Cells In Peripheral Lymphoid Organs Research Articles

BAP31 Plays an Essential Role in Mouse B Cell Development via Regulation of BCR Signaling.

B cell receptor-associated protein 31 (BAP31) is a transmembrane protein that is widely expressed and primarily located in the endoplasmic reticulum (ER). B cells play a crucial role in the immune system, and BAP31 significantly contributes to the functions of various immune cells. However, the specific role of BAP31 in B lymphocytes development remains unknown. In this study, we utilized a mouse model with BAP31 deleted from B cells to investigate its effects. Our findings reveal a block in early B cell development in the bone marrow and a significant decrease in the number of B cells in peripheral lymphoid organs taken from BAP31 B cell conditional knockout (BAP31-BCKO) mice. B cell receptor (BCR) signaling is crucial for the normal development and differentiation of B lymphocytes. BAP31, an endoplasmic reticulum membrane protein, directly regulates the BCR signaling pathway and was shown to be significantly positively correlated with B cell activation and proliferation. These findings establish BAP31 as a crucial regulator of early B cell development.

Innate-like CD27+CD45RBhigh γδ T Cells Require TCR Signaling for Homeostasis in Peripheral Lymphoid Organs.

TCR signaling is required for homeostasis of naive αβ T cells. However, whether such a signal is necessary for γδ T cell homeostasis in the periphery remains unknown. In this study, we present evidence that a portion of Vγ2+ γδ T cells, one of the major γδ T cell subsets in the secondary lymphoid organs, requires TCR signaling for homeostasis. To attenuate γδTCR signals, we generated mice lacking Eγ4 (Eγ4-/-), an enhancer located at the 3'-most end of the TCRγ locus. Overall, we found that in thymus, Eγ4 loss altered V-J rearrangement, chromatin accessibility, and transcription of the TCRγ locus in a distance-dependent manner. Vγ2+ γδ T cells in Eγ4-/- mice developed normally both fetal and adult mouse thymi but were relatively reduced in number in spleen and lymph nodes. Although Vγ2 TCR transcription decreased in all subpopulations of Eγ4-/- mice, the number of Vγ2+ γδ T cells decreased and TCR signaling was attenuated only in the innate-like CD27+CD45RBhigh subpopulation in peripheral lymphoid organs. Consistently, CD27+CD45RBhigh Vγ2+ γδ T cells from Eγ4-/- mice transferred into Rag2-deficient mice were not efficiently recovered, suggesting that continuous TCR signaling is required for their homeostasis. Finally, CD27+CD45RBhigh Vγ2+ γδ T cells from Eγ4-/- mice showed impaired TCR-induced activation and antitumor responses. These results suggest that normal homeostasis of innate-like CD27+CD45RBhigh Vγ2+ γδ T cells in peripheral lymphoid organs requires TCR signaling.

Conditional abrogation of Ddx3x reveals its essential role in lymphocyte development and partial compensation by Y chromosome

Abstract Ddx3x on the X-chromosome encodes a DEAD-box RNA helicase with putative roles in RNA metabolism, cell cycle progression, apoptosis, and viral immunity. We previously found that hematopoietic-specific hemizygosity of Ddx3x studies caused a marked reduction in the frequencies of natural killer (NK) and B cells in peripheral lymphoid organs of male mice (Liu et al. bioRxiv 2018). No homozygous Ddx3x-deficient female pups were ever obtained, suggesting that hematopoietic loss of this gene contributes to the embryonic lethality observed in germline Ddx3x knockout mice. To assess cell-lineage intrinsic roles for Ddx3x in B-cell and NK-cell development, we bred Ddx3x-floxed mice with Mb1-Cre and Ncr1-iCre mice, respectively. While hemizygous male Ddx3x-deficient mice display mild reductions in B-cell (Mb1-Cre) and NK-cell (Ncr1-iCre) frequencies, homozygous Ddx3x-deficient female mice from each were almost completely devoid of the relevant cell lineages. B-cell loss was evident from the pro-B cells stage, with B cells surviving beyond this stage showing evidence of having escaped deletion of Ddx3x. Ncr1-iCre-mediated deletion of Ddx3x completely abrogated development of both NK cells and other Ncr1-expressing innate lymphoid cells. Thus, DDX3 plays an essential role in the lymphocyte development, where Ddx3y may partially compensate for loss of Ddx3x in these lineages.

Contribution of the Microbiome to Maintenance of the CD4:CD8 Ratio in Inbred and Congenic Mouse Strains

Abstract The gut microbiome is known to play an integral role in the regulation of the immune system. Previous studies indicate that species diversity and overall abundance of commensal bacteria in the gut influences immune system function by altering total T cell counts and the ratio of CD4+ to CD8+ T cells in peripheral lymphoid organs and blood. In normal individuals, the CD4:CD8 ratio is greater than one. However, the congenic B10.A mouse strain in our conventional facility consistently demonstrates an inverted CD4:CD8 ratio in a sex- and age-dependent manner, in contrast to both the parental C57Bl/10 strain and B10.A kept under SPF conditions. To determine whether this phenomenon is due to the composition and diversity of the gut microbiome affecting the homeostasis of the CD4:CD8 ratio, we altered the microbiome by supplementing the diet with the prebiotic inulin and looked for changes in the number of Peyer’s patches and changes in the CD4:CD8 ratio in gut lymphoid organs and blood in both B10.A and C57Bl/10 strains. In addition, we followed the changes in the microbiome upon treatment. We find that the mice in our facility have lower microbiome diversity and very different composition from mice kept at SPF conditions. The inulin treatment significantly increased the CD4:CD8 ratio in the blood of the C57Bl/10 mice, but not the B10.A mice. In addition, males of both strains had a significant increase in Peyer’s patch number, while the females had a significant increase in the CD4:CD8 ratio in the Peyer’s patches.

Investigating T Cell Receptor Signals In Situ by Two-Photon Microscopy of Thymocytes Expressing Genetic Reporters in Low-Density Chimeras.

T cell development is a dynamic process accompanied by extensive thymocyte migration, cellular interactions, and T cell receptor (TCR) signaling. In particular, thymic selection processes that ensure a functional, self-tolerant repertoire require TCR interactions with self-peptide presented by major histocompatibility complex molecules expressed by specialized thymic antigen-presenting cells. The quantity and quality of these TCR signals influence T cell fate. Two-photon microscopy, which enables live imaging of cells in intact tissue, has emerged as a powerful tool to gain insights into thymocyte migration and TCR signaling during T cell development in situ. Here we describe the generation of non-irradiated, low-density chimeric mice by neonatal injection of adult bone marrow engineered to express fluorescent TCR signaling reporters for imaging by two-photon microscopy. We also describe how the thymic lobes from chimeric mice are prepared for live imaging of thymocyte behavior and TCR signaling events. While we focus on imaging TCR signals associated with T cell development in the thymus, these techniques can also be adapted to study TCR signaling in mature T cells in peripheral lymphoid organs.

Runx1 is a key regulator of T cell anergy

Abstract The transcription factor Runx1 is critical for T cell development and maturation. CD4-Cre Runx1 conditional knockout mice have a block in T cell maturation, leading to complement deposition on recent thymic emigrants, and leaving very few CD4+T cells in peripheral lymphoid organs. Interestingly, thymic- and splenic-derived T cells from CD4-Cre Runx1 cKO mice exhibit increased expression of markers indicative of anergy including FR4 and CD73, which is not seen in other genetically modified mice with a block in T cell maturation. These data suggest Runx1 plays a role in regulating the development of T cell anergy in CD4+T cells. We have generated a 1:1 mixed bone marrow chimera (BMC) system with Estrogen Receptor-Cre (ER-Cre) Runx1 conditional knockout and wild type B6.SJL bone marrow to delete Runx1 in mature CD4+ T cells. Upon tamoxifen treatment and deletion of Runx1, the ER-Cre Runx1 cKO CD4+ T cells spontaneously develop an anergic phenotype as they fail to proliferate upon TCR/CD28 stimulation, and co-express CD73 and FR4. This cell surface phenotype is cell intrinsic since wild type B6.SJL CD4+ T cells in the mixed bone marrow chimera do not upregulate CD73 and FR4 upon tamoxifen treatment. Surprisingly, the mixed BMC system reveals both the ER-Cre Runx1 cKO and the wild type B6.SJL peripheral T cells fail to proliferate in response to TCR/CD28 stimulation, suggesting Runx1 also regulates a cell-extrinsic suppressive mechanism controlling T cell tolerance. This cell-extrinsic induction of anergy requires Runx1-deficient CD4+ T cells, but it is not dependent on Runx1-deficient Tregs. Thus, Runx1 is a key regulator of T cell anergy, and further analysis of this BMC model will serve to uncover the mechanism.

Aire-expressing ILC3-like cells in the lymph node display potent APC features

The autoimmune regulator (Aire) serves an essential function for T cell tolerance by promoting the "promiscuous" expression of tissue antigens in thymic epithelial cells. Aire is also detected in rare cells in peripheral lymphoid organs, but the identity of these cells is poorly understood. Here, we report that Aire protein-expressing cells in lymph nodes exhibit typical group 3 innate lymphoid cell (ILC3) characteristics such as lymphoid morphology, absence of "classical" hematopoietic lineage markers, and dependence on RORγt. Aire+ cells are more frequent among lineage-negative RORγt+ cells of peripheral lymph nodes as compared with mucosa-draining lymph nodes, display a unique Aire-dependent transcriptional signature, express high surface levels of MHCII and costimulatory molecules, and efficiently present an endogenously expressed model antigen to CD4+ T cells. These findings define a novel type of ILC3-like cells with potent APC features, suggesting that these cells serve a function in the control of T cell responses.

The role of Runx1 in the regulation of T cell tolerance

Abstract The transcription factor Runx1 is critical for T cell development and maturation. CD4-Cre Runx1 conditional knockout mice have a block in T cell maturation, leading to complement deposition on CD4+ recent thymic emigrants, leaving very few CD4+ T cells in peripheral lymphoid organs. Consistent with a block in maturation, peripheral Runx1-deficient CD4+ T cells fail to produce normal levels of TNF-a upon stimulation. These CD4+ T cells that persist in CD4-Cre Runx1 cKO mice possess a phenotype not found in other genetically modified mice with a block in T cell maturation. Thymic- and splenic-derived T cells from the CD4-Cre Runx1 cKO exhibit altered expression of markers indicative of anergy including FR4 and CD73. This suggests Runx1 plays a role in regulating the development of T cell tolerance which is disrupted upon deletion of Runx1 in CD4+ T Cells. To test this, we have generated a mixed bone marrow chimera (BMC) system with Estrogen Receptor-Cre Runx1 knockout and B6.SJL bone marrow to knock out Runx1 in mature T cells. Surprisingly, in the mixed BMC both the ER-Cre Runx1 cKO and the B6.SJL peripheral T cells acquire a functionally hyporesponsive phenotype, suggesting that Runx1 regulates an extrinsic signaling mechanism controlling tolerance. Moving forward, this BMC model allows us to investigate the development of this anergic phenotype in mature T cells, and tests the hypothesis that Runx1 plays a critical role in regulating T cell tolerance.

Deletion of the Mineralocorticoid Receptor in Myeloid Cells Attenuates Central Nervous System Autoimmunity.

Myeloid cells play an important role in the pathogenesis of multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). Monocytes, macrophages, and microglia can adopt two distinct phenotypes, with M1-polarized cells being more related to inflammation and autoimmunity while M2-polarized cells contribute to tissue repair and anti-inflammatory processes. Here, we show that deletion of the mineralocorticoid receptor (MR) in bone marrow-derived macrophages and peritoneal macrophages caused their polarization toward the M2 phenotype with its distinct gene expression, altered phagocytic and migratory properties, and dampened NO production. After induction of EAE, mice that are selectively devoid of the MR in their myeloid cells (MRlysM mice) showed diminished clinical symptoms and ameliorated histological hallmarks of neuroinflammation. T cells in peripheral lymphoid organs of these mice produced less pro-inflammatory cytokines while their proliferation and the abundance of regulatory T cells were unaltered. The numbers of inflammatory monocytes and reactive microglia in the central nervous system (CNS) in MRlysM mice were significantly lower and they adopted an M2-polarized phenotype based on their gene expression profile, presumably explaining the ameliorated neuroinflammation. Our results indicate that the MR in myeloid cells plays a critical role for CNS autoimmunity, providing a rational to interfere with diseases such as MS by pharmacologically targeting this receptor.

A Coronin 1-Dependent Decision Switch in Juvenile Mice Determines the Population of the Peripheral Naive T Cell Compartment.

Following thymic maturation, T cells egress as recent thymic emigrants to peripheral lymphoid organs where they undergo an additional maturation step to mature naive T cells that circulate through secondary lymphoid organs ready to be activated upon pathogenic challenges. Thymic maturation and peripheral T cell survival depend on several signaling cascades, but whether a dedicated mechanism exists that exclusively regulates homeostasis of mature naive T cells without affecting thymocytes and/or recent thymic emigrants remains unknown. In this article, we provide evidence for a specific and exclusive role of the WD repeat containing protein coronin 1 in the maintenance of naive T cells in peripheral lymphoid organs. We show that coronin 1 is dispensable for thymocyte survival and development, egress from the thymus, and survival of recent thymic emigrants. Importantly, coronin 1-deficient mice possessed comparable levels of peripheral T cells within the first 2 wk after birth but failed to populate the peripheral T cell compartment at later stages. Furthermore, dendritic cell- and IL-2/7-dependent T cell survival was found to be independent of coronin 1. Together, these results suggest the existence of a hitherto unrecognized coronin 1-dependent decision switch early during life that is responsible for peripheral naive T cell survival and homeostasis.

Proteasome inhibition ameliorates experimental Sjögren’s syndrome by suppressing Th17 and B cell responses

Abstract Primary Sjögren’s syndrome (SS) is a chronic autoimmune disease that mainly affects salivary and lacrimal glands. Currently, there is a lack of effective therapies for SS patients. Increasing evidence indicates that Bortezomib (BTZ), the first proteasome inhibitor approved for treating multiple myeloma, shows beneficial effects in treating lupus. Although clinical findings have revealed increased expression of proteasome in SS patients, it remains unclear whether proteasome inhibition is an effective approach for treating SS. In this study, we evaluated the therapeutic effects of BTZ on experimental SS (ESS) mouse model. Mice were immunized with proteins extracted from salivary glands (SG) to induce ESS and received either vehicle or BTZ treatment. Compared with vehicle-treated counterparts, BTZ-treated mice displayed markedly higher saliva flow rates and ameliorated tissue destructions accompanied with less lymphocytes infiltration in SG. Notably, mice with BTZ treatment showed significantly decreased Th17 but not Th1 responses, and reduced germinal center B cells and plasma cells in peripheral lymphoid organs. In culture, BTZ treatment significantly suppressed Th17 cells differentiation and proliferation. Moreover, adoptively transferred naïve CD4 T cells differentiated into Th17 cells and induced salivary dysfunction in immunized Il17a−/− mice. However, the BTZ-treated recipient mice exhibited suppressed Th17 responses with ameliorated reduction in salivary secretion. Taken together, our findings have shown that BTZ treatment can suppress Th17 and B cell responses and effectively ameliorate ESS development in mice, which may contribute to the validation of BTZ as a promising candidate for treating SS.

Neutrophils modulate the progression of B cell auto-reactivity in systemic lupus erythematosus

Abstract The central feature of systemic lupus erythematosus (SLE) pathogenesis is loss of immunologic self-tolerance. Here, we address a current controversy regarding whether neutrophils influence the development of B cell auto-reactivity SLE. While both human and murine lupus neutrophils produce factors known to fuel adaptive immune dysregulation, including type I interferon, B cell survival factors, and extracellular traps (a putative source of self-antigen), some studies have contended that neutrophils in peripheral lymphoid organs (PLO) suppress B cell activation and differentiation. In order to ask whether neutrophils exert regulatory or deleterious effects on loss of B cell self-tolerance and immune activation, we compare changes in SLE progression following neutrophil depletion in the NZB/W lupus model, either during or after establishment of disease. Following depletion early in disease, we observe pronounced acceleration of proteinuria, anti-dsDNA titers, and germinal center formation. However, neutrophil depletion after onset of overt disease pathology (including proteinuria) does not strongly alter SLE progression, implicating neutrophils as playing a protective role only apparent during disease onset. To elucidate the specific mechanisms underlying neutrophil effects on B cell auto-reactivity, we examine the cytokine profile of neutrophils in direct proximity to B cells in PLO during several stages of disease. With progression of disease, we observe an influx of interferon-alpha-producing neutrophils in direct proximity to B cells in PLO. These data delineate a shifting balance of both regulatory and activating roles for neutrophils in auto-reactive B cell activation/proliferation during SLE progression.

An Efficient and High Yield Method for Isolation of Mouse Dendritic Cell Subsets.

Dendritic cells (DCs) are professional antigen-presenting cells primarily responsible for acquiring, processing and presenting antigens on antigen presenting molecules to initiate T-cell-mediated immunity. Dendritic cells can be separated into several phenotypically and functionally heterogeneous subsets. Three important subsets of splenic dendritic cells are plasmacytoid, CD8α(Pos) and CD8α(Neg) cells. The plasmacytoid DCs are natural producers of type I interferon and are important for anti-viral T cell immunity. The CD8α(Neg) DC subset is specialized for MHC class II antigen presentation and is centrally involved in priming CD4 T cells. The CD8α(Pos) DCs are primarily responsible for cross-presentation of exogenous antigens and CD8 T cell priming. The CD8α(Pos) DCs have been demonstrated to be most efficient at the presentation of glycolipid antigens by CD1d molecules to a specialized T cell population known as invariant natural killer T (iNKT) cells. Administration of Flt-3 ligand increases the frequency of migration of dendritic cell progenitors from bone marrow, ultimately resulting in expansion of dendritic cells in peripheral lymphoid organs in murine models. We have adapted this model to purify large numbers of functional dendritic cells for use in cell transfer experiments to compare in vivo proficiency of different DC subsets.

Generation of tumor-infiltrating lymphocytes from pancreatic cancer lesions for cellular therapy

We investigated the influence of Panagen DNA preparations on laboratory animals and IFN-induced human dendritic cells, as well as analyzed the data from a phase II clinical trial in the therapy of breast cancer. It was shown that this treatment resulted in increased number of CD8+/perforin+ T cells in peripheral lymphoid organs of experimental animals, in mixed lymphocyte culture population and in peripheral blood of breast cancer patients. Moreover, we demonstrated that when Panagen DNA preparations are used in combination with the standard FAC-based breast cancer therapies, non-specific immune response activity remains at the same levels as observed prior to therapy, whereas in FAC-placebo patients, non-specific immunity is greatly diminished.

Loss of RUNX1/AML1 arginine-methylation impairs peripheral T cell homeostasis.

RUNX1 (previously termed AML1) is a frequent target of human leukaemia-associated gene aberrations, and it encodes the DNA-binding subunit of the Core-Binding Factor transcription factor complex. RUNX1 expression is essential for the initiation of definitive haematopoiesis, for steady-state thrombopoiesis, and for normal lymphocytes development. Recent studies revealed that protein arginine methyltransferase 1 (PRMT1), which accounts for the majority of the type I PRMT activity in cells, methylates two arginine residues in RUNX1 (R206 and R210), and these modifications inhibit corepressor-binding to RUNX1 thereby enhancing its transcriptional activity. In order to elucidate the biological significance of these methylations, we established novel knock-in mouse lines with non-methylable, double arginine-to-lysine (RTAMR-to-KTAMK) mutations in RUNX1. Homozygous Runx1(KTAMK) (/) (KTAMK) mice are born alive and appear normal during adulthood. However, Runx1(KTAMK) (/) (KTAMK) mice showed a reduction in CD3(+) T lymphoid cells and a decrease in CD4(+) T cells in peripheral lymphoid organs, in comparison to their wild-type littermates, leading to a reduction in the CD4(+) to CD8(+) T-cell ratio. These findings suggest that arginine-methylation of RUNX1 in the RTAMR-motif is dispensable for the development of definitive haematopoiesis and for steady-state platelet production, however this modification affects the role of RUNX1 in the maintenance of the peripheral CD4(+) T-cell population.

AIDing Chromatin and Transcription-Coupled Orchestration of Immunoglobulin Class-Switch Recombination.

Secondary diversification of the antibody repertoire upon antigenic challenge, in the form of immunoglobulin heavy chain (IgH) class-switch recombination (CSR) endows mature, naïve B cells in peripheral lymphoid organs with a limitless ability to mount an optimal humoral immune response, thus expediting pathogen elimination. CSR replaces the default constant (CH) region exons (Cμ) of IgH with any of the downstream CH exons (Cγ, Cε, or Cα), thereby altering effector functions of the antibody molecule. This process depends on, and is orchestrated by, activation-induced deaminase (AID), a DNA cytidine deaminase that acts on single-stranded DNA exposed during transcription of switch (S) region sequences at the IgH locus. DNA lesions thus generated are processed by components of several general DNA repair pathways to drive CSR. Given that AID can instigate DNA lesions and genomic instability, stringent checks are imposed that constrain and restrict its mutagenic potential. In this review, we will discuss how AID expression and substrate specificity and activity is rigorously enforced at the transcriptional, post-transcriptional, post-translational, and epigenetic levels, and how the DNA-damage response is choreographed with precision to permit targeted activity while limiting bystander catastrophe.

Loss of β‐arrestin 2 exacerbates experimental autoimmune encephalomyelitis with reduced number of Foxp3+ CD4+ regulatory T cells

β-Arrestins are well-known regulators and mediators of G protein-coupled receptor signalling, and accumulating evidence reveals that they are functionally involved in inflammation and autoimmune diseases. Of the two β-arrestins, β-arrestin 1 is documented to play regulatory roles in an animal model of multiple sclerosis (MS), whereas the role of β-arrestin 2 is less clear. Here, we show that β-arrestin 2-deficient mice displayed the exacerbated and sustained symptoms of experimental autoimmune encephalomyelitis (EAE), an animal model of MS. At the cellular level, deficiency of β-arrestin 2 led to a decreased number of Foxp3(+) CD4(+) regulatory T (Treg) cells in peripheral lymphoid organs of EAE mice. Consistently, our in vitro observations also revealed that loss of β-arrestin 2 impaired the conversion of Foxp3(-) CD4(+) T cells into Foxp3(+) CD4(+) inducible Treg cells. Taken together, our data suggest that β-arrestin 2 plays a regulatory role in MS, that is opposite to that of β-arrestin 1, in autoimmune diseases such as MS, which is at least partially through regulation of iTreg cell differentiation.

The Development of Unconventional Extrathymic Activated CD4+CD8+T Cells in Chagas Disease

The numbers of extrathymic CD4+CD8+double-positive (DP) T cells are augmented in various pathophysiological conditions, such as infectious diseases caused by intracellular pathogens, organs subjected to autoimmune attack and malignant tumors. The roles performed by extrathymic DP T cells are not clear, and it is not known how they are distributed in the body. In animals they have been considered memory cells involved in adaptive immune responses against virus infections or participating in pathological responses. In experimentalTrypanosoma cruziinfections, there is a severe thymic atrophy and this results in the release of activated DP T cells to peripheral organs. In severe cardiac forms of human chronic Chagas disease activated HLA-DR+DP T cells are present in the blood. In investigating the basis of premature thymocyte release during chagasic thymic atrophy we found that the parasitetrans-sialidase (TS) altered intrathymic thymocyte maturation and was associated with increased numbers of recent T cells in peripheral lymphoid organs. In what follows we propose to describe what is known about the origin of the extrathymic DP T cells in human Chagas disease and animal models of the disease.

CD8+ T cell help is required for efficient induction of EAE in Lewis rats

The role of CD8+ T cells in multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE) is still unclear. We describe here significantly reduced disease activity of EAE both in Lewis rats depleted of CD8+ T cells by monoclonal antibodies and CD8 knockout rats, which was accompanied by reduced leukocyte infiltration into the spinal cord. We detected myelin basic protein (MBP)-specific CD4+ T cells in peripheral lymphoid organs of CD8-depleted animals which, however, failed to differentiate into interferon-γ-producing effector cells. Our results indicate that CD8+ T cells interact with myelin-specific CD4+ T cells early in EAE enabling them to differentiate into pathogenic effector cells.

KRP-203, Sphingosine 1-Phosphate Receptor Type 1 Agonist, Ameliorates Atherosclerosis in LDL-R −/− Mice

Sphingosine 1-phosphate (S1P) partly accounts for antiatherogenic properties of high-density lipoproteins. We previously demonstrated that FTY720, a synthetic S1P analog targeting all S1P receptors but S1P receptor type 2, inhibits murine atherosclerosis. Here, we addressed the identity of S1P receptor mediating atheroprotective effects of S1P. Low-density lipoprotein receptor-deficient mice on cholesterol-rich diet were given selective S1P receptor type 1 agonist KRP-203 (3.0 mg/kg per day; 6 and 16 weeks). KRP-203 substantially reduced atherosclerotic lesion formation without affecting plasma lipid concentrations. However, KRP-203 induced lymphopenia, reduced total (CD4(+), CD8(+)) and activated (CD69(+)/CD8(+), CD69(+)/CD4(+)) T cells in peripheral lymphoid organs, and interfered with lymphocyte function, as evidenced by decreased T-cell proliferation and interleukin-2 and interferon-γ production in activated splenocytes. Cyto- and chemokine (tumor necrosis factor-α, regulated and normal T cell expressed and secreted) levels in plasma and aortas were reduced by KRP-203 administration. Moreover, macrophages from KRP-203-treated mice showed reduced expression of activation marker MCH-II and poly(I:C)-elicited production of tumor necrosis factor-α, monocyte chemoattractant protein-1, and interleukin-6. In vitro studies demonstrated that KRP-203 reduced tumor necrosis factor-α, interleukin-6, and interferon-γ-induced protein-10 production; IκB and signal transducer and activator of transcription-1 phosphorylation; and nuclear factor κB and signal transducer and activator of transcription-1 activation in poly(I:C)-, lipopolysaccharide-, or interferon-γ-stimulated bone marrow macrophages, respectively. Present results demonstrate that activation of S1P signaling pathways inhibit atherosclerosis by modulating lymphocyte and macrophage function and suggest that S1P receptor type 1 at least partially mediates antiatherogenic effects of S1P.