Repression of major histocompatibility complex IA expression by glucocorticoids: the glucocorticoid receptor inhibits the DNA binding of the X box DNA binding protein

Mild and moderate chronic hypercapnia elicit distinct transcriptomic responses of immune function in cardiorespiratory nuclei

Chronic hypercapnia (CH) is a hallmark of respiratory-related diseases, and the level of hypercapnia can acutely or progressively become more severe. Previously, we have shown time-dependent adaptations in steady-state physiology during mild (arterial Pco2 ∼55 mmHg) and moderate (∼60 mmHg) CH in adult goats, including transient (mild CH) or sustained (moderate CH) suppression of acute chemosensitivity suggesting limitations in adaptive respiratory control mechanisms as the level of CH increases. Changes in specific markers of glutamate receptor plasticity, interleukin-1ß, and serotonergic modulation within key nodes of cardiorespiratory control do not fully account for the physiological adaptations to CH. Here, we used an unbiased approach (bulk tissue RNA sequencing) to test the hypothesis that mild or moderate CH elicits distinct gene expression profiles in important brain stem regions of cardiorespiratory control, which may explain the contrasting responses to CH. Gene expression profiles from the brain regions validated the accuracy of tissue biopsy methodology. Differential gene expression analyses revealed greater effects of CH on brain stem sites compared with the medial prefrontal cortex. Mild CH elicited an upregulation of predominantly immune-related genes and predicted activation of immune-related pathways and functions. In contrast, moderate CH broadly led to downregulation of genes and predicted inactivation of cellular pathways related to the immune response and vascular function. These data suggest that mild CH leads to a steady-state activation of neuroinflammatory pathways within the brain stem, whereas moderate CH drives the opposite response. Transcriptional shifts in immune-related functions may underlie the cardiorespiratory network's capability to respond to acute, more severe hypercapnia when in a state of progressively increased CH.NEW & NOTEWORTHY Mild chronic hypercapnia (CH) broadly upregulated immune-related genes and a predicted activation of biological pathways related to immune cell activity and the overall immune response. In contrast, moderate CH primarily downregulated genes related to major histocompatibility complex signaling and vasculature function that led to a predicted inactivation of pathways involving the immune response and vascular endothelial function. The severity-dependent effect on immune responses suggests that neuroinflammation has an important role in CH and may be important in the maintenance of proper ventilatory responses to acute and chronic hypercapnia.

Effect of DMARDs on the immunogenicity of vaccines

Vaccines are important for protecting individuals at increased risk of severe infections, including patients undergoing DMARD therapy. However, DMARD therapy can also compromise the immune system, leading to impaired responses to vaccination. This Review focuses on the impact of DMARDs on influenza and SARS-CoV-2 vaccinations, as such vaccines have been investigated most thoroughly. Various data suggest that B cell depletion therapy, mycophenolate mofetil, cyclophosphamide, azathioprine and abatacept substantially reduce the immunogenicity of these vaccines. However, the effects of glucocorticoids, methotrexate, TNF inhibitors and JAK inhibitors on vaccine responses remain unclear and could depend on the dosage and type of vaccination. Vaccination is aimed at initiating robust humoral and cellular vaccine responses, which requires efficient interactions between antigen-presenting cells, T cells and B cells. DMARDs impair these cells in different ways and to different degrees, such as the prevention of antigen-presenting cell maturation, alteration of T cell differentiation and selective inhibition of B cell subsets, thus inhibiting processes that are necessary for an effective vaccine response. Innovative modified vaccination strategies are needed to improve vaccination responses in patients undergoing DMARD therapy and to protect these patients from the severe outcomes of infectious diseases.

The genetic polymorphisms at the promoter region of HLA-DQB1 gene, creating responsive elements for NF1/CTF and converting the TFII-D binding site to GR-alpha

Human leukocyte antigen-DQB1 (HLA-DQB1, OMIM: 604305) is the human major histocompatibility complex (MHC) system. HLA genes are classified into three classes (I, II, and III). The HLA-DQB1 belongs to class II, is mainly involved in the actions of the human immune system and plays a fundamental role in donor-recipient matching in transplantation and can be associated with most autoimmune diseases. In this study, the potential influence(s) of the G-71C (rs71542466) and T-80C (rs9274529) genetic polymorphisms were investigated. These polymorphisms, located in the HLA-DQB1 promoter region, have a significant frequency in the world population. The online software ALGGEN-PROMO.v8.3 was used in this work. The results indicate that the C allele at the -71 position actually creates a new potential binding site for NF1/CTF and the C allele at the -80 position changes the TFII-D binding site into a GR-alpha response element. The NF1/CTF plays the role of activator and the GR-alpha is the inhibitor; thus, according to the roles of these transcription factors, it is suggested that the above-mentioned polymorphisms alter the expression levels of HLA-DQB1. Therefore, this genetic variation is associated with autoimmune diseases; however, this cannot be generalized because this is the first report and more studies are needed in the future.

Effect of Cytomegalovirus on the Immune System: Implications for Aging and Mental Health

Human cytomegalovirus (HCMV) is a major modulator of the immune system leading to long-term changes in T-lymphocytes, macrophages, and natural killer (NK) cells among others. Perhaps because of this immunomodulatory capacity, HCMV infection has been linked with a host of deleterious effects including accelerated immune aging (premature mortality, increased expression of immunosenescence-linked markers, telomere shortening, speeding-up of epigenetic "clocks"), decreased vaccine immunogenicity, and greater vulnerability to infectious diseases (e.g., tuberculosis) or infectious disease-associated pathology (e.g., HIV). Perhaps not surprisingly given the long co-evolution between HCMV and humans, the virus has also been associated with beneficial effects, such as increased vaccine responsiveness, heterologous protection against infections, and protection against relapse in the context of leukemia. Here, we provide an overview of this literature. Ultimately, we focus on one other deleterious effect of HCMV, namely the emerging literature suggesting that HCMV plays a pathophysiological role in psychiatric illness, particularly depression and schizophrenia. We discuss this literature through the lens of psychological stress and inflammation, two well-established risk factors for psychiatric illness that are also known to predispose to reactivation of HCMV.

Disease status in human and experimental arthritis, and response to TNF blockade, is associated with MHC class II invariant chain (CD74) isoform expression

Splice variants of CD74 differentially modulate the activity of cathepsin L (CTSL). As CD74 and CTSL participate in the pathogenesis of inflammatory diseases such as rheumatoid arthritis (RA), we determined whether splice variants of CD74 could be biomarkers of disease activity. Gene expression was measured in mice with collagen-induced arthritis using quantitative PCR (qPCR). In vitro studies using murine macrophage/DC-lineage cells determined the relative influence of macrophage phenotype on isoform expression and the potential to produce CTSL in response to TNF. CD74 splice variants were measured in human RA synovium and RA patients' monocytes. In arthritic mice, the expression of the p41 CD74 isoform was significantly higher in severely affected paws compared with unaffected paws or the paws of naïve mice; the p41 isoform significantly correlated with the expression of TNF in arthritic paws. Compared with M2-like macrophages, M1-like macrophages expressed increased levels of CD74 and had higher expression, secretion and activity of CTSL. RA patients that responded to TNF blockade had significantly higher expression levels of CD74 in circulating monocytes after treatment, compared with non-responders. The expression of the human CD74 isoform a was significantly higher in RA synovia, compared with osteoarthritis synovia, and was associated with CSTL enzymatic activity. This study is the first to demonstrate differential expression of the CD74 p41 isoform in an auto-immune disorder and in response to therapy. The differential expression of CD74 splice variants indicates an association, and potentially a mechanistic role, in the pathogenesis of RA.

Immune system regulation and role of the human leukocyte antigen in posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) is a debilitating condition that adversely affect mental and physical health. Recent studies have increasingly explored the role of the immune system in risk for PTSD and its related symptoms. Dysregulation of the immune system may lead to central nervous system tissue damage and impair learning and memory processes. Individuals with PTSD often have comorbid inflammatory or auto-immune disorders. Evidence shows associations between PTSD and multiple genes that are involved in immune-related or inflammatory pathways. In this review, we will summarize the evidence of immune dysregulation in PTSD, outlining the contributions of distinct cell types, genes, and biological pathways. We use the Human Leukocyte Antigen (HLA) locus to illustrate the contribution of genetic variation to function in different tissues that contribute to PTSD etiology, severity, and comorbidities.

Induction of CIITA by IFN-γ in macrophages involves STAT1 activation by JAK and JNK

The induction of major histocompatibility complex (MHC) class II proteins by interferon gamma (IFN-γ) in macrophages play an important role during immune responses. Here we explore the signaling pathways involved in the induction by IFN-γ of the MHC II transactivator (CIIta) required for MHC II transcriptional activation. Cyclophilin A (CypA) is required for IFN-γ-dependent induction of MHC II in macrophages, but not when it is mediated by GM-CSF. The effect of CypA appears to be specific because it does not affect the expression of other molecules or genes triggered by IFN-γ, such as FcγR, NOS2, Lmp2, and Tap1. We found that CypA inhibition blocked the IFN-γ-induced expression of CIIta at the transcriptional level in two phases. In an early phase, during the first 2 h of IFN-γ treatment, STAT1 is phosphorylated at Tyrosine 701 and Serine 727, residues required for the induction of the transcription factor IRF1. In a later phase, STAT1 phosphorylation and JNK activation are required to trigger CIIta expression. CypA is needed for STAT1 phosphorylation in this last phase and to bind the CIIta promoter. Our findings demonstrate that STAT1 is required in a two-step induction of CIIta, once again highlighting the significance of cross talk between signaling pathways in macrophages.

Melanoma Metastases to the Adrenal Gland Are Highly Resistant to Immune Checkpoint Inhibitors

BACKGROUND

Adrenal gland metastases (AGMs) are common in advanced-stage melanoma, occurring in up to 50% of patients. The introduction of immune checkpoint inhibitors (ICIs) has markedly altered the outcome of patients with melanoma. However, despite significant successes, anecdotal evidence has suggested that treatment responses in AGMs are significantly lower than in other metastatic sites. We sought to investigate whether having an AGM is associated with altered outcomes and whether ICI responses are dampened in the adrenal glands.

PATIENTS AND METHODS

We retrospectively compared ICI responses and overall survival (OS) in 68 patients with melanoma who were diagnosed with an AGM and a control group of 100 patients without AGMs at a single institution. Response was determined using RECIST 1.1. OS was calculated from time of ICI initiation, anti-PD-1 initiation, initial melanoma diagnosis, and stage IV disease diagnosis. Tumor-infiltrating immune cells were characterized in 9 resected AGMs using immunohistochemical analysis.

RESULTS

Response rates of AGMs were significantly lower compared with other metastatic sites in patients with AGMs (16% vs 22%) and compared with those without AGMs (55%). Patients with AGMs also had significantly lower median OS compared with those without AGMs (3.1 years vs not reached, respectively). We further observed that despite this, AGMs exhibited high levels of tumor-infiltrating immune cells.

CONCLUSIONS

In this cohort of patients with melanoma, those diagnosed with an AGM had lower ICI response rates and OS. These results suggest that tissue-specific microenvironments of AGMs present unique challenges that may require novel, adrenal gland-directed therapies or surgical resection.

Tumor Microenvironment in Adrenocortical Carcinoma: Barrier to Immunotherapy Success?

Adrenocortical carcinoma is a rare malignancy with aggressive behavior, with up to 40% of patients presenting with metastases at the time of diagnosis. Both conventional chemotherapeutic regimens and novel immunotherapeutic agents, many of which are currently being tested in ongoing clinical trials, have yielded modest results so far, bringing the need for a deeper understanding of adrenal cancer behavior to the forefront. In the recent years, the tumor microenvironment has emerged as a major determinant of cancer response to immunotherapy and an increasing number of studies on other solid tumors have focused on manipulating the microenvironment in the favor of the host and discovering new potential target molecules. In the present review we aim to explore the characteristics of adrenocortical cancer's microenvironment, highlighting the mechanisms of immune evasion responsible for the modest immunotherapeutic results, and identify novel potential strategies.

New insights into the cell- and tissue-specificity of glucocorticoid actions

Glucocorticoids (GCs) are endogenous hormones that are crucial for the homeostasis of the organism and adaptation to the external environment. Because of their anti-inflammatory effects, synthetic GCs are also extensively used in clinical practice. However, almost all cells in the body are sensitive to GC regulation. As a result, these mediators have pleiotropic effects, which may be undesirable or detrimental to human health. Here, we summarize the recent findings that contribute to deciphering the molecular mechanisms downstream of glucocorticoid receptor activation. We also discuss the complex role of GCs in infectious diseases such as sepsis and COVID-19, in which the balance between pathogen elimination and protection against excessive inflammation and immunopathology needs to be tightly regulated. An understanding of the cell type- and context-specific actions of GCs from the molecular to the organismal level would help to optimize their therapeutic use.

More Than Suppression: Glucocorticoid Action on Monocytes and Macrophages

Uncontrolled inflammation is a leading cause of many clinically relevant diseases. Current therapeutic strategies focus mainly on immunosuppression rather than on the mechanisms of inflammatory resolution. Glucocorticoids (GCs) are still the most widely used anti-inflammatory drugs. GCs affect most immune cells but there is growing evidence for cell type specific mechanisms. Different subtypes of monocytes and macrophages play a pivotal role both in generation as well as resolution of inflammation. Activation of these cells by microbial products or endogenous danger signals results in production of pro-inflammatory mediators and initiation of an inflammatory response. GCs efficiently inhibit these processes by down-regulating pro-inflammatory mediators from macrophages and monocytes. On the other hand, GCs act on “naïve” monocytes and macrophages and induce anti-inflammatory mediators and differentiation of anti-inflammatory phenotypes. GC-induced anti-inflammatory monocytes have an increased ability to migrate toward inflammatory stimuli. They remove endo- and exogenous danger signals by an increased phagocytic capacity, produce anti-inflammatory mediators and limit T-cell activation. Thus, GCs limit amplification of inflammation by repressing pro-inflammatory macrophage activation and additionally induce anti-inflammatory monocyte and macrophage populations actively promoting resolution of inflammation. Further investigation of these mechanisms should lead to the development of novel therapeutic strategies to modulate undesirable inflammation with fewer side effects via induction of inflammatory resolution rather than non-specific immunosuppression.

Lack of immunotoxic effects of repeated exposure to atrazine associated with the adaptation of adrenal gland activation

T cell-dependent IgM antibody production and natural killer cell (NKC) activity were assessed in SD rats orally administered atrazine for 28 days to males (0, 6.5, 25, or 100 mg/kg/day) or females (0, 3, 6, or 50 mg/kg/day), or 30 or 500 ppm in diet (3 or 51 mg/kg/day). Anti-asialo GM1 antibodies (NKC) and cyclophosphamide (antibody-forming cell assay [AFC]) served as positive controls. Pituitary (ACTH, prolactin), adrenal (corticosterone, progesterone, aldosterone), and gonadal (androgens, estrogens) hormones were assessed after 1, 7, and/or 28 days of treatment. Food intake and body weights were significantly reduced in the highest dosed males, and transiently affected in females. Urinary corticosterone levels were not increased in atrazine-treated groups in either sex at any time point measured (10, 22, or 24 days). Corticosterone and progesterone were elevated in males after a single atrazine dose ≥6.5 mg/kg/day, but not after 7, 14, or 28 doses. There were no effects on adrenal, pituitary, or gonadal hormones in females. Atrazine did not suppress the AFC response or decrease NKC function after 28 days in males or females. Atrazine had no effect on spleen weights or spleen cell numbers in males or females, although thymus weights were elevated in males receiving the highest dose. The lack of immunotoxic effect of atrazine was associated with diminished adrenal activation over time in males, and no effects on adrenal hormones in females.

High-Risk Human Papillomavirus E7 Alters Host DNA Methylome and Represses HLA-E Expression in Human Keratinocytes

Human papillomavirus (HPV) infection distinctly alters methylation patterns in HPV-associated cancer. We have recently reported that HPV E7-dependent promoter hypermethylation leads to downregulation of the chemokine CXCL14 and suppression of antitumor immune responses. To investigate the extent of gene expression dysregulated by HPV E7-induced DNA methylation, we analyzed parallel global gene expression and DNA methylation using normal immortalized keratinocyte lines, NIKS, NIKS-16, NIKS-18, and NIKS-16∆E7. We show that expression of the MHC class I genes is downregulated in HPV-positive keratinocytes in an E7-dependent manner. Methylome analysis revealed hypermethylation at a distal CpG island (CGI) near the HLA-E gene in NIKS-16 cells compared to either NIKS cells or NIKS-16∆E7 cells, which lack E7 expression. The HLA-E CGI functions as an active promoter element which is dramatically repressed by DNA methylation. HLA-E protein expression on cell surface is downregulated by high-risk HPV16 and HPV18 E7 expression, but not by low-risk HPV6 and HPV11 E7 expression. Conversely, demethylation at the HLA-E CGI restores HLA-E protein expression in HPV-positive keratinocytes. Because HLA-E plays an important role in antiviral immunity by regulating natural killer and CD8+ T cells, epigenetic downregulation of HLA-E by high-risk HPV E7 may contribute to virus-induced immune evasion during HPV persistence.

Ursodeoxycholic acid in cholestasis: linking action mechanisms to therapeutic applications

UDCA (ursodeoxycholic acid) is the therapeutic agent most widely used for the treatment of cholestatic hepatopathies. Its use has expanded to other kinds of hepatic diseases, and even to extrahepatic ones. Such versatility is the result of its multiple mechanisms of action. UDCA stabilizes plasma membranes against cytolysis by tensioactive bile acids accumulated in cholestasis. UDCA also halts apoptosis by preventing the formation of mitochondrial pores, membrane recruitment of death receptors and endoplasmic-reticulum stress. In addition, UDCA induces changes in the expression of metabolizing enzymes and transporters that reduce bile acid cytotoxicity and improve renal excretion. Its capability to positively modulate ductular bile flow helps to preserve the integrity of bile ducts. UDCA also prevents the endocytic internalization of canalicular transporters, a common feature in cholestasis. Finally, UDCA has immunomodulatory properties that limit the exacerbated immunological response occurring in autoimmune cholestatic diseases by counteracting the overexpression of MHC antigens and perhaps by limiting the production of cytokines by immunocompetent cells. Owing to this multi-functionality, it is difficult to envisage a substitute for UDCA that combines as many hepatoprotective effects with such efficacy. We predict a long-lasting use of UDCA as the therapeutic agent of choice in cholestasis.

Identification of glucocorticoid-regulated genes that control cell proliferation during murine respiratory development

Glucocorticoids play a vital role in fetal respiratory development and act via the intracellular glucocorticoid receptor (GR) to regulate transcription of key target genes. GR-null mice die at birth due to respiratory dysfunction associated with hypercellularity and atelectasis. To identify events associated with this lung phenotype we examined perinatal cellular proliferation rates and apoptotic indices. We demonstrate that compared to wild-type controls, day 18.5 postcoitum (p.c.) GR-null mouse lungs display significantly increased cell proliferation rates (1.8-fold P < 0.05) and no change in apoptosis. To examine underlying molecular mechanisms, we compared whole genome expression profiles by microarray analysis at 18.5 days p.c. Pathways relating to cell proliferation, division and cell cycle were significantly down-regulated while pathways relating to carbohydrate metabolism, kinase activities and immune responses were significantly up-regulated. Differential levels of gene expression were verified by quantitative-RT-PCR and/or Northern analysis. Key regulators of proliferation differentially expressed in the lung of 18.5 p.c. GR-null lungs included p21 CIP1 (decreased 2.9-fold, P < 0.05), a negative regulator of the cell cycle, and Mdk (increased 6.0-fold, P < 0.05), a lung growth factor. The more under-expressed genes in 18.5 p.c. GR-null lungs included Chi3l3 (11-fold, P < 0.05), a macrophage inflammatory response gene and Ela1 (9.4-fold, P < 0.05), an extracellular matrix remodeling enzyme. Our results demonstrate that GR affects the transcriptional status of a number of regulatory processes during late fetal lung development. Amongst these processes is cell proliferation whereby GR induces expression of cell cycle repressors while suppressing induction of a well characterized cell cycle stimulator.

Lipopolysaccharide up-regulates MHC class II expression on dendritic cells through an AP-1 enhancer without affecting the levels of CIITA

The expression of MHC class II genes is strictly tissue specific. In a limited number of cells, the expression of these genes is inducible by cytokines and only in dendritic and B cells is expression constitutive. LPS blocks the cytokine-dependent induction of these genes, but enhances their expression in dendritic and the B cell line A20. We have observed that LPS increased surface expression by raising I-A protein and mRNA levels. LPS does not enhance the expression of the transactivator CIITA. In transient transfection experiments, LPS induced the expression of the I-Abeta promoter, which contains an AP-1 box located between 1722 and 1729 bp upstream of the transcriptional start site. Mutation of this box abrogated the effect of LPS. The AP-1 box still responded to LPS when we moved it to -611 bp or even when it was in the opposite direction. LPS induced a complex that bound to the AP-1 box. However, in dendritic cells, the complex comprised c-jun and c-fos while in A20 cells only c-jun. This was confirmed by chromatin immune precipitation assays and the distinct induction of c-jun and c-fos mRNAs. Therefore, our results indicate that LPS exerts a novel regulatory mechanism in the control of MHC class II gene expression.

In vivo, RFX5 binds differently to the human leucocyte antigen-E, -F, and -G gene promoters and participates in HLA class I protein expression in a cell type-dependent manner

We analysed the regulation of human leucocyte antigen (HLA)-E, -F and -G genes, focusing on the SXY module, a promoter region that controls major histocompatibility complex (MHC) class II expression and participates in the expression of classical HLA class I molecules. It comprises the X1, X2 and Y boxes, bound by RFX, X2-BP/ATF/CREB and NFY factors, respectively. The complex recruits the master control factor CIITA. The SXY module is conserved in HLA-E and HLA-F gene promoters, whereas in the HLA-G promoter, the only conserved boxes are S and X1. Chromatin immunoprecipitation assays, performed on HLA-G positive and negative cell lines, demonstrated the in situ binding of RFX5 and CIITA to HLA-E and HLA-F, but not to HLA-G, promoters. In B cells from bare lymphocyte syndrome patients lacking RFX5 or CIITA, we observed lower steady-state levels of HLA-E and HLA-F transcripts but did not find any significant decrease in the cell-surface expression of HLA-E/classical HLA class I. In RFX5-deficient fibroblasts, the cell-surface expression of HLA molecules was decreased. RFX5 and CIITA are thus not involved in HLA-G expression and their importance for the surface expression of HLA-E/classical HLA class I molecules may vary depending on the cell type.

In vivo, RFX5 binds differently to the human leucocyte antigen-E, -F, and -G gene promoters and participates in HLA class I protein expression in a cell type-dependent manner

We analysed the regulation of human leucocyte antigen (HLA)-E, -F and -G genes, focusing on the SXY module, a promoter region that controls major histocompatibility complex (MHC) class II expression and participates in the expression of classical HLA class I molecules. It comprises the X1, X2 and Y boxes, bound by RFX, X2-BP/ATF/CREB and NFY factors, respectively. The complex recruits the master control factor CIITA. The SXY module is conserved in HLA-E and HLA-F gene promoters, whereas in the HLA-G promoter, the only conserved boxes are S and X1. Chromatin immunoprecipitation assays, performed on HLA-G positive and negative cell lines, demonstrated the in situ binding of RFX5 and CIITA to HLA-E and HLA-F, but not to HLA-G, promoters. In B cells from bare lymphocyte syndrome patients lacking RFX5 or CIITA, we observed lower steady-state levels of HLA-E and HLA-F transcripts but did not find any significant decrease in the cell-surface expression of HLA-E/classical HLA class I. In RFX5-deficient fibroblasts, the cell-surface expression of HLA molecules was decreased. RFX5 and CIITA are thus not involved in HLA-G expression and their importance for the surface expression of HLA-E/classical HLA class I molecules may vary depending on the cell type.

Steroid receptor coactivator 1 links the steroid and interferon gamma response pathways

We show here that steroid receptor coactivator 1 (SRC-1) is a coactivator of MHC class II genes that stimulates their interferon gamma (IFNgamma) and class II transactivator (CIITA)-mediated expression. SRC-1 interacts physically with the N-terminal activation domain of CIITA through two regions: one central [extending from amino acids (aa) 360-839] that contains the nuclear receptors binding region and one C-terminal (aa 1138-1441) that contains the activation domain 2. Using chromatin immunoprecipitation assays we show that SRC-1 recruitment on the class II promoter is enhanced upon IFNgamma stimulation. Most importantly, SRC-1 relieves the inhibitory action of estrogens on the IFNgamma-mediated induction of class II genes in transient transfection assays. We provide evidence that inhibition by estradiol is due to multiple events such as slightly reduced recruitment of CIITA and SRC-1 and severely inhibited assembly of the preinitiation complex.

Stress and the immune system

Stressors can positively or adversely affect immune and inflammatory responses. However, the current understanding of these effects at the cellular and molecular levels is not sufficient to allow prediction of the effects of a particular stressor on a particular immune or inflammatory function. Three complementary conceptual frameworks are presented that may prove useful in developing such an understanding. In addition, specific examples of the action of particular stress mediators on particular immune or inflammatory end points are discussed, and the relationship of these observations to the conceptual frameworks is indicated. Several of the effects discussed are relevant clinically, and the prospects for pharmacological intervention to prevent adverse effects of stressors on the immune system are discussed. Finally, some of the factors that can (sometimes unexpectedly) influence the outcome of stress-immunology studies and some of the pitfalls that continue to make this area of research controversial in some circles are discussed.

Inhibition of IFN-gamma signaling by glucocorticoids

Recent reports suggest that a novel mechanism of glucocorticoid (GC) immunosuppressive action is inhibition of signaling by IL-2 and IL-12, cytokines that use the Janus kinase-STAT signaling pathway. We investigated whether GCs could also block activation of Janus kinase-STAT signaling by IFN-gamma, a potent proinflammatory cytokine. Addition of dexamethasone to PBMC cultures resulted in a dramatic inhibition of IFN-gamma activation of STAT1. Several days of exposure to GCs were required for inhibition of IFN-gamma signaling to become apparent, and the underlying mechanism was down-regulation of STAT1 expression. GCs suppressed the expression of STAT1 mRNA, but did not affect STAT1 protein stability. STAT1 expression and IFN-gamma signaling were preferentially suppressed in macrophages. GCs did not act directly on macrophages, but worked indirectly by regulating macrophage-lymphocyte interactions that control STAT1 expression. GCs inhibited IFN-gamma-inducible gene expression, thus demonstrating the physiological significance of inhibition of signal transduction. Our results identify a novel level of regulation of IFN-gamma signaling, whereby GCs control the amplitude of IFN-gamma signaling by regulating STAT1 expression. These results suggest that inhibition of IFN-gamma signaling contributes to the immunosuppressive action of GCs.

Glucocorticoid regulation of human eosinophil gene expression

Molecular analysis of steroid-regulated gene expression in freshly isolated human eosinophils is difficult due to the inherent high rate of spontaneous apoptosis and elevated levels of endogenous ribonucleases. To circumvent these limitations, we determined if the human eosinophilic cell line EoL-1 could serve as an in vitro model of glucocorticoid signaling. We found by optimizing growth conditions in low serum-containing media that dexamethasone (Dex) treatment of EoL-1 cells induced an apoptotic pathway that was inhibited by interleukin-5 (IL-5). Moreover, gene expression profiling using RNA from untreated EoL-1 cells and from freshly isolated human eosinophils identified 380 commonly expressed genes, including the eosinophil markers granule major basic protein, prostaglandin-endoperoxide synthase 1 and arachidonate 15-lipoxygenase. Expression profiling was performed using EoL-1 cells that had been treated with dexamethasone for 0, 4, 12, 24 and 48h identifying 162 genes as differentially expressed. Two of the most highly upregulated genes based on expression profiling were the transcription factor Ets-2 and the MHC Class II genes (Q, R, and P). Expression of these genes in EoL-1 cells was shown to be dexamethasone-induced at the RNA and protein levels which is consistent with the known function of Ets-2 in controlling cell cycle progression and the role of MHC Class II antigens in mediating eosinophil functions.

Transcriptional regulation of the mouse fatty acid amide hydrolase gene

Fatty acid amide hydrolase (FAAH) is a membrane-bound enzyme that inactivates a family of fatty acid amide molecules which are implicated in physiological processes such as pain and sleep. We cloned a 1.9 kb fragment of the 5'-untranslated region of the mouse FAAH gene into the pGL3 basic luciferase reporter vector and showed that this sequence has promoter activity in vitro. By primer extension analysis, we have determined the transcription start site to be 200 bases upstream of the ATG initiation codon and found that a TATA motif was absent. A number of putative response elements, including those for estrogen and glucocorticoids, were identified in this sequence. We have demonstrated that the estrogen and glucocorticoid receptors down-regulate transcriptional activity independent of their ligand. These data should help in understanding the mechanisms of FAAH gene transcription.

Immunosenescence of macrophages: reduced MHC class II gene expression

In order to determine the effect of aging on macrophages, we produced bone marrow-derived macrophages in vitro from young and aged mice. We analyzed the effect of aging on the genomic expression of macrophages in these conditions, without the influence of other cell types that may be affected by aging. Macrophages from young and aged mice were present in similar numbers and showed an identical degree of differentiation, cell size, DNA content and cell surface markers. After incubation with interferon-gamma (IFN-gamma), the expression at the cell surface of the MHC class II gene IA complex product and the levels of intracellular IAbeta protein and mRNA were lower in aged macrophages. Moreover, the transcription of IAbeta gene was impaired in aged macrophages. The amount of transcription factors that bound to the W and X boxes, but not to the Y box of the IAbeta promoter gene were lower in aged macrophages. Similar levels of CIITA mRNA were found after IFN-gamma treatment of both young and aged macrophages. This shows that neither the initial cascade that starts after the interaction of IFN-gamma with the receptor, nor the second signals involved in the expression of CIITA, are impaired in aged macrophages. These data could explain, at least in part, the impaired immune response associated to senescence.

IFN-gamma-dependent transcription of MHC class II IA is impaired in macrophages from aged mice

To determine the effect of aging on IFN-gamma-induced MHC class II antigen expression, we produced bone marrow-derived macrophages in vitro. In these conditions, we analyzed the effect of aging on the genomic expression of macrophages without the influence of other cell types that may be affected by aging. Although macrophages from young and aged mice showed an identical degree of differentiation, after incubation with IFN-gamma, the expression at the cell surface of the IA complex and the levels of IAbeta protein and mRNA were lower in aged macrophages. Moreover, the transcription of the IAbeta gene was impaired in aged macrophages. The amount of transcription factors that bound to the W and X, but not to the Y, boxes of the IAbeta promoter gene was lower in aged macrophages. Similar levels of CIITA mRNA were found after IFN-gamma treatment of both young and aged macrophages. This shows that neither the initial cascade that starts after the interaction of IFN-gamma with the receptor nor the second signals involved in the expression of CIITA are impaired in aged macrophages. These data indicate that aging is associated with low levels of MHC class II gene induction by IFN-gamma because of impaired transcription.

Effect of transforming growth factor-beta1 on microglial MHC-class II expression

In the present report, the effects of IFN-gamma and transforming growth factor beta1 (TGF-beta1) on major histocompatibility complex class II (MHC-II) gene expression in isolated mouse brain microglial cells, in the MH-S macrophage cell line and in the primary mouse macrophage cultures were examined. IFN-gamma is a potent inducer of MHC-II gene and this induction was further elevated in microglia by TGF-beta1, while TGF-beta1 inhibited IFN-gamma, induction in macrophages. The enhancing effect of TGF-beta1 was also detected in microglia at the protein level. Transient transfection of microglia with 5' deletional mutants of the MHC-II IAalpha promoter linked to the chloramphenicol acetyltransferase reporter gene demonstrated that TGF-beta1 acts at the transcriptional level to enhance the MHC-II expression induced by IFN-gamma.

Differential regulation of major histocompatibility complex class II expression and nitric oxide release by beta-amyloid in rat astrocyte and microglia

Astrocytes and microglial cells were examined for expression of two immunologically important molecules, major histocompatibility complex class II (MHC-II) and nitric oxide (NO) following treatment with IFN-gamma and beta-amyloid (betaA) peptides, betaA(1-42) and betaA(25-35). IFN-gamma is a potent inducer of both MHC-II gene expression and NO production. The induction of MHC-II was inhibited by both betaA peptides in astrocytes but they had little or no effect in microglia. betaA peptides had no effect on NO release in astrocytes but on microglia betaA(1-42) synergistically induced NO release with IFN-gamma. Transient transfection of astrocytes with 5' deletional mutants of MHC-II IAalpha promoter linked to the chloramphenicol acetyl transferase reporter gene (IAalpha-CAT), demonstrated that betaA acts at the transcriptional level to downregulate IFN-gamma induced MHC-II gene expression in astrocytes. In previous studies, the induction of MHC-II on glial cells were suggested to be involved in the pathogenesis of neurodegenerative diseases and MHC-II(+) microglial cells were observed at much higher frequency than astrocytes. This study provides information on the regulation of the MHC-II gene expression in astrocytes and in microglial cells by betaA and this pathway may be critically involved in the immune/inflammatory regulation within the central nervous system.

Dexamethasone inhibits IFNgamma-induced MHC class II expression of intestinal epithelial cells independently of the TGF-beta1 regulatory pathway

BACKGROUND

In the presence of inflammation, an increased expression of enterocyte MHC class II is observed, leading to altered mucosal antigen handling. Corticosteroids are potent anti-inflammatory drugs, widely used in treating inflammatory bowel disorders. However, their diverse mechanisms of action are only partially understood.

AIM

To evaluate effect and mechanisms of corticosteroids on intestinal crypt epithelial cell MHC class II.

METHODS

The effect of dexamethasone treatment on cytokine-induced MHC class II expression was measured in IEC-6 cells by immunofluorescence and flow cytometry. To determine the role of the TGF-beta1 regulatory pathway in mediating the effects of dexamethasone, neutralizing anti-TGF-beta antibodies were used. Additionally, endogenous and dexamethasone-stimulated IEC-6 cell TGF-beta1 production was measured by ELISA.

RESULTS

Dexamethasone potently down-regulated IFNgamma-induced class II expression on IEC-6 cells, in a dose-dependent manner. TGF-beta1 had a similar inhibitory effect on class II expression. However, neutralizing anti-TGF-beta antibodies did not alter the effect of dexamethasone. Furthermore, dexamethasone reduced endogenous TGF-beta1 synthesis.

CONCLUSIONS

Corticosteroids inhibit cytokine-induced MHC class II expression on IEC-6 cells in a TGF-beta1 independent way. This effect may markedly alter enterocytic antigen presentation, reducing the aberrant state of activation of mucosal immune cells.

IFN-γ Up-Regulates the A2B Adenosine Receptor Expression in Macrophages: A Mechanism of Macrophage Deactivation

Adenosine is a potent endogenous anti-inflammatory agent released by cells in metabolically unfavorable conditions, such as hypoxia or ischemia. Adenosine modulates different functional activities in macrophages. Some of these activities are believed to be induced through the uptake of adenosine into the macrophages, while others are due to the interaction with specific cell surface receptors. In murine bone marrow-derived macrophages, the use of different radioligands for adenosine receptors suggests the presence of A2B and A3 adenosine receptor subtypes. The presence of A2B receptors was confirmed by flow cytometry using specific Abs. The A2B receptor is functional in murine macrophages, as indicated by the fact that agonists of A2B receptors, but not agonists for A1, A2A, or A3, lead to an increase in cAMP levels. IFN-γ up-regulates the surface protein and gene expression of the A2B adenosine receptor by induction of de novo synthesis. The up-regulation of A2B receptors correlates with an increase in cAMP production in macrophages treated with adenosine receptor agonist. The stimulation of A2B receptors by adenosine or its analogues inhibits the IFN-γ-induced expression of MHC class II genes and also the IFN-γ-induced expression of nitric oxide synthase and of proinflammatory cytokines. Therefore, the up-regulation of the A2B adenosine receptor expression induced by IFN-γ could be a feedback mechanism for macrophage deactivation.

Interactions between the class II transactivator and CREB binding protein increase transcription of major histocompatibility complex class II genes

Class II major histocompatibility (class II) genes are regulated in a B-cell-specific and gamma interferon-inducible fashion. The master switch for the expression of these genes is the class II transactivator (CIITA). In this report, we demonstrate that one of the functions of CIITA is to recruit the CREB binding protein (CBP) to class II promoters. Not only functional but also specific binding interactions between CIITA and CBP were demonstrated. Moreover, a dominant negative form of CBP decreased the activity of class II promoters and levels of class II determinants on the surface of cells. Finally, the inhibition of class II gene expression by the glucocorticoid hormone could be attributed to the squelching of CBP by the glucocorticoid receptor. We conclude that CBP, a histone acetyltransferase, plays an important role in the transcription of class II genes.

Involvement of CREB binding protein in expression of major histocompatibility complex class II genes via interaction with the class II transactivator

The class II transactivator (CIITA) is a key regulatory factor that controls expression of the major histocompatibility complex (MHC) class II genes that are essential components for antigen presentation and thus regulation of the immune response. We show here that the adenovirus E1A protein interferes with the action of CIITA and inhibits both B-cell-specific and gamma interferon (IFN-gamma)-induced expression of MHC class II promoters. Transfection studies provide evidence for the functional role of the CREB-binding protein (CBP) in IFN-gamma and CIITA-mediated MHC class II promoter activation. We demonstrate that the N-terminally located transcription activation domain of CIITA physically interacts with both the N-terminal and the E1A-binding (C/H3) regions of CBP. These results suggest the involvement of a multisubunit complex, which contains the gene-specific coactivator CIITA and the versatile coactivator CBP, in MHC class II gene regulation, which may be responsible for both high-level expression and modulation by different signaling pathways.

Effect of ethanol on B cell expression of major histocompatibility class II proteins in immunized mice

Acute or chronic exposure to ethanol (EtOH), as well as other stimuli that induce a neuroendocrine stress response, can decrease the expression of MHC class II proteins (immune-associated antigens, Ia) on B cells and macrophages. In a mouse model for binge drinking, it has been shown that this decrease is caused by EtOH-induced increases in endogenous glucocorticoids. Decreased Ia expression would be expected to suppress T-dependent humoral responses, and such suppression has been noted in our model. However, it has been reported that activated B cells are much less susceptible to glucocorticoid-induced decreases in Ia expression than are resting B cells. Thus, it is not clear that the decreased Ia observed in our previous studies with non-immunized mice could account for decreased humoral responses, because it has not been directly determined that decreased Ia expression occurs in immunized mice. To examine this issue, splenocytes from mice immunized with sheep erythrocytes were studied by flow cytometry. Mice were treated with EtOH by gavage and immunized 12 h later, because our previous results indicate that this produces maximal suppression of the humoral response. In immunized mice, EtOH decreased Ia expression on B cells at 6 and 12 h after immunization, but not at 24 or 74 h. In a dose-response study, a substantial decrease in Ia expression on B cells was observed at an EtOH dosage of 6.0 or 7.0 g/kg. Thus, decreased Ia expression is a potential mechanism for EtOH-induced suppression of the humoral response. A glucocorticoid antagonist (RU 486) partially blocked the EtOH-induced decrease in Ia expression, suggesting that glucocorticoids are involved in the reduction of Ia expression in immunized mice. Direct administration of corticosterone to produce blood levels comparable to those noted in EtOH-treated mice did not significantly decrease Ia expression, but Ia expression tended to be lower in mice treated with corticosterone. Taken together, these results indicate that glucocorticoids play some role in decreasing Ia expression in immunized mice, but they are less important than in non-immunized mice.

Adrenal hormone modulation of type 1 and type 2 cytokine production by spleen cells: dexamethasone and dehydroepiandrosterone suppress interleukin-2, interleukin-4, and interferon-gamma production in vitro

Our previous work has documented that physical or psychological stress can alter interleukin (IL)-2, IL-4, and interferon (IFN)-gamma production by spleen or lymph node cells in vitro. To determine if adrenal hormones might be mediating these stress-induced changes in type 1 and type 2 cytokines and immune effector functions, we cultured spleen cells in vitro with either the synthetic glucocorticoid dexamethasone (DEX) or the putative restorative hormone dehydroepiandrosterone (DHEA). Spleen cells were obtained from either young (5-6 weeks old) or mature (7-8 months old) BALB/c mice that were either unimmunized or immunized with the T-cell-dependent antigen keyhole limpet hemocyanin (KLH). We determined that DEX suppressed production of all three cytokines examined. DHEA was not associated with any enhancement of cytokine production. These data challenge the hypothesis that glucocorticoids can differentially regulate Th1-like versus Th2-like cytokine production. Further, they suggest that in stress paradigms in which differential regulation of cytokine production and effector function has been observed, other neuroendocrine factors in addition to glucocorticoids must be relevant.

Repression mechanisms of the I-A beta gene of the major histocompatibility complex

The mechanisms of regulation of I-A beta gene expression in the murine major histocompatibility complex by transcriptional repression are reviewed. Active and passive repression mechanisms are presented. The transcription factor PU.1 actively inhibits the expression of I-A beta through the binding to a DNA sequence near the Y box, a cis-element in the promoter necessary for transcription. This interaction probably interferes with the preinitiation complex assembly. NF-Y is a transcription factor that binds to the Y box and has two constituents: NF-YA (that binds weakly to DNA) and NF-YB (that increases the binding of NF-YA to DNA). The dbpA protein represses the expression of I-A beta by a quenching mechanism, forming a complex with NF-YA and the dbpB protein by sequestering the NF-YB protein. A similar mechanism is observed with the glucocorticoid receptor that binds to the X-box binding proteins and inhibits their interaction with the X box. These results are examples of cross-talk between proteins, which may help us to understand the regulation of I-A beta gene expression.

Expression of MHC class II CD4+ and ED1 molecules in association with selective hippocampal neuronal degeneration after long-term adrenalectomy

The neuroendocrine and the immune systems are interconnected. Monoclonal antibodies against major histocompatibility complex (MHC) class I, class II, CD4, CD8, pan T cells, and macrophages were used for immunostaining brains from adrenalectomized (ADX) and shamoperated rats to investigate the potential involvement of the immune/inflammatory mechanisms in the neurodegeneration of hippocampus after ADX. Our results demonstrate upregulation of MHC class II, CD4 antigens and activated microglial marker-ED1 expression selectively in the hippocampus after ADX. The absence of CD5 reactivity precludes that these activated cells were T lymphocytes. The activated microglial cells may either be instrumental in the hippocampal neuronal loss or activated secondarily to the neuronal degeneration after long-term adrenalectomy.

Identification of the transcription factors NF-YA and NF-YB as factors A and B that bound to the promoter of the major histocompatibility complex class II gene I-A beta

The Y box is a conserved sequence in the promoter of major histocompatibility complex (MHC) class II genes, which contains a CCAAT sequence (CCAAT box). Previously, we partially purified the DNA-binding protein that recognizes the Y box of the I-A beta gene and showed that it consisted of two components (factors A and B) both of which were necessary for optimal DNA binding. The genes for the heteromeric protein NF-Y (NF-YA and NF-YB), which binds to the I-E alpha Y box have been cloned. We subsequently isolated the genes for NF-YA and NF-YB using oligonucleotides designed from the published sequences. NF-YA and NF-YB were tested for binding to the I-A beta and I-E alpha Y boxes. While neither NF-YA or NF-YB alone bound to the Y box, when the components were mixed the complex bound to the I-A beta Y box with high affinity. Moreover, NF-YA and NF-YB could be complemented for binding to DNA by factor B or factor A, respectively. These results suggest that the active binding protein is NF-YA in factor A extracts and NF-YB in factor B extracts. Finally, antibodies against NF-YA and NF-YB were shown to induce a supershift when nuclear extracts were added to the double-stranded oligodeoxynucleotide covering the Y box of the I-A beta gene. Antisense expression constructs of both NF-YA and NF-YB were made and their effect on expression from the I-A beta promoter was tested. Either antisense construction, when transfected into cells, lowered the expression of a reporter gene linked to the I-A beta promoter. This study provides direct evidence of the identification of NF-YA and NF-YB as the previously described factors A and B. Moreover, these results strongly implicate NF-Y in the expression of the MHC class II gene I-A beta.

Molecular mechanisms of anti-inflammatory action of glucocorticoids

Glucocorticoid hormones are effective in controlling inflammation, but the mechanisms that confer this action are largely unknown. Recent advances in this field have shown that both positive and negative regulation of gene expression are necessary for this process. The genes whose activity are modulated in the anti-inflammatory process code for several cytokines, adhesion molecules and enzymes. Most of them do not carry a classical binding site for regulation by a glucocorticoid receptor, but have instead regulatory sequences for transcription factors such as AP-1 or NF-kappa B. This makes them unusual targets for glucocorticoid action and emphasizes the need for novel regulatory mechanisms. Recent studies describe an important contribution by protein-protein interactions, in which several domains of the receptor participate; these studies provide a better understanding of the action of the receptor and offer opportunities for the design of steroidal compounds that could function more effectively as anti-inflammatory drugs.

Identification of a transcription factor that binds to the S box of the I-A beta gene of the major histocompatibility complex

Class II genes of the MHC show a striking homology upstream of the transcription start site that is composed of three conserved sequences (S, X and Y boxes, each separated by 15-20 bp). The presence of the S-box sequence in the mouse MHC class II gene I-A Beta was examined for its influence on the expression of this gene. Deletion or mutation of the S box decreased the induction of chloramphenicol acetyltransferase (CAT) activity in B lymphocytes by 32%. In macrophages, deletion or mutation of the S box abolished interferon-gamma (IFN-gamma) inducibility of CAT activity. Using a gel-retardation assay, we have identified a nuclear factor whose binding site overlaps the 7-mer conserved sequence of the S box. This factor is present in lymphocytes, macrophages, mastocytes and fibroblasts. Surprisingly, binding of this nuclear factor to DNA was induced by IFN-gamma in bone-marrow-derived macrophages, but not in macrophage-like cell lines. The binding site for this factor was defined by DNase I footprinting and partially purified by using an affinity column containing double-stranded oligonucleotides containing a sequence of the S box. A prominent protein of 43 kDa was found that bound specifically to the S-box sequence.

Repression of I-A beta gene expression by the transcription factor PU.1

The PU.1 protein is an ets-related transcription factor that is expressed in macrophages and B lymphocytes. We present evidence that PU.1 binds to the promoter of the I-A beta gene, i.e. a PU box located next to the Y box. Transfection of PU.1 in B lymphocytes or in interferon-gamma-treated macrophages represses I-A beta gene expression. The inhibitory effect of PU.1 was obtained with the DNA binding domain of the protein, but not with the activation domain. Using the gel shift retardation assay we found that in vitro transcribed/translated NF-YA and NF-YB bind to the Y box of the I-A beta promoter. When PU.1 was added to the assay, a supershifted DNA band was found, indicating that PU.1 and NFY proteins bind to the same DNA molecule. We conclude that I-A beta gene expression is repressed by PU.1 binding to the PU box domain.

Glucocorticoids down-regulate dendritic cell function in vitro and in vivo

Exogenous glucocorticoid hormones are widely used as therapeutical agents, whereas endogenous glucocorticoids may act as physiological immunosuppressants involved in the control of immune and inflammatory responses. The optimal activation of T lymphocytes requires two distinct signals: the major histocompatibility complex-restricted presentation of the antigen and an additional co-stimulatory signal provided by the antigen-presenting cells. There is ample evidence that, among the cells able to present the antigen, the dendritic cells (DC) have the unique property to activate antigen-specific, naive T cells in vitro and in vivo, and are therefore required for the induction of primary immune responses. In this work, we tested whether glucocorticoids affected the capacity of DC to sensitize naive T cells. Our data show that, in vitro, the steroid hormone analog dexamethasone (Dex) affects the viability of DC, selectively down-regulates the expression of co-stimulatory molecules on viable DC, and strongly reduces their immunostimulatory properties. In vivo, a single injection of Dex results in impaired antigen presenting function, a finding which correlates with reduced numbers of splenic DC. These results show that glucocorticoids regulate DC maturation and immune function in vitro and in vivo and suggest that this mechanism may play a role in preventing overstimulation of the immune system.

Listeria monocytogenes infection in pregnant mice: abnormalities in the function of non-adherent accessory light density dendritic cells

Pregnant A/J mice were found to be more susceptible to the lethal effect of Listeria monocytogenes bacteria than virgin females. However, during the first four days of post-infection there was no difference in the elimination of Listeria from the spleens of pregnant and virgin mice. This suggests that the increase in the susceptibility of pregnant mice to pathogenic activity of L. monocytogenes was related to the diminution in Listeria-specific cellular reactions. Indeed, we found that non-adherent light density dendritic cells (DCs) from pregnant mice showed a marked reduction in the ability to form clusters with L. monocytogenes immune T lymphocytes and it is known that cell cluster formation between antigen presenting cells (APC) and responding T cells is required for antigen recognition as well as for cell proliferation. DCs from pregnant mice also demonstrated the decrease and an instability in the expression of H-2 class II molecules which play a crucial role in the recognition of exogenous antigens. The abnormalities demonstrated in the function of the light density dendritic cells from the spleens of pregnant mice could compromise cellular reactions to L. monocytogenes bacteria possibly resulting in increased susceptibility of pregnant mice to experimental listeriosis.

Repression of major histocompatibility complex I-A beta gene expression by dbpA and dbpB (mYB-1) proteins

The induction of major histocompatibility complex class II gene expression is mediated by three DNA elements in the promoters of these genes (W, X, and Y boxes). The Y box contains an inverted CCAAT box sequence, and the binding activity to the CAAT box is mediated by factor NF-Y, which is composed of subunits NF-YA and NF-YB. We have found that transfection of either dbpA or dbpB (mYB-1) or both inhibits I-A beta gene expression. Although the genes for some members of the Y-box family of binding proteins have been isolated by screening an expression library using the Y-box sequence, under our conditions no binding of dbpA or dbpB to the Y box of the I-A beta or I-E alpha promoter was detected. This suggested that repression of I-A beta gene expression by dbpA and dbpB was not due to competition for binding to the Y-box sequence. The results suggest two other mechanisms by which dbpA and dbpB can inhibit transcription from the I-A beta promoter. When dbpA was added, the binding of NF-YA to DNA increased, which could be explained by interaction between these two proteins whose purpose is to increase the binding affinity of NF-YA for DNA. However, this complex was unable to stimulate transcription from the I-A beta promoter. Thus, dbpA competed for the interaction between NF-YA and NF-YB by binding to NF-YA. When dbpB factor was added together with NF-YA and NF-YB, the binding of the NF-YA--NF-YB complex was reduced. This suggested that dbpB may complete with NF-YB for interaction with NF-YA. These results provide an example of how dbpA and dbpB may regulate transcription of promoters that utilize NF-Y as a transcription factor.

Hormone-independent repression of AP-1-inducible collagenase promoter activity by glucocorticoid receptors

The role of the ligand in glucocorticoid receptor-mediated transactivation and transrepression of gene expression was investigated. Half-maximal transactivation of a mouse mammary tumor virus-chloramphenicol acetyltransferase reporter gene in transfected cells expressing the human glucocorticoid receptor mutant GRL753F, from which the rate of ligand dissociation is four to five times higher than the rate of dissociation from normal receptors, required a 200- to 300-fold-higher concentration of dexamethasone than was required in cells expressing the normal receptor. Immunocytochemical analysis demonstrated that this difference was not the result of a failure of the mutant receptor to accumulate in the nucleus after steroid treatment. In contrast, in cells cotransfected with a reporter gene containing the AP-1-inducible collagenase gene promoter, the concentration of dexamethasone required for 50% transrepression was the same for mutant and normal receptors. Efficient receptor-mediated transrepression was also observed with the double mutant GRL753F/C421Y, in which the first cysteine residue of the proximal zinc finger has been replaced by tyrosine, indicating that neither retention of the ligand nor direct binding of the receptor to DNA is required. RU38486 behaved as a full agonist with respect to transrepression. In addition, receptor-dependent transrepression, but not transactivation, was observed in transfected cells after heat shock in the absence of the ligand. Taken together, these results suggest that unlike transactivation, transrepression of AP-1 activity by the nuclear glucocorticoid receptor is ligand independent.

The effects of glucocorticoids on human eosinophils

It is readily apparent that eosinophils are important targets of steroid effects. Disruption of the cytokine network by glucocorticoids can indirectly diminish eosinophil generation, survival, and function. In addition, glucocorticoids appear to have direct effects on the survival, and perhaps on the function, of these cells. Rapid advances in our knowledge of the biochemistry of signal transduction, as well as the interaction between cell surface receptors and RNA transcription machinery, will allow detailed analysis of the mechanisms by which the function and life cycle of eosinophils are influenced by glucocorticoids.

Transplantation immunology

A major function of the immune response is the discrimination of self from nonself. It is this response that must be overcome in transplant rejection. Progress in understanding these basic immune mechanisms has helped to improve clinical outcome and lays the foundation for a new generation of therapies.