describe the current knowledge about CD3⁺CD20⁺ T-cell biology, and discuss their functional roles in autoimmune diseases as well as cancer and infectious diseases.

EP4 Antagonism by E7046 diminishes Myeloid immunosuppression and synergizes with Treg-reducing IL-2-Diphtheria toxin fusion protein in restoring anti-tumor immunity

Reprogramming of immunosuppressive tumor microenvironment (TME) by targeting alternatively activated tumor associated macrophages (M2TAM), myeloid-derived suppressor cells (MDSC), and regulatory T cells (Tregs), represents a promising strategy for developing novel cancer immunotherapy. Prostaglandin E2 (PGE₂), an arachidonic acid pathway metabolite and mediator of chronic inflammation, has emerged as a powerful immunosuppressor in the TME through engagement with one or more of its 4 receptors (EP1-EP4). We have developed E7046, an orally bioavailable EP4-specific antagonist and show here that E7046 has specific and potent inhibitory activity on PGE₂-mediated pro-tumor myeloid cell differentiation and activation. E7046 treatment reduced the growth or even rejected established tumors in vivo in a manner dependent on both myeloid and CD8⁺ T cells. Furthermore, co-administration of E7046 and E7777, an IL-2-diphtheria toxin fusion protein that preferentially kills Tregs, synergistically disrupted the myeloid and Treg immunosuppressive networks, resulting in effective and durable anti-tumor immune responses in mouse tumor models. In the TME, E7046 and E7777 markedly increased ratios of CD8⁺granzymeB⁺ cytotoxic T cells (CTLs)/live Tregs and of M1-like/M2TAM, and converted a chronic inflammation phenotype into acute inflammation, shown by substantial induction of STAT1/IRF-1 and IFNγ-controlled genes. Notably, E7046 also showed synergistic anti-tumor activity when combined with anti-CTLA-4 antibodies, which have been reported to diminish intratumoral Tregs. Our studies thus reveal a specific myeloid cell differentiation-modifying activity by EP4 blockade and a novel combination of E7046 and E7777 as a means to synergistically mitigate both myeloid and Treg-derived immunosuppression for cancer treatment in preclinical models.

Diversity in Compartmental Dynamics of Gene Regulatory Networks: The Immune Response in Primary Influenza A Infection in Mice

Current approaches to study transcriptional profiles post influenza infection typically rely on tissue sampling from one or two sites at a few time points, such as spleen and lung in murine models. In this study, we infected female C57/BL6 mice intranasally with mouse-adapted H3N2/Hong Kong/X31 avian influenza A virus, and then analyzed the gene expression profiles in four different compartments (blood, lung, mediastinal lymph nodes, and spleen) over 11 consecutive days post infection. These data were analyzed by an advanced statistical procedure based on ordinary differential equation (ODE) modeling. Vastly different lists of significant genes were identified by the same statistical procedure in each compartment. Only 11 of them are significant in all four compartments. We classified significant genes in each compartment into co-expressed modules based on temporal expression patterns. We then performed functional enrichment analysis on these co-expression modules and identified significant pathway and functional motifs. Finally, we used an ODE based model to reconstruct gene regulatory network (GRN) for each compartment and studied their network properties.

The MS4A family: counting past 1, 2 and 3

The MS4A (membrane-spanning 4-domain family, subfamily A) family of proteins contains some well-known members including MS4A1 (CD20), MS4A2 (FcɛRIβ) and MS4A3 (HTm4). These three MS4A family members are expressed on the cell surface of specific leukocyte subsets and have been well characterized as having key roles in regulating cell activation, growth and development. However, beyond MS4A1-3 there are a large number of related molecules (18 to date in humans) where our understanding of their biological roles is at a relatively nascent stage. This review examines the larger MS4A family focusing on their structure, expression, regulation and characterized and/or emerging biological roles. Our own work on one family member MS4A8B, and its possible role in epithelial cell regulation, is also highlighted.

The CD20 homologue MS4A4 directs trafficking of KIT toward clathrin-independent endocytosis pathways and thus regulates receptor signaling and recycling

MS4A4 traffics through endocytic recycling pathways and stabilizes surface KIT expression by regulating endocytosis and recycling. Silencing MS4A4 reduces KIT recruitment to lipid raft microdomains and PLCg1 signaling while promoting AKT signaling, cell migration, and proliferation. This study is the first to describe functions for human MS4A4.

MS4A family members differentially regulate the cell cycle, and aberrant, or loss of, expression of MS4A family proteins has been observed in colon and lung cancer. However, the precise functions of MS4A family proteins and their mechanistic interactions remain unsolved. Here we report that MS4A4 facilitates trafficking of the receptor tyrosine kinase KIT through endocytic recycling rather than degradation pathways by a mechanism that involves recruitment of KIT to caveolin-1–enriched microdomains. Silencing of MS4A4 in human mast cells altered ligand-induced KIT endocytosis pathways and reduced receptor recycling to the cell surface, thus promoting KIT signaling in the endosomes while reducing that in the plasma membrane, as exemplified by Akt and PLCγ1 phosphorylation, respectively. The altered endocytic trafficking of KIT also resulted in an increase in SCF-induced mast cell proliferation and migration, which may reflect altered signaling in these cells. Our data reveal a novel function for MS4A family proteins in regulating trafficking and signaling, which could have implications in both proliferative and immunological diseases.

MS4A Cluster in Alzheimer's Disease

Several variants within membrane-spanning 4-domains subfamily A (MS4A) gene cluster have recently been implicated the association of Alzheimer's disease (AD) by serial recent genome-wide association studies (GWAS). As cell membrane proteins, MS4A family members are found to participate in the regulation of calcium signaling which have been widely discussed in neurodegeneration and AD. Besides, although the MS4A family members are poorly characterized, an important role in immunity has already been identified for several members of this cluster (such as MS4A1, MS4A2, and MS4A4B), indicating the possible involvement of MS4A gene cluster in AD pathogenesis. In this article, we briefly summarize the structure, localization, and function of MS4A gene cluster, review recent genetic and expression findings concerning the association of MS4A gene cluster with AD pathogenesis, and also speculate the possible roles of MS4A gene cluster in this disease. Based on the contributing effects of MS4A gene cluster in AD pathogenesis, targeting MS4A gene cluster might provide new opportunities for AD treatment.

Rituximab efficiently depletes increased CD20-expressing T cells in multiple sclerosis patients

In multiple sclerosis (MS), B cell-depleting therapy using monoclonal anti-CD20 Abs, including rituximab (RTX) and ocrelizumab, effectively reduces disease activity. Based on indirect evidence, it is generally believed that elimination of the Ag-presenting capabilities and Ag nonspecific immune functions of B cells underlie the therapeutic efficacy. However, a small subset of T lymphocytes (T cells) was shown to also express CD20, but controversy prevails surrounding the true existence of this T cell subpopulation. Using single-cell imaging flow cytometry and expression profiling of sorted lymphocyte subsets, we unequivocally demonstrate the existence of CD3(+)CD20(dim) T cells. We show that in MS patients, increased levels of CD3(+)CD20(dim) T cells are effectively depleted by RTX. The pathological relevance of this T cell subset in MS remains to be determined. However, given their potential proinflammatory functionality, depletion of CD20-expressing T cells may also contribute to the therapeutic effect of RTX and other mAbs targeting CD20.

Anti-MS4a4B treatment abrogates MS4a4B-mediated protection in T cells and ameliorates experimental autoimmune encephalomyelitis

Recent data show that anti-CD20 therapy is effective for some autoimmune diseases, including multiple sclerosis (MS). However, the efficacy of anti-CD20 therapy for MS is largely limited because anti-CD20 antibodies target only B cells. In previous studies, we have investigated the function of MS4a4B, a novel CD20 homologue, in T cell proliferation. Here, we found that MS4a4B regulates not only T cell proliferation but also T cell apoptosis. Knockdown of MS4a4B by MS4a4B-siRNA or MS4a4B-shRNA-expressing vector promoted apoptosis in primary T cells and T32 cell line. In contrast, vector-driven over-expression of MS4a4B reduced apoptosis in EL-4 cells. Machinery analysis showed that MS4a4B-mediated T cell survival was associated with decreased activity of caspases 3, 8 and 9. Interestingly, binding of anti-MS4a4B antibodies to T cells induced activated T cells to undergo apoptosis. To test whether anti-MS4a4B antibody interferes with MS4a4B-mediated protection of T cells, we injected anti-MS4a4B antibodies into mice with experimental autoimmune encephalomyelitis (EAE). The results show that anti-MS4a4B treatment ameliorated the severity of EAE, accompanied by decreased Th1 and Th17 cell responses and reduced levels of pro-inflammatory cytokines in the central nervous system, suggesting that MS4a4B may serve as a target of antibody-based therapy for T cell-mediated diseases.

Transcriptional heterogeneity of IgM+ cells in rainbow trout (Oncorhynchus mykiss) tissues

Two major classes of B lymphocytes have been described to date in rainbow trout: IgM⁺ and IgT⁺ cells. IgM⁺ cells are mainly localized in the spleen, peripheral blood and kidney but are also found in other tissues. However, differences among IgM⁺ cell populations attending to its location are poorly defined in fish. Thus, the aim of this work was to characterize the expression of different immune molecules such as chemokine receptors, Toll-like receptors (TLRs) and transcription factors on sorted IgM⁺ lymphocytes from different rainbow trout tissues. IgM⁺ populations from blood, spleen, kidney, gills, intestine and liver were isolated by cell sorting and the constitutive levels of transcription of these genes evaluated by real-time PCR. To further characterize B cells, we identified an MS4A sequence. In humans, the MS4A family includes several genes with immune functions, such as the B cell marker CD20 or FcRβ. Subsequently, we have also evaluated the mRNA levels of this MS4A gene in the different IgM⁺ populations. The relevant differences in transcriptional patterns observed for each of these IgM⁺ populations analyzed, point to the presence of functionally different tissue-specific B cell populations in rainbow trout. The data shown provides a pattern of genes transcribed in IgM⁺ B cells not previously revealed in teleost fish. Furthermore, the constitutive expression of all the TLR genes analyzed in IgM⁺ cells suggests an important role for these cells in innate immunity.

TCR stimulation upregulates MS4a4B expression through induction of AP-1 transcription factor during T cell activation

MS4a4B is a novel member of the membrane-spanning 4-domain family, subfamily A (MS4A) specifically expressed in mouse T cells. We have shown previously that expression of MS4a4B in T cells is upregulated upon T cell activation, suggesting that MS4a4B may play a functional role in regulation of T cell responses. However, little is known about the mechanisms that regulate MS4a4B gene expression. In this study, we explored the potential mechanism underlying TCR-stimulation-induced expression of MS4a4B by promoter analysis. We cloned 2495bp of 5'-flanking region upstream of the MS4a4B start code and inserted the DNA fragment into pGL4.20 reporter plasmid. To analyze promoter activity of the cloned DNA fragment, we transiently transfected EL4 thymoma cells and the T32 cell line with reporter plasmids. Expression of reporter gene was determined by dual-luciferase assay. Potential activator- and repressor-binding sites were analyzed by serial length of 5'-deletion. We have identified at least two potential activator binding regions and two potential repressor binding regions. The activator binding sites have been localized to two fragments, which are a 442-base pair region (region A) positioned from -1176 to -735, and a 119-base pair region (region B) positioned -188 to -70 respectively. MatInspector analysis showed that region A contains the consensus binding motif of the AP-1 family of transcription factors. Machinery analysis showed that nuclear proteins extracted from anti-CD3/anti-CD28-activated primary T cells specifically bind to the AP-1 binding element. In contrast, blockade by AP-1 inhibitor in culture decreased MS4a4B expression in T cells. Our data demonstrate that TCR-stimulation induces transactivation of AP-1 transcription factor, which subsequently binds to the MS4a4B promoter and upregulates expression of MS4a4B in activated T cells.

MS4a4B, a CD20 homologue in T cells, inhibits T cell propagation by modulation of cell cycle

MS4a4B, a CD20 homologue in T cells, is a novel member of the MS4A gene family in mice. The MS4A family includes CD20, FcεRIβ, HTm4 and at least 26 novel members that are characterized by their structural features: with four membrane-spanning domains, two extracellular domains and two cytoplasmic regions. CD20, FcεRIβ and HTm4 have been found to function in B cells, mast cells and hematopoietic cells respectively. However, little is known about the function of MS4a4B in T cell regulation. We demonstrate here that MS4a4B negatively regulates mouse T cell proliferation. MS4a4B is highly expressed in primary T cells, natural killer cells (NK) and some T cell lines. But its expression in all malignant T cells, including thymoma and T hybridoma tested, was silenced. Interestingly, its expression was regulated during T cell activation. Viral vector-driven overexpression of MS4a4B in primary T cells and EL4 thymoma cells reduced cell proliferation. In contrast, knockdown of MS4a4B accelerated T cell proliferation. Cell cycle analysis showed that MS4a4B regulated T cell proliferation by inhibiting entry of the cells into S-G2/M phase. MS4a4B-mediated inhibition of cell cycle was correlated with upregulation of Cdk inhibitory proteins and decreased levels of Cdk2 activity, subsequently leading to inhibition of cell cycle progression. Our data indicate that MS4a4B negatively regulates T cell proliferation. MS4a4B, therefore, may serve as a modulator in the negative-feedback regulatory loop of activated T cells

Hepatic gene expression profile in mice perorally infected with Echinococcus multilocularis eggs

Background

Alveolar echinococcosis (AE) is a severe chronic hepatic parasitic disease currently emerging in central and eastern Europe. Untreated AE presents a high mortality (>90%) due to a severe hepatic destruction as a result of parasitic metacestode proliferation which behaves like a malignant tumor. Despite this severe course and outcome of disease, the genetic program that regulates the host response leading to organ damage as a consequence of hepatic alveolar echinococcosis is largely unknown.

Methodology/Principal Findings

We used a mouse model of AE to assess gene expression profiles in the liver after establishment of a chronic disease status as a result of a primary peroral infection with eggs of the fox tapeworm Echinococcus multilocularis. Among 38 genes differentially regulated (false discovery rate adjusted p≤0.05), 35 genes were assigned to the functional gene ontology group <immune response>, while 3 associated with the functional group <intermediary metabolism>. Upregulated genes associated with <immune response> could be clustered into functional subgroups including <macrophages>, <APCs>, <lymphocytes, chemokines and regulation>, <B-cells> and <eosinophils>. Two downregulated genes related to <lymphocytes, chemokines and regulation> and <intermediary metabolism>, respectively. The <immune response> genes either associated with an <immunosupression> or an <immunostimulation> pathway. From the overexpressed genes, 18 genes were subsequently processed with a Custom Array microfluidic card system in order to assess respective expression status at the mRNA level relative to 5 reference genes (Gapdh, Est1, Rlp3, Mdh-1, Rpl37) selected upon a constitutive and stable expression level. The results generated by the two independent tools used for the assessment of gene expression, i.e., microarray and microfluidic card system, exhibited a high level of congruency (Spearman correlation rho = 0.81, p = 7.87e-5) and thus validated the applied methods.

Conclusions/Significance

Based on this set of biomarkers, new diagnostic targets have been made available to predict disease status and progression. These biomarkers may also offer new targets for immuno-therapeutic intervention.

Phylogenetic analysis of the MS4A and TMEM176 gene families

Background

The MS4A gene family in humans includes CD20 (MS4A1), FcRβ (MS4A2), Htm4 (MS4A3), and at least 13 other syntenic genes encoding membrane proteins, most having characteristic tetraspanning topology. Expression of MS4A genes is variable in tissues throughout the body; however, several are limited to cells in the hematopoietic system where they have known roles in immune cell functions. Genes in the small TMEM176 group share significant sequence similarity with MS4A genes and there is evidence of immune function of at least one of the encoded proteins. In this study, we examined the evolutionary history of the MS4A/TMEM176 families as well as tissue expression of the phylogenetically earliest members, in order to investigate their possible origins in immune cells.

Principal Findings

Orthologs of human MS4A genes were found only in mammals; however, MS4A gene homologs were found in most jawed vertebrates. TMEM176 genes were found only in mammals and bony fish. Several unusual MS4A genes having 2 or more tandem MS4A sequences were identified in the chicken (Gallus gallus) and early mammals (opossum, Monodelphis domestica and platypus, Ornithorhyncus anatinus). A large number of highly conserved MS4A and TMEM176 genes was found in zebrafish (Danio rerio). The most primitive organism identified to have MS4A genes was spiny dogfish (Squalus acanthus). Tissue expression of MS4A genes in S. acanthias and D. rerio showed no evidence of expression restricted to the hematopoietic system.

Conclusions/Significance

Our findings suggest that MS4A genes first appeared in cartilaginous fish with expression outside of the immune system, and have since diversified in many species into their modern forms with expression and function in both immune and nonimmune cells.

Timing and tuning of CD27-CD70 interactions: the impact of signal strength in setting the balance between adaptive responses and immunopathology

SUMMARY

After binding its natural ligand cluster of differentiation 70 (CD70), CD27, a tumor necrosis factor receptor (TNFR)-associated factor-binding member of the TNFR family, regulates cellular activity in subsets of T, B, and natural killer cells as well as hematopoietic progenitor cells. In normal immune responses, CD27 signaling appears to be limited predominantly by the restricted expression of CD70, which is only transiently expressed by cells of the immune system upon activation. Studies performed in CD27-deficient and CD70-transgenic mice have defined a non-redundant role of this receptor-ligand pair in shaping adaptive T-cell responses. Moreover, adjuvant properties of CD70 have been exploited for the design of anti-cancer vaccines. However, continuous CD27-CD70 interactions may cause immune dysregulation and immunopathology in conditions of chronic immune activation such as during persistent virus infection and autoimmune disease. We conclude that optimal tuning of CD27-CD70 interaction is crucial for the regulation of the cellular immune response. We provide a detailed comparison of costimulation through CD27 with its closely related family members 4-1BB (CD137), CD30, herpes virus entry mediator, OX40 (CD134), and glucocorticoid-induced TNFR family-related gene, and we argue that these receptors do not have a unique function per se but that rather the timing, context, and intensity of these costimulatory signals determine the functional consequence of their activity.

CD27 instructs CD4+ T cells to provide help for the memory CD8+ T cell response after protein immunization

For optimal quality, memory CD8(+) T cells require CD4(+) T cell help. We have examined whether CD4(+) T cells require CD27 to deliver this help, in a model of intranasal OVA protein immunization. CD27 deficiency reduced the capacity of CD4(+) T cells to support Ag-specific CD8(+) T cell accumulation at the tissue site after primary and secondary immunization. CD27-dependent CD4(+) T cell help for the memory CD8(+) T cell response was delivered during priming. It did not detectably affect formation of CD8(+) memory T cells, but promoted their secondary expansion. CD27 improved survival of primed CD4(+) T cells, but its contribution to the memory CD8(+) T cell response relied on altered CD4(+) T cell quality rather than quantity. CD27 induced a Th1-diagnostic gene expression profile in CD4(+) T cells, which included the membrane molecule MS4A4B. Accordingly, CD27 increased the frequency of IFN-gamma- and IL-2-producing CD4(+) T cells. It did not affect CD40L expression. Strikingly, MS4A4B was also identified as a unique marker of CD8(+) memory T cells that had received CD27-proficient CD4(+) T cell help during the primary response. This apparent imprinting effect suggests a role for MS4A4B as a downstream effector in CD27-dependent help for CD8(+) T cell memory.

Indoleamine 2,3-dioxygenase in lung dendritic cells promotes Th2 responses and allergic inflammation

Indoleamine 2,3 dioxygenase (IDO) has emerged as an important mediator of immune tolerance via inhibition of Th1 responses. However, the role of IDO in antigen-induced tolerance or allergic inflammation in the airways that is regulated by Th2 responses has not been elucidated. By using IDO(-/-) mice, we found no impairment of airway tolerance, but, surprisingly, absence of IDO provided significant relief from establishment of allergic airways disease, as evident from attenuated Th2 cytokine production, airway inflammation, mucus secretion, airway hyperresponsiveness, and serum ovalbumin-specific IgE. Myeloid dendritic cells isolated from lung-draining lymph nodes of mice immunized for either Th1 or Th2 response revealed fewer mature dendritic cells in the lymph nodes of IDO(-/-) mice. However, the net functional impact of IDO deficiency on antigen-induced responses was more remarkable in the Th2 model than in the Th1 model. Collectively, these data suggest that IDO is not required for the induction of immune tolerance in the airways but plays a role in promoting Th2-mediated allergic airway inflammation via unique effects on lung dendritic cells.

Deficient SOCS3 expression in CD4+CD25+FoxP3+ regulatory T cells and SOCS3-mediated suppression of Treg function

Naturally occurring CD4+CD25+FoxP3+ regulatory T cells (Treg) suppress T helper (Th) cell-mediated immune responses. The cytokines IL-2 and IL-6 are known to influence Treg function. However, their relative effects on Th cells versus Treg are not well understood. Stimulation with IL-2, and to a lesser extent, IL-6, enhanced Treg proliferation, FoxP3 and CTLA4 maintenance, and suppressive function. In contrast, when IL-2 or IL-6 were added to Treg/Th cell cocultures, suppression was inhibited. The molecule SOCS3 negatively regulates responses to IL-2 and IL-6. Interestingly, unlike Th cells, Treg were found to be deficient in SOCS3 protein expression. The significance of this finding lies in the need for Treg to rapidly respond to these cytokines to prevent unwarranted immune responses to self-antigens. Overexpression of SOCS3 in Treg decreased their proliferation, FoxP3 and CTLA-4 expression and suppressive function. Thus, up-regulation of SOCS3 expression may be a useful therapeutic approach in diseases where inhibition of Treg is desirable.