Peroxisome proliferator-activated receptor γ B cell-specific-deficient mice have an impaired antibody response

Combining supervised machine learning with statistics reveals differential gene expression patterns related to energy metabolism in the jejuna of chickens divergently selected for antibody response to sheep red blood cells

Since the 1970s, 2 lines of White Leghorn chickens, HAS and LAS, have been continuously divergently selected for 5-day postinjection antibody titer to injection with sheep red blood cells (SRBC). Antibody response is a complex genetic trait and characterizing differences in gene expression could facilitate better understanding of physiological changes due to selection and antigen exposure. At 41 d of age, randomly selected HAS and LAS chickens, which had been coraised from hatch, were either injected with SRBC (HASI and LASI) or kept as the noninjected cohort (HASN and LASN). Five days later, all were euthanized, and samples collected from the jejunum for RNA isolation and sequencing. Resulting gene expression data were analyzed combining traditional statistics with machine learning to obtain signature gene lists for functional analysis. Differences in ATP production and cellular processes were observed in the jejunum between lines and following SRBC injection. HASN vs. LASN exhibited upregulation of ATP production, immune cell motility, and inflammation. LASI exhibits upregulation of ATP production and protein synthesis vs. LASN, reflective of what was observed in HASN vs. LASN. In contrast, no corresponding upregulation of ATP production was observed in HASI vs. HASN, and most other cellular processes appear inhibited. Without exposure to SRBC, gene expression in the jejunum indicates HAS generates more ATP than LAS, suggesting HAS maintains a "primed" system; and gene expression of HASI vs. HASN further suggests this basal ATP production is sufficient for robust antibody responses. Conversely, LASI vs. LASN jejunal gene expression implies a physiological need for increased ATP production with only minimal correlating antibody production. The results of this experiment provide insight into energetic resource needs and allocations in the jejunum in response to genetic selection and antigen exposure in HAS and LAS which may help explain phenotypic differences observed in antibody response.

Mitochondria as disease-relevant organelles in rheumatoid arthritis

Mitochondria are the controllers of cell metabolism and are recognized as decision makers in cell death pathways, organizers of cytoplasmic signaling networks, managers of cellular stress responses, and regulators of nuclear gene expression. Cells of the immune system are particularly dependent on mitochondrial resources, as they must swiftly respond to danger signals with activation, trafficking, migration, and generation of daughter cells. Analogously, faulty immune responses that lead to autoimmunity and tissue inflammation rely on mitochondria to supply energy, cell building blocks and metabolic intermediates. Emerging data endorse the concept that mitochondrial fitness, and the lack of it, is of particular relevance in the autoimmune disease rheumatoid arthritis (RA) where deviations of bioenergetic and biosynthetic flux affect T cells during early and late stages of disease. During early stages of RA, mitochondrial deficiency allows naïve RA T cells to lose self-tolerance, biasing fundamental choices of the immune system toward immune-mediated tissue damage and away from host protection. During late stages of RA, mitochondrial abnormalities shape the response patterns of RA effector T cells engaged in the inflammatory lesions, enabling chronicity of tissue damage and tissue remodeling. In the inflamed joint, autoreactive T cells partner with metabolically reprogrammed tissue macrophages that specialize in antigen-presentation and survive by adapting to the glucose-deplete tissue microenvironment. Here, we summarize recent data on dysfunctional mitochondria and mitochondria-derived signals relevant in the RA disease process that offer novel opportunities to deter autoimmune tissue inflammation by metabolic interference.

The role of peroxisome proliferator-activated receptors in the modulation of hyperinflammation induced by SARS-CoV-2 infection: A perspective for COVID-19 therapy

Coronavirus disease 2019 (COVID-19) is a severe respiratory disease caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that affects the lower and upper respiratory tract in humans. SARS-CoV-2 infection is associated with the induction of a cascade of uncontrolled inflammatory responses in the host, ultimately leading to hyperinflammation or cytokine storm. Indeed, cytokine storm is a hallmark of SARS-CoV-2 immunopathogenesis, directly related to the severity of the disease and mortality in COVID-19 patients. Considering the lack of any definitive treatment for COVID-19, targeting key inflammatory factors to regulate the inflammatory response in COVID-19 patients could be a fundamental step to developing effective therapeutic strategies against SARS-CoV-2 infection. Currently, in addition to well-defined metabolic actions, especially lipid metabolism and glucose utilization, there is growing evidence of a central role of the ligand-dependent nuclear receptors and peroxisome proliferator-activated receptors (PPARs) including PPARα, PPARβ/δ, and PPARγ in the control of inflammatory signals in various human inflammatory diseases. This makes them attractive targets for developing therapeutic approaches to control/suppress the hyperinflammatory response in patients with severe COVID-19. In this review, we (1) investigate the anti-inflammatory mechanisms mediated by PPARs and their ligands during SARS-CoV-2 infection, and (2) on the basis of the recent literature, highlight the importance of PPAR subtypes for the development of promising therapeutic approaches against the cytokine storm in severe COVID-19 patients.

Fatty acid metabolism in adaptive immunity

Fatty acids (FAs) not only are a key component of cellular membrane structure, but also have diverse functions in biological processes. Recent years have seen great advances in understanding of how FA metabolism contributes to adaptive immune response. Here, we review three key processes, FA biosynthesis, FA oxidation and FA uptake, and how they direct T and B cell functions during immune challenges. Then, we will focus on the relationship between microbiota derived FAs, short-chain FAs, and adaptive immunity. Along the way, we will also discuss the outstanding controversies and challenges in the field.

The Role of Transcription Factor PPAR-γ in the Pathogenesis of Psoriasis, Skin Cells, and Immune Cells

The peroxisome proliferator-activated receptor PPAR-γ is one of three PPAR nuclear receptors that act as ligand-activated transcription factors. In immune cells, the skin, and other organs, PPAR-γ regulates lipid, glucose, and amino acid metabolism. The receptor translates nutritional, pharmacological, and metabolic stimuli into the changes in gene expression. The activation of PPAR-γ promotes cell differentiation, reduces the proliferation rate, and modulates the immune response. In the skin, PPARs also contribute to the functioning of the skin barrier. Since we know that the route from identification to the registration of drugs is long and expensive, PPAR-γ agonists already approved for other diseases may also represent a high interest for psoriasis. In this review, we discuss the role of PPAR-γ in the activation, differentiation, and proliferation of skin and immune cells affected by psoriasis and in contributing to the pathogenesis of the disease. We also evaluate whether the agonists of PPAR-γ may become one of the therapeutic options to suppress the inflammatory response in lesional psoriatic skin and decrease the influence of comorbidities associated with psoriasis.

Altered Phenotype and Enhanced Antibody-Producing Ability of Peripheral B Cells in Mice with Cd19-Driven Cre Expression

Given the importance of B lymphocytes in inflammation and immune defense against pathogens, mice transgenic for Cre under the control of Cd19 promoter (Cd19^Cre/+ mice) have been widely used to specifically investigate the role of loxP-flanked genes in B cell development/function. However, impacts of expression/insertion of the Cre transgene on the phenotype and function of B cells have not been carefully studied. Here, we show that the number of marginal zone B and B1a cells was selectively reduced in Cd19^Cre/+ mice, while B cell development in the bone marrow and total numbers of peripheral B cells were comparable between Cd19^Cre/+ and wild type C57BL/6 mice. Notably, humoral responses to both T cell-dependent and independent antigens were significantly increased in Cd19^Cre/+ mice. We speculate that these differences are mainly attributable to reduced surface CD19 levels caused by integration of the Cre-expressing cassette that inactivates one Cd19 allele. Moreover, our literature survey showed that expression of Cd19^Cre/+ alone may affect the development/progression of inflammatory and anti-infectious responses. Thus, our results have important implications for the design and interpretation of results on gene functions specifically targeted in B cells in the Cd19^Cre/+ mouse strain, for instance, in the context of (auto) inflammatory/infectious diseases.

E-series resolvin metabolome, biosynthesis and critical role of stereochemistry of specialized pro-resolving mediators (SPMs) in inflammation-resolution: Preparing SPMs for long COVID-19, human clinical trials, and targeted precision nutrition

The COVID-19 pandemic has raised international awareness of the importance of rigorous scientific evidence and the havoc caused by uncontrolled excessive inflammation. Here we consider the evidence on whether the specialized pro-resolving mediators (SPMs) are ready to meet this challenge as well as targeted metabololipidomics of the resolution-inflammation metabolomes. Specific stereochemical mechanisms in the biosynthesis of SPMs from omega-3 essential fatty acids give rise to unique local-acting lipid mediators. SPMs possess stereochemically defined potent bioactive structures that are high-affinity ligands for cognate G protein-coupled surface receptors that evoke the cellular responses required for efficient resolution of acute inflammation. The SPMs biosynthesized from the major omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are coined Resolvins (resolution phase interaction products; E series and D-series), Protectins and Maresins (macrophage mediators in resolving inflammation). Their biosynthesis and stereochemical assignments are established and confirmed (>1,441 resolvin publications in PubMed.gov) as well as their functional roles on innate immune cells and adaptive immune cells (both lymphocyte T-cell subsets and B-cells). The resolution of a protective acute inflammatory response is governed mainly by phagocytes that actively clear apoptotic cells, debris, blood clots and pathogens. These resolution phase functions of the acute inflammatory response are enhanced by SPMs, which together prepare the inflammatory loci for homeostasis and stimulate tissue regeneration via activating stem cells and the biosynthesis of novel cys-SPMs (e.g. MCTRs, PCTRs and RCTRs). These cys-SPMs also activate regeneration, are organ protective and stimulate resolution of local inflammation. Herein, we review the biosynthesis and functions of the E-series resolvins, namely resolvin E1 (the first n-3 resolvin identified), resolvin E2, resolvin E3 and resolvin E4 biosynthesized from their precursor eicosapentaenoic acid (EPA), and the critical role of total organic synthesis in confirming SPM complete stereochemistry, establishing their potent functions in resolution of inflammation, and novel structures. The physical properties of each biologically derived SPM, i.e., ultra-violet (UV) absorbance, chromatographic behavior, and tandem mass spectrometry (MS2) fragmentation, were matched to SPMs biosynthesized and prepared by stereospecific total organic synthesis. We briefly review this approach, also used with the endogenous D-series resolvins, protectins and maresins confirming their potent functions in resolution of inflammation, that paves the way for their rigorous evaluation in human tissues and clinical trials. The assignment of complete stereochemistry for each of the E and D series Resolvins, Protectins and Maresins was a critical and required step that enabled human clinical studies as in SPM profiling in COVID-19 infections and experimental animal disease models that also opened the promise of resolution physiology, resolution pharmacology and targeted precision nutrition as new areas for monitoring health and disease mechanisms.

Alterations in Lysosome Homeostasis in Lipid-Related Disorders: Impact on Metabolic Tissues and Immune Cells

Lipid-related disorders, which primarily affect metabolic tissues, including adipose tissue and the liver are associated with alterations in lysosome homeostasis. Obesity is one of the more prevalent diseases, which results in energy imbalance within metabolic tissues and lysosome dysfunction. Less frequent diseases include Niemann-Pick type C (NPC) and Gaucher diseases, both of which are known as Lysosomal Storage Diseases (LSDs), where lysosomal dysfunction within metabolic tissues remains to be fully characterized. Adipocytes and hepatocytes share common pathways involved in the lysosome-autophagic axis, which are regulated by the function of cathepsins and CD36, an immuno-metabolic receptor and display alterations in lipid diseases, and thereby impacting metabolic functions. In addition to intrinsic defects observed in metabolic tissues, cells of the immune system, such as B cells can infiltrate adipose and liver tissues, during metabolic imbalance favoring inflammation. Moreover, B cells rely on lysosomes to promote the processing and presentation of extracellular antigens and thus could also present lysosome dysfunction, consequently affecting such functions. On the other hand, growing evidence suggests that cells accumulating lipids display defective inter-organelle membrane contact sites (MCSs) established by lysosomes and other compartments, which contribute to metabolic dysfunctions at the cellular level. Overall, in this review we will discuss recent findings addressing common mechanisms that are involved in lysosome dysregulation in adipocytes and hepatocytes during obesity, NPC, and Gaucher diseases. We will discuss whether these mechanisms may modulate the function of B cells and how inter-organelle contacts, emerging as relevant cellular mechanisms in the control of lipid homeostasis, have an impact on these diseases.

PPAR agonists as effective adjuvants for COVID-19 vaccines, by modifying immunogenetics: a review of literature

BACKGROUND

Several coronavirus vaccine have been fast-tracked to halt the pandemic, the usage of immune adjuvants that can boost immunological memory has come up to the surface. This is particularly of importance in view of the rates of failure of seroconversion and re-infection after COVID-19 infection, which could make the vaccine role and response debatable. Peroxisome proliferator-activated receptors (PPARs) have an established immune-modulatory role, but their effects as adjuvants to vaccination have not been explored to date. It is increasingly recognized that PPAR agonists can upregulate the levels of anti-apoptotic factors such as MCL-1. Such effect can improve the results of vaccination by enhancing the longevity of long-lived plasma cells (LLPCs). The interaction between PPAR agonists and the immune system does not halt here, as T cell memory is also stimulated through enhanced T regulatory cells, antagonizing PD-L1 and switching the metabolism of T cells to fatty acid oxidation, which has a remarkable effect on the persistence of T memory cells. What is even of a more significant value is the effect of PPAR gamma on ensuring a profound secretion of antibodies upon re-exposure to the offending antigen through upregulating lipoxin B4, therefore potentially assisting the vaccine response and deterring re-infection.

SHORT CONCLUSION

In view of the above, we suggest the use of PPAR as adjuvants to vaccines in general especially the emerging COVID-19 vaccine due to their role in enhancing immunologic memory through DNA-dependent mechanisms.

Protein/AS01B vaccination elicits stronger, more Th2-skewed antigen-specific human T follicular helper cell responses than heterologous viral vectors

Interactions between B cells and CD4⁺ T follicular helper (Tfh) cells are key determinants of humoral responses. Using samples from clinical trials performed with the malaria vaccine candidate antigen Plasmodium falciparum merozoite protein (PfRH5), we compare the frequency, phenotype, and gene expression profiles of PfRH5-specific circulating Tfh (cTfh) cells elicited by two leading human vaccine delivery platforms: heterologous viral vector prime boost and protein with AS01_B adjuvant. We demonstrate that the protein/AS01_B platform induces a higher-magnitude antigen-specific cTfh cell response and that this correlates with peak anti-PfRH5 IgG concentrations, frequency of PfRH5-specific memory B cells, and antibody functionality. Furthermore, our data indicate a greater Th2/Tfh2 skew within the polyfunctional response elicited following vaccination with protein/AS01_B as compared to a Th1/Tfh1 skew with viral vectors. These data highlight the impact of vaccine platform on the cTfh cell response driving humoral immunity, associating a high-magnitude, Th2-biased cTfh response with potent antibody production.

CD4 Tfh comparison in malaria vaccine trials using leading human vaccine platforms

Protein/AS01_B drives stronger antigen-specific Tfh responses than viral vectors

Greater T(f)h2 skewing of antigen-specific CD4 T cells in protein/AS01_B vaccinees

Antigen-specific CD4 T(fh) cell parameters correlate with functional antibody

In vivo liposomal delivery of PPARα/γ dual agonist tesaglitazar in a model of obesity enriches macrophage targeting and limits liver and kidney drug effects

Macrophages are important regulators of obesity-associated inflammation and PPARα and -γ agonism in macrophages has anti-inflammatory effects. In this study, we tested the efficacy with which liposomal delivery could target the PPARα/γ dual agonist tesaglitazar to macrophages while reducing drug action in common sites of drug toxicity: the liver and kidney, and whether tesaglitazar had anti-inflammatory effects in an in vivo model of obesity-associated dysmetabolism. Methods: Male leptin-deficient (ob/ob) mice were administered tesaglitazar or vehicle for one week in a standard oral formulation or encapsulated in liposomes. Following the end of treatment, circulating metabolic parameters were measured and pro-inflammatory adipose tissue macrophage populations were quantified by flow cytometry. Cellular uptake of liposomes in tissues was assessed using immunofluorescence and a broad panel of cell subset markers by flow cytometry. Finally, PPARα/γ gene target expression levels in the liver, kidney, and sorted macrophages were quantified to determine levels of drug targeting to and drug action in these tissues and cells. Results: Administration of a standard oral formulation of tesaglitazar effectively treated symptoms of obesity-associated dysmetabolism and reduced the number of pro-inflammatory adipose tissue macrophages. Macrophages are the major cell type that took up liposomes with many other immune and stromal cell types taking up liposomes to a lesser extent. Liposome delivery of tesaglitazar did not have effects on inflammatory macrophages nor did it improve metabolic parameters to the extent of a standard oral formulation. Liposomal delivery did, however, attenuate effects on liver weight and liver and kidney expression of PPARα and -γ gene targets compared to oral delivery. Conclusions: These findings reveal for the first time that tesaglitazar has anti-inflammatory effects on adipose tissue macrophage populations in vivo. These data also suggest that while nanoparticle delivery reduced off-target effects, yet the lack of tesaglitazar actions in non-targeted cells such (as hepatocytes and adipocytes) and the uptake of drug-loaded liposomes in many other cell types, albeit to a lesser extent, may have impacted overall therapeutic efficacy. This fulsome analysis of cellular uptake of tesaglitazar-loaded liposomes provides important lessons for future studies of liposome drug delivery.

Neonatal Bisphenol A Exposure Affects the IgM Humoral Immune Response to 4T1 Breast Carcinoma Cells in Mice

Bisphenol A (BPA) is an endocrine disruptor of estrogenic nature. During the early stages of development, any exposure to BPA can have long-term effects. In this work, we study the potential alterations to the humoral antitumor immune (IgM) response in adult life after a single neonatal exposure to BPA. Female syngeneic BALB/c mice were exposed to a single dose of BPA of 250 μg/kg. Once sexual maturity was reached, a breast tumor was induced. After 25 days, the serum was obtained, and the populations of B cells in the spleen and lymph nodes were analyzed by flow cytometry. The reactivity of IgM was evaluated by 2D immunoblots. No significant changes were found in the B cell populations in the peripheral lymph nodes and the spleen. The level of ERα expression was not significantly different. However, the IgM reactivity was affected. In individuals treated with BPA, a decrease in the number of IgMs that recognize tumor antigens was observed. The possibility that these antibodies are the high affinity products of the adaptive response is discussed. The recognition of IgG was also evaluated but a null recognition was found in the controls as in the individuals treated with the 4T1 cells.

Intranasal immunization with pneumococcal surface protein A in the presence of nanoparticle forming polysorbitol transporter adjuvant induces protective immunity against the Streptococcus pneumoniae infection

Developing effective mucosal subunit vaccine for the Streptococcus pneumoniae has been unsuccessful mainly because of their poor immunogenicity with insufficient memory T and B cell responses. We thus address whether such limitation can be overcome by introducing effective adjuvants that can enhance immunity and show here that polysorbitol transporter (PST) serves as a mucosal adjuvant for a subunit vaccine against the Streptococcus pneumoniae. Pneumococcal surface protein A (PspA) with PST adjuvant induced protective immunity against S. pneumoniae challenge, especially long-term T and B cell immune responses. Moreover, we found that the PST preferentially induced T helper (Th) responses toward Th2 or T follicular helper (Tfh) cells and, importantly, that the responses were mediated through antigen-presenting cells via activating a peroxisome proliferator-activated receptor gamma (PPAR-γ) pathway. Thus, these data indicate that PST can be used as an effective and safe mucosal vaccine adjuvant against S. pneumoniae infection. STATE OF SIGNIFICANCE: In this study, we suggested the nanoparticle forming adjuvant, PST works as an effective adjuvant for the pneumococcal vaccine, PspA. The PspA subunit vaccine together with PST adjuvant efficiently induced protective immunity, even in the long-term memory responses, against Streptococcus pneumoniae lethal challenge. We found that PspA with PST adjuvant induced dendritic cell activation followed by follicular helper T cell responses through PPAR-γ pathway resulting long-term memory antibody-producing cells. Consequently, in this paper, we suggest the mechanism for safe nanoparticle forming subunit vaccine adjuvant against pneumococcal infection.

B-cell-specific-peroxisome proliferator-activated receptor γ deficiency augments contact hypersensitivity with impaired regulatory B cells

Nuclear receptor peroxisome proliferator-activated receptor γ (PPAR-γ) activation can prevent immunoinflammatory disorders and diabetes. B cells play protective roles during inflammation as well. However, the roles of endogenous PPAR-γ in the regulatory properties of B cells to relieve inflammation remain unknown. Here, we developed B-cell-specific PPAR-γ knockout (B-PPAR-γ^-/- ) mice and found that the conditional deletion of PPAR-γ in B cells resulted in exaggerated contact hypersensitivity (CHS). Meanwhile, interferon-γ (IFN-γ) of CD4⁺ CD8⁺ T cells was up-regulated in B-PPAR-γ^-/- mice in CHS. This showed that the regulatory function of B cells in B-PPAR-γ^-/- mice declined in vivo. Whereas splenic CD5⁺ CD1d^hi regulatory B-cell numbers and peripheral regulatory T-cell numbers were not changed in naive B-PPAR-γ^-/- mice. Loss of PPAR-γ in B cells also did not affect either CD86 or FasL expression in splenic CD5⁺ CD1d^hi regulatory B cells after activation. Notably, interleukin-10 (IL-10) production in CD5⁺ CD1d^hi regulatory B cells reduced in B-PPAR-γ-deficient mice. In addition, functional IL-10-producing CD5⁺ CD1d^hi regulatory B cells decreased in B-PPAR-γ^-/- mice in the CHS model. These findings were in accordance with augmented CHS. The current work indicated the involvement of endogenous PPAR-γ in the regulatory function of B cells by disturbing the expansion of IL-10-positive regulatory B cells.

Lack of Adipocytes Alters Hematopoiesis in Lipodystrophic Mice

Adult hematopoiesis takes place in the perivascular zone of the bone cavity, where endothelial cells, mesenchymal stromal/stem cells and their derivatives such as osteoblasts are key components of bone marrow (BM) niches. Defining the contribution of BM adipocytes to the hematopoietic stem cell niche remains controversial. While an excess of medullar adiposity is generally considered deleterious for hematopoiesis, an active role for adipocytes in shaping the niche has also been proposed. We thus investigated the consequences of total adipocyte deletion, including in the BM niche, on adult hematopoiesis using mice carrying a constitutive deletion of the gene coding for the nuclear receptor peroxisome proliferator-activated receptor-γ (PPARγ). We show that Pparg ^Δ/Δ lipodystrophic mice exhibit severe extramedullary hematopoiesis (EMH), which we found to be non-cell autonomous, as it is reproduced when wild-type donor BM cells are transferred into Pparg ^Δ/Δ recipients. This phenotype is not due to a specific alteration linked to Pparg deletion, such as chronic inflammation, since it is also found in AZIP^tg/+ mice, another lipodystrophic mouse model with normal PPARγ expression, that display only very moderate levels of inflammation. In both models, the lack of adipocytes alters subpopulations of both myeloid and lymphoid cells. The CXCL12/CXCR4 axis in the BM is also dysregulated in an adipocyte deprived environment supporting the hypothesis that adipocytes are required for normal hematopoietic stem cell mobilization or retention. Altogether, these data suggest an important role for adipocytes, and possibly for the molecular interactions they provide within the BM, in maintaining the appropriate microenvironment for hematopoietic homeostasis.

Corticosteroids inhibit anti-IgE activities of specialized proresolving mediators on B cells from asthma patients

Specialized proresolving mediators (SPMs) promote the resolution of inflammation and exert beneficial effects in animal models of chronic inflammatory diseases, including asthma. Previously, we have shown that certain SPMs reduce IgE production in B cells from healthy individuals, which has a critical role in allergic asthma. Here, we investigated the effects of SPMs on B cell IgE production in asthma patients. Peripheral blood mononuclear cells from asthma patients were treated with 17-HDHA or RvD1, and IgE levels were measured. RvD1 and 17-HDHA dampened IgE production in B cells from most asthma patients, whereas B cells from a subset of patients taking oral steroids were refractory to SPM treatment. Molecular mechanisms underlying the interaction between corticosteroids and SPMs were investigated by treating B cells from nonasthmatic donors with corticosteroids in vitro. Corticosteroids blocked the inhibitory effects of 17-HDHA and RvD1 on B cell IgE production by abolishing the suppressive activity of these mediators on IgE class switching. Corticosteroids decreased the expression of transcriptional repressor Bcl-6 as well as its suppressive activity on epsilon germline transcription. We conclude that 17-HDHA and RvD1 can reduce IgE production in asthma patients not taking high doses of steroids but that corticosteroids interfere with the ability of B cells to respond to proresolving mediators.

Tissue Phthalate Levels Correlate With Changes in Immune Gene Expression in a Population of Juvenile Wild Salmon

Phthalates have detrimental effects on health and have been shown to dysregulate the immune system of mammals, birds, and fish. We recently reported that di(2-ethylhexyl) phthalate exposure reduces the abundance and inhibits the proliferation of rainbow trout (Oncorhynchus mykiss) IgM(+) B lymphocytes and expression of secreted immunoglobulin heavy-chain mu transcripts in an in vitro culture system. We proposed that phthalates act as immunomodulators by modifying the normal B cell-activation pathways by accelerating B cell differentiation while suppressing plasmablast expansion, thus resulting in fewer IgM-secreting plasma cells. This hypothesis was tested here in an in vivo field study of juvenile Dolly Varden (Salvelinus malma) from a plastic-polluted lake in the Gulf of Alaska. Fish tissues were analyzed for both phthalate levels using liquid chromatography-coupled tandem mass spectrometry and for changes in immune gene expression using reverse transcriptase-real time polymerase chain reaction. Results showed that fish with higher tissue levels of di(2-ethylhexyl) phthalate, di(n-butyl) phthalate, and/or dimethyl phthalate expressed significantly fewer secreted and membrane-bound immunoglobulin heavy-chain mu and Blimp1 transcripts in their hematopoietic tissue. This suggests that in vivo uptake of phthalates in fish changes the expression of B cell-specific genes. Chronic exposure to phthalates likely dysregulates normal B-lymphoid development and antibody responses in salmonids and may increase susceptibility to infection. Given the conserved nature of B-lineage cells in vertebrate animals, other marine species may be similarly affected by chronic phthalate exposure.

DNA cytosine hydroxymethylation levels are distinct among non-overlapping classes of peripheral blood leukocytes

BACKGROUND

Peripheral blood leukocytes are the most commonly used surrogates to study epigenome-induced risk and epigenomic response to disease-related stress. We considered the hypothesis that the various classes of peripheral leukocytes differentially regulate the synthesis of 5-methylcytosine (5mCG) and its removal via Ten-Eleven Translocation (TET) dioxygenase catalyzed hydroxymethylation to 5-hydroxymethylcytosine (5hmCG), reflecting their responsiveness to environment. Although it is known that reductions in TET1 and/or TET2 activity lead to the over-proliferation of various leukocyte precursors in bone marrow and in development of chronic myelomonocytic leukemia and myeloproliferative neoplasms, the role of 5mCG hydroxymethylation in peripheral blood is less well studied.

RESULTS

We developed simplified protocols to rapidly and reiteratively isolate non-overlapping leukocyte populations from a single small sample of fresh or frozen whole blood. Among peripheral leukocyte types we found extreme variation in the levels of transcripts encoding proteins involved in cytosine methylation (DNMT1, 3A, 3B), the turnover of 5mC by demethylation (TET1, 2, 3), and DNA repair (GADD45A, B, G) and in the global and gene-region-specific levels of DNA 5hmCG (CD4+ T cells≫CD14+ monocytes>CD16+ neutrophils>CD19+ B cells>CD56+ NK cells>Siglec8+ eosinophils>CD8+ T cells).

CONCLUSIONS

Our data taken together suggest a potential hierarchy of responsiveness among classes of leukocytes with CD4+, CD8+ T cells and CD14+ monocytes being the most distinctly poised for a rapid methylome response to physiological stress and disease.

PPARγ and the Innate Immune System Mediate the Resolution of Inflammation

The resolution of inflammation is an active and dynamic process, mediated in large part by the innate immune system. Resolution represents not only an increase in anti-inflammatory actions, but also a paradigm shift in immune cell function to restore homeostasis. PPARγ, a ligand activated transcription factor, has long been studied for its anti-inflammatory actions, but an emerging body of literature is investigating the role of PPARγ and its ligands (including thiazolidinediones, prostaglandins, and oleanolic acids) in all phases of resolution. PPARγ can shift production from pro- to anti-inflammatory mediators by neutrophils, platelets, and macrophages. PPARγ and its ligands further modulate platelet and neutrophil function, decreasing trafficking, promoting neutrophil apoptosis, and preventing platelet-leukocyte interactions. PPARγ alters macrophage trafficking, increases efferocytosis and phagocytosis, and promotes alternative M2 macrophage activation. There are also roles for this receptor in the adaptive immune response, particularly regarding B cells. These effects contribute towards the attenuation of multiple disease states, including COPD, colitis, Alzheimer's disease, and obesity in animal models. Finally, novel specialized proresolving mediators-eicosanoids with critical roles in resolution-may act through PPARγ modulation to promote resolution, providing another exciting area of therapeutic potential for this receptor.

Targeted Mutation of Nuclear Bone Morphogenetic Protein 2 Impairs Secondary Immune Response in a Mouse Model

We recently identified a nuclear variant of the BMP2 growth factor, called nBMP2. In an effort to understand the function of this variant protein, we generated a mouse line in which BMP2 is expressed and functions normally, but nBMP2 is excluded from the nucleus. This novel mutation allows the study of nBMP2 without compromising BMP2 function. To determine whether nBMP2 plays a role in immune function, we performed a series of experiments in which we compared mouse survival, organ weights, immune cells numbers, and bacterial load in wild type and nBmp2NLS^tm mice following primary and secondary challenges with Staphylococcus aureus. Following primary challenge with S. aureus, wild type and nBmp2NLS^tm mice showed no differences in survival or bacterial load and generated similar numbers and types of leukocytes, although mutant spleens were smaller than wild type. Secondary bacterial challenge with S. aureus, however, produced differences in survival, with increased mortality seen in nBmp2NLS^tm mice. This increased mortality corresponded to higher levels of bacteremia in nBmp2NLS^tm mice and to a reduced enlargement of mutant spleens in response to the secondary infection. Together, these results suggest that the recently described nuclear variant of BMP2 is necessary for efficient secondary immune responses.

Di(2-ethylhexyl) phthalate inhibits B cell proliferation and reduces the abundance of IgM-secreting cells in cultured immune tissues of the rainbow trout

Plasticizer di(2-ethylhexyl) phthalate (DEHP) and its active metabolite MEHP have important immunotoxic effects in mammalian species, including inhibition of cell proliferation, inflammation inhibition, lowering of the antibody response, and apoptosis. Virtually nothing is known about the potential detrimental effects of DEHP/MEHP on the teleost immune system, although phthalates are a likely threat to fish health. Here we investigated whether short-term in vitro DEHP exposure would affect B lineage cells in the rainbow trout, using cultured immune tissues. Cell culture conditions, evidence of cellular incorporation of DEHP, and possible effects of DEHP on immune genes were first established using the mouse pre-B cell line PD31 and data confirmed a dose-dependent cellular uptake of DEHP using liquid chromatography-coupled ion trap mass spectrometry. Effects of in vitro DEHP exposure on trout B cell proliferation were tested by flow cytometry. Significant, dose-dependent inhibition was evident in both anterior and posterior kidney cultures after 24 h exposure to ≥4 μM DEHP. DEHP-induced cell death was not significant for the range of DEHP tested. Further, the abundance of IgM-secreting plasmablasts and plasma cells was significantly reduced after in vitro exposure of ≥16 μM DEHP for 2 or 7 days. Finally, in vitro DEHP exposure significantly lowered the levels of secreted HCmu transcripts in a dose-dependent manner. B lineage cells from posterior kidney were more sensitive to effects of in vitro DEHP exposure than those from anterior kidney. Together, the data support a model where DEHP modifies the normal B cell activation pathways in rainbow trout, promoting B cell differentiation while suppressing plasmablast expansion, resulting in fewer IgM-secreting plasma cells. Insufficient production of protective antibody make fish more susceptible to infection, and increases their risk for disease and mortality in polluted waters.

The specialized proresolving mediator 17-HDHA enhances the antibody-mediated immune response against influenza virus: a new class of adjuvant?

Influenza viruses remain a critical global health concern. More efficacious vaccines are needed to protect against influenza virus, yet few adjuvants are approved for routine use. Specialized proresolving mediators (SPMs) are powerful endogenous bioactive regulators of inflammation, with great clinical translational properties. In this study, we investigated the ability of the SPM 17-HDHA to enhance the adaptive immune response using an OVA immunization model and a preclinical influenza vaccination mouse model. Our findings revealed that mice immunized with OVA plus 17-HDHA or with H1N1-derived HA protein plus 17-HDHA increased Ag-specific Ab titers. 17-HDHA increased the number of Ab-secreting cells in vitro and the number of HA-specific Ab-secreting cells present in the bone marrow. Importantly, the 17-HDHA-mediated increased Ab production was more protective against live pH1N1 influenza infection in mice. To our knowledge, this is the first report on the biological effects of ω-3-derived SPMs on the humoral immune response. These findings illustrate a previously unknown biological link between proresolution signals and the adaptive immune system. Furthermore, this work has important implications for the understanding of B cell biology, as well as the development of new potential vaccine adjuvants.