Three distinct classes of regulatory cytokines control endothelial cell MHC antigen expression. Interactions with immune gamma interferon differentiate the effects of tumor necrosis factor and lymphotoxin from those of leukocyte alpha and fibroblast beta interferons

Single cell atlas of kidney cancer endothelial cells reveals distinct expression profiles and phenotypes

BACKGROUND

Tumor endothelial cells (TECs) represent the primary interface between the tumor microenvironment and circulating immune cells, however their phenotypes are incompletely understood in highly vascularized clear cell renal cell carcinoma (ccRCC).

METHODS

We purified tumor and matched normal endothelial cells (NECs) from ccRCC specimens and performed single-cell RNA-sequencing to create a reference-quality atlas available as a searchable web resource for gene expression patterns. We established paired primary TECs and NECs cultures for ex vivo functional testing.

RESULTS

TECs from multiple donors shared a common phenotype with increased expression of pathways related to extracellular matrix regulation, cell-cell communication, and insulin-like growth factor signaling. This phenotype was shared with hepatocellular carcinoma associated TECs, suggesting convergent TEC phenotypes between unrelated tumors. Cultured TECs stably maintained a core program of differentially regulated genes which promoted resistance to apoptosis after vascular endothelial growth factor removal and increased adhesiveness to subsets of immune cells including regulatory T-cells.

CONCLUSIONS

Our studies demonstrate that TECs have a distinct phenotype that is shared by TECs from different tumor types and stable in ex vivo culture. The distinct adhesive interaction of TECs with immune cells raises the possibility of their modulation to improve immune cell-based therapies for RCC.

Heterogeneity in allospecific T cell function in transplant-tolerant hosts determines susceptibility to rejection following infection

Even when successfully induced, immunological tolerance to solid organs remains vulnerable to inflammatory insults, which can trigger rejection. In a mouse model of cardiac allograft tolerance in which infection with Listeria monocytogenes (Lm) precipitates rejection of previously accepted grafts, we showed that recipient CD4+ TCR75 cells reactive to a donor MHC class I-derived peptide become hypofunctional if the allograft is accepted for more than 3 weeks. Paradoxically, infection-induced transplant rejection was not associated with transcriptional or functional reinvigoration of TCR75 cells. We hypothesized that there is heterogeneity in the level of dysfunction of different allospecific T cells, depending on duration of their cognate antigen expression. Unlike CD4+ TCR75 cells, CD4+ TEa cells specific for a peptide derived from donor MHC class II, an alloantigen whose expression declines after transplantation but remains inducible in settings of inflammation, retained function in tolerant mice and expanded during Lm-induced rejection. Repeated injections of alloantigens drove hypofunction in TEa cells and rendered grafts resistant to Lm-dependent rejection. Our results uncover a functional heterogeneity in allospecific T cells of distinct specificities after tolerance induction and reveal a strategy to defunctionalize a greater repertoire of allospecific T cells, thereby mitigating a critical vulnerability of tolerance.

Interferons and Resistance Mechanisms in Tumors and Pathogen-Driven Diseases—Focus on the Major Histocompatibility Complex (MHC) Antigen Processing Pathway

Interferons (IFNs), divided into type I, type II, and type III IFNs represent proteins that are secreted from cells in response to various stimuli and provide important information for understanding the evolution, structure, and function of the immune system, as well as the signaling pathways of other cytokines and their receptors. They exert comparable, but also distinct physiologic and pathophysiologic activities accompanied by pleiotropic effects, such as the modulation of host responses against bacterial and viral infections, tumor surveillance, innate and adaptive immune responses. IFNs were the first cytokines used for the treatment of tumor patients including hairy leukemia, renal cell carcinoma, and melanoma. However, tumor cells often develop a transient or permanent resistance to IFNs, which has been linked to the escape of tumor cells and unresponsiveness to immunotherapies. In addition, loss-of-function mutations in IFN signaling components have been associated with susceptibility to infectious diseases, such as COVID-19 and mycobacterial infections. In this review, we summarize general features of the three IFN families and their function, the expression and activity of the different IFN signal transduction pathways, and their role in tumor immune evasion and pathogen clearance, with links to alterations in the major histocompatibility complex (MHC) class I and II antigen processing machinery (APM). In addition, we discuss insights regarding the clinical applications of IFNs alone or in combination with other therapeutic options including immunotherapies as well as strategies reversing the deficient IFN signaling. Therefore, this review provides an overview on the function and clinical relevance of the different IFN family members, with a specific focus on the MHC pathways in cancers and infections and their contribution to immune escape of tumors.

Role of Exercise Intensity on Th1/Th2 Immune Modulations During the COVID-19 Pandemic

The COVID-19 pandemic has led to several pioneering scientific discoveries resulting in no effective solutions with the exception of vaccination. Moderate exercise is a significant non-pharmacological strategy, to reduce the infection-related burden of COVID-19, especially in patients who are obese, elderly, and with additional comorbidities. The imbalance of T helper type 1 (Th1) or T helper type 2 (Th2) cells has been well documented among populations who have suffered as a result of the COVID-19 pandemic, and who are at maximum risk of infection and mortality. Moderate and low intensity exercise can benefit persons at risk from the disease and survivors by favorable modulation in Th1/Th2 ratios. Moreover, in COVID-19 patients, mild to moderate intensity aerobic exercise also increases immune system function but high intensity aerobic exercise may have adverse effects on immune responses. In addition, sustained hypoxia in COVID-19 patients has been reported to cause organ failure and cell death. Hypoxic conditions have also been highlighted to be triggered in COVID-19-susceptible individuals and COVID-19 survivors. This suggests that hypoxia inducible factor (HIF 1α) might be an important focus for researchers investigating effective strategies to minimize the effects of the pandemic. Intermittent hypoxic preconditioning (IHP) is a method of exposing subjects to short bouts of moderate hypoxia interspersed with brief periods of normal oxygen concentrations (recovery). This methodology inhibits the production of pro-inflammatory factors, activates HIF-1α to activate target genes, and subsequently leads to a higher production of red blood cells and hemoglobin. This increases angiogenesis and increases oxygen transport capacity. These factors can help alleviate virus induced cardiopulmonary hemodynamic disorders and endothelial dysfunction. Therefore, during the COVID-19 pandemic we propose that populations should engage in low to moderate exercise individually designed, prescribed and specific, that utilizes IHP including pranayama (yoga), swimming and high-altitude hiking exercise. This would be beneficial in affecting HIF-1α to combat the disease and its severity. Therefore, the promotion of certain exercises should be considered by all sections of the population. However, exercise recommendations and prescription for COVID-19 patients should be structured to match individual levels of capability and adaptability.

Pro-inflammatory Cytokines Alter the Immunopeptidome Landscape by Modulation of HLA-B Expression

Antigen presentation on HLA molecules is a major mechanism by which the immune system monitors self and non-self-recognition. Importantly, HLA-I presentation has gained much attention through its role in eliciting anti-tumor immunity. Several determinants controlling the peptides presented on HLA have been uncovered, mainly through the study of model substrates and large-scale immunopeptidome analyses. These determinants include the relative abundances of proteins in the cell, the stability or turnover rate of these proteins and the binding affinities of a given peptide to the HLA haplotypes found in a cell. However, the regulatory principles involved in selection and regulation of specific antigens in response to tumor pro-inflammatory signals remain largely unknown. Here, we chose to examine the effect that TNFα and IFNγ stimulation may exert on the immunopeptidome landscape of lung cancer cells. We show that the expression of many of the proteins involved in the class I antigen presentation pathway are changed by pro-inflammatory cytokines. Further, we could show that increased expression of the HLA-B allomorph drives a significant change in HLA-bound antigens, independently of the significant changes observed in the cellular proteome. Finally, we observed increased HLA-B levels in correlation with tumor infiltration across the TCGA lung cancer cohorts. Taken together, our results suggest that the immunopeptidome landscape should be examined in the context of anti-tumor immunity whereby signals in the microenvironment may be critical in shaping and modulating this important aspect of host-tumor interactions.

Antigen Presentation by Vascular Cells

Antigen presentation by cells of the vessel wall may initiate rapid and localized memory immune responses in peripheral tissues. Peptide antigens displayed on major histocompatibility complex (MHC) molecules on the surface of endothelial cells (ECs) can be recognized by T cell receptors on circulating effector memory T cells (T_EM), triggering both transendothelial migration and activation. The array of co-stimulatory receptors, adhesion molecules, and cytokines expressed by ECs serves to modulate T cell activation responses. While the effects of these interactions vary among species, vascular beds, and vascular segments within the same tissue, they are capable of triggering allograft rejection without direct involvement of professional antigen-presenting cells and may play a similar role in host defense against infections and in autoimmunity. Once across the endothelium, extravasating T_EM then contact mural cells of the vessel wall, including pericytes or vascular smooth muscle cells, which may also present antigens and provide signals that further regulate T cell responses. Collectively, these interactions provide an unexplored opportunity in which targeting of vascular cells can be used to modulate immune responses. In organ transplantation, targeting ECs with siRNA to reduce expression of MHC molecules may additionally mitigate perioperative injuries by preformed alloantibodies, further reducing the risk of graft rejection. Similarly, genetic manipulation of vascular cells to minimize antigen-dependent responses can be used to increase perfusion of tissue engineered organs without triggering rejection.

Label-free quantification and shotgun analysis of complex proteomes by one-dimensional SDS-PAGE/NanoLC-MS: evaluation for the large scale analysis of inflammatory human endothelial cells

To perform differential studies of complex protein mixtures, strategies for reproducible and accurate quantification are needed. Here, we evaluated a quantitative proteomic workflow based on nanoLC-MS/MS analysis on an LTQ-Orbitrap-VELOS mass spectrometer and label-free quantification using the MFPaQ software. In such label-free quantitative studies, a compromise has to be found between two requirements: repeatability of sample processing and MS measurements, allowing an accurate quantification, and high proteomic coverage of the sample, allowing quantification of minor species. The latter is generally achieved through sample fractionation, which may induce experimental bias during the label-free comparison of samples processed, and analyzed independently. In this work, we wanted to evaluate the performances of MS intensity-based label-free quantification when a complex protein sample is fractionated by one-dimensional SDS-PAGE. We first tested the efficiency of the analysis without protein fractionation and could achieve quite good quantitative repeatability in single-run analysis (median coefficient of variation of 5%, 99% proteins with coefficient of variation <48%). We show that sample fractionation by one-dimensional SDS-PAGE is associated with a moderate decrease of quantitative measurement repeatability while largely improving the depth of proteomic coverage. We then applied the method for a large scale proteomic study of the human endothelial cell response to inflammatory cytokines, such as TNFα, interferon γ, and IL1β, which allowed us to finely decipher at the proteomic level the biological pathways involved in endothelial cell response to proinflammatory cytokines.

Transcriptional profiling of human brain endothelial cells reveals key properties crucial for predictive in vitro blood-brain barrier models

Brain microvascular endothelial cells (BEC) constitute the blood-brain barrier (BBB) which forms a dynamic interface between the blood and the central nervous system (CNS). This highly specialized interface restricts paracellular diffusion of fluids and solutes including chemicals, toxins and drugs from entering the brain. In this study we compared the transcriptome profiles of the human immortalized brain endothelial cell line hCMEC/D3 and human primary BEC. We identified transcriptional differences in immune response genes which are directly related to the immortalization procedure of the hCMEC/D3 cells. Interestingly, astrocytic co-culturing reduced cell adhesion and migration molecules in both BECs, which possibly could be related to regulation of immune surveillance of the CNS controlled by astrocytic cells within the neurovascular unit. By matching the transcriptome data from these two cell lines with published transcriptional data from freshly isolated mouse BECs, we discovered striking differences that could explain some of the limitations of using cultured BECs to study BBB properties. Key protein classes such as tight junction proteins, transporters and cell surface receptors show differing expression profiles. For example, the claudin-5, occludin and JAM2 expression is dramatically reduced in the two human BEC lines, which likely explains their low transcellular electric resistance and paracellular leakiness. In addition, the human BEC lines express low levels of unique brain endothelial transporters such as Glut1 and Pgp. Cell surface receptors such as LRP1, RAGE and the insulin receptor that are involved in receptor-mediated transport are also expressed at very low levels. Taken together, these data illustrate that BECs lose their unique protein expression pattern outside of their native environment and display a more generic endothelial cell phenotype. A collection of key genes that seems to be highly regulated by the local surroundings of BEC within the neurovascular unit are presented and discussed.

IFN-γ induces IFN-α and IFN-β expressions in cultured rat intestinal mucosa microvascular endothelial cells

Although researchers have recently begun to pay more attention to the immunological characteristics of microvascular endothelial cells (MVECs), there are no reports on whether activation of MVECs by interferon-γ (IFN-γ) exerts any influence on the expressions of IFN-α/β. In the present study, we examined the influence of IFN-γ on the expressions of IFN-α/β in rat intestinal mucous MVECs (RIMMVECs). Different concentrations of IFN-γ were used to stimulate cultured RIMMVECs in vitro, and the cells and cell supernatants were collected at different time intervals. The influence of IFN-γ on the expressions of IFN-α/β in the RIMMVECs was examined at the mRNA and protein levels by real-time quantitative PCR and enzyme-linked immunosorbent assay (ELISA), respectively. The results indicated that IFN-γ was able to activate RIMMVECs, thereby leading to upregulated expressions of IFN-α/β. The real-time quantitative PCR analyses indicated that the IFN-α/β mRNA expression levels in RIMMVECs achieved their peak values after stimulation with IFN-γ at 20 ng/mL for 6 h and were increased by 14.88- and 3.82-fold, respectively, when compared with the levels in negative control cells. The ELISA analyses revealed that the IFN-α/β protein expression levels achieved their peak values after stimulation with IFN-γ at 40 ng/mL. The expression of IFN-α protein achieved its peak value at 12 h, while the expression of IFN-β protein achieved its peak value after 6 h. The present results suggest that the expression and secretion of IFNs may participate in the immunologic barrier function of MVECs.

Endothelial cells in allograft rejection

In organ transplantation, blood borne cells and macromolecules (e.g., antibodies) of the host immune system are brought into direct contact with the endothelial cell lining of graft vessels. In this location, graft endothelial cells play several roles in allograft rejection, including the initiation of rejection responses by presentation of alloantigen to circulating T cells; the development of inflammation and thrombosis; and as targets of injury and agents of repair.

Endothelial cells in allograft rejection

In organ transplantation, blood borne cells and macromolecules (e.g., antibodies) of the host immune system are brought into direct contact with the endothelial cell lining of graft vessels. In this location, graft endothelial cells play several roles in allograft rejection, including the initiation of rejection responses by presentation of alloantigen to circulating T cells; the development of inflammation and thrombosis; and as targets of injury and agents of repair.

Hepatocytes express abundant surface class I MHC and efficiently use transporter associated with antigen processing, tapasin, and low molecular weight polypeptide proteasome subunit components of antigen processing and presentation pathway

Hepatic expression levels of class I MHC Ags are generally regarded as very low. Because the status of these Ags and their ability to present peptides are important for the understanding of pathogen clearance and tolerogenic properties of the liver, we set out to identify the factors contributing to the reported phenotype. Unexpectedly, we found that the surface densities of K(b) and D(b) on C57BL/6 mouse hepatocytes are nearly as high as on splenocytes, as are the lysate concentrations of mRNA encoding H chain and beta(2)-microglobulin (beta(2)m). In contrast, the components of the peptide-loading pathway are reduced in hepatocytes. Despite the difference in the stoichiometric ratios of H chain/beta(2)m/peptide-loading machineries, both cell types express predominantly thermostable class I and are critically dependent on TAP and tapasin for display of surface Ags. Minor differences in the expression patterns in tapasin(-/-) background suggest cell specificity in class I assembly. Under immunostimulatory conditions, such as exposure to IFN-gamma or Listeria monocytogenes, hepatocytes respond with a vigorous mRNA synthesis of the components of the Ag presentation pathway (up to 10-fold enhancement) but up-regulate H chain and beta(2)m to a lesser degree (<2-fold). This type of response should promote rapid influx of newly generated peptides into the endoplasmic reticulum and preferential presentation of foreign/induced Ag by hepatic class I.

[Cytokine participation in the acute rejection of intestinal transplantation in rats]

BACKGROUND

Intestinal transplantation is a possible treatment for patients with short bowel syndrome, aiming the reintroduction of oral diet. However, the major obstacle in this procedure is the strong rejection. Delay in rejection diagnosis may be irreversible and lethal.

AIM

To define method for early diagnosis of rejection based on the presence of interleucin-6 (IL-6) e interferon- gamma (IFN-gamma) from intestinal allograft.

MATERIAL AND METHODS

Isogenic rats Brown-Norway (BN) and Lewis (LEW) were submitted to intestinal heterotopic allotransplantation and divided in two groups: LEW donor to LEW recipient isograft group (C) and BN donor to LEW recipient allograft group (Tx). According to the day of sacrifice, Tx group were subdivided in three subgroups with eight animals each as follow: Tx3--sacrificed at third postoperative day (POD), Tx5--sacrificed at fifth POD and Tx7--sacrificed at seventh POD. Eight animals from control group were subdivided in three moments according to the time of biopsy from the graft as follow: C3--biopsy at third POD; C5--biopsy at fifth POD and C7--biopsy at seventh POD. All animals from control group were sacrificed at seventh POD. Rejection parameters were compared between the control groups (C3 vs C5, C3 vs C7 and C5 vs C7, and allograft group (Tx3 vs Tx5, Tx3 vs Tx7 and Tx5 vs Tx7). The same parameters were analyzed between the control group and allograft groups (C3 vs Tx3, C5 vs Tx5 and C7 vs Tx7).

RESULTS

In C group no statistical significant difference regarding the immunoexpression of the cytokines, while in Tx group, immunoexpression of IL-6 and IFN-gamma were remarkable since the fifth postoperative day.

Non-HLA-type endothelial cell reactive alloantibodies in pre-transplant sera of kidney recipients trigger apoptosis

The vascular endothelium of transplanted organs represents an important target for allograft-directed immune responses. Although HLA antigens expressed on graft endothelial cells (EC) can become targets of the host immune response, the role of other, non-HLA-encoded EC antigens has been proposed but is still unclear. The aim of this study was to investigate the presence of and to characterize anti-EC antibodies (AECA) in 57 kidney transplant recipients according to their HLA-immunization status. Flow cytometry in pretransplant sera was used to detect AECA reactive with surface antigens on ABO and HLA-typed primary cultures of arterial ECs, stimulated or not with tumor necrosis factor-alpha (TNFalpha) or interferon-gamma (IFNgamma). FACS analysis revealed the presence of AECA in 47% of HLA-sensitized (PRA = 10%: mostly IgG) vs. 16.0% in nonsensitized patients (PRA < 10%) (p < 0.02). No significant correlation was found between the presence of AECA and acute rejection occurrence and graft outcome. Non-HLA reactive AECA are directed against TNFalpha- and IFNgamma-inducible membrane molecule(s), and react with two predominant antigens of approximately 35 kDa and approximately 50 kDa expressed on ECs but not on B cells. Binding of AECA decreases in vitro EC viability by 50-60% by promoting EC apoptosis, as demonstrated by DNA fragmentation assays.

Regulation of the expression of mouse TAP-associated glycoprotein (tapasin) by cytokines

The expression of antigen presenting MHC class I molecules can be enhanced through cytokines, e.g. upon infection with bacteria or viruses, either directly by enhancing class I gene transcription or by increasing the amounts of accessory proteins of the loading complex. Tapasin plays a significant role in the peptide loading of class I molecules. Here, we describe recognition motifs of cytokine inducible transcription factors in the promoter region of the mouse tapasin gene, most of them clustered within the 140 base pairs upstream of the start codon. Tapasin mRNA was strongly induced in vivo after infection with the facultatively intracellular bacterium Listeria monocytogenes in an IFN-gamma-dependent fashion. Accordingly, both tapasin mRNA and protein were strongly induced in a time and dose dependent manner in embryonic fibroblasts treated with the cytokines IFN-gamma and IFN-beta, and weakly induced after treatment with TNF-alpha. Co-stimulation of tapasin by TNF-alpha and IFN-gamma resulted in a weak synergistic effect. Using fibroblasts either lacking IRF-1 or inhibited in protein synthesis we show that secondary transcription factors are necessary for a maximal stimulation of tapasin expression upon IFN-gamma stimulation. The sequential induction of TAP1, LMP2, and tapasin before the stimulated expression of class I heavy chain is discussed.

Cross-primed CD8(+) T cells mediate graft rejection via a distinct effector pathway

To prevent bystander destruction of healthy host tissues, cytotoxic CD8(+) T lymphocytes are fitted with specific receptors that direct their destructive forces specifically against chosen targets. We show here, however, that anti-H-Y monospecific, H-2(b-restricted MataHari CD8(+) T cells reject H-2(k) male skin grafts, with which they cannot directly interact. Such rejection is interferon-gamma-dependent and only occurs if the recipient endothelium expresses H-2(b). The findings suggest an alternate indirect effector pathway that requires processing and presentation of the donor H-Y antigen by recipient endothelium and have implications for both transplantation and autoimmune disease.

Significance of interferon-gamma in coronary artery bypass surgery

BACKGROUND

Gamma interferon (IFN-gamma) is produced by activated natural killer and T cells under pathologic circumstances. The objective of our study was to compare the level of IFN-gamma in open and endoscopic methods of vein harvesting for coronary artery bypass surgery (CABG).

METHOD

Ninety samples of human saphenous veins harvested from patients prepared for CABG. Pre- and post-procedure sera of the patients, in addition to supernatants of 3-day endothelial cell culture, were analyzed for IFN-gamma.

RESULTS

The mean preoperative IFN-gamma level (0.09+/-0.03 pg/mL) and that for postoperative sera (0.08+/-0.02 pg/mL) were not significantly different (P = 0.2). The mean IFN-gamma level in endothelial cell culture from the endoscopic (0.18+/-0.21 pg/mL) and the open method (0.19+/-0.39 pg/mL) were not significant (P = 0.89).

CONCLUSION

We recommend the endoscopic method of vein harvesting because of its lower morbidity and earlier hospital discharge.

Type 1/Type 2 immunity in infectious diseases

T helper type 1 (Th1) lymphocytes secrete secrete interleukin (IL)-2, interferon-gamma, and lymphotoxin-alpha and stimulate type 1 immunity, which is characterized by intense phagocytic activity. Conversely, Th2 cells secrete IL-4, IL-5, IL-9, IL-10, and IL-13 and stimulate type 2 immunity, which is characterized by high antibody titers. Type 1 and type 2 immunity are not strictly synonymous with cell-mediated and humoral immunity, because Th1 cells also stimulate moderate levels of antibody production, whereas Th2 cells actively suppress phagocytosis. For most infections, save those caused by large eukaryotic pathogens, type 1 immunity is protective, whereas type 2 responses assist with the resolution of cell-mediated inflammation. Severe systemic stress, immunosuppression, or overwhelming microbial inoculation causes the immune system to mount a type 2 response to an infection normally controlled by type 1 immunity. In such cases, administration of antimicrobial chemotherapy and exogenous cytokines restores systemic balance, which allows successful immune responses to clear the infection.

Evidence for a genetic predisposition towards acute rejection after kidney and simultaneous kidney-pancreas transplantation

BACKGROUND

In vitro production of tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), interleukin 10 (IL-10), and transforming growth factor-beta (TGF-beta) correlate with their respective genetic polymorphisms. We analyzed the relationship between these genetic polymorphisms and posttransplant outcome.

METHODS

Using DNA polymerase chain reaction (PCR) technology, polymorphisms for TNF-alpha, IFN-gamma, IL-10, and TGF-beta were determined for 82 kidney (K) and 19 simultaneous kidney-pancreas (SKP) recipients. These results were analyzed with regard to the incidence of acute rejection (AR), and the timing and severity of the first AR episode.

RESULTS

A high TNF-alpha production phenotype correlated with recurrent acute rejection (AR) episodes (P<0.026). Compared with the low TNF-alpha production phenotype, more patients with the high production phenotype had a post-AR serum creatinine >2.0 mg/dl, but this was not statistically significant (64 vs. 35%, P=0.12). There was no relationship between TNF-alpha genotype and the time to first AR episode or incidence of graft loss. IFN-gamma production phenotype showed no correlation with any of these clinical outcome parameters. There was an increase in AR incidence as the IL-10 production phenotype increased (low, intermediate, high), but only in low TNF-alpha producer phenotypes (P=0.023).

CONCLUSIONS

Patients with a polymorphic cytokine genotype putatively encoding for high in vivo TNF-alpha production, and to a lesser extent IL-10 cytokine genotypes putatively encoding for higher levels of in vivo IL-10 production, had a worse clinical outcome regarding AR episodes. These data support the hypothesis that the strength of alloimmune responsiveness after transplantation in part is genetically determined.

Interferon-alpha (IFN-alpha) stimulates anti-melanoma cytotoxic T lymphocyte (CTL) generation in mixed lymphocyte tumour cultures (MLTC)

IFN-alpha administration after primary tumour resection improves the survival of melanoma patients at high risk of relapse. To investigate whether this response might be due to stimulation of anti-tumour immunity, the effect of IFN-alpha on anti-melanoma CTL generation in MLTC was measured. IFN-alpha increased both allogeneic and autologous anti-melanoma CTL generation from peripheral blood lymphocytes stimulated with irradiated primary melanoma cultures. IFN-alpha up-regulated MHC class I expression on primary melanoma cultures, whereas IFN-gamma up-regulated both MHC class I and II expression. However, the effect of IFN-alpha on anti-melanoma CTL generation was often more potent than that of IFN-gamma, equalling the effect of the optimal combination of IL-2 and IL-12. Pre-treatment of primary melanoma cultures with IFN-gamma was sufficient for CTL generation in MLTC, whereas IFN-alpha needed to be present during the MLTC. While direct anti-proliferative effects of IFN-alpha on some tumour cells have been described, IFN-alpha did not inhibit proliferation of primary melanoma cultures. These results suggest that the clinical effects of IFN-alpha in melanoma patients may be immune-mediated.

Modulation of major histocompatibility class II protein expression by varicella-zoster virus

We sought to investigate the effects of varicella-zoster virus (VZV) infection on gamma interferon (IFN-gamma)-stimulated expression of cell surface major histocompatibility complex (MHC) class II molecules on human fibroblasts. IFN-gamma treatment induced cell surface MHC class II expression on 60 to 86% of uninfected cells, compared to 20 to 30% of cells which had been infected with VZV prior to the addition of IFN-gamma. In contrast, cells that were treated with IFN-gamma before VZV infection had profiles of MHC class II expression similar to those of uninfected cell populations. Neither IFN-gamma treatment nor VZV infection affected the expression of transferrin receptor (CD71). In situ and Northern blot hybridization of MHC II (MHC class II DR-alpha) RNA expression in response to IFN-gamma stimulation revealed that MHC class II DR-alpha mRNA accumulated in uninfected cells but not in cells infected with VZV. When skin biopsies of varicella lesions were analyzed by in situ hybridization, MHC class II transcripts were detected in areas around lesions but not in cells that were infected with VZV. VZV infection inhibited the expression of Stat 1alpha and Jak2 proteins but had little effect on Jak1. Analysis of regulatory events in the IFN-gamma signaling pathway showed that VZV infection inhibited transcription of interferon regulatory factor 1 and the MHC class II transactivator. This is the first report that VZV encodes an immunomodulatory function which directly interferes with the IFN-gamma signal transduction via the Jak/Stat pathway and enables the virus to inhibit IFN-gamma induction of cell surface MHC class II expression. This inhibition of MHC class II expression on VZV-infected cells in vivo may transiently protect cells from CD4(+) T-cell immune surveillance, facilitating local virus replication and transmission during the first few days of cutaneous lesion formation.

Endothelial cells expressing an inflammatory phenotype are lysed by superantigen-targeted cytotoxic T cells

The objective of this study was to investigate whether the superantigen staphylococcal enterotoxin A (SEA), which binds to HLA class II and T-cell receptor Vbeta chains, can direct cytotoxic T cells to lyse cytokine-stimulated endothelial cells (EC). In addition, we wanted to determine whether SEA-primed cytotoxic T cells could be targeted to EC surface molecules as a means of a novel cancer immunotherapy. Human umbilical vein EC (HUVEC), dermal microvascular EC (HMVEC), or the EC line EA.hy926 stimulated with gamma interferon (IFN-gamma) or tumor necrosis factor alpha (TNF-alpha) displayed upregulated HLA class II and adhesion molecule (CD54 and CD106) expression, respectively. SEA-primed T cells induced a strong cytotoxicity against IFN-gamma- and TNF-alpha-activated EA.hy926 which had been preincubated with SEA. Blocking of CD54 completely abrogated the T-cell attack. SEA-D227A, which has a mutated class II binding site, did not promote any cytotoxicity. A strong lysis was observed when a fusion protein consisting of protein A and SEA-D227A was added together with T cells to TNF-alpha-induced EA.hy926 and HUVEC precoated with monoclonal antibodies (MAb) directed against HLA class I, CD54, or CD106 molecules. Finally, an scFv antibody fragment reactive with an unknown EC antigen was fused with SEA-D227A. Both EA.hy926 and HMVEC were efficiently lysed by scFv-SEA-D227A-triggered cytotoxic T cells. Taken together, superantigen-activated T-cell-dependent EC killing was induced when EC expressed an inflammatory phenotype. Moreover, specific MAb targeting of the superantigen to surface antigens induced EC lysis. Our data suggest that directed T-cell-mediated lysis of unwanted proliferating EC, such as those in the tumor microvasculature, can be clinically useful.

MHC class I expression in murine skin: developmentally controlled and strikingly restricted intraepithelial expression during hair follicle morphogenesis and cycling, and response to cytokine treatment in vivo

Hair bulb keratinocytes generate one of the few "immune privileged" tissue compartments of the mammalian organism by suppressing classical MHC class I (MHC Ia) antigens. Expression of non-classical MHC class I (MHC Ib) antigens in the follicle has been found, but only in its distal epithelium. Here, we have defined when during murine hair follicle morphogenesis these peculiar MHC Ia and Ib expression patterns are established, how they change during the murine hair cycle, and how different MHC I modulatory agents alter follicular MHC Ia and Ib expression in vivo. During neonatal hair follicle morphogenesis in C57BL/6 mice, distal follicle keratinocytes began to express MHC Ia (H2b) only late in development. The MHC Ib antigens, Qa-1 and Qa-2, did not become visible until the initiation of follicle cycling, with Qa-1 expression being more widespread than that of Qa-2. H2b, Qa-1, and TAP-1 immunoreactivity on previously negative keratinocytes of the proximal anagen hair bulb was upregulated by intradermal injection of the proinflammatory cytokine interferon-gamma, but not by tumor necrosis factor-alpha or interleukin-1beta. Injection of the reportedly MHC class I downregulating agents interleukin-10, insulin-like growth factor-1, transforming growth factor-beta, alpha-melanocyte stimulating hormone, or dexamethasone, however, all failed to downregulate constitutive or interferon-gamma-induced follicular MHC Ia expression. This shows that the hair follicle is a previously unrecognized site of Qa-1 expression and that interferon-gamma is a key regulator of follicular MHC I expression in vivo. It also suggests that the developmental and immunologic controls of MHC I expression by follicle keratinocytes differ from those of other epithelial cells.

Major histocompatibility complex class II-dependent antigen presentation by human intestinal endothelial cells

BACKGROUND & AIMS

In the normal gut, human intestinal microvascular endothelial cells (HIMECs) express major histocompatibility complex (MHC) class II molecules. Enhanced expression is found in chronic inflammation. We examined the cytokine regulation of MHC class II molecules and the associated invariant chain (Ii) in HIMECs and investigated whether such cells can process and present a complex protein antigen to T cells.

METHODS

Enzyme-linked immunosorbent assay, flow cytometry, immunoelectron microscopy, as well as T-cell activation assay with HIMECs and HLA-DR-restricted T-cell clones were employed.

RESULTS

In unstimulated HIMEC monolayers, HLA-DR, -DP, and -DQ and Ii were undetectable at the protein level, but interferon gamma (IFN-gamma) (100 U/mL) induced expression that peaked for DR after 2-3 days, for DP after 4-6 days, for DQ after 10-12 days, and for Ii after 2-3 days. Tumor necrosis factor alpha had no effect alone but enhanced class II expression in combination with IFN-gamma, most notably for DQ and DP. HLA-DR3-restricted and Mycobacterium tuberculosis heat shock 65-kilodalton-specific T-cell clones were activated to produce IFN-gamma in response to relevant antigen presented by IFN-gamma-treated HIMECs. This response was inhibited by blocking monoclonal antibody to HLA-DR and by chloroquine when compared to professional antigen-presenting cells, HIMECs activated T-cell clones quite efficiently.

CONCLUSIONS

These data suggest that microvascular endothelial cells can present complex protein antigens in the human gut.

Strain difference in the induction of T-cell activation-associated, interferon gamma-dependent hepatic injury in mice

A single intravenous injection of concanavalin A (Con A) induces T-cell activation-associated inflammatory injury selectively in the liver. This study investigated the strain difference in the development of Con A-induced hepatic injury. Normal C57BL/6 and BALB/c spleen cells produced comparable levels of T-cell-derived lymphokines (interferon gamma [IFN-gamma], tumor necrosis factor alpha [TNF-alpha], and interleukin-2 [IL-2]) following in vitro stimulation with Con A. A single intravenous injection of Con A to C57BL/6 mice induced the plasma levels of TNF-alpha and IL-2 comparable with or slightly higher than those observed in BALB/c mice, whereas the same treatment resulted in an apparently lower level of IFN-gamma production in C57BL/6 mice. RNA from livers of Con A-treated C57BL/6 mice exhibited lower levels of IFN-gamma mRNA than RNA of BALB/c livers. Unexpectedly, a dramatic difference in the severity of hepatic injury was observed between C57BL/6 and BALB/c. Namely, the peak alanine transaminase (ALT) level was more than 15,000 U/L and inducible as early as 8 hours after injection of 0.2 mg Con A per mouse in the C57BL/6 strain, whereas the peak was approximately 3,000 U/L and induced as late as 24 hours after Con A injection in the BALB/c strain. The increase in plasma ALT levels was limited to less than 10% by injection of anti-IFN-gamma monoclonal antibody (mAb) in both strains. The C57BL/6 strain inducing lower levels of IFN-gamma exhibited higher IFN-gamma responsiveness as exemplified by the intrahepatic expression of an IFN-gamma-inducible gene, an inducible type of nitric oxide (NO) synthase (iNOS). These results indicate that, while IFN-gamma produced in vivo by activated T cells induces hepatic injury, there exists a striking strain difference in the induction of IFN-gamma-dependent hepatic injury.

MHC class II expression on human heart microvascular endothelial cells: exquisite sensitivity to interferon-gamma and natural killer cells

BACKGROUND

Immunocytochemical analysis of human organs in situ reveals differential expression of MHC class II antigens by microvascular endothelial cells (MVEC) and endothelial cells (EC) from large vessels. In view of the role of EC as initiators of allograft rejection, it is of interest to understand the regulation of MHC class II regulation by human MVEC. We have previously isolated, cultured, and characterized MVEC from the human heart, showing that although these cells were initially MHC class II positive, the antigens were lost after about 14 days in culture. These results suggest that basal expression in vivo is maintained by circulating factors.

METHODS

Here we have compared the sensitivity of human heart MVEC, human umbilical vein endothelial cells (HUVEC), and adult large vessel EC (aorta, coronary artery, and pulmonary artery) to interferon (IFN)-gamma and natural killer (NK) cell-mediated induction of MHC class II antigens. MVEC and HUVEC were cultured with 1, 5, 10, 50, 100, and 500 U/ml of IFN-gamma for 4 days, the cells were washed, and flow cytometry was used to examine HLA-DR expression at days 1, 2, 4, 7, 10, 14, and 21. EC were also cultured with purified NK cells in the presence and absence of neutralizing antibodies to IFN-gamma, and MHC class II expression was analyzed.

RESULTS

As little as 5 U/ml of IFN-gamma produced 98% positive cells in heart MVEC compared with 100-500 U/ml needed for the same effect in HUVEC or other large vessel EC (coronary, aorta, pulmonary). Class II expression was maintained longer by MVEC (for 17 days) compared with HUVEC (for 10 days). NK cells and supernatant from MVEC/NK cultures induced MHC class II antigens on MVEC and HUVEC in a dose-dependent fashion; the MVEC showed an enhanced sensitivity compared with the HUVEC. The NK effects were inhibited by neutralizing antibodies to IFN-gamma. The allostimulatory ability of MHC class II-positive EC was shown to be proportional to the amount of MHC class II on the cell surface.

CONCLUSIONS

The results suggest that basal expression of MHC class II on human MVEC is maintained by circulating IFN-gamma and NK cells. This conclusion has implications for therapeutic interventions.

Tumor necrosis factor-alpha: a neuromodulator in the CNS

In the central nervous system (CNS), the cytokine tumor necrosis factor-alpha (TNF alpha) is produced by both neurons and glial cells, participates in developmental modeling, and is involved in many pathophysiological conditions. There are activity-dependent expressions of TNF alpha as well as low levels of secretion in the resting state. In contrast to the conventional view of a cytotoxic effect of TNF alpha, accumulating evidence suggests a beneficial effect when TNF alpha is applied at optimal doses and at specific periods of time. The bimodal effect is related to subtypes of receptors, activation of different signal transduction pathways, and the presence of other molecules that alter the intracellular response elements such as immediate-early genes. TNF alpha may be an important neuromodulator in development of the CNS, diseases of demyelination and degeneration, and in the process of regeneration. It could induce growth-promoting cytokines and neurotrophins, or it could increase the production of antiproliferative cytokines, nitric oxide, and free radicals, thereby contributing to apoptosis.

Cytokine patterns in adults with AIDS

BACKGROUND

It has been reported that in HIV infected patients enhanced production of IL-4 and IL-10 in response to stimulation of peripheral blood lymphocytes with phytohemagglutinin is associated with disease progression. Some have proposed that a switch from a cytokine profile associated with CD4+ Th1 predominance (IL-2, IFN-G, TNF-B) to Th2 predominance (IL-4, IL-5) plays a major role in the progression of HIV infection. Others find no clear evidence for the dichotomy of Th1 and Th2 predominance in HIV infected patients Discrepant results have been reported in studied populations in which only a few cytokines have been examined.

METHODS

Thirty-one adult patients with AIDS but without other active infections provided serum and peripheral blood lymphocytes for determination of cytokine levels. Their responses were compared to those of five normal healthy volunteers without active infection. ELISA techniques were employed to quantitate cytokine levels. Both circulating lymphocyte and enriched lymphocyte populations were studied with and without stimulation employing phytohemagglutinin and/or rhIL-2.

RESULTS

Patterns of cytokine expression were analyzed in 31 adult patients with AIDS but without other active infections. All had CD4+ cell counts below 50 and large viral loads (Roche PCR). The unstimulated cytokine profile in these patients generally showed marked elevations in IL-1, IL-3, IL-4, IFN-G, TNF-A, TNF-B, OSM, and TGF-B. Minimal elevations compared to normal healthy volunteers were noted for IL-2, IL-6, IL-8, IL-12, IFN-A, and IL-6SR. The levels of RANTES were lower than in normal healthy volunteers. Responses of peripheral blood lymphocytes to stimulation with phytohemagglutinin showed enhancement of all cytokines in all subjects studied though the response was much less marked in AIDS patients than in normal volunteers with the exception of IL-3, IL-4, IL-8, TNF-B, and TGF-B which are increased. Little difference in IL-2 and IL-12 expression was noted between stimulated peripheral blood lymphocytes of AIDS patients and normal healthy volunteers. No relation was noted with patient age or with any use of antiretroviral agents. Recombinant human IL-2 was a less potent stimulant than was phytohemagglutinin.

CONCLUSION

The character of cytokine response in AIDS patients may be directly related to the stimulus employed in test systems. There is no evidence for Th1/Th2 dysregulation. Cytokine elevations in AIDS patients generally are reflective of chronic infection (the virus). Lymphocytes from AIDS patients do not respond as well to stimulation as do those from normal healthy volunteers. The stimulated lymphocyte response in AIDS patients suggests there is underlying low-grade host versus virus reaction in these patients (exaggerated responses of IL-3, IL-4, IL-8, TGF-B).

Cellular responses to interferon-gamma

Interferons are cytokines that play a complex and central role in the resistance of mammalian hosts to pathogens. Type I interferon (IFN-alpha and IFN-beta) is secreted by virus-infected cells. Immune, type II, or gamma-interferon (IFN-gamma) is secreted by thymus-derived (T) cells under certain conditions of activation and by natural killer (NK) cells. Although originally defined as an agent with direct antiviral activity, the properties of IFN-gamma include regulation of several aspects of the immune response, stimulation of bactericidal activity of phagocytes, stimulation of antigen presentation through class I and class II major histocompatibility complex (MHC) molecules, orchestration of leukocyte-endothelium interactions, effects on cell proliferation and apoptosis, as well as the stimulation and repression of a variety of genes whose functional significance remains obscure. The implementation of such a variety of effects by a single cytokine is achieved by complex patterns of cell-specific gene regulation: Several IFN-gamma-regulated genes are themselves components of transcription factors. The IFN-gamma response is itself regulated by interaction with responses to other cytokines including IFN-alpha/beta, TNF-alpha, and IL-4. Over 200 genes are now known to be regulated by IFN-gamma and they are listed in a World Wide Web document that accompanies this review. However, much of the cellular response to IFN-gamma can be described in terms of a set of integrated molecular programs underlying well-defined physiological systems, for example the induction of efficient antigen processing for MHC-mediated antigen presentation, which play clearly defined roles in pathogen resistance. A promising approach to the complexity of the IFN-gamma response is to extend the analysis of the less understood IFN-gamma-regulated genes in terms of molecular programs functional in pathogen resistance.

The locus-specific enhancer activity of the class I major histocompatibility complex interferon-responsive element is associated with a gamma-interferon (IFN)-inducible factor distinct from STAT1alpha, p48, and IFN regulatory factor-1

Recent analyses of the upstream regulatory regions of the class I major histocompatibility complex genes in higher primates provided a generalized structural basis for the differential expression of A- and B-locus gene products in response to specific physiological stimulus. Among the regulatory sequences that differ between the loci is the interferon-responsive element (IRE). While the B-IRE is conserved, the A-IREs have species-specific sequence variation. We previously demonstrated that the B-IRE was an interferon (IFN)-inducible enhancer, whereas none of the A-IREs were functional. In the present study, we examined the biochemical basis for the enhancer activity of the conserved B-IRE and found that this may be attributed to a novel gamma-IFN-inducible factor. This factor accumulated in nuclei of cells within minutes of exposure to gamma-IFN. Its appearance was independent of de novo protein synthesis. However, it was not detected in nuclei of cells treated with herbimycin A, suggesting that its appearance depends on a protein kinase activation pathway. Supershift assays indicated that it was distinct from STAT1alpha, IFN regulatory factor-1, and p48, transcription factors known to bind IRE-like sequences found in regulatory regions of many non-major histocompatibility complex gamma-IFN-responsive genes. Competition assays show that this novel factor bound B-IRE with relatively high affinity, about 100-fold more than that for the A-IRE sequence. This factor was also present in STAT1alpha and p48 somatic mutants that also exhibited B-IRE enhancer activity in reporter gene bioassays in a manner similar to those seen with wild type cells. These observations indicate the existence of a novel gamma-IFN-dependent transcriptional activation pathway that correlates with the differential enhancer activity of the HLA-B IRE.

Potentiation of inhaled staphylococcal enterotoxin B-induced toxicity by lipopolysaccharide in mice

Nonhuman primates are the established model for evaluating toxic responses to staphylococcal enterotoxins (SEs), as they react similarly to humans. Rodents are generally considered unresponsive to SEs. Binding affinities and T-cell reactivity suggest that SE binds more efficiently to primate major histocompatability complex class II receptors than to mouse receptors. We investigated the potentiation of staphylococcal enterotoxin B (SEB) inhalation toxicity by lipopolysaccharide (LPS) in BALB/c mice. Lethality occurred only when SEB was potentiated by LPS. Neither SEB nor LPS produced lethal effects alone. Temporal responses of interleukin 1 alpha, tumor necrosis factor alpha, interleukin 2, and interferon-gamma evoked by inhaled SEB were enhanced by LPS. By 24 hr after intoxication, serum cytokines decreased to baseline levels, and consistent pulmonary perivascular leukocytic infiltrates were evident histologically. Histologic lesions induced by inhalation exposure to SEB by mice, with or without potentiation by LPS, were similar to those in the rhesus monkey. Predominant pulmonary lesions included severe, diffuse interstitial and alveolar pulmonary edema, leukocytic infiltrates, mild perivascular edema, and alveolar fibrin deposition. Although the mechanism of aerosolized SEB-induced toxicity has not been completely resolved, similarities in histologic lesions, cytokine responses, and acute dose-response suggest the LPS-potentiated mouse model may be a credible alternative to the nonhuman primate model.

ESM-1 is a novel human endothelial cell-specific molecule expressed in lung and regulated by cytokines

We here report the identification of a novel human endothelial cell-specific molecule (called ESM-1) cloned from a human umbilical vein endothelial cell (HUVEC) cDNA library. Constitutive ESM-1 gene expression (as demonstrated by Northern blot and reverse transcription-polymerase chain reaction analysis) was found in HUVECs but not in the other human cell lines tested. The cDNA sequence contains an open reading frame of 552 nucleotides and a 1398-nucleotide 3'-untranslated region including several domains involved in mRNA instability and five putative polyadenylation consensus sequences. The deduced 184-amino acid sequence defines a cysteine-rich protein with a functional NH2-terminal hydrophobic signal sequence. Searches in several data bases confirmed the unique identity of this sequence. A rabbit immune serum raised against the 14-kDa COOH-terminal peptide of ESM-1 immunoprecipitated a 20-kDa protein only in ESM-1-transfected COS cells. Immunoblotting and immunoprecipitation of HUVEC lysates revealed a specific 20-kDa band corresponding to ESM-1. In addition, constitutive ESM-1 gene expression was shown to be tissue-restricted to the human lung. Southern blot analysis suggests that a single gene encodes ESM-1. A time-dependent up-regulation of ESM-1 mRNA was seen after addition of tumor necrosis factor alpha (TNFalpha) or interleukin (IL)-1beta but not with IL-4 or interferon gamma (IFNgamma) alone. In addition, when IFNgamma was combined with TNFalpha, IFNgamma inhibited the TNFalpha-induced increase of ESM-1 mRNA level. These data suggest that ESM-1 may have potent implications in the areas of vascular cell biology and human lung physiology.

Comparative effects of bluetongue virus infection of ovine and bovine endothelial cells

Bluetongue virus (BTV) infection results in disparate clinical syndromes among ruminant species. An in vitro model system of BTV/target cell interaction was developed using umbilical vein endothelial cells (EC)from fetal lambs and calves. These cells had microscopic, ultrastructural, and immunocytochemical features typical of EC. BTV infection in these cells was examined using virus binding assays, plaque assays, a whole-cell enzyme-linked immunosorbent assay, flow cytometry, electron microscopy, and a bioassay for interferon activity. EC from both species supported cytopathic BTV infections. Ovine EC bound more BTV initially and produced more virus over time, whereas bovine EC underwent more rapid lysis subsequent to infection. An ultrastructural comparison of BTV-infected ovine and bovine EC, grown as differentiated capillary-like cords on a laminin-rich matrix or as monolayers, revealed no significant interspecies differences in viral morphogenesis between 1 minute and 24 hours after infection. The intracellular distribution of BTV nonstructural protein 1, which localized to virus inclusion bodies and tubules, was identical for ovine and bovine endothelial cells. Ovine and bovine EC produced a soluble mediator of interferon activity in response to BTV infection; however, ovine EC produced higher levels of interferon activity at lower levels of infection. These findings indicate differences in BTV-EC interaction that may contribute to the pathogenesis of the severe inflammatory disease that is characteristic of clinical bluetongue disease in sheep.

Human leukocyte antigen system and the immune response to it

Immunologic rejection of tissue grafts follows recognition of donor alloantigens; either those resulting from ABO incompatibility of those encoded by the human major histocompatibility complex, HLA. Alloantigens encoded by HLA are present on membrane proteins that are expressed constitutively by tissues or whose expression can be induced by cytokines released during inflammation. Genes of the HLA complex are highly polymorphic resulting in variations in amino acid sequence that shape the peptide binding pocket of HLA molecules and define the complementary structure that interacts with the T lymphocyte receptor for antigen. Variants of HLA proteins expressed by the allografts that are not expressed by the recipient can stimulate the immune response to the allograft resulting in rejection both by humoral antibody and through attack by T lymphocytes. Class II HLA antigens on donor cells can stimulate these responses directly by contact with recipient T cells. However, rejection also may result when HLA antigens are released from the graft, processed to peptides, and presented to recipient T cells by cells expressing recipient HLA Class II molecules. Rejection can be avoided by preventing activation of T lymphocytes, by minimizing differences in HLA proteins between recipient and donor or by avoiding preexisting responses to donor HLA antigens.

Counteracting effect of IFN-beta on IFN-gamma-induced proliferation of human astrocytes in culture

Recent clinical trials have shown that interferon beta (IFN-beta) is effective in reducing exacerbations in relapsing-remitting MS, while interferon gamma (IFN-gamma) precipitates the relapses. To investigate mechanisms underlying the beneficial effects of IFN-beta and the detrimental effects of IFN-gamma in MS, cell growth-regulatory effects of IFNs were examined in astrocyte-enriched cultures isolated from fetal brains of 12-20 weeks' gestation. Treatment with IFN-gamma (50 or 500 IU ml-1) stimulated significantly the proliferation of astrocytes in 6 out of 9 culture series examined, while IFN-beta (50 or 500 IU ml-1) inhibited the astrocytic proliferation in 3 out of 9 cultures, and IFN-alpha (50 or 500 IU ml-1) did not affect the proliferation IFN-beta and to a lesser degree IFN-alpha reduced the astrocytic proliferation induced by IFN-gamma-treatment in 8 out of 9 culture series. The counteracting effect of IFN-alpha/IFN-beta against IFN-gamma-induced astrocytic proliferation was verified by the DNA content distribution analysis of propidium iodide-labeled cells. The antagonistic effect of IFN-alpha/IFN-beta on the growth-promoting activity of IFN-gamma in cultured human astrocytes suggests that interferons serve as growth regulators of astrocytes at sites of reactive gliosis lesions of MS.

Protective effects of niacinamide in staphylococcal enterotoxin-B-induced toxicity

Staphylococcal enterotoxins (SE) interact with major histocompatibility complex (MHC) class II cell-surface receptors, eliciting signal transduction in antigen-presenting cells (APC). Subsequent toxin-class II complex interaction with specific T-cell receptors induces T-cell activation. We investigated the effect of niacinamide and interleukin (IL)-10 on SEB-induced responses. In a macrophage cell line, niacinamide (ED50--2mM) and IL-10 (ED50--7U/ml) inhibited interferon (IFN)-gamma-induced MHC class II expression in a dose-dependent manner. Also, niacinamide was a potent inhibitor of T-cell proliferation induced by SEB (ED50-- 1 mM) while IL-10 has minimal effects. In mice, the temporal responses of IL-1alpha, tumor necrosis factor (TNF)-alpha, IL-2, and IFN-gamma evoked by SEB were synergistically potentiated by lipopolysaccharide (LPS). Lethality occurred only when SEB was potentiated by LPS. Niacinamide or IL-10 improved survival of mice after lethal SEB challenge. Niacinamide reduced cytokine serum levels, although the pattern differed from that of IL-10. Niacinamide primarily reduced IL-2 and IFN-gamma, while IL-10 predominantly reduced IL-1alpha and TNF-alpha. The immunomodulatory effects of niacinamide observed on SEB-induced activation of APC and T-cells in vitro and in the LPS potentiated murine model for SEB-induced toxicity suggest it may have therapeutic value.

Lymphocytes induce enhanced expression of HLA class I antigens on cytomegalovirus-infected syngeneic human endothelial cells

Human cytomegalovirus (HCMV) infection has been associated with enhanced expression of HLA antigens on the endothelium and with cellular infiltrates within the graft following human organ transplantation. We investigated the interactions between human cytomegalovirus-infected cultured endothelial cells and cocultured syngeneic as well as allogeneic lymphocytes. Our objective was to find out whether cocultured lymphocytes elicit HCMV-mediated immune responses. In this report we focus on the modified expression of HLA antigens on the surface membrane of human umbilical vein endothelial cells (HUVECs). Endothelial expression of HLA class I and II antigens was measured by means of flow cytometry. Cocultures of HCMV-infected HUVECs with unprimed autologous PBLs led to virus-specific lymphocyte response, resulting in enhanced expression of HLA class I on HUVECs. This effect was only observed when lymphocytes were added to HUVECs during the very early phase after virus inoculation and was due to the stimulation of the CD8+ T-cell subpopulation. The modification of endothelial HLA expression was not observed in transwell cocultures, indicating the importance of cellular contact between endothelial cells and lymphocytes to elicit this effect. We conclude that HCMV-infected endothelial cells may induce virus-specific responses of unprimed syngeneic lymphocytes that lead to upregulated HLA class I expression on the endothelium. This pathway might be of important relevance for graft rejection crises after transplantation.

Interferon-beta downregulates interferon-gamma-induced class II MHC molecule expression and morphological changes in primary cultures of human brain microvessel endothelial cells

Regulation of class II MHC (Ia) antigen expression by interferons beta and gamma was studied in an in vitro model of the blood-brain barrier. Primary cultures of human brain microvessel endothelial cells were incubated with IFN-beta, gamma or a combination of the two cytokines and surface expression of class II MHC molecules was investigated with the immunogold silver staining technique and enzyme-linked immunosorbent assay. Treatment of monolayers with IFN-beta (100-6000 U/ml) failed to induce Class II MHC molecules. Co-incubation with IFN-gamma (100 U/ml), with or without pretreatment with IFN-beta, significantly inhibited the IFN-gamma-induced de novo expression in a concentration-dependent manner. Downregulation was less significant when incubation with both cytokines was preceded by 2-day treatment with IFN-gamma and was not observed in cultures incubated for an additional 4 days with IFN-gamma. Endothelial cells treated with IFN-gamma exhibited prominent morphological changes and frequent overlapping. These changes were not observed in the presence of either IFN-beta or both cytokines in the media. IFN-beta alone, or in combination with IFN-gamma, significantly inhibited the growth of endothelial cells, while only slight inhibition was observed with IFN-gamma. The results of these studies suggest that IFN-beta may function in modulating IFN-gamma-mediated immune responses in the human central nervous system at the level of the blood-brain barrier and this negative regulatory mechanism may be, at least in part, responsible for the recently reported beneficial effect of IFN-beta in relapsing-remitting multiple sclerosis.

Cytokine-regulated production of the major histocompatibility complex class-III-encoded complement proteins factor B and C4 by human glomerular mesangial cells

Local production of complement within normal or diseased kidneys could be of importance during local inflammatory reactions. In the present study, we demonstrate that human MCs are able to synthesize the MHC class-III-encoded complement proteins factor B and C4 in vitro. This synthesis is strongly upregulated following stimulation with cytokine-containing supernatants of activated peripheral blood mononuclear cells. All primary cell lines tested so far are able to synthesize factor B and C4 after stimulation. To determine more specifically whether defined cytokines are able to enhance factor B and C4 complement production, MCs were stimulated with IL-1 alpha, IFN-gamma, and TNF-alpha. Factor B synthesis was increased in a dose-dependent fashion by IL-1 alpha, TNF-alpha, and IFN-gamma, whereas C4 synthesis was only upregulated by IFN-gamma. Furthermore, factor B synthesis was upregulated after stimulation with IFN-alpha, -beta, and -gamma and C4 synthesis only by IFN-gamma. The synthesis of factor B and C4 was inhibited by cycloheximide, suggesting de novo protein synthesis. The cytoplasmic localization of both components was shown by immunofluorescence studies. Northern and dot blot analysis revealed induction of factor B and C4 mRNA after stimulation with cytokines.

Role of vascular endothelial cells in the allograft response

Following transplantation endothelial cells lining an allograft come into contact with immune cells of the recipient. Activation of an immune response, by graft endothelial or other cells, will lead to local increases in cytokine production and cell-mediated lysis. Inflammatory cytokines have been shown, mainly in vitro, to have marked effects on endothelial function and act to produce a pro-thrombotic, pro-adhesive and promitogenic phenotype. These data are reviewed and ways in which these changes could lead to rejection due to graft lysis or vascular occlusion are discussed.

Bacterial stimulators of macrophages

Our current understanding of the interaction between bacteria and macrophages, cells of the immune system that play a major role in the defense against infection, is summarized. Cell-surface structures of Gram-negative and Gram-positive bacteria that account for these interactions are described in detail. Besides surface structures, soluble bacterial molecules, toxins that are derived from pathogenic bacteria, are also shown to modulate macrophage functions. In order to affect macrophage functions, bacterial surface structures have to be recognized by the macrophage and toxins have to be taken up. Subsequently, signal transduction mechanisms are initiated that enable the macrophage to respond to the invading bacteria. To destroy bacteria, macrophages employ many strategies, among which antigen processing and presentation to T cells, phagocytosis, chemotaxis, and different bactericidal mechanisms are considered to be the main weapons.

The role of interferon beta in human cytomegalovirus-mediated inhibition of HLA DR induction on endothelial cells

Human cytomegalovirus (HCMV), a member of the virus family Herpesviridae that is associated with extensive worldwide morbidity and mortality in immunocompromised hosts, inhibits interferon-gamma (IFN gamma)-mediated induction of human leukocyte antigen (HLA) class II antigens on endothelial cells. In this study, the ability of HCMV-infected endothelial cells to synthesize interferon-beta (IFN beta), and the role of IFN beta in HCMV-mediated inhibition of HLA class II induction, was investigated. As determined by an encephalomyocarditis virus protection assay, HCMV-infected endothelial cell culture supernatants contained 240 IU/ml of IFN type I activity, of which 99.9% was IFN beta, as compared to the absence of IFN beta in mock-infected culture supernatants. UV-irradiated supernatants from HCMV-infected cultures inhibited induction of HLA class II in noninfected cultures by 24%. This inhibition could be abolished with 500 NU/ml of anti-IFN beta antibody. Addition of anti-IFN beta antibody directly to HCMV-infected cultures mitigated but did not abolish HLA class II antigen inhibition. Dual immunohistochemistry for HCMV and HLA DR demonstrated that infected cells, in contrast to noninfected cells, were rarely induced to express HLA class II even in the presence of anti-IFN beta antibody. These findings suggest that HCMV inhibits induction of HLA class II antigens by IFN beta dependent and independent mechanisms.

Intercellular adhesion molecule-1 (ICAM-1) expression and soluble ICAM-1 (sICAM-1) production by cytokine-activated human aortic endothelial cells: a possible role for ICAM-1 and sICAM-1 in atherosclerotic aortic aneurysms

The interactions of inflammatory cells, cytokines, and cell adhesion molecules (CAM) may be important in the pathogenesis of vascular diseases such as abdominal aortic aneurysms (AAA), in which inflammation plays a role. The aim of this study was to investigate the pathogenic role of ICAM-1, a molecule involved in leucocyte-endothelial interactions, in vascular inflammation. ELISA of human explant culture supernatants revealed a four-fold increase in sICAM-1 production by AAA (n = 9) versus normal (n = 8) aortic explants. Human aortic endothelial cell (hAEC) culture was used for further studies as an in vitro model for aortic inflammatory conditions. Tumour necrosis factor-alpha (TNF-alpha) or IL-1 beta treatment of hAEC resulted in an up to 1.8-fold significant increase in sICAM-1 production compared with resting cells. In addition, the expression of ICAM-1 on cytokine-stimulated versus resting hAEC was measured by radioimmunoassay. TNF-alpha significantly induced ICAM-1 expression on these cells. These results suggest that different forms of ICAM-1, present on or released by the activated aortic endothelium, may be involved in leucocyte adhesion to and migration into the vessel wall.

Polyinosinic:polycytidylic acid is a potent activator of endothelial cells

Polyinosinic:polycytidylic acid (poly I:C) is a synthetic double-stranded polyribonucleotide that elicits immune responses analogous to those observed during viral infection. It is also known to modulate the expression of certain autoimmune disorders including diabetes mellitus in the BB rat and NOD mouse. The mechanism underlying these immunomodulatory effects is not known, but it could involve activation of vascular endothelium. We now report that parenteral poly I:C induces rat pancreatic endothelium to hyperexpress intercellular adhesion molecule 1 (CD54). This is accompanied by a perivascular recruitment of mononuclear cells to the exocrine pancreas. Corollary in vitro studies demonstrated that poly I:C is a potent activator of both rat and human endothelial cells in culture. It upregulates endothelial expression of several leukocyte adhesion molecules, stimulates the release of interleukin-6 and interleukin-8, and antagonizes interferon-gamma induction of major histocompatibility complex class II expression. We conclude that poly I:C activates endothelial cells to express surface molecules and cytokines in a pattern classically associated with leukocyte recruitment. These effects may in part contribute to the immunomodulatory effects of poly I:C in animal models of autoimmunity.

Cytomegalovirus inhibits major histocompatibility class II expression on infected endothelial cells

Persistent human cytomegalovirus (HCMV) infections are responsible for significant morbidity and mortality in immunocompromised individuals. One mechanism by which HCMV may develop persistence after primary infection is through inhibition of host cell human leukocyte antigen (HLA) class II expression with resultant escape from normal antiviral immune surveillance. Immunofluorescence flow cytometry of human endothelial cell (EC) cultures infected with HCMV AD169 and an EC propagated strain, VHL/E, showed a marked reduction in interferon-gamma (IFN-gamma)-induced surface expression of HLA-DR. This inhibition did not occur when EC were treated with ultraviolet-inactivated virus and IFN-gamma. HCMV, as determined by dual-labeling immunohistochemistry, inhibited induction of surface and cytoplasmic class II antigens specifically in infected cells. HCMV infection also inhibited IFN-gamma and tumor necrosis factor-alpha up-regulation of HLA class I expression. Northern blot analysis of infected, IFN-gamma-treated human umbilical vein endothelial cells revealed an absence of class II mRNA. Persistence of HCMV may result in part from its ability to inhibit HLA class II induction in infected cells.

HLA class I heavy-chain gene promoter elements mediating synergy between tumor necrosis factor and interferons

The cytokines tumor necrosis factor (TNF), beta interferon (IFN-beta), and IFN-gamma increase major histocompatibility complex class I molecule expression. A greater than additive (i.e., synergistic) induction of class I heavy-chain mRNA is observed in HeLa cells treated with TNF in combination with either type of IFN. To define the cis-acting elements mediating cytokine synergy, the promoter of a human major histocompatibility complex class I heavy-chain gene (HLA-B7) was placed in front of a reporter gene and transfected into HeLa cells. Deletion analysis mapped the elements required for synergy to a 40-bp region containing a kappa B-like element, which is necessary for the response to TNF, and an interferon consensus sequence (ICS), which is necessary for the responses to IFNs. When the orientation of these elements was reversed or their normal 20-bp spacing was reduced by 5 or 10 bp, i.e., one half or one full turn of the DNA helix, essentially equivalent responses were obtained, suggesting that these parameters are not critical. In electromobility shift assays, a p50-containing NF-kappa B nuclear factor from TNF-treated cells binds kappa B-containing probes, and ISGF-2 from IFN-gamma-treated cells binds ICS-containing probes. A probe containing both the kappa B and ICS elements (kappa B-ICS) forms a novel complex with nuclear factors isolated from cells treated with both TNF and IFN-gamma; this complex also forms when nuclear factors from individually cytokine-treated cells are mixed in vitro. The natural variant ICS found in HLA-A responds to IFN-gamma and can mediate synergy with TNF. However, the variant kappa B found in HLA-C does not respond to TNF, nor can it mediate synergy between TNF and IFN-gamma. These observations suggest that synergy between TNF and IFNs in the induction of HLA class I gene expression results from the sum of individual interactions of cytokine-activated enhancer-binding factors with the transcription initiation complex.