Evidence of CD4 + regulatory T cells in the non-obese diabetic male mouse

Summary The NOD mouse, which shows many features of human IDDM, is extensively used to evaluate the role of T lymphocytes in the pathogenesis of autoimmune diabetes. The development of diabetes in this model appears to be controlled by a finely tuned immunoregulatory balance between autoaggressive T cells and regulatory immune phenomena, the disruption of which may result in destruction of insulin-secreting cells. The absolute requirement of sublethal irradiation to permit transfer of the disease to non-diabetic adult syngeneic mice provides indirect evidence for the presence of regulatory T cells in non-diabetic NOD mice. We have previously reported that the reconstitution of irradiated recipients by CD4 + T cells from nondiabetic female NOD mice blocks the transfer of diabetes by spleen cells from diabetic donors. We now report evidence that anti-CD4 monoclonal antibodies can substitute for irradiation in rendering adult NOD male mice susceptible to diabetes transfer by diabetogenic spleen cells. Efficient diabetes transfer can be achieved in non-irradiated adult NOD recipients provided they are thymectomized and CD4 + T-cell depleted prior to the transfer. The role of thymectomy is to limit T cell regeneration after anti-T cell monoclonal antibody challenge. Our data confirm that regulatory CD4 + T-cells, which efficiently counterbalance diabetogenic cells, are present in adult NOD male animals.Abbreviations FITC fluorescein isothiocynate - HBSS Hank's balanced salt solution - IDDM insulin-dependent diabetes mellitus - IL interleukin - NOD non-obese diabetic - TH T helper     

Regulation of CD8+ regulatory T cells: Interruption of the NKG2A–Qa-1 interaction allows robust suppressive activity and resolution of autoimmune disease

Regulation of autoreactive CD4 T cells is essential to maintain self-tolerance and prevent autoimmune disease. Although CD8 T regulatory (Treg) cells that recognize self-peptides restricted by Qa-1 (HLA-E in humans) inhibit autoreactive CD4 cells and attenuate experimental autoimmune encephalomyelitis (EAE), the mechanism of this interaction is unclear. We generated Qa-1 mutant knock-in mice that impair Qa-1 binding to the T cell receptor (TCR) and CD94/NKG2A receptors. Analysis of these mice showed that TCR-dependent recognition of Qa-1–peptide complexes on target CD4 cells is essential for suppression by CD8 Treg cells. Further analysis revealed that genetic disruption of the Qa-1–CD94/NKG2A interaction unleashes robust CD8 Treg cell activity that completely abolishes development of EAE.     

Immunosuppression by CD4+ regulatory T cells induced by chronic retroviral infection

Normal levels of CD4(+) regulatory T cells are critical for the maintenance of immunological homeostasis and the prevention of autoimmune diseases. However, we now show that the expansion of CD4(+) regulatory T cells in response to a chronic viral infection can lead to immunosuppression. Mice persistently infected with Friend retrovirus develop approximately twice the normal percentage of splenic CD4(+) regulatory T cells and lose their ability to reject certain tumor transplants. The role of CD4(+) regulatory T cells was demonstrated by the transmission of immunosuppression to uninfected mice by adoptive transfers of CD4(+) T cells. CD4(+) T cells from chronically infected mice were also immunosuppressive in vitro, inhibiting the generation of cytolytic T lymphocytes in mixed lymphocyte cultures. Inhibition occurred at the level of blast-cell formation through a mechanism or mechanisms involving transforming growth factor-beta and the cell surface molecule CTLA-4 (CD152). These results suggest a possible explanation for HIV- and human T cell leukemia virus-I-induced immunosuppression in the absence of T cell depletion.     

CD4+ T cell mediated intestinal immunity: chronic inflammation versus immune regulation

BACKGROUND: Several studies have suggested that chronic inflammatory bowel disease may be a consequence of antigen specific recognition by appropriate T cells which expand and induce immunopathology. AIMS: We wished to investigate whether autoreactive CD4+ T cells can initiate the disease on recognition of enterocyte specific antigens directly and if induction of mucosal tolerance occurs. METHODS: Transgenic mice (VILLIN-HA) were generated that showed specific expression of haemagglutinin from influenza virus A exclusively in enterocytes of the intestinal epithelium. To investigate the impact of enterocyte specific haemagglutinin expression in an autoimmune environment, we mated VILLIN-HA mice with T cell receptor (TCR)-HA mice expressing an alpha/beta-TCR, which recognises an MHC class II restricted epitope of haemagglutinin, and analysed the HA specific T cells for induction of autoimmunity or tolerance. RESULTS: In VILLIN-HAxTCR-HA mice, incomplete central deletion of HA specific lymphocytes occurred. Peripheral HA specific lymphocytes showed an activated phenotype and increased infiltration into the intestinal mucosa, but not into other organs of double transgenic mice. Enterocyte specific lamina propria lymphocytes showed a dose dependent proliferative response on antigen stimulation whereas the proliferative capacity of intraepithelial lymphocytes was reduced. Mucosal lymphocytes from VILLIN-HAxTCR-HA mice secreted lower amounts of interferon gamma and interleukin (IL)-2 but higher levels of tumour necrosis factor alpha, monocyte chemoattractant protein 1, and IL-6. Mucosal immune reactions were accompanied by broad changes in the gene expression profile with expression of proinflammatory genes, but strikingly also a remarkable set of genes discussed in the context of peripheral induction of regulatory T cells, including IL-10, Nrp-1, and Foxp3. CONCLUSIONS: Enterocyte specific antigen expression is sufficient to trigger a specific CD4+ T cell response leading to mucosal infiltration. In our model, progression to overt clinical disease was counteracted most likely by induction of regulatory T cells.     

Diversity of regulatory CD4+T cells controlling distinct organ-specific autoimmune diseases

Depletion of selected regulatory CD4+ T cell subsets induces the spontaneous onset of various immune or autoimmune disorders. It is not clear, however, whether a given subset, notably CD4+CD25+ regulatory T cells, protects from a wide spectrum of immune disorders, or whether specialized subsets of regulatory T cells control each given disease or group of diseases. We report here, using diabetes prone nonobese diabetic (NOD) mice, that depending on the regulatory T cells that are depleted, i.e., CD25+, CD62L+, or CD45RB(low), distinct immune diseases appear after transfer into NOD severe combined immunodeficiency (SCID) recipients. Thus, reconstitution of NOD SCID mice with CD25- T cells induces major gastritis and late-onset diabetes, but no or mild colitis. Reconstitution with CD62L- T cells induces fulminant diabetes with no colitis or gastritis. Reconstitution with CD45RB(high) T cells induces major colitis with wasting disease and no or very moderate gastritis and diabetes. Major differences among the three regulatory T cell subsets are also seen in vitro. The bulk of suppressor cells inhibiting the proliferation of CD4+CD25- T cells in coculture is concentrated within the CD25+ but not the CD62L+ or CD45RB(low) T cell subsets. Similarly, cytokine production patterns are significantly different for each regulatory T cell subset. Collectively, these data point to the diversity and organ selectivity of regulatory T cells controlling distinct autoimmune diseases whatever the underlying mechanisms.     

Murine models for systemic lupus erythematosus and Sj?gren's syndrome.

Of the types of defects that have been observed in autoimmune mice, two are common to most strains and appear to be of critical importance in the development of autoimmune disease. The first of these is a deficiency in the maintenance of self-tolerance by B or T lymphocytes. This is an intrinsic defect due to genetic abnormalities that presumably affect an early developmental signaling mechanism. The disruption of early B- and T-cell development leads to the appearance of lymphocytes that are predisposed to loss of tolerance. In certain strains of autoimmune mice, it also leads to overproduction of Ly1+ (CD5+) B cells or CD4-CD8-B220+ T cells, which apparently do not contribute to autoimmunity. The second type of defect is a strain-specific, antigen-driven autoimmune disease syndrome. This defect is limited by the affinities of the available T-cell receptor and immunoglobulin variable regions and the efficiency of antigen presentation. Current evidence suggests that the major histocompatibility complex molecules play the most important role in determining which autoantigens lead to a pathogenic antigen-driven immune response. For example, the type and magnitude of the autoimmune response may be directed by the production of specific cytokines. The type of antigen and the context of its presentation can bias the production of cytokines that favor the production of the Th2 subset of CD4+ T helper cells. These cells secrete predominantly interleukin-4, interleukin-5, and interleukin-10, and may contribute to a chronic response and autoimmune disease.     

Regulatory T cells in human autoimmune thyroid disease

CONTEXT: T regulatory cells have a key role in the pathogenesis of autoimmune diseases in different animal models. However, less information is available regarding these cells in human autoimmune thyroid diseases (AITD). OBJECTIVE: The objective of the study was to analyze different regulatory T cell subsets in patients with AITD. DESIGN: We studied by flow cytometry and immunohistochemistry different T regulatory cell subsets in peripheral blood mononuclear cells (PBMCs) and thyroid cell infiltrates from 20 patients with AITD. In addition, the function of T(REG) lymphocytes was assessed by cell proliferation assays. Finally, TGF-beta mRNA in thyroid tissue and its in vitro synthesis by thyroid mononuclear cells (TMCs) was determined by RNase protection assay and quantitative PCR. RESULTS: PBMCs from AITD patients showed an increased percent of CD4+ lymphocytes expressing glucocorticoid-induced TNF receptor (GITR), Foxp3, IL-10, TGF-beta, and CD69 as well as CD69+CD25(bright), CD69+TGF-beta, and CD69+IL-10+ cells, compared with controls. TMCs from these patients showed an increased proportion of CD4+GITR+, CD4+CD69+, and CD69+ cells expressing CD25(bright), GITR, and Foxp3, compared with autologous PBMCs. Furthermore, a prominent infiltration of thyroid tissue by CD69+, CD25+, and GITR+ cells, with moderate levels of Foxp3+ lymphocytes, was observed. The suppressive function of peripheral blood T(REG) cells was defective in AITD patients. Finally, increased levels of TGF-beta mRNA were found in thyroid tissue, and thyroid cell infiltrates synthesized in vitro significant levels of TGF-beta upon stimulation through CD69. CONCLUSIONS: Although T regulatory cells are abundant in inflamed thyroid tissue, they are apparently unable, in most cases, to downmodulate the autoimmune response and the tissue damage seen in AITD.     

An important regulatory role for CD4+CD8 alpha alpha T cells in the intestinal epithelial layer in the prevention of inflammatory bowel disease

The normal immunoregulatory mechanisms that maintain homeostasis in the intestinal mucosa, despite continuous provocation by environmental antigens, are jeopardized in inflammatory bowel diseases. Although previous studies have suggested that intestinal intraepithelial lymphocytes prevent spontaneous intestinal inflammation, there is limited knowledge about the characteristics of regulatory cells in the intestinal intraepithelial lymphocytes population. Here we show that CD4(+)CD8 alpha alpha(+) double-positive cells present in the intestinal intraepithelial lymphocytes population can suppress T helper 1-induced intestinal inflammation in an IL-10-dependent fashion. CD4(+) T cells stimulated along the Th2 but not the Th1 lineage, when transferred to RAG-1-/- mice, acquire CD8 alpha alpha expression on reaching the intestinal epithelium, and on arrival there, augment their production of IL-10. We show that a precursor CD4(+) T cell after limited, but not repeated, stimulation by IL-4 is able to become a double-positive-regulatory cell on exposure to the intestinal microenvironment in mice. Both CD8 alpha alpha acquisition and IL-10 production depend critically on the NF-kappa B-GATA-3-axis that we have previously shown is essential for differentiation to the Th2 phenotype and for the induction of airway inflammation. Our studies identify a mechanism for the generation of regulatory T cells in the intestine that may play an important role in controlling inflammatory bowel disease.     

Regulatory potential and control of Foxp3 expression in newborn CD4+ T cells

Thymectomy at day 3 after birth leads to autoimmune disease in some genetic backgrounds. Disease is thought to be caused by the lack/paucity of regulatory T cells. We show that 3-day-old mice already contain a significant compartment of Foxp3-expressing CD25(+)CD4(+) splenocytes. Whereas, in adult spleen, the subsets of regulatory T cells (CD25(+) and/or CD103(+)) express high amounts of Foxp3 mRNA, in 3-day-old mice, both thymic and splenic CD25(+)CD4(+) T cell subsets express lower amounts of Foxp3 mRNA, and CD103(+) cells are barely detected. In adult day 3-thymectomized mice, the CD25(+)CD4(+) T cell subset is overrepresented (most of the cells being CD103(+)) and expresses high amounts of Foxp3 mRNA, independent of the development of autoimmune gastritis. These cells control inflammatory bowel disease and the homeostatic expansion of lymphocytes. This study demonstrates that the peripheral immune system of newborn mice is endowed of a remarkable regulatory potential, which develops considerably in the absence of thymic supply.     

CD8+CD28- regulatory T lymphocytes prevent experimental inflammatory bowel disease in mice

BACKGROUND & AIMS: Immune responses to innocuous intestinal antigens appear tightly controlled by regulatory T lymphocytes. While CD4+ T lymphocytes have recently attracted the most attention, CD8+ regulatory T-cell populations are also believed to play an important role in control of mucosal immunity. However, CD8+ regulatory T-cell function has mainly been studied in vitro and no direct in vivo evidence exists that they can control mucosal immune responses. We investigated the capacity of CD8+CD28- T cells to prevent experimental inflammatory bowel disease (IBD) in mice. METHODS: CD8+CD28- regulatory T cells were isolated from unmanipulated mice and tested for their capacity to inhibit T-cell activation in allogeneic mixed lymphocyte cultures in vitro and to prevent IBD induced by injection of CD4+CD45RB(high) cells into syngeneic immunodeficient RAG-2 mutant mice. RESULTS: CD8+CD28- T lymphocytes inhibited proliferation and interferon gamma production by CD4+ responder T cells in vitro. CD8+CD28- regulatory T cells freshly isolated from spleen or gut efficiently prevented IBD induced by transfer of colitogenic T cells into immunodeficient hosts. Regulatory CD8+CD28- T cells incapable of producing interleukin-10 did not prevent colitis. Moreover, IBD induced with colitogenic T cells incapable of responding to transforming growth factor beta could not be prevented with CD8+CD28- regulatory T cells. CD8+CD28+ T cells did not inhibit in vitro or in vivo immune responses. CONCLUSIONS: Our findings show that naturally occurring CD8+CD28- regulatory T lymphocytes can prevent experimental IBD in mice and suggest that these cells may play an important role in control of mucosal immunity.     

Effective treatment of collagen-induced arthritis by adoptive transfer of CD25+ regulatory T cells

OBJECTIVE: Regulatory T cells play an important role in the prevention of autoimmunity and have been shown to be effective in the treatment of experimental colitis, a T cell-mediated and organ-specific disease. We previously demonstrated that intrinsic CD25+ regulatory T cells modulate the severity of collagen-induced arthritis (CIA), which, in contrast to colitis, is a systemic antibody-mediated disease and an accepted model of rheumatoid arthritis. We undertook this study to determine whether regulatory T cells have the potential to be used therapeutically in arthritis. METHODS: We transferred CD4+,CD25+ T cells into mice exhibiting arthritis symptoms, both immunocompetent mice and mice subjected to lethal irradiation and rescued with syngeneic bone marrow transplantation. RESULTS: A single transfer of regulatory T cells markedly slowed disease progression, which could not be attributed to losses of systemic type II collagen-specific T and B cell responses, since these remained unchanged after adoptive transfer. However, regulatory T cells could be found in the inflamed synovium soon after transfer, indicating that regulation may occur locally in the joint. CONCLUSION: Our data indicate that CD25+ regulatory T cells can be used for the treatment of systemic, antibody-mediated autoimmune diseases, such as CIA.     

TGF-beta regulates in vivo expansion of Foxp3-expressing CD4+CD25+ regulatory T cells responsible for protection against diabetes

CD4+CD25+ regulatory T cells are essential in the protection from organ-specific autoimmune diseases. In the pancreas, they inhibit actions of autoreactive T cells and thereby prevent diabetes progression. The signals that control the generation, the maintenance, or the expansion of regulatory T cell pool in vivo remain poorly understood. Here we show that a transient pulse of transforming growth factor beta (TGF-beta) in the islets during the priming phase of diabetes is sufficient to inhibit disease onset by promoting the expansion of intraislet CD4+CD25+ T cell pool. Approximately 40-50% of intraislet CD4+ T cells expressed the CD25 marker and exhibited characteristics of regulatory T cells including small size, high level of intracellular CTLA-4, expression of Foxp3, and transfer of protection against diabetes. Results from in vivo incorporation of BrdUrd revealed that the generation of a high frequency of regulatory T cells in the islets is due to in situ expansion upon TGF-beta expression. Thus, these findings demonstrate a previously uncharacterized mechanism by which TGF-beta inhibits autoimmune diseases via regulation of the size of the CD4+CD25+ regulatory T cell pool in vivo.     

Th17细胞分化及与疾病关系的研究新进展

Th17细胞是一类新型CD4^＋T细胞,它与Th1、Th2、Tregs细胞一起构成了CD4^＋T细胞的4个主要亚群。它由初始T细胞在转化生长因子（TGF）-β和白细胞介素（IL）-6联合诱导下分化而来。这一分化过程在细胞和分子水平都受到精细的调节。IL-17是Th17细胞最主要的分泌产物,在自身免疫性疾病、某些感染性疾病以及肿瘤中起到重要的调节作用。因此Th17细胞及其相关因子可能为此类疾病的治疗提供新的靶点和途径。     

Functional plasticity of an antigen-specific memory CD4 T cell population

The protective nature of memory immune responses is attributed largely to terminally differentiated memory T cells that retain memory of the antigen via the antigen receptor and memory of the effector functions that initially cleared the pathogen. It is not known whether a given population of antigen-specific memory T cells is endowed with functional flexibility to provide protective responses against antigens reencountered in different immunological contexts. Here, we examine functional properties of influenza hemagglutinin (HA)-specific memory CD4 T cells recovered from adoptive hosts that received in vitro-activated HA-specific T cell receptor-transgenic CD4 T cells 2 months to 1 year previously. We demonstrate that this HA-specific memory CD4 T cell population bearing a clonal T cell receptor can produce predominantly T helper 1 or T helper 2 effector cytokines depending on the nature of the recall stimulus. Our findings reveal remarkable functional plasticity within an antigen-specific memory T cell population and have direct implications for modulating memory T cell function in vaccine design and treatments for autoimmune diseases.     

Role of CD4(+) CD25(+) regulatory T cells in T helper 2 cell-mediated allergic inflammation in the airways

It has recently been shown that CD4(+) CD25(+) T cells are immunoregulatory T cells that prevent CD4(+) T cell-mediated organ-specific autoimmune diseases. To determine whether CD4(+) CD25(+) T cells downregulate Th2 cell-mediated allergic inflammation in the airways, we studied antigen-induced eosinophil recruitment in the airways in BALB/c Rag-2(-)(/-) mice transferred with CD4(+) CD25(+) T cell-depleted or unfractionated T cells from ovalbumin-specific TCR transgenic mice. Antigen-induced eosinophil recruitment into the airways was significantly decreased in the mice transferred with CD4(+) CD25(+) T cell-depleted splenocytes as compared with those transferred with unfractionated splenocytes. On the other hand, the depletion of CD4(+) CD25(+) T cells increased antigen-induced neutrophil and T cell recruitment in the airways of the mice. The depletion of CD4(+) CD25(+) T cells also decreased antigen-induced IL-4 and IL-5 production in the airways of the mice. Finally, the depletion of CD4(+) CD25(+) T cells prevented antigen-induced Th2 cell differentiation in vitro but increased the differentiation of Th1 cells. These results indicate that CD4(+) CD25(+) T cells modulate the Th1 and Th2 cell balance toward Th2 cells and thus upregulate Th2 cell-mediated allergic inflammation in the airways.     

Unique role of CD4+CD62L+ regulatory T cells in the control of autoimmune diabetes in T cell receptor transgenic mice

Converging experimental evidence indicates that CD4(+) regulatory T cells control progression of autoimmune insulitis in nonobese diabetic (NOD) mice. Here, we studied the nature of these regulatory T cells and their mode of action in diabetes-prone NOD Rag(-/-) or severe combined immunodeficient (SCID) mice harboring a transgenic T cell receptor derived from the diabetogenic T cell clone BDC2.5. We first show that diabetes onset is prevented in such mice by infusion of polyclonal CD4(+) T cells expressing L-selectin (CD62L) but not prevented or only marginally prevented by CD4(+)CD25(+) T cells. Similarly, we found with a cotransfer model that CD4(+)CD62L(+) T cells but not CD4(+)CD25(+) T cells inhibited diabetes transfer into NOD SCID recipients by transgenic NOD BDC2.5 SCID cells. Unexpectedly, cotransfer of transgenic NOD BDC2.5 SCID cells and spleen cells from WT diabetic NOD mice did not induce diabetes, whereas each individual population did so. Data are presented arguing for the role of CD4(+)CD62L(+) T cells present within the polyclonal diabetogenic population in mediating this apparently paradoxical effect. Collectively, these data confirm the central role of CD4(+)CD62L(+) regulatory T cells in controlling disease onset in a well defined transgenic model of autoimmune diabetes and suggest the intervention of homeostatic mechanisms as part of their mode of action.     

Aetiopathogenesis of autoimmune hepatitis

The histological hallmark of autoimmune hepatitis（AIH） is a dense portal mononuclear cell infiltrate that invades the surrounding parenchyma and comprises T and B lymphocytes,macrophages,and plasma cells.An unknown but powerful stimulus must be promoting the formation of this massive inflammatory cellular reaction that is likely to initiate and perpetuate liver damage.An autoimmune attack can follow different pathways to inflict damage on hepatocytes.Liver damage is likely to be orchestrated by CD4^＋ T lymphocytes recognizing an autoantigenic liver peptide.To trigger an autoimmune response,the peptide must be embraced by an HLA class Ⅱ molecule and presented to naive CD4^＋ T helper（Th0） cells by professional antigen presenting cells,with the co-stimulation of ligand-ligand fostering interaction between the two cells.Th0 cells become activated,differentiate into functional phenotypes according to the cytokines prevailing in the microenvironment and the nature of the antigen,and initiate a cascade of immune reactions determined by the cytokines produced by the activated T cells.Th1 cells,arising in the presence of the macrophage-derived interleukin（IL） -12,secrete mainly IL-2 and interferon-gamma（IFN-γ）,which activate macrophages,enhance expression of HLA classⅠ（increasing liver cell vulnerability to a CD8^＋ T cell cytotoxic attack）,and induce expression of HLA class Ⅱ molecules on hepatocytes.Th2 cells,which differentiate from Th0 if the microenvironment is rich in IL-4,produce mainly IL-4,IL-10,and IL-13 which favour autoantibody production by B lymphocytes.Physiologically,Th1 and Th2 antagonize each other.Th17 cells,a recently described population,arise in the presence of transforming growth factor beta（TGF-β） and IL-6 and appear to have an important effector role in inflammation and autoimmunity.Theprocess of autoantigen recognition is strictly controlled by regulatory mechanisms,such as those exerted by CD4^＋CD25^＋ regulatory T cells,which derive from Th0 in the presen     

Characterization of immunologic tolerance induced by transfusion of UV-B--irradiated allogeneic mononuclear leukocytes

Transfusions of UV-B--irradiated peripheral blood mononuclear cells (UV-B--PBMCs) from BALB/c (H-2(d)) mice into CBA (H-2(k)) mice can induce humoral immune tolerance to H-2(d) antigens, and the induced tolerance is partially mediated by negative regulatory PBMCs. To further identify which subset of spleen mononuclear leukocytes (MNLs) in the tolerant CBA mice is responsible for the negative regulatory activity, adoptive transfer experiments were conducted using spleen MNLs from the tolerant CBA mice. Results showed that only CD4(+) T cells could transfer the negative regulatory activity in a dose-dependent manner. This negative regulatory activity was significantly reduced when CD25(+) helper T cells were removed. Further study suggested that inhibition of IL-12 production by UV-B--irradiated PBMCs played a role in the induction of immune tolerance. In vitro study of the cytokine production profile by CBA CD4(+) T cells, after stimulation with gamma-irradiated BALB/c spleen cells, revealed an enhanced production of the type 2 T-cell cytokines after tolerance induction. Induction of tolerance also prevented the development of cytotoxic T cells in CBA mice against BALB/c MNLs. Adoptive transfer study suggested that the cellular immune tolerance was also mediated by CD4(+) negative regulatory T cells. The induced immune tolerance was nullified after 400 cGy sublethal gamma irradiation. These results suggest that the ex vivo study of cytokine production by T cells may be used to monitor tolerance induction and the selection of gamma radiation dose is critical for potential clinical application of the tolerance induced by UV-B--PBMCs. (Blood. 2001;98:1239-1245)     

Lymphocytes in obesity-related adipose tissue inflammation

Inflammation in the white adipose tissue (WAT) is considered a major player in the development of insulin resistance. The role of macrophages accumulating in the WAT during obesity, promoting WAT inflammation and insulin resistance is well established. In contrast, less is known about the role of lymphocytes. Recent studies have implicated different lymphocyte subsets in WAT inflammation. For instance, cytotoxic CD8(+) T cells infiltrating the WAT may contribute to the recruitment, differentiation and activation of macrophages. On the other hand, a differential role for CD4(+) Th1 and CD4(+) Th2 cells has been suggested. Levels of WAT regulatory T cells decrease during the course of obesity and may represent a crucial factor for the maintenance of insulin sensitivity. Moreover, activation of natural killer T cells, an innate-like T cell population, which recognises lipid antigens, promotes insulin resistance and WAT inflammation. Finally, B cells may infiltrate WAT very early in response to high-fat feeding and worsen glucose metabolism through modulation of T cells and the production of pathogenic antibodies. These interesting new findings however bear controversies and introduce novel, yet unanswered, questions. Here, we review and discuss the impact of the different lymphocyte subsets in obesity-related WAT inflammation and attempt to identify the open questions to be answered by future studies.