Glucocorticoids regulate TCR-induced elevation of CD4: functional implications

A Glucocorticoid-Mediated Immunoregulatory Circuit Integrated at Brain Levels: Our Early Studies and a Present View

BACKGROUND

It was known since the 1940s that pharmacological administration of glucocorticoids can inhibit inflammatory and immune processes, and these hormones are still today among the most widely used therapeutic tools to treat diseases with immune components. However, it became clear later that endogenous glucocorticoids can either support or restrain immune processes.

SUMMARY

Early studies showed that (a) endogenous levels of glucocorticoids can modulate immune cell activity; (b) the immune response itself can stimulate the hypothalamus-pituitary-adrenal (HPA) axis to release glucocorticoids to levels that can exert immunoregulatory effects; (c) immune products, later identified as cytokines, mediate this effect. On these bases, the existence of a glucocorticoid-mediated immunoregulatory circuit was proposed. It was also shown that increased levels of endogenous glucocorticoids exert protective effects during infections and other diseases with immune components. However, it was found in animal models and in humans that these effects can be blunted in several immune-linked diseases by defects at several levels, for example, by glucocorticoid resistance or by adrenal insufficiency. Evidence was later provided that the glucocorticoid-mediated immunoregulatory circuit can also be activated by cytokines produced not only as consequence of immune stimulation but also following psycho/sensorial and physical stimuli. Thus, this circuit can be integrated at brain levels and, besides stimulating the HPA axis, cytokines can also affect synaptic plasticity, most likely via a tripartite synapse, with astrocytes as neuro-immune cells acting as the third component.

KEY MESSAGES

It is now well established that the glucocorticoid-mediated immunoregulatory circuit plays a central role in maintaining health. However, several variables can condition the efficacy of the effect of endogenous glucocorticoids. Furthermore, since cytokines and other immune products have many other neuroendocrine and metabolic effects, other neuroendocrine-immune circuits could simultaneously operate or become predominant during different pathologies. The consideration of these aspects might help to implement strategies to eventually decrease therapeutic doses of exogenous glucocorticoids.

In vivo CAR T cell therapy against angioimmunoblastic T cell lymphoma

BACKGROUND

For angioimmunoblastic T cell lymphoma (AITL), a rare cancer, no specific treatments are available and survival outcome is poor. We previously developed a murine model for AITL that mimics closely human disease and allows to evaluate new treatments. As in human AITL, the murine CD4+ follicular helper T (Tfh) cells are drivers of the malignancy. Therefore, chimeric antigen receptor (CAR) T cell therapy might represent a new therapeutic option.

METHODS

To prevent fratricide among CAR T cells when delivering an CD4-specific CAR, we used a lentiviral vector (LV) encoding an anti-CD4 CAR, allowing exclusive entry into CD8 T cells.

RESULTS

These anti-CD4CAR CD8-targeted LVs achieved in murine AITL biopsies high CAR-expression levels in CD8 T cells. Malignant CD4 Tfh cells were eliminated from the mAITL lymphoma, while the CAR + CD8 T cells expanded upon encounter with the CD4 receptor and were shaped into functional cytotoxic cells. Finally, in vivo injection of the CAR + CD8-LVs into our preclinical AITL mouse model carrying lymphomas, significantly prolonged mice survival. Moreover, the in vivo generated functional CAR + CD8 T cells efficiently reduced neoplastic T cell numbers in the mAITL tumors.

CONCLUSION

This is the first description of in vivo generated CAR T cells for therapy of a T cell lymphoma. The strategy described offers a new therapeutic concept for patients suffering from CD4-driven T cell lymphomas.

Soluble factors from TLR4- or TCR-activated cells contribute to stability of the resting phenotype and increase the expression of CXCR4 of human memory CD4 T cells

It has been proposed that cytokines can induce activation of resting T cells in an antigen-independent manner. However, experimental conditions have included the use of fetal serum and nanogram concentrations of added cytokines. To evaluate the effect of cytokines and chemokines generated by activated immune cells on the phenotypic profile of human memory CD4 T cells, the cells were cultured in FBS-free conditions in the presence of IL-15 and 5% of hAB serum and incubated with conditioned medium (CM) obtained from PBMC activated through the TCR using anti-CD3/CD28/CD2 antibodies (TCR-CM) or through TLR4 using bacterial LPS (TLR4-CM). Cytokines and chemokines present in the CMs were evaluated by ProcartaPlex immunoassay. Cell viability, proliferation, and surface markers were determined by flow cytometry on day 2, 5, and 8 of culture. Cell viability was maintained by TLR4-CM plus IL-15 for 8 days but decreased in the presence of the TCR-CM plus IL-15. In combination with IL-15, the TLR4-CM, but not the TCR-CM, maintained the expression of CD3 and CD4 stable. Both conditions stabilized the expression of CD45RO and CCR5. Thus, the TLR4-CM better supported the viability and stability of the memory phenotype. None of the CMs induced proliferation or expression of activation markers; however, they induced an increased expression of CXCR4. This study indicates that resting memory CD4 T cells are not activated by, but may be sensitive to soluble factors produced by antigen or PAMP-stimulated cells, which may contribute to their homeostasis and favor the CXCR4 expression.

Plasma steroids and immune measures vary with restraint duration in a toad (Rhinella icterica)

Immunoenhancing effects have been widely described following acute stressors in several vertebrates, and valuable contributions have been made from studies on acute stress to understand hormonal-immune interactions. However, most studies focus on hormonal and immune responses after standardized time lapses, neglecting potential influence of duration of exposition to stressor. Herein, we investigate fluctuations of plasma hormone concentrations (corticosterone and testosterone) and immunity (neutrophil to lymphocyte ratio, phagocytosis of blood cells, and plasma bacterial killing ability) in a toad species (Rhinella icterica) in response to six different periods of exposure to restraint stress. We observed increased plasma corticosterone concentrations following restraint in all sampled times (0.5 to 48 h), with the highest values being observed during the first hour (0.5 to 1 h). Restraint-induced increases in the neutrophil to lymphocyte ratio and phagocytosis percentage were observed from the first 0.5 h, gradually increasing after that with the time of restraint. We also observed decreased testosterone plasma concentrations in response to a more prolonged restraint (24 and 48 h). No changes were observed in plasma bacterial killing ability following restraint. Together, our results demonstrate dynamic time-related hormonal and immune changes. These results point to the fact that for some species measuring hormonal and immune variables at single time points following a stressor might work better when preceded by a study of the temporal changes of the response variables to the stimuli applied. Also, time of response needs to be considered when different variables are used as proxies of stress.

IL10- and IL35-Secreting MutuDC Lines Act in Cooperation to Inhibit Memory T Cell Activation Through LAG-3 Expression

Dendritic cells (DCs) are professional antigen-presenting cells involved in the initiation of immune responses. We generated a tolerogenic DC (tolDC) line that constitutively secretes interleukin-10 (IL10-DCs), expressed lower levels of co-stimulatory and MHCII molecules upon stimulation, and induced antigen-specific proliferation of T cells. Vaccination with IL10-DCs combined with another tolDC line that secretes IL-35, reduced antigen-specific local inflammation in a delayed-type hypersensitivity assay independently on regulatory T cell differentiation. In an autoimmune model of rheumatoid arthritis, vaccination with the combined tolDCs after the onset of the disease impaired disease development and promoted recovery of mice. After stable memory was established, the tolDCs promoted CD4 downregulation and induced lymphocyte activation gene 3 (LAG-3) expression in reactivated memory T cells, reducing T cell activation. Taken together, our findings indicate the benefits of combining anti-inflammatory cytokines in an antigen-specific context to treat excessive inflammation when memory is already established.

Interactions Between the Neuroendocrine System and T Lymphocytes in Diabetes

It is well established that there is a fine-tuned bidirectional communication between the immune and neuroendocrine tissues in maintaining homeostasis. Several types of immune cells, hormones, and neurotransmitters of different chemical nature are involved as communicators between organs. Apart of being key players of the adaptive arm of the immune system, it has been recently described that T lymphocytes are involved in the modulation of metabolism of several tissues in health and disease. Diabetes may result mainly from lack of insulin production (type 1 diabetes) or insufficient insulin and insulin resistance (type 2 diabetes), both influenced by genetic and environmental components. Herein, we discuss accumulating data regarding the role of the adaptive arm of the immune system in the pathogenesis of diabetes; including the action of several hormones and neurotransmitters influencing on central and peripheral T lymphocytes development and maturation, particularly under the metabolic burden triggered by diabetes. In addition, we comment on the role of T-effector lymphocytes in adipose and liver tissues during diabetes, which together enhances pancreatic β-cell stress aggravating the disease.

Pathological Role of Anti-CD4 Antibodies in HIV-Infected Immunologic Nonresponders Receiving Virus-Suppressive Antiretroviral Therapy

Increased mortality and morbidity occur among human immunodeficiency virus (HIV)-infected patients in whom CD4+ T-cell counts do not increase despite viral suppression with antiretroviral therapy (ART). Here we identified an underlying mechanism. Significantly elevated plasma levels of anti-CD4 immunoglobulin G (IgG) were found in HIV-positive immunologic nonresponders (ie, HIV-positive individuals with CD4+ T-cell counts of ≤350 cells/μL), compared with levels in HIV-positive immunologic responders (ie, HIV-positive individuals with CD4+ T-cell counts of ≥500 cells/μL) and healthy controls. Higher plasma level of anti-CD4 IgG correlated with blunted CD4+ T-cell recovery. Furthermore, purified anti-CD4 IgG from HIV-positive immunologic nonresponders induced natural killer (NK) cell-dependent CD4+ T-cell cytolysis and apoptosis through antibody-dependent cell-mediated cytotoxicity (ADCC) in vitro. We also found that anti-CD4 IgG-mediated ADCC exerts greater apoptosis of naive CD4+ T cells relative to memory CD4+ T cells. Consistently, increased frequencies of CD107a+ NK cells and profound decreases of naive CD4+ T cells were observed in immunologic nonresponders as compared to responders and healthy controls ex vivo. These data indicate that autoreactive anti-CD4 IgG may play an important role in blunted CD4+ T-cell reconstitution despite effective ART.

Glucocorticoids

Glucocorticoids remain part of the treatment strategy in many rheumatic diseases, because of their anti-inflammatory and immunosuppressive actions. Unfortunately, their clinically desired effects are linked to adverse effects, especially at higher dosages and longer duration of treatment. In this review, we describe new insights into the mechanisms of anti-inflammatory glucocorticoid actions and provide an update on recent approaches to improve the risk/benefit ratio of glucocorticoid therapy. Improved knowledge of the immunomodulatory role of endogenous glucocorticoids has evolved, and we report on the therapeutic potential of targeting glucocorticoid pre-receptor metabolism for metabolic and inflammatory diseases.

Epigenetic mechanisms in stress and adaptation

Epigenetic mechanisms are processes at the level of the chromatin that control the expression of genes but their role in neuro-immuno-endocrine communication is poorly understood. This review focuses on epigenetic modifications induced by a range of stressors, both physical and psychological, and examines how these variations can affect the biological activity of cells. It is clear that epigenetic modifications are critical in explaining how environmental factors, which have no effect on the DNA sequence, can have such profound, long-lasting influences on both physiology and behavior. A signaling pathway involving activation of MEK-ERK1/2, MSK1, and Elk-1 signaling molecules has been identified in the hippocampus which results in the phospho-acetylation of histone H3 and modification of gene expression including up-regulation of immediate early genes such as c-Fos. This pathway can be induced by a range of challenging experiences including forced swimming, Morris water maze learning, fear conditioning and exposure to the radial maze. Glucocorticoid (GC) hormones, released as part of the stress response and acting via glucocorticoid receptors (GRs), enhance signaling through the ERK1/2/MSK1-Elk-1 pathway and thereby increase the impact on epigenetic and gene expression mechanisms. The role of synergetic interactions between these pathways in adaptive responses to stress and learning and memory paradigms is discussed, in addition we speculate on their potential role in immune function.

Winter day lengths enhance T lymphocyte phenotypes, inhibit cytokine responses, and attenuate behavioral symptoms of infection in laboratory rats

Annual variations in day length (photoperiod) trigger changes in the immune and reproductive system of seasonally-breeding animals. The purpose of this study was to determine whether photoperiodic changes in immunity depend on concurrent photoperiodic responses in the reproductive system, or whether immunological responses to photoperiod occur independent of reproductive responses. Here we report photoperiodic changes in enumerative, functional, and behavioral aspects of the immune system, and in immunomodulatory glucocorticoid secretion, in reproductively non-photoperiodic Wistar rats. T-cell numbers (CD3+, CD8+, CD8+CD25+, CD4+CD25+) were higher in the blood of rats housed in short as opposed to long-day lengths for 10 weeks. Following a simulated bacterial infection (Escherichia coli LPS; 125 microg/kg) the severity of several acute-phase sickness behaviors (anorexia, cachexia, neophobia, and social withdrawal) were attenuated in short days. LPS-stimulated IL-1beta and IL-6 production were comparable between photoperiods, but plasma TNFalpha was higher in long-day relative to short-day rats. In addition, corticosterone concentrations were higher in short-day relative to long-day rats. The data are consistent with the hypothesis that photoperiodic regulation of the immune system can occur entirely independently of photoperiodic regulation of the reproductive system. In the absence of concurrent reproductive responses, short days increase the numbers of leukocytes capable of immunosurveillance and inhibition of inflammatory responses, increase proinflammatory cytokine production, increase immunomodulatory glucocorticoid secretion, and ultimately attenuate behavioral responses to infection. Seasonal changes in the host immune system, endocrine system, and behavior may contribute to the seasonal variability in disease outcomes, even in reproductively non-photoperiodic mammals.

Prenatal stress has pro-inflammatory consequences on the immune system in adult rats

The in utero environment is critical for initiating the ontogeny of several physiological systems, including the immune surveillance. Yet, little is known about adverse early experiences on the offspring's immunity and vulnerability to disease. The present work aimed at investigating the impact of restraint prenatal stress (PS) on the development and responsiveness of in vitro and in vivo cellular and humoral immunity of male progeny aged 7 weeks and 6 months. In adult 6-month-old rats, we detected increased circulating CD8(+)-expressing and NK cells in PS rats as compared to controls, associated with higher mRNA expression of IFN-gamma. In addition, in vitro stimulation with phytohemagglutinin-A induced an increase in both the proliferation of T lymphocytes and the secretion of IFN-gamma in PS rats. Interestingly, these alterations were undetectable in younger PS rats (7-week old), except for a slight increase in the mRNA expression of several pro-inflammatory cytokines in peripheral blood mononuclear cells. Moreover, in vivo neutralization of IFN-gamma in young rats had no effects in PS group. In conclusion, we report for the first time long-lasting pro-inflammatory consequences of PS in rats.

Stress and autoimmune thyroid diseases

Autoimmune thyroid diseases (AITD) are the far most common autoimmune disorders, their prevalence in Western countries exceeding 5% of the general population. In the large majority of individual cases the clinical impact of AITD is not severe, however, their widespread diffusion renders them a significant health problem. AITD are heterogeneous in their clinical presentation: the two main forms are autoimmune thyroiditis (AT) and Graves' disease (GD). Although they probably share, at least in part, a common genetic background and may occur in the same family as well as in the same individual, they are definitely two distinct diseases both in their clinical presentation and their pathophysiology. In fact, AT causes structural thyroid damage (mainly via cell-mediated immune destruction of thyroid follicular cells) which results, as a rule, in functional impairment (hypothyroidism); however, depending on clinical variants, evolution towards hypothyroidism may be very low, or thyroid function impairment occurs after an initial phase of mild thyrotoxicosis due to relatively rapid gland destruction. GD patients have hyperthyroidism, often severe, due to autoantibody-mediated thyrotropin receptor stimulation, with thyroid cell hyperplasia and hyperfunction. Such a functional heterogeneity is a key feature for the clinical management: as a matter of fact, therapy of AITD is mainly therapy of thyroid dysfunction. Moreover, since hyperthyroidism is quite early perceived by the patient as a cause of discomfort, the timing of the natural history of GD is relatively well defined; on the other hand, AT may be asymptomatic for a long time and defining its natural history in a single patient may be difficult. In some AITD patients (mainly, but not exclusively, with GD), clinical features not directly related to thyroid dysfunction, such as orbitopathy, are present. Graves' orbitopathy is probably related, at least in part, to autoantibodies directed to thyrotropin receptor; it may be, in a minority of patients, severe and sight-threatening, and represents an independent clinical problem.

TCR signaling inhibits glucocorticoid-induced apoptosis in murine thymocytes depending on the stage of development

Signaling by either the TCR or glucocorticoid receptor (GR) induces apoptosis in thymocytes. Interestingly, it has been shown previously that hybridoma T cells escape apoptosis induced by either TCR or GR when both of these receptors signal simultaneously. Whether such mutual antagonism is present in primary thymocytes was the subject of the present study. Both glucocorticoids (GC) and anti-TCR/CD28 (or anti-CD3/CD28) mAb induced apoptosis in total thymocytes. When these signals were present at the same time, GC-induced apoptosis was partially inhibited by TCR/CD3 signaling. Costimulation by anti-CD28 enhanced the inhibitory effects of anti-CD3 on GC-induced apoptosis about 30-fold. However, subset analysis revealed that most cells rescued from GC-induced apoptosis were mature CD4+ and CD8+ thymocytes, and these cells were resistant to TCR/CD3-induced apoptosis in the absence of GC. Similar results were obtained with mature splenic CD4+ and CD8+ T cells. TCR/CD3 signaling alone, while inducing apoptosis in CD4+(CD8+)TCRlow thymocytes, rescued a small subset of CD4+(CD8+)TCRlow thymocytes from GC-induced apoptosis. Thus, TCR signaling increasingly reverses GC-induced apoptosis as thymocyte development progresses. As GC are infinitely present in vivo, these findings support a model wherein TCR signaling may be required to prevent GC-induced apoptosis both under basal and immune challenging conditions.

Effects of IL-7 and dexamethasone: Induction of CD25, the high affinity IL-2 receptor, on human CD4+ cells

Since we have previously shown that dexamethasone (Dex) enhances the proportion of murine Treg cells, we tested the effect of IL-7, a promoter of T cell survival, together with Dex on human CD4+CD25+ Treg cells in an in vitro setting. The results showed that IL-7 in concert with Dex markedly augmented the generation of CD4+CD25+ T cells. To discern the origin of the induced CD4+CD25+ T cells, MACS-purified CD4+CD25-, and CD4+CD25+ cells were cultured in the presence of Dex and/or IL-7 for 4 days. Although two thirds of CD4+CD25- T cells became CD4+CD25+ T cells, they had no suppressive activity. In contrast, the original CD4+CD25+ T cells maintained suppressive activity after Dex/IL-7 treatment, however, there was not a significant expansion in their cell number. Dex and IL-7 did not induce additional Treg cells, but additively induced the expression of the activation marker CD25 by CD4+CD25- T cells. This combination may provide a novel means of priming CD4 T cells to respond to IL-2 and may prove useful in up-regulation of normal immune responses in immune deficient diseases.

The hypothalamic-pituitary-adrenal axis and viral infection

The hypothalamic-pituitary-adrenal (HPA) axis plays an important immunomodulatory role during viral infection. Activation of the HPA axis ultimately leads to elevated plasma levels of glucocorticoid (GC) hormones with the ability to mediate adaptive behavioral, metabolic, cardiovascular and immune system effects. In this review, we focus on the modulation of anti-viral immunity and viral pathogenesis by the HPA axis.

Increased splenocyte proliferative response and cytokine production in beta-endorphin-deficient mice

We used beta-endorphin-deficient mice as a novel approach to confirm the physiological role that opioid peptides play in the development or regulation of the immune system. We found that mice lacking beta-endorphin possessed an enhanced immune response, measured in terms of splenocyte proliferation and interleukin (IL)-2 mRNA levels, in vitro production of the splenic macrophage inflammatory cytokines IL-6 and Tumor Necrosis Factor (TNF)-alpha and plasma IL-6 following lipopolysaccharide (LPS) administration. beta-Endorphin-deficient mice had attenuated increases of plasma ACTH and corticosterone levels in response to LPS. These results are consistent with a postulated inhibitory role of endogenous beta-endorphin on the immune system at multiple levels.

Reversible disruption of thymic function by steroid treatment

The effect of steroid treatment on the thymic output of T cells was examined in an avian model. Recent thymic emigrants in chickens transiently express the chicken T cell Ag 1 thymocyte marker, and thymic function can be monitored indirectly by measuring the levels of TCR gene rearrangement excision circles in peripheral T cells. Both parameters were used to show that intensive steroid treatment induces thymic involution and a profound reduction in the supply of naive T cells to the periphery. Conversely, resident T cells in the peripheral lymphocyte pool were relatively spared. Thymopoiesis immediately recovered following cessation of steroid treatment, concurrent with restoration of the thymic output of newly formed T cells. Repopulation of the peripheral T cell pool recapitulated the ontogenetic pattern of gamma delta T cell replenishment before alpha beta T cell reseeding, thereby indicating the complete recovery of thymic function after a course of steroid treatment.

Alterations in immune cell phenotype and function after experimental spinal cord injury

Traumatic injury to the spinal cord initiates a cascade of inflammatory-mediated injury and repair processes within the nervous system. In parallel, spinal injury could influence peripheral mechanisms of host defense (e.g., wound healing, antibody production) by altering lymphocyte phenotype and function. The goal of this study was to evaluate the physiological impact of spinal contusion injury on phenotypic and functional indices of lymphocyte activation. A flow cytometric time-course analysis of lymphocytes isolated from lymph node and spleen revealed an increase in CD4+ and a decrease in CD8+ lymphocytes during the first week post injury. The functional potential of lymphocytes was also evaluated based on their ability to proliferate in the presence of a biologically relevant antigen (myelin basic protein, MBP) or a lymphocyte mitogen. The data revealed increased proliferation to MBP by 3 days postinjury in lymphocytes isolated from lymph node but not spleen. By 1 week postinjury, increased proliferation to mitogen was noted in both the lymph node and the spleen suggesting a general increase in lymphocyte reactivity during this time interval. Circulating corticosterone (CORT), an endogenous glucocorticoid with significant effects on lymphocyte phenotype and function, was elevated within 24 h after spinal cord injury (SCI) and remained above control levels throughout the duration of our studies (up to 1 month postinjury). The present data suggest injury-associated changes in immune cell phenotype and function paralleled by the activation of the hypothalamic-pituitary-adrenal (HPA) axis.