Cannabinoid receptor 2 positions and retains marginal zone B cells within the splenic marginal zone

2-Arachidonoylglycerol Modulates CXCL12-Mediated Chemotaxis in Mantle Cell Lymphoma and Chronic Lymphocytic Leukemia

To survive chemotherapy, lymphoma cells can relocate to protective niches where they receive support from the non-malignant cells. The biolipid 2-arachidonoylglycerol (2-AG), an agonist for the cannabinoid receptors CB1 and CB2, is released by stromal cells in the bone marrow. To investigate the role of 2-AG in lymphoma, we analyzed the chemotactic response of primary B-cell lymphoma cells enriched from peripheral blood of twenty-two chronic lymphocytic leukemia (CLL) and five mantle cell lymphoma (MCL) patients towards 2-AG alone and/or to the chemokine CXCL12. The expression of cannabinoid receptors was quantified using qPCR and the protein levels visualized by immunofluorescence and Western blot. Surface expression of CXCR4, the main cognate receptor to CXCL12, was analyzed by flow cytometry. Phosphorylation of key downstream signaling pathways activated by 2-AG and CXCL12 were measured by Western blot in three MCL cell lines and two primary CLL samples. We report that 2-AG induces chemotaxis in 80% of the primary samples, as well as 2/3 MCL cell lines. 2-AG induced in a dose-dependent manner, the migration of JeKo-1 cell line via CB1 and CB2. 2-AG affected the CXCL12-mediated chemotaxis without impacting the expression or internalization of CXCR4. We further show that 2-AG modulated p38 and p44/42 MAPK activation. Our results suggest that 2-AG has a previously unrecognized role in the mobilization of lymphoma cells by effecting the CXCL12-induced migration and the CXCR4 signaling pathways, however, with different effects in MCL compared to CLL.

miR-142 favors naïve B cell residence in peripheral lymph nodes

B lymphocyte development proceeds through a well-ordered sequence of steps, leading to the formation of a sizeable mature B population recognizing a diversity of antigens. These latter cells are ultimately responsible for the production of antibodies upon immune challenges. The detection of threats to the organism is facilitated by the ability of naïve follicular B cells, the main subset of mature B cells in mice, to circulate between lymphoid tissues in search of their cognate antigens. miRNA-mediated fine-tuning of mRNA stability and translation participates in the optimal expression of genetic programs. This regulatory mechanism has been shown to contribute to B cell biology, although the role of individual miRNAs remains understudied. Here, we selectively inactivated the miR-142 locus in B cells. As a consequence, the mature B compartment was visibly perturbed, in agreement with work in miR-142 knockout mice. However, our strategy allowed us to identify roles for the miR-142 locus in B cell physiology obscured by the complexity of the immune phenotype in the null mutant mice. Thus, these miRNAs are necessary for the proper formation of the pre-B cell compartment during development. More remarkably, naïve follicular B cells demonstrated altered migratory properties upon conditional inactivation of the miR-142 locus. The latter mutant cells expressed reduced levels of the homing molecule CD62L. They also migrated more efficiently towards sphingosine-1-phosphate in vitro and displayed an increased abundance of the sphingosine-1-phosphate receptor 1, compatible with improved lymphocyte egress in vivo. In line with these observations, the ablation of the miR-142 locus in B cells caused a paucity of B cells in the lymph nodes. Mutant B cell accumulation in the latter tissues was also compromised upon transfer into a wild-type environment. These changes coincided with suboptimal levels of FOXO1, a positive regulator of CD62L transcription, in mutant B cells. Overall, our findings indicate contributions for the miR-142 locus in various aspects of the B cell life cycle. Notably, this locus appears to favor the establishment of the migratory behavior required for naïve follicular B cell patrolling activity.

Development and function of tissue-resident memory B cells

Barrier tissues are the primary site of infection for pathogens likely to cause future pandemics. Tissue-resident lymphocytes can rapidly detect pathogens upon infection of barrier tissues and are critical in preventing viral spread. However, most vaccines fail to induce tissue-resident lymphocytes and are instead reliant on circulating antibodies to mediate protective immunity. Circulating antibody titers wane over time following vaccination leaving individuals susceptible to breakthrough infections by variant viral strains that evade antibody neutralization. Memory B cells were recently found to establish tissue residence following infection of barrier tissues. Here, we summarize emerging evidence for the importance of tissue-resident memory B cells in the establishment of protective immunity against viral and bacterial challenge. We also discuss the role of tissue-resident memory B cells in regulating the progression of non-infectious diseases. Finally, we examine new approaches to develop vaccines capable of eliciting barrier immunity.

Chemo- and mechanosensing by dendritic cells facilitate antigen surveillance in the spleen

Spleen dendritic cells (DC) are critical for initiation of adaptive immune responses against blood-borne invaders. Key to DC function is their positioning at sites of pathogen entry, and their abilities to selectively capture foreign antigens and promptly engage T cells. Focusing on conventional DC2 (cDC2), we discuss the contribution of chemoattractant receptors (EBI2 or GPR183, S1PR1, and CCR7) and integrins to cDC2 positioning and function. We give particular attention to a newly identified role in cDC2 for adhesion G-protein coupled receptor E5 (Adgre5 or CD97) and its ligand CD55, detailing how this mechanosensing system contributes to splenic cDC2 positioning and homeostasis. Additional roles of CD97 in the immune system are reviewed. The ability of cDC2 to be activated by circulating missing self-CD47 cells and to integrate multiple red blood cell (RBC)-derived inputs is discussed. Finally, we describe the process of activated cDC2 migration to engage and prime helper T cells. Throughout the review, we consider the insights into cDC function in the spleen that have emerged from imaging studies.

Development of Tbet- and CD11c-expressing B cells in a viral infection requires T follicular helper cells outside of germinal centers

Tbet+CD11c+ B cells arise during type 1 pathogen challenge, aging, and autoimmunity in mice and humans. Here, we examined the developmental requirements of this B cell subset. In acute infection, T follicular helper (Tfh) cells, but not Th1 cells, drove Tbet+CD11c+ B cell generation through proximal delivery of help. Tbet+CD11c+ B cells developed prior to germinal center (GC) formation, exhibiting phenotypic and transcriptional profiles distinct from GC B cells. Fate tracking revealed that most Tbet+CD11c+ B cells developed independently of GC entry and cell-intrinsic Bcl6 expression. Tbet+CD11c+ and GC B cells exhibited minimal repertoire overlap, indicating distinct developmental pathways. As the infection resolved, Tbet+CD11c+ B cells localized to the marginal zone where splenic retention depended on integrins LFA-1 and VLA-4, forming a competitive memory subset that contributed to antibody production and secondary GC seeding upon rechallenge. Therefore, Tbet+CD11c+ B cells comprise a GC-independent memory subset capable of rapid and robust recall responses.

Clinical effects of a single dose of cannabinoids to patients with chronic lymphocytic leukemia

This phase II clinical trial investigates a one-time oromucosal dose of tetrahydrocannabinol/cannabidiol (THC/CBD) in 23 patients with indolent leukemic B cell lymphomas. Primary endpoint was a significant reduction in leukemic B cells. Grade 1 - 2 adverse events were seen in 91% of the patients; most common were dry mouth (78%), vertigo (70%), and somnolence (43%). After THC/CBD a significant reduction in leukemic B cells (median, 11%) occurred within two hours (p = .014), and remained for 6 h without induction of apoptosis or proliferation. Normal B cells and T cells were also reduced. CXCR4 expression increased on leukemic cells and T cells. All effects were gone by 24 h. Our results show that a single dose of THC/CBD affects a wide variety of leukocytes and only transiently reduce malignant cells in blood. Based on this study, THC/CBD shows no therapeutic potential for indolent B cell lymphomas (EudraCT trial no. 2014-005553-39).

Endocannabinoids in immune regulation and immunopathologies

Endocannabinoids are key bioactive components of the endocannabinoid system, and the profound influence of endocannabinoids on the modulation of the immune system is being increasingly appreciated. The knowledge of endocannabinoid-immune cell crosstalk will pave the way to therapeutic implications of modulators of this pathway in autoimmune and chronic inflammatory disorders. Endocannabinoids seem to exert both anti-inflammatory and pro-inflammatory effects in specific contexts, based on specific receptor engagement and the downstream signalling pathways involved. In this review, we summarized the biosynthesis, signalling and degradation of two well-studied endocannabinoids-anandamide and 2-arachidonylglycerol in immune cells. Then, we discussed the effects of these two endocannabinoids on the functioning of major innate and adaptive immune cells, along with the choice of receptors employed in such interactions. Finally, we outline our current knowledge on the involvement of anandamide and 2-arachidonylglycerol in context of inflammation, allergies, autoimmunity and metabolic disorders.

Cannabinoid Receptors: An Update on Cell Signaling, Pathophysiological Roles and Therapeutic Opportunities in Neurological, Cardiovascular, and Inflammatory Diseases

The identification of the human cannabinoid receptors and their roles in health and disease, has been one of the most significant biochemical and pharmacological advancements to have occurred in the past few decades. In spite of the major strides made in furthering endocannabinoid research, therapeutic exploitation of the endocannabinoid system has often been a challenging task. An impaired endocannabinoid tone often manifests as changes in expression and/or functions of type 1 and/or type 2 cannabinoid receptors. It becomes important to understand how alterations in cannabinoid receptor cellular signaling can lead to disruptions in major physiological and biological functions, as they are often associated with the pathogenesis of several neurological, cardiovascular, metabolic, and inflammatory diseases. This review focusses mostly on the pathophysiological roles of type 1 and type 2 cannabinoid receptors, and it attempts to integrate both cellular and physiological functions of the cannabinoid receptors. Apart from an updated review of pre-clinical and clinical studies, the adequacy/inadequacy of cannabinoid-based therapeutics in various pathological conditions is also highlighted. Finally, alternative strategies to modulate endocannabinoid tone, and future directions are also emphasized.

G-protein coupled receptors and ligands that organize humoral immune responses

B-cell responses are dynamic processes that depend on multiple types of interactions. Rare antigen-specific B cells must encounter antigen and specialized systems are needed-unique to each lymphoid tissue type-to ensure this happens efficiently. Lymphoid tissue barrier cells act to ensure that pathogens, while being permitted entry for B-cell recognition, are blocked from replication or dissemination. T follicular helper (Tfh) cells often need to be primed by dendritic cells before supporting B-cell responses. For most responses, antigen-specific helper T cells and B cells need to interact, first to initiate clonal expansion and the plasmablast response, and later to support the germinal center (GC) response. Newly formed plasma cells need to travel to supportive niches. GC B cells must become confined to the follicle center, organize into dark and light zones, and interact with Tfh cells. Memory B cells need to be positioned for rapid responses following reinfection. Each of these events requires the actions of multiple G-protein coupled receptors (GPCRs) and their ligands, including chemokines and lipid mediators. This review will focus on the guidance cue code underlying B-cell immunity, with an emphasis on findings from our laboratory and on newer advances in related areas. We will discuss our recent identification of geranylgeranyl-glutathione as a ligand for P2RY8. Our goal is to provide the reader with a focused knowledge about the GPCRs guiding B-cell responses and how they might be therapeutic targets, while also providing examples of how multiple types of GPCRs can cooperate or act iteratively to control cell behavior.

Drugs of Abuse Induced-Subversion of the Peripheral Immune Response and Central Glial Activity: Focus on Novel Therapeutic Approaches

BACKGROUND

Drugs of abuse affect both central nervous system (CNS) and peripheral immune function. Besides the involvement of dopamine and glutamate systems, chronic exposure to drugs of abuse alters immune homeostasis, promoting a pro-inflammatory status. At the same time, impaired peripheral immunity leads to an increased susceptibility to infections in drug abusers.

DISCUSSION

There is evidence that certain drugs, such as opioids, activate microglial cells and astrocytes which, in turn, provoke central neuroinflammation. Particularly, opioids bind the Toll-like receptor (TLR)-4 with increased expression of nuclear factor kappa-light-chain-enhancer of activated B cells and release of pro-inflammatory cytokines. Peripheral mediators released by immune cells also contribute to aggravate central neuroinflammation.

CONCLUSION

These are based either on the inhibition of TLR-4 activation by drugs of abuse or on the correction of dopamine and glutamate pathways. Finally, a hypothetic nutraceutical intervention with polyphenols in view of their anti-inflammatory and anti-oxidant properties will be outlined as an adjuvant treatment for drugs of abuse-related disorders.

Cannabinoid receptor 2 deficiency exacerbates inflammation and neutrophil recruitment

Cannabinoid receptor (CB)₂ is an immune cell–localized GPCR that has been hypothesized to regulate the magnitude of inflammatory responses. However, there is currently no consensus as to the mechanism by which CB₂ mediates its anti-inflammatory effects in vivo. To address this question, we employed a murine dorsal air pouch model with wild-type and CB₂^−/− 8–12-wk-old female and male C57BL/6 mice and found that acute neutrophil and lymphocyte antigen 6 complex, locus C^hi monocyte recruitment in response to Zymosan was significantly enhanced in CB₂^−/− mice. Additionally, levels of matrix metalloproteinase 9 and the chemokines C-C motif chemokine ligand (CCL)2, CCL4, and C-X-C motif chemokine ligand 10 in CB₂^−/− pouch exudates were elevated at earlier time points. Importantly, using mixed bone marrow chimeras, we revealed that the proinflammatory phenotype in CB₂^−/− mice is neutrophil-intrinsic rather than stromal cell–dependent. Indeed, neutrophils isolated from CB₂^−/− mice exhibited an enhanced migration-related transcriptional profile and increased adhesive phenotype, and treatment of human neutrophils with a CB₂ agonist blocked their endothelial transmigration. Overall, we have demonstrated that CB₂ plays a nonredundant role during acute neutrophil mobilization to sites of inflammation and, as such, it could represent a therapeutic target for the development of novel anti-inflammatory compounds to treat inflammatory human diseases.—Kapellos, T. S., Taylor, L., Feuerborn, A., Valaris, S., Hussain, M. T., Rainger, G. E., Greaves, D. R., Iqbal, A. J. Cannabinoid receptor 2 deficiency exacerbates inflammation and neutrophil recruitment.

Sphingosine Kinases promote IL-17 expression in human T lymphocytes

Sphingosine 1-phosphate (S1P) has a role in many cellular processes. S1P is involved in cell growth and apoptosis, regulation of cell trafficking, production of cytokines and chemokines. The kinases SphK1 and SphK2 (SphKs) phosphorilate Sphingosine (Sph) to S1P and several phosphatases revert S1P to sphingosine, thus assuring a balanced pool that can be depleted by a Sphingosine lyase in hexadecenal compounds and aldehydes. There are evidences that SphK1 and 2 may per se control cellular processes. Here, we report that Sph kinases regulate IL-17 expression in human T cells. SphKs inhibition impairs the production of IL-17, while their overexpression up-regulates expression of the cytokine through acetylation of IL-17 promoter. SphKs were up-regulated also in PBMCs of patients affected by IL-17 related diseases. Thus, S1P/S1P kinases axis is a mechanism likely to promote IL-17 expression in human T cells, representing a possible therapeutic target in human inflammatory diseases.

Gαi Signaling Promotes Marginal Zone B Cell Development by Enabling Transitional B Cell ADAM10 Expression

The follicular (FO) versus marginal zone (MZ) B cell fate decision in the spleen depends upon BCR, BAFF, and Notch2 signaling. Whether or how G_i signaling affects this fate decision is unknown. Here, we show that direct contact with Notch ligand expressing stromal cells (OP9-Delta-like 1) cannot promote normal MZ B cell development when progenitor B cells lack Gα_i proteins, or if Gi signaling is disabled. Consistent with faulty ADAM10-dependent Notch2 processing, Gα_i-deficient transitional B cells had low ADAM10 membrane expression levels and reduced Notch2 target gene expression. Immunoblotting Gα_i-deficient B cell lysates revealed a reduction in mature, processed ADAM10. Suggesting that Gα_i signaling promotes ADAM10 membrane expression, stimulating normal transitional B cells with CXCL12 raised it, while inhibiting Gα_i nucleotide exchange blocked its upregulation. Surprisingly, inhibiting Gα_i nucleotide exchange in transitional B cells also impaired the upregulation of ADAM10 that occurs following antigen receptor crosslinking. These results indicate that Gα_i signaling supports ADAM10 maturation and activity in transitional B cells, and ultimately Notch2 signaling to promote MZ B cell development.

Pericardial Adipose Tissue Regulates Granulopoiesis, Fibrosis, and Cardiac Function After Myocardial Infarction

Background:

The pericardial adipose tissue (AT) contains a high density of lymphoid clusters. It is unknown whether these clusters play a role in post–myocardial infarction (MI) inflammatory responses and cardiac outcome.

Methods:

Lymphoid clusters were examined in epicardial AT of humans with or without coronary artery disease. Murine pericardial lymphoid clusters were visualized in mice subjected to coronary artery ligation. To study the relevance of pericardial clusters during inflammatory responses after MI, we surgically removed the pericardial AT and performed B-cell depletion and granulocyte-macrophage colony-stimulating factor blockade. Leukocytes in murine hearts, pericardial AT, spleen, mediastinal lymph nodes, and bone marrow were quantified by flow cytometry. Cannabinoid receptor CB2 (CB2 –/– ) mice were used as a model for enhanced B-cell responses. The effect of impaired dendritic cell (DC) trafficking on pericardial AT inflammatory responses was tested in CCR7 –/– mice subjected to MI. Cardiac fibrosis and ventricular function were assessed by histology and echocardiography.

Results:

We identified larger B-cell clusters in epicardial AT of human patients with coronary artery disease in comparison with controls without coronary artery disease. Infarcted mice also had larger pericardial clusters and 3-fold upregulated numbers of granulocyte-macrophage colony-stimulating factor–producing B cells within pericardial AT, but not spleen or lymph nodes. This was associated with higher DC and T-cell counts in pericardial AT, which outnumbered DCs and T cells in lymph nodes. Analysis of DC maturation markers, tracking experiments with fluorescently labeled cells, and use of CCR7-deficient mice suggested that activated DCs migrate from infarcts into pericardial AT via CCR7. B-cell depletion or granulocyte-macrophage colony-stimulating factor neutralization inhibited DC and T-cell expansion within pericardial AT, and translated into reduced bone marrow granulopoiesis and cardiac neutrophil infiltration 3 days after MI. The relevance of the pericardial AT in mediating all these effects was confirmed by removal of pericardial AT and ex vivo coculture with pericardial AT and granulocyte progenitors. Finally, enhanced fibrosis and worsened ejection fraction in CB2 –/– mice were limited by pericardial AT removal.

Conclusions:

Our findings unveil a new mechanism by which the pericardial AT coordinates immune cell activation, granulopoiesis, and outcome after MI.

2-AG limits Theiler's virus induced acute neuroinflammation by modulating microglia and promoting MDSCs

The innate immune response is mediated by primary immune modulators such as cytokines and chemokines that together with immune cells and resident glia orchestrate CNS immunity and inflammation. Growing evidence supports that the endocannabinoid 2-arachidonoylglycerol (2-AG) exerts protective actions in CNS injury models. Here, we used the acute phase of Theiler's virus induced demyelination disease (TMEV-IDD) as a model of acute neuroinflammation to investigate whether 2-AG modifies the brain innate immune responses to TMEV and CNS leukocyte trafficking. 2-AG or the inhibition of its hydrolysis diminished the reactivity and number of microglia at the TMEV injection site reducing their morphological complexity and modulating them towards an anti-inflammatory state via CB2 receptors. Indeed, 2-AG dampened the infiltration of immune cells into the CNS and inhibited their egress from the spleen, resulting in long-term beneficial effects at the chronic phase of the disease. Intriguingly, it is not a generalized action over leukocytes since 2-AG increased the presence and suppressive potency of myeloid derived suppressor cells (MDSCs) in the brain resulting in higher apoptotic CD4⁺ T cells at the injection site. Together, these data suggest a robust modulatory effect in the peripheral and central immunity by 2-AG and highlight the interest of modulating endogenous cannabinoids to regulate CNS inflammatory conditions.

Peripheral modulation of the endocannabinoid system in metabolic disease

Dysfunction of the endocannabinoid system (ECS) has been identified in metabolic disease. Cannabinoid receptor 1 (CB₁) is abundantly expressed in the brain but also expressed in the periphery. Cannabinoid receptor 2 (CB₂) is more abundant in the periphery, including the immune cells. In obesity, global antagonism of overexpressed CB₁ reduces bodyweight but leads to centrally mediated adverse psychological outcomes. Emerging research in isolated cultured cells or tissues has demonstrated that targeting the endocannabinoid system in the periphery alleviates the pathologies associated with metabolic disease. Further, peripheral specific cannabinoid ligands can reverse aspects of the metabolic phenotype. This Keynote review will focus on current research on the functionality of peripheral modulation of the ECS for the treatment of obesity.

Genetic Models of Macrophage Depletion

Macrophages are a heterogeneous population of innate immune cells and are distributed in most adult tissues. Certain tissue-resident macrophages with a prenatal origin, together with postnatal monocyte-derived macrophages, serve as the host scavenger system to eliminate invading pathogens, malignant cells, senescent cells, dead cells, cellular debris, and other foreign substances. As a key member of the mononuclear phagocyte system, macrophages play essential roles in regulation of prenatal development, tissue homeostasis, and disease progression. Over the past two decades, considerable efforts have been made to generate genetic models of macrophage ablation in mice. These models support investigations of the precise functions of tissue-specific macrophages under physiological and pathological conditions. Herein, we overview the currently available mouse strains for in vivo genetic ablation of macrophages and discuss their respective advantages and limitations.

Cholesterol Accumulation in CD11c+ Immune Cells Is a Causal and Targetable Factor in Autoimmune Disease

Liver X receptors (LXRs) are regulators of cholesterol metabolism that also modulate immune responses. Inactivation of LXR α and β in mice leads to autoimmunity; however, how the regulation of cholesterol metabolism contributes to autoimmunity is unclear. Here we found that cholesterol loading of CD11c⁺ cells triggered the development of autoimmunity, whereas preventing excess lipid accumulation by promoting cholesterol efflux was therapeutic. LXRβ-deficient mice crossed to the hyperlipidemic ApoE-deficient background or challenged with a high-cholesterol diet developed autoantibodies. Cholesterol accumulation in lymphoid organs promoted T cell priming and stimulated the production of the B cell growth factors Baff and April. Conversely, B cell expansion and the development of autoantibodies in ApoE/LXR-β-deficient mice was reversed by ApoA-I expression. These findings implicate cholesterol imbalance as a contributor to immune dysfunction and suggest that stimulating HDL-dependent reverse cholesterol transport could be beneficial in the setting of autoimmune disease.

Ageing adversely affects the migration and function of marginal zone B cells

Marginal zone (MZ) B cells are positioned within the spleen to capture blood-borne antigen and immune complexes and deliver them to follicular dendritic cells in the B-cell follicles. We show that within the spleens of aged mice antigen capture by MZ B cells, and their ability to shuttle between the follicle and MZ, were impaired. The ability of aged MZ B cells to migrate towards the MZ chemoattractant sphingosine-1-phosphate was increased, suggesting that aged MZ B cells had a greater propensity to be retained within the MZ. An extrinsic impairment in aged B-cell migration towards the MZ was demonstrated using bone marrow chimeras. The follicular shuttling of MZ B cells derived from either young or aged bone marrow was similarly reduced in aged recipient spleens, showing that ageing effects on splenic stromal cells were responsible for the impaired follicular shuttling of MZ B cells. MZ B cells rapidly mount T-cell-independent (TI) antibody-responses to microbial polysaccharide antigen. In aged mice the ability to produce immunoglobulins in response to the TI type 1 antigen TNP-LPS was impaired. These ageing-related changes to the MZ and MZ B cells have implications for the clearance of blood-borne pathogens. Indeed elderly people have increased susceptibility to Streptococcus pneumoniae, a TI antigen, and decreased responses to vaccination. A thorough analysis of the mechanisms that underpin the ageing-related decline in the status of the MZ and MZ B cells will help the design of novel treatments to improve immunity in the elderly.

Cannabinoid Receptors Are Overexpressed in CLL but of Limited Potential for Therapeutic Exploitation

The cannabinoid receptors 1 and 2 (CNR1&2) are overexpressed in a variety of malignant diseases and cannabinoids can have noteworthy impact on tumor cell viability and tumor growth. Patients diagnosed with chronic lymphocytic leukemia (CLL) present with very heterogeneous disease characteristics translating into highly differential risk properties. To meet the urgent need for refinement in risk stratification at diagnosis and the search for novel therapies we studied CNR expression and response to cannabinoid treatment in CLL. Expression levels of CNR1&2 were determined in 107 CLL patients by real-time PCR and analyzed with regard to prognostic markers and survival. Cell viability of primary CLL cells was determined in suspension and co-culture after incubation in increasing cannabinoid concentrations under normal and reduced serum conditions and in combination with fludarabine. Impact of cannabinoids on migration of CLL cells towards CXCL12 was determined in transwell plates. We found CNR1&2 to be overexpressed in CLL compared to healthy B-cells. Discriminating between high and low expressing subgroups, only high CNR1 expression was associated with two established high risk markers and conferred significantly shorter overall and treatment free survival. Viability of CLL primary cells was reduced in a dose dependent fashion upon incubation with cannabinoids, however, healthy cells were similarly affected. Under serum reduced conditions, no significant differences were observed within suspension and co-culture, respectively, however, the feeder layer contributed significantly to the survival of CLL cells compared to suspension culture conditions. No significant differences were observed when treating CLL cells with cannabinoids in combination with fludarabine. Interestingly, biologic activity of cannabinoids was independent of both CNR1&2 expression. Finally, we did not observe an inhibition of CXCL12-induced migration by cannabinoids. In contrast to other tumor entities, our data suggest a limited usability of cannabinoids for CLL therapy. Nonetheless, we could define CNR1 mRNA expression as novel prognostic marker.

Expression analysis of cannabinoid receptors 1 and 2 in B cells during pregnancy and their role on cytokine production

The endocannabinoid system consists in a family of lipids that binds to and activates cannabinoid receptors. There are two receptors so far described, the cannabinoid receptor 1 (CB1) and 2 (CB2). In the context of pregnancy, the endocannabinoid system was shown participates in different key aspects of reproductive events. B-lymphocytes are pleiotropic cells belonging to the adaptive arm of the immune system. Besides immunoglobulin production, B-lymphocytes were recently shown to be actively involved in antigen presentation as well as cytokine production, thus playing a central role in immunity. In this study we first aimed to characterize the expression of CB1 and CB2 receptors in B cells during pregnancy and then analyze the impact of their activation in term of cytokine production by B cells from pregnant and non-pregnant mice. We observed that the expression of CB1 and CB2 receptors in B-lymphocytes is differentially regulated during pregnancy. While CB2 expression is down regulated CB1 is augmented in B-lymphocytes of pregnant mice. Additionally, the treatment of activated B-lymphocytes with specific CB1 and CB2 agonists, showed a different response in term of cytokine production. Particularly, CB1 against boosted the production of the anti-inflammatory cytokine IL-10 by activated B-lymphocytes from pregnant mice.

IL-10+ Innate-like B Cells Are Part of the Skin Immune System and Require α4β1 Integrin To Migrate between the Peritoneum and Inflamed Skin

The skin is an important barrier organ and frequent target of autoimmunity and allergy. In this study, we found innate-like B cells that expressed the anti-inflammatory cytokine IL-10 in the skin of humans and mice. Unexpectedly, innate-like B1 and conventional B2 cells showed differential homing capacities with peritoneal B1 cells preferentially migrating into the inflamed skin of mice. Importantly, the skin-homing B1 cells included IL-10-secreting cells. B1 cell homing into the skin was independent of typical skin-homing trafficking receptors and instead required α4β1-integrin. Moreover, B1 cells constitutively expressed activated β1 integrin and relocated from the peritoneum to the inflamed skin and intestine upon innate stimulation, indicating an inherent propensity to extravasate into inflamed and barrier sites. We conclude that innate-like B cells migrate from central reservoirs into skin, adding an important cell type with regulatory and protective functions to the skin immune system.

Expression Analysis of CB2-GFP BAC Transgenic Mice

The endocannabinoid system (ECS) is a retrograde messenger system, consisting of lipid signaling molecules that bind to at least two G-protein-coupled receptors, Cannabinoid receptor 1 and 2 (CB1 and 2). As CB2 is primarily expressed on immune cells such as B cells, T cells, macrophages, dendritic cells, and microglia, it is of great interest how CB2 contributes to immune cell development and function in health and disease. Here, understanding the mechanisms of CB2 involvement in immune-cell function as well as the trafficking and regulation of CB2 expressing cells are crucial issues. Up to now, CB2 antibodies produce unclear results, especially those targeting the murine protein. Therefore, we have generated BAC transgenic GFP reporter mice (CB2-GFPTg) to trace CB2 expression in vitro and in situ. Those mice express GFP under the CB2 promoter and display GFP expression paralleling CB2 expression on the transcript level in spleen, thymus and brain tissue. Furthermore, by using fluorescence techniques we show that the major sources for GFP-CB2 expression are B cells in spleen and blood and microglia in the brain. This novel CB2-GFP transgenic reporter mouse line represents a powerful resource to study CB2 expression in different cell types. Furthermore, it could be used for analyzing CB2-mediated mobilization and trafficking of immune cells as well as studying the fate of recruited immune cells in models of acute and chronic inflammation.

Downstream effects of endocannabinoid on blood cells: implications for health and disease

Endocannabinoids (eCBs), among which N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) are the most biologically active members, are polyunsaturated lipids able to bind cannabinoid, vanilloid and peroxisome proliferator-activated receptors. Depending on the target engaged, these bioactive mediators can regulate different signalling pathways, at both central and peripheral levels. The biological action of eCBs is tightly controlled by a plethora of metabolic enzymes which, together with the molecular targets of these substances, form the so-called "endocannabinoid system". The ability of eCBs to control manifold peripheral functions has received a great deal of attention, especially in the light of their widespread distribution in the body. In particular, eCBs are important regulators in blood, where they modulate haematopoiesis, platelet aggregation and apoptosis, as well as chemokine release and migration of immunocompetent cells. Here, we shall review the current knowledge on the pathophysiological roles of eCBs in blood. We shall also discuss the involvement of eCBs in those disorders affecting the haematological system, including cancer and inflammation. Knowledge gained to date underlines a fundamental role of the eCB system in blood, thus suggesting that it may represent a therapeutic promise for a broad range of diseases involving impaired hematopoietic cell functions.

B-cell intrinsic TLR7 signals promote depletion of the marginal zone in a murine model of Wiskott-Aldrich syndrome

Patients with Wiskott-Aldrich syndrome (WAS) exhibit prominent defects in splenic marginal zone (MZ), resulting in abnormal T-cell-independent antibody responses and increased bacterial infections. B-cell-intrinsic deletion of the affected gene WAS protein (WASp) markedly reduces splenic MZ B cells, without impacting the rate of MZ B-cell development, suggesting that abnormal B-cell retention within the MZ accounts for MZ defects in WAS. Since WASp regulates integrin-dependent actin cytoskeletal rearrangement, we previously hypothesized that defective B-cell integrin function promotes MZ depletion. In contrast, we now report that B-cell-intrinsic deletion of the TLR signaling adaptor MyD88 is sufficient to restore the MZ in WAS. We further identify TLR7, an endosomal single-stranded RNA (ssRNA) receptor, as the MyD88-dependent receptor responsible for WAS MZ depletion. These findings implicate spontaneous activation of MZ B cells by ssRNA-containing self-ligands (likely derived from circulating apoptotic material) as the mechanism underlying MZ depletion in WAS. Together, these data suggest a previously unappreciated role for B-cell intrinsic TLR signals in MZ homeostasis, of relevance to both pathogen responses and to the development of systemic autoimmunity.

B Lymphocyte-Specific Loss of Ric-8A Results in a Gα Protein Deficit and Severe Humoral Immunodeficiency

Resistance to inhibitors of cholinesterase 8A (Ric-8A) is a highly evolutionarily conserved cytosolic protein initially identified in Caenorhabditis elegans, where it was assigned a regulatory role in asymmetric cell divisions. It functions as a guanine nucleotide exchange factor for Gαi, Gαq, and Gα12/13 and as a molecular chaperone required for the initial association of nascent Gα subunits with cellular membranes in embryonic stem cell lines. To test its role in hematopoiesis and B lymphocytes specifically, we generated ric8 (fl/fl) vav1-cre and ric8 (fl/fl) mb1-cre mice. The major hematopoietic cell lineages developed in the ric8 (fl/fl) vav1-cre mice, notwithstanding severe reduction in Gαi2/3, Gαq, and Gα13 proteins. B lymphocyte-specific loss of Ric-8A did not compromise bone marrow B lymphopoiesis, but splenic marginal zone B cell development failed, and B cells underpopulated lymphoid organs. The ric8 (fl/fl) mb1-cre B cells exhibited poor responses to chemokines, abnormal trafficking, improper in situ positioning, and loss of polarity components during B cell differentiation. The ric8 (fl/fl) mb1-cre mice had a severely disrupted lymphoid architecture and poor primary and secondary Ab responses. In B lymphocytes, Ric-8A is essential for normal Gα protein levels and is required for B cell differentiation, trafficking, and Ab responses.

Influence of rimonabant treatment on peripheral blood mononuclear cells; flow cytometry analysis and gene expression profiling

The cannabinoid receptor type 1 (CB1) antagonist rimonabant has been used as treatment for obesity. In addition, anti-proliferative effects on mitogen-activated leukocytes have been demonstrated in vitro. We have previously shown that rimonabant (SR141716A) induces cell death in ex vivo isolated malignant lymphomas with high expression of CB1 receptors. Since CB1 targeting may be part of a future lymphoma therapy, it was of interest to investigate possible effects on peripheral blood mononuclear cells (PBMC) in patients treated with rimonabant. We therefore evaluated leukocyte subsets by 6 color flow cytometry in eight patients before and at treatment with rimonabant for 4 weeks. Whole-transcript gene expression profiling in PBMC before and at 4 weeks of rimonabant treatment was done using Affymetrix Human Gene 1.0 ST Arrays. Our data show no significant changes of monocytes, B cells, total T cells or T cell subsets in PBMC during treatment with rimonabant. There was a small but significant increase in CD3-, CD16+ and/or CD56+ cells after rimonabant therapy. Gene expression analysis detected significant changes in expression of genes associated with innate immunity, cell death and metabolism. The present study shows that normal monocytes and leukocyte subsets in blood remain rather constant during rimonabant treatment. This is in contrast to the induction of cell death previously observed in CB1 expressing lymphoma cells in response to treatment with rimonabant in vitro. These differential effects observed on normal and malignant lymphoid cells warrant investigation of CB1 targeting as a potential lymphoma treatment.

The endocannabinoid system and its therapeutic implications in rheumatoid arthritis

Since the discovery of the endogenous receptor for Δ(9)-tetrahydrocannabinol, a main constituent of marijuana, the endocannabinoid system (comprising cannabinoid receptors and their endogenous ligands, as well as the enzymes involved in their metabolic processes) has been implicated as having multiple regulatory functions in many central and peripheral conditions, including rheumatoid arthritis (RA). RA is an immune-mediated inflammatory disease that is associated with the involvement of many kinds of cells (such as fibroblastlike synoviocytes [FLSs], osteoclasts, T cells, B cells, and macrophages) and molecules (such as interleukin-1β, tumor necrosis factor-α, interleukin-6, matrix metalloproteinases [MMPs], and chemokines). Increasing evidence suggests that the endocannabinoid system, especially cannabinoid receptor 2 (CB2), has an important role in the pathophysiology of RA. Many members of the endocannabinoid system are reported to inhibit synovial inflammation, hyperplasia, and cartilage destruction in RA. In particular, specific activation of CB2 may relieve RA by inhibiting not only the production of autoantibodies, proinflammatory cytokines, and MMPs, but also bone erosion, immune response mediated by T cells, and the proliferation of FLSs. In this review, we will discuss the possible functions of the endocannabinoid system in the modulation of RA, which may be a potential target for treatment.

Endocannabinoid signalling in innate and adaptive immunity

The immune system can be modulated and regulated not only by foreign antigens but also by other humoral factors and metabolic products, which are able to affect several quantitative and qualitative aspects of immunity. Among these, endocannabinoids are a group of bioactive lipids that might serve as secondary modulators, which when mobilized coincident with or shortly after first-line immune modulators, increase or decrease many immune functions. Most immune cells express these bioactive lipids, together with their set of receptors and of enzymes regulating their synthesis and degradation. In this review, a synopsis of the manifold immunomodulatory effects of endocannabinoids and their signalling in the different cell populations of innate and adaptive immunity is appointed, with a particular distinction between mice and human immune system compartments.

Genetic Manipulation of the Endocannabinoid System

The physiological and pathophysiological functions of the endocannabinoid system have been studied extensively using transgenic and targeted knockout mouse models. The first gene deletions of the cannabinoid CB(1) receptor were described in the late 1990s, soon followed by CB(2) and FAAH mutations in early 2000. These mouse models helped to elucidate the fundamental role of endocannabinoids as retrograde transmitters in the CNS and in the discovery of many unexpected endocannabinoid functions, for example, in the skin, bone and liver. We now have knockout mouse models for almost every receptor and enzyme of the endocannabinoid system. Conditional mutant mice were mostly developed for the CB(1) receptor, which is widely expressed on many different neurons, astrocytes and microglia, as well as on many cells outside the CNS. These mouse strains include "floxed" CB(1) alleles and mice with a conditional re-expression of CB(1). The availability of these mice made it possible to decipher the function of CB(1) in specific neuronal circuits and cell populations or to discriminate between central and peripheral effects. Many of the genetic mouse models were also used in combination with viral expression systems. The purpose of this review is to provide a comprehensive overview of the existing genetic models and to summarize some of the most important discoveries that were made with these animals.

Tissue-resident memory T cells

Tissue-resident memory T (Trm) cells constitute a recently identified lymphocyte lineage that occupies tissues without recirculating. They provide a first response against infections reencountered at body surfaces, where they accelerate pathogen clearance. Because Trm cells are not present within peripheral blood, they have not yet been well characterized, but are transcriptionally, phenotypically, and functionally distinct from recirculating central and effector memory T cells. In this review, we will summarize current knowledge of Trm cell ontogeny, regulation, maintenance, and function and will highlight technical considerations for studying this population.

Perturbations of the endocannabinoid system in mantle cell lymphoma: correlations to clinical and pathological features

The cannabinoid receptors are upregulated in many types of cancers, including mantle cell lymphoma (MCL) and have been suggested to constitute novel therapeutic targets. The expression pattern of the key members of the endocannabinoid system was analyzed in a well-characterized MCL patient cohort and correlated to biological features. 107 tumor tissues were analyzed for the mRNA levels of cannabinoid receptors 1 and 2 (CNR1 and CNR2) and the two main enzymes regulating the endocannabinoid anandamide levels in tissue: NAPEPLD and FAAH (participating in synthesis and degradation, respectively). NAPEPLD, CNR1 and CNR2 were overexpressed while FAAH expression was reduced in MCL compared to non-malignant B-cells. Both low CNR1 and high FAAH levels correlated with lymphocytosis (p=0.016 and p=0.022, respectively) and with leukocytosis (p=0.0018 and p=0.047). Weak to moderate CNR1 levels were a feature of SOX11 negative MCL (p=0.006). Both high CNR2 and high FAAH levels correlated to anemia (p=0.0006 and p=0.038, respectively). In conclusion, the relative expression of the anandamide synthesizing and metabolizing enzymes in MCL is heavily perturbed. This finding, together with high expression of cannabinoid receptors, could favor enhanced anandamide signaling and suggest that targeting the endocannabinoid system might be considered as part of lymphoma therapy.

Immune system: a possible nexus between cannabinoids and psychosis

BACKGROUND

Endocannabinoid system is involved in the regulation of the brain-immune axis. Cannabis consumption is related with the development, course, and severity of psychosis. The epidemiological evidence for increased occurrence of immunological alterations in patients with psychosis has not been sufficiently addressed. The aim of this review is to establish whether there is any scientific evidence of the influence of cannabinoids on aspects of immunity that affect susceptibility to psychotic disorder induction.

METHODS

A comprehensive search of PubMed/MEDLINE, EMBASE and ISI Web of Knowledge was performed using combinations of key terms distributed into three blocks: "immune", "cannabinoid", and "endocannabinoid receptor". Studies were considered to be eligible for the review if they were original articles, they reported a quantitative or qualitative relation between cannabinoid ligands, their receptors, and immune system, and they were carried out in vitro or in mammals, included humans. All the information was systematically extracted and evaluated.

RESULTS

We identified 122 articles from 446 references. Overall, endocannabinoids enhanced immune response, whereas exogenous cannabinoids had immunosuppressant effects. A general change in the immune response from Th1 to Th2 was also demonstrated for cannabinoid action. Endogenous and synthetic cannabinoids also modulated microglia function and neurotransmitter secretion.

CONCLUSION

The actions of cannabinoids through the immune system are quite regular and predictable in the peripheral but remain fuzzy in the central nervous system. Despite this uncertainty, it may be hypothesized that exposure to exocannabinoids, in particular during adolescence might prompt immunological dysfunctions that potentially cause a latent vulnerability to psychosis. Further investigations are warranted to clarify the relationship between the immunological effects of cannabis and psychosis.

Cell-based assays for IGF-I bioactivity measurement: overview, limitations and current trends

Insulin-like growth factor-I (IGF-I) is an important growth promoting protein that is involved in numerous cellular responses and multiple biological systems. Although the molecular structure, function and recombinant production of IGF-I in various hosts have been the subject of much researches over the recent past, methods to determine the bioactivity of this protein have not been fully explored. Several assays have traditionally been used to measure IGF-I bioactivity, but have not become a routine laboratory practice due to the high cost involved and technical problems. Thus, there is still a need for a rapid, technically simple and accurate assay to determine IGF-I bioactivity. This review highlights the various cell-based assays currently commercially available for measuring the bioactivity of IGF-I along with their limitations. This is aimed at presenting the modern-day IGF researcher with a holistic overview of the current trends and future prospects regarding IGF-I bioactivity determinations.

What we know and do not know about the cannabinoid receptor 2 (CB2)

It has been well appreciated that the endocannabinoid system can regulate immune responses via the cannabinoid receptor 2 (CB2), which is primarily expressed by cells of the hematopoietic system. The endocannabinoid system is composed of receptors, ligands and enzymes controlling the synthesis and degradation of endocannabinoids. Along with endocannabinoids, both plant-derived and synthetic cannabinoids have been shown to bind to and signal through CB2 via G proteins leading to both inhibitory and stimulatory signals depending on the biological process. Because no cannabinoid ligand has been identified that only binds to CB2, the generation of mice deficient in CB2 has greatly expanded our knowledge of how CB2 contributes to immune cell development and function in health and disease. In regards to humans, genetic studies have associated CB2 with a variety of human diseases. Here, we review the endocannabinoid system with an emphasis on CB2 and its role in the immune system.

The spleen in local and systemic regulation of immunity

The spleen is the main filter for blood-borne pathogens and antigens, as well as a key organ for iron metabolism and erythrocyte homeostasis. Also, immune and hematopoietic functions have been recently unveiled for the mouse spleen, suggesting additional roles for this secondary lymphoid organ. Here we discuss the integration of the spleen in the regulation of immune responses locally and in the whole body and present the relevance of findings for our understanding of inflammatory and degenerative diseases and their treatments. We consider whether equivalent activities in humans are known, as well as initial therapeutic attempts to target the spleen for modulating innate and adaptive immunity.

Identification of co-expressed gene signatures in mouse B1, marginal zone and B2 B-cell populations

In mice, three major B-cell subsets have been identified with distinct functionalities: B1 B cells, marginal zone B cells and follicular B2 B cells. Here, we used the growing body of publicly available transcriptomics data to create an expression atlas of 84 gene expression microarray data sets of distinct mouse B-cell subsets. These data were subjected to network-based cluster analysis using BioLayout Express(3D). Using this analysis tool, genes with related functions clustered together in discrete regions of the network graph and enabled the identification of transcriptional networks that underpinned the functional activity of distinct cell populations. Some gene clusters were expressed highly by most of the cell populations included in this analysis (such as those with activity related to house-keeping functions). Others contained genes with expression patterns specific to distinct B-cell subsets. While these clusters contained many genes typically associated with the activity of the cells they were specifically expressed in, many novel B-cell-subset-specific candidate genes were identified. A large number of uncharacterized genes were also represented in these B-cell lineage-specific clusters. Further analysis of the activities of these uncharacterized candidate genes will lead to the identification of novel B-cell lineage-specific transcription factors and regulators of B-cell function. We also analysed 36 microarray data sets from distinct human B-cell populations. These data showed that mouse and human germinal centre B cells shared similar transcriptional features, whereas mouse B1 B cells were distinct from proposed human B1 B cells.

Blood, sphingosine-1-phosphate and lymphocyte migration dynamics in the spleen

The spleen, the largest secondary lymphoid organ, has long been known to play important roles in immunity against blood-borne invaders. Yet how cells migrate within the spleen to ensure fast and effective responses is only now coming to light. Chemokines and oxysterols guide lymphocytes from sites of release at terminal arterioles into the lymphocyte-rich white pulp. Sphingosine-1-phosphate (S1P) and S1P-receptor-1 (S1PR1) promote lymphocyte egress from white to red pulp and back to circulation. Intravital two-photon microscopy has shown that marginal zone (MZ) B cells that are enriched between white and red pulps undergo continual oscillatory migration between the MZ and follicles, ferrying antigens. Cycles of G-protein-coupled receptor kinase-2 (GRK2) mediated S1PR1 desensitization and resensitization underlie this remarkable behavior. The findings discussed in this review have implications for understanding how splenic antibody and T-cell responses are mounted, how the immunosuppressant drug FTY720 (fingolimod) affects the spleen, and how cell shuttling behaviors contribute to immunity.

IRF4 controls the positioning of mature B cells in the lymphoid microenvironments by regulating NOTCH2 expression and activity

The transcription factor IRF4 limits the retention of B cells in the marginal zone by inhibiting NOTCH2 signaling.

The transcription factor interferon regulatory factor-4 (IRF4) is expressed in B cells at most developmental stages. In antigen-activated B cells, IRF4 controls germinal center formation, class-switch recombination, and the generation of plasma cells. Here we describe a novel function for IRF4 in the homeostasis of mature B cells. Inducible deletion of irf4 specifically in B cells in vivo led to the aberrant accumulation of irf4-deleted follicular B cells in the marginal zone (MZ) area. IRF4-deficient B cells showed elevated protein expression and activation of NOTCH2, a transmembrane receptor and transcriptional regulator known to be required for MZ B cell development. Administration of a NOTCH2-inhibitory antibody abolished nuclear translocation of NOTCH2 in B cells within 12 h and caused a rapid and progressive disintegration of the MZ that was virtually complete 48 h after injection. The disappearance of the MZ was accompanied by a transient increase of MZ-like B cells in the blood rather than increased B cell apoptosis, demonstrating that continued NOTCH2 activation is critical for the retention of B cells in the MZ. Our results suggest that IRF4 controls the positioning of mature B cells in the lymphoid microenvironments by regulating NOTCH2 expression. These findings may have implications for the understanding of B cell malignancies with dysregulated IRF4 and NOTCH2 activity.

Natural killer T (NKT)-B-cell interactions promote prolonged antibody responses and long-term memory to pneumococcal capsular polysaccharides

Innate-like natural killer T (NKT) cells critically enhance cell and humoral immunity against infections through recognition of conserved microbial lipid antigens presented by CD1d-expressing antigen-presenting cells, and provision of CD40L and cytokine signals. Whereas NKT cells efficiently licensed dendritic cells to prime potent effector and memory T cells, studies based on model antigens such as alphagalactosylceramide-nitrophenyl conjugates concluded that help to B cells was associated with NKT follicular helper differentiation, but limited to short-term responses without induction of memory. We revisited this surprising conclusion in the context of the extracellular encapsulated pathogen Streptococcus pneumoniae, where recognition of lipid and capsular polysaccharide antigens by NKT cells and B cells, respectively, provide critical host protection. Using liposomal nanoparticles displaying synthetic lipid and polysaccharide antigens to elicit pure and direct NKT-B-cell interactions in vivo, we observed intense and prolonged antibody responses with isotype switch, affinity maturation, and long-lasting B-cell memory, despite modest or absent NKT follicular helper differentiation. Furthermore, conditional ablation of Cd1d demonstrated a requirement for a two-step process involving first cognate interactions with dendritic cells, for NKT cell activation, and then with B cells, for induction of isotype switch and memory. Thus, NKT help to B cells represents both a major arm of antimicrobial defense and a promising target for B-cell vaccines.

Ontology based molecular signatures for immune cell types via gene expression analysis

Background

New technologies are focusing on characterizing cell types to better understand their heterogeneity. With large volumes of cellular data being generated, innovative methods are needed to structure the resulting data analyses. Here, we describe an ‘Ontologically BAsed Molecular Signature’ (OBAMS) method that identifies novel cellular biomarkers and infers biological functions as characteristics of particular cell types. This method finds molecular signatures for immune cell types based on mapping biological samples to the Cell Ontology (CL) and navigating the space of all possible pairwise comparisons between cell types to find genes whose expression is core to a particular cell type’s identity.

Results

We illustrate this ontological approach by evaluating expression data available from the Immunological Genome project (IGP) to identify unique biomarkers of mature B cell subtypes. We find that using OBAMS, candidate biomarkers can be identified at every strata of cellular identity from broad classifications to very granular. Furthermore, we show that Gene Ontology can be used to cluster cell types by shared biological processes in order to find candidate genes responsible for somatic hypermutation in germinal center B cells. Moreover, through in silico experiments based on this approach, we have identified genes sets that represent genes overexpressed in germinal center B cells and identify genes uniquely expressed in these B cells compared to other B cell types.

Conclusions

This work demonstrates the utility of incorporating structured ontological knowledge into biological data analysis – providing a new method for defining novel biomarkers and providing an opportunity for new biological insights.

Cannabinoid Receptor 2 (CB2) Plays a Role in the Generation of Germinal Center and Memory B Cells, but Not in the Production of Antigen-Specific IgG and IgM, in Response to T-dependent Antigens

The cannabinoid receptor 2 (CB2) has been reported to modulate B cell functions including migration, proliferation and isotype class switching. Since these processes are required for the generation of the germinal center (GC) and antigen-specific plasma and memory cells following immunization with a T-dependent antigen, CB2 has the capacity to alter the quality and magnitude of T-dependent immune responses. To address this question, we immunized WT and CB2^−/− mice with the T-dependent antigen 4-hydroxy-3-nitrophenylacetyl (NP)-chicken-gamma-globulin (CGG) and measured GC B cell formation and the generation of antigen-specific B cells and serum immunoglobulin (Ig). While there was a significant reduction in the number of splenic GC B cells in CB2^−/− mice early in the response there was no detectable difference in the number of NP-specific IgM and IgG₁ plasma cells. There was also no difference in NP-specific IgM and class switched IgG₁ in the serum. In addition, we found no defect in the homing of plasma cells to the bone marrow (BM) and affinity maturation, although memory B cell cells in the spleen were reduced in CB2^−/− mice. CB2-deficient mice also generated similar levels of antigen-specific IgM and IgG in the serum as WT following immunization with sheep red blood cells (sRBC). This study demonstrates that although CB2 plays a role in promoting GC and memory B cell formation/maintenance in the spleen, it is dispensable on all immune cell types required for the generation of antigen-specific IgM and IgG in T-dependent immune responses.

B-cell biology and development

B cells develop from hematopoietic precursor cells in an ordered maturation and selection process. Extensive studies with many different mouse mutants provided fundamental insights into this process. However, the characterization of genetic defects causing primary immunodeficiencies was essential in understanding human B-cell biology. Defects in pre-B-cell receptor components or in downstream signaling proteins, such as Bruton tyrosine kinase and B-cell linker protein, arrest development at the pre-B-cell stage. Defects in survival-regulating proteins, such as B-cell activator of the TNF-α family receptor (BAFF-R) or caspase recruitment domain-containing protein 11 (CARD11), interrupt maturation and prevent differentiation of transitional B cells into marginal zone and follicular B cells. Mature B-cell subsets, immune responses, and memory B-cell and plasma cell development are disturbed by mutations affecting Toll-like receptor signaling, B-cell antigen receptor coreceptors (eg, CD19), or enzymes responsible for immunoglobulin class-switch recombination. Transgenic mouse models helped to identify key regulatory mechanisms, such as receptor editing and clonal anergy, preventing the activation of B cells expressing antibodies recognizing autoantigens. Nevertheless, the combination of susceptible genetic backgrounds with the rescue of self-reactive B cells by T cells allows the generation of autoreactive clones found in patients with many autoimmune diseases and even in those with primary immunodeficiencies. The rapid progress of functional genomic research is expected to foster the development of new tools that specifically target dysfunctional B lymphocytes to treat autoimmunity, B-cell malignancies, and immunodeficiency.

Oxysterol gradient generation by lymphoid stromal cells guides activated B cell movement during humoral responses

7α,25-dihydroxycholesterol (7α,25-OHC) is a ligand for the G protein-coupled receptor EBI2; however, the cellular sources of this oxysterol are undefined. 7α,25-OHC is synthesized from cholesterol by the stepwise actions of two enzymes, CH25H and CYP7B1, and is metabolized to a 3-oxo derivative by HSD3B7. We showed that all three enzymes control EBI2 ligand concentration in lymphoid tissues. Lymphoid stromal cells were the main CH25H- and CYP7B1-expressing cells required for positioning of B cells, and they also mediated 7α,25-OHC inactivation. CH25H and CYP7B1 were abundant at the follicle perimeter, whereas CH25H expression by follicular dendritic cells was repressed. CYP7B1, CH25H, and HSD3B7 deficiencies each resulted in defective T cell-dependent plasma cell responses. These findings establish that CYP7B1 and HSD3B7, as well as CH25H, have essential roles in controlling oxysterol production in lymphoid tissues, and they suggest that differential enzyme expression in stromal cell subsets establishes 7α,25-OHC gradients required for B cell responses.

The role of CB1 in immune modulation by cannabinoids

There is clear evidence that CB(2), historically referred to as the peripheral cannabinoid receptor, mediates many of the immune modulatory effects of cannabinoids. However, cannabinoid receptors cannot be classified simply as central or peripheral since CB(2) has been shown to play a role in the central nervous system (CNS) and CB(1) mediates many immune system effects. Although Cnr1 mRNA and CB(1) protein expression is lower than Cnr2 mRNA or CB(2) protein expression in cells of the immune system, several studies have shown direct modulation of immune function via CB(1) by endogenous and exogenous cannabinoids in T cells, innate cells, and to a lesser extent, B cells. In addition, indirect, but CB(1)-dependent, mechanisms of immune modulation exist. In fact, the mechanism by which cannabinoids attenuate neuroinflammation via CB(1) is likely a combination of immune suppression and neuroprotection. Although many studies demonstrate that agonists for CB(1) are immune suppressive and anti-inflammatory, CB(1) antagonists also exhibit anti-inflammatory properties. Overall, the data demonstrate that many of the immune modulatory effects of cannabinoids are mediated via CB(1).

The location of splenic NKT cells favours their rapid activation by blood-borne antigen

Natural killer T (NKT) cells play an important role in mounting protective responses to blood-borne infections. However, though the spleen is the largest blood filter in the body, the distribution and dynamics of NKT cells within this organ are not well characterized. Here we show that the majority of NKT cells patrol around the marginal zone (MZ) and red pulp (RP) of the spleen. In response to lipid antigen, these NKT cells become arrested and rapidly produce cytokines, while the small proportion of NKT cells located in the white pulp (WP) exhibit limited activation. Importantly, disruption of the splenic MZ by chemical or genetic approaches results in a severe reduction in NKT cell activation indicating the need of cooperation between both MZ macrophages and dendritic cells for efficient NKT cell responses. Thus, the location of splenic NKT cells in the MZ and RP facilitates their access to blood-borne antigen and enables the rapid initiation of protective immune responses.