Differential regulation of HLA-DR mRNAs and cell surface antigens by interferon

Relevance of Mu-Opioid Receptor Splice Variants and Plasticity of Their Signaling Sequelae to Opioid Analgesic Tolerance

Opioid dose escalation to effectively control pain is often linked to the current prescription opioid abuse epidemic. This creates social as well as medical imperatives to better understand the mechanistic underpinnings of opioid tolerance to develop interventions that minimize it, thereby maximizing the analgesic effectiveness of opioids. Profound opioid analgesic tolerance can be observed in the absence of mu-opioid receptor (MOR) downregulation, aggregate MOR G protein uncoupling, and MOR desensitization, in the absence of impaired G protein coupled receptor kinase phosphorylation, arrestin binding, or endocytosis. Thus, we have explored alternative biochemical sequelae that might better account for opioid analgesic tolerance. Our findings indicate that substantial plasticity among upstream and downstream components of opioid receptor signaling and the emergence of alternative signaling pathways are major contributors to opioid analgesic tolerance. An exemplar of this plasticity is our findings that chronic morphine upregulates the MOR variants MOR-1B2 and MOR-1C1 and phosphorylation of their C-terminal sites not present in MOR-1, events causally associated with the chronic morphine-induced shift in MOR G protein coupling from predominantly Gi/Go inhibitory to Gs-stimulatory adenylyl cyclase signaling. The unique feature(s) of these variants that underlies their susceptibility to adapting to chronic morphine by altering the nature of their G protein coupling reveals the richness and pliability of MOR signaling that is enabled by generating a wide diversity of MOR variants. Furthermore, given differential anatomical expression patterns of MOR variants, MOR splice variant-dependent adaptations to chronic morphine could enable mechanistic underpinnings of tolerance and dependence that are CNS region- and cell-specific.

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.

Selective up-regulation of functional mu-opioid receptor splice variants by chronic opioids

We recently reported (Verzillo, et al. J. Neurochem: 130, 790-796, 2014) that chronic systemic morphine selectively up-regulates mRNA encoding two C-terminal μ-opioid receptor (MOR) splice variants, MOR-1C1 and MOR-1B2 (MOR-1B2/-1C1). Given the known disconnects between changes in levels of mRNA and corresponding protein, it is essential to directly demonstrate that chronic opioid treatment elevates functional MOR-1B2/-1C1 protein prior to inferring relevance of these MOR variants to spinal opioid tolerance mechanisms. Accordingly, we investigated the ability of chronic opioid exposure to up-regulate MOR protein in Chinese hamster ovary cells stably transfected with rat MOR variants MOR-1B2, MOR-1C1, or MOR-1 (considered to be the predominant MOR). Findings revealed that chronic treatment with the clinically relevant opioids morphine, oxycodone and hydrocodone substantially up-regulated membrane MOR-1B2/-1C1 protein. This up-regulation was abolished by the protein synthesis inhibitor cycloheximide, eliminating contributions from receptor redistribution. The increment in MOR-1B2/-1C1 protein was paralleled by a significant increment in opioid agonist-stimulated GTPγS-binding (reflective of increased aggregate MOR G protein coupling) indicating that up-regulated MOR-1B2/-1C1 represented functional receptors. Strikingly, these tolerance-associated adaptations of MOR-1B2/-1C1 differed considerably from those of MOR-1. Antithetical regulation of MOR-1B2/-1C1 and MOR-1 by chronic opioids has significant implications for the design of new therapeutic agents to counteract opioid analgesic tolerance and accompanying addiction. Since chronic opioids induce MOR-1B2/-1C1 up-regulation in spinal cord of males, but not females, elucidating cellular compartments and intracellular pathways mediating MOR-1B2/-1C1 up-regulation and defining their unique signaling attributes would enable a precision medicinal approach to pain management and addiction therapy. In the spinal cord of males, but not females, chronic morphine up-regulates mRNA encoding two mu-opioid receptor (MOR) variants, MOR-1B2 and MOR-1C1 (MOR-1B2/-1C1). We now demonstrate that chronic treatment with the clinically relevant opioids morphine, hydrocodone or oxycodone up-regulates MOR-1B2/-1C1 functional protein, which is dependent on de novo protein synthesis. Findings underscore the importance of unique signaling attributes of MOR variants to sexually dimorphic tolerance mechanisms.

The immunocytokine NHS-IL12 as a potential cancer therapeutic

Targeted delivery of IL-12 might turn this cytokine into a safer, more effective cancer therapeutic. Here we describe a novel immunocytokine, NHS-IL12, consisting of two molecules of IL-12 fused to a tumor necrosis-targeting human IgG1 (NHS76). The addition of the human IgG1 moiety resulted in a longer plasma half-life of NHS-IL12 than recombinant IL-12, and a selective targeting to murine tumors in vivo. Data from both in vitro assays using human PBMCs and in vivo primate studies showed that IFN-gamma production by immune cells is attenuated following treatment with the immunocytokine, suggesting an improved toxicity profile than seen with recombinant IL-12 alone. NHS-IL12 was superior to recombinant IL-12 when evaluated as an anti-tumor agent in three murine tumor models. Mechanistic studies utilizing immune cell subset-depleting antibodies, flow cytometric methods, and in vitro cytotoxicity and ELISA assays all indicated that the anti-tumor effects of NHS-IL12 were primarily CD8+ T cell-dependent and likely IL-12-mediated. Combining NHS-IL12 treatment with a cancer vaccine, radiation, or chemotherapy resulted in greater anti-tumor effects than each individual therapy alone. These preclinical findings provide a rationale for the clinical testing of this immunocytokine, both as a single agent and in combination with vaccines, radiation and chemotherapy.

A role for glycogen synthase kinase-3 in antagonizing mycobacterial immune evasion by negatively regulating IL-10 induction

Mtb dysregulates monocyte/macrophage functions to produce a large amount of the immunosuppressive cytokine IL-10. An important function of IL-10 in promoting Mtb survival is the suppression of antigen presentation of monocytes/macrophages to T cells. This dampens the host immune responses and provides an opportunity for immune evasion. GSK3 has been shown to control the balance between pro- and anti-inflammatory cytokine productions. Here, we investigated whether GSK3 regulates IL-10 expression and mediates a protective role upon live mycobacterial challenge using BCG as a model. Our results showed that BCG increased Akt phosphorylation and inhibited GSK3 activity, resulting in increased IL-10 production. We confirmed further that suppression of GSK3 activities by a specific chemical inhibitor strongly enhanced BCG-induced IL-10 production. We also showed that IL-10 secreted by BCG-infected human PBMo was a major suppressor of subsequent IFN-gamma production by PBMC and HLA-DR expression on PBMo in response to BCG. Neutralization of PBMo-secreted IL-10 by anti-IL-10 antibodies restored the IFN-gamma production and HLA-DR surface expression. Taken together, GSK3 negatively regulates mycobacteria-induced IL-10 production in human PBMo. The kinase may play a role in restoring IFN-gamma secretions and subsequent antigen presentation in response to mycobacterial infection. In conclusion, our results suggest a significant role for GSK3 in guarding against mycobacterial evasion of immunity via IL-10 induction in the host.

Age-dependent decrease in serum soluble interferon-gamma receptor (sIFN-gammaR) in healthy Japanese individuals; population study of serum sIFN-gammaR level in Japanese

We planned to investigate the clinical significance of serum soluble interferon-gamma receptor (sIFN-gammaR) level in pediatric patients. The diagnostic application of the measurement of serum sIFN-gammaR level depends critically on the control value. However, there is no information of the control value of serum sIFN-gammaR for children. In the present study, we determined the serum sIFN-gammaR level of healthy Japanese children using an ELISA. The serum sIFN-gammaR level of children (0-14 years old) was significantly higher than that of adults (over 15 years old) (p < 0.01, n = 104). Thus, it is recommended that, when the serum sIFN-gammaR level of patients is evaluated, it should be compared against age-matched controls. We also preliminarily applied this assay as a diagnostic parameter for the patients with diarrhea positive (D+) hemolytic uremic syndrome (HUS).

The role of type I interferons in TLR responses

Recent advances in unravelling the complexities of the signalling pathways that constitute innate immunity have highlighted type I interferon as a key component in the response to infection. Here we focus on the emerging field of pattern-recognition receptor signalling, specifically Toll-like receptors and retinoic acid inducible gene-like helicases, from the perspective of this 50-year-old cytokine. The type I interferon gene family encompasses more than 20 subtypes, whose nature and properties have been extensively studied during its relatively long history. In this review we update and integrate available data on the mechanics of activation of the interferon genes and the role of this cytokine family in the innate immune response.

Phase 2 trial of the continuous IV administration of interferon-beta in patients with disseminated malignant melanoma

BACKGROUND

Interferons have been reported to significantly contribute to tumor suppression via both induction of p53 gene expression and inhibition of angiogenesis.

OBJECTIVE

The assessment of treatment toxicity and antitumoral effectiveness of continuous IV administration of interferon-beta based on an overall evaluation of laboratory, radiographic, and clinical parameters observed during the trial.

METHODS

The authors treated patients with advanced malignant melanoma with continuous IV infusions of 1 x 10(6) IU interferon-beta daily ( approximately 0.6 x 10(6) IU interferon-beta/m2 daily).

RESULTS

Continuous IV administration of interferon-beta had no significant effect on overall patient outcome. Interferon side effects were not a reason for treatment discontinuation in any of the patients observed during this trial.

CONCLUSIONS

Continuous IV interferon-beta had no significant effect on overall patient outcome in a group of patients with advanced malignant melanoma. To our knowledge, this is the first report on the continuous IV administration of interferon-beta in patients with advanced malignant melanoma.

Effective Suppression of Class I Major Histocompatibility Complex Expression by the US11 or ICP47 Genes Can Be Limited by Cell Type or Interferon-γExposure

An impediment encountered in many viral-based gene therapy clinical trials has been the rapid destruction of the transgene by the host's immune response. The processing and presentation of antigens through the class I major histocompatibility complex (MHC) pathway is the initial specific response to viral infection. Disruption of the class I MHC pathway by herpes simplex virus (HSV) or the human cytomegalovirus (HCMV) results in a decrease of the CD8(+) cytotoxic T lymphocyte (CTL) response and prolongs survival of infected cells in the host. Two viral immune suppression genes that interfere with the class I MHC presentation pathway, the HSV type I ICP47 gene and HCMV US11 gene, were cloned and each incorporated into a retroviral vector. HSV ICP47 and HCMV US11 transgenes were expressed in multiple cells lines and compared for their abilities to reduce antigen presentation on the cell surface by class I MHC. Retroviral supernatants were used to transduce human, canine, and rat cell lines. Fluorescence-activated cell sorter (FACS) analysis of US11- and ICP47-transduced cell lines demonstrated substantial reductions in class I MHC cell surface expression in most cell lines except in rodent cells where ICP47 is nonfunctional. The decrease in the level of class I MHC expression for ICP47 transduced cell lines ranged from 31-98% relative to negative controls. US11 decreased class I cell surface MHC by 67-96%. When both ICP47 and US11 are expressed in human cells, a further reduction of class I MHC was observed. Next, human A375 melanoma cells were tested to determine if the resulting reduction in cell surface class I MHC would reduce in vitro cytotoxicity by CTL. A375 cells expressing either ICP47 or US11 demonstrated a twofold to threefold reduction of specific lysis by primed CD8(+) CTL. These data clearly establish an ability to convey immune protection to human cells by viral genes. However, further analysis demonstrated that interferon (IFN)-gamma could reverse part or all of the downregulation of class I MHC induced by the ICP47 or US11 genes. The ICP47 and US11 genes, when expressed in target cells, decrease class I MHC presentation and as such might be used in strategies to create local immunosuppression against transgenes or allografts.

Regression of AK7 malignant mesothelioma established in immunocompetent mice following intratumoral gene transfer of interferon gamma

Malignant mesothelioma (MM) is a lethal tumor linked with a prior exposure to asbestos in which limited progress has been made so far using conventional therapies. MM is an example of a "nonimmunogenic" tumor characterized by a fibrous stroma and an absence of infiltrating T lymphocytes. High levels of transforming growth factor-beta (TGF-beta) produced by mesothelioma cells have been related to the immune tolerance towards the tumor. In order to evaluate the effect of local delivery of cytokines such as interferon gamma (IFN-gamma) by gene transfer, we characterized and used a murine model, AK7, which appeared very similar to human mesothelioma. AK7 cells expressed low levels of major histocompatibility class I and class II antigens and secreted high levels of latent TGF-beta. The TGF-beta pathway in AK7 cells is operative but inefficient because endogenous TGF-beta is predominantly inactive. Treatment of pre-established AK7 tumors by direct intratumoral injection of an adenovirus vector expressing murine IFN-gamma, Ad.mIFN-gamma, led to significant tumor regression. Peripheral tumor infiltration by CD4+ and CD8+ T lymphocytes in the treated tumors appeared to be because of the induction of an immune response. Tumor relapse was observed, which could be due to local TGF-beta secretion by remaining tumor cells.

A 3'-transcribed region of the HLA-A2 gene mediates posttranscriptional stimulation by IFN-gamma

The expression of several MHC class I genes is up-regulated at the transcriptional level by IFN-gamma. Posttranscriptional mechanisms also have been implicated, but not well characterized. To investigate the mechanism of IFN-gamma stimulation of the human MHC class I gene HLA-A2, several human tumor cell lines were transfected with reporter gene constructs driven by the HLA-A2 promoter. We have previously shown that the extended 525-bp HLA-A2 promoter alone, which includes a 5' IFN-stimulated response element consensus sequence, is not sufficient for IFN-gamma response in either K562 or Jurkat cells. In the current study, stable transfection of a genomic HLA-A2 gene construct, containing both 5'- and 3'-flanking sequences, resulted in stimulation of the gene by IFN-gamma. Nuclear run-on assays revealed that, unlike other class I genes, IFN-gamma stimulation of HLA-A mRNA accumulation occurs almost entirely through posttranscriptional mechanisms. RNA stability assays showed that the effect is not mediated by alteration of the half-life of the HLA-A2 mRNA. Formation of the 3' end was unaffected by IFN-gamma treatment. Sequences that mediate the majority of IFN-gamma induction of HLA-A2 mRNA reside in a 127-bp 3'-transcribed region of the gene. This region contains the terminal splice site, the usage of which is not affected by IFN-gamma treatment. These results demonstrate a novel posttranscriptional mechanism of regulation of MHC class I genes by IFN-gamma.

BLIMP-I mediates extinction of major histocompatibility class II transactivator expression in plasma cells

Class II transactivator (CIITA), a coactivator required for class II major histocompatibility complex (MHC) transcription, is expressed in B cells but extinguished in plasma cells. This report identifies B lymphocyte-induced maturation protein I (BLIMP-I), a transcriptional repressor that is capable of triggering plasma cell differentiation, as a developmentally regulated repressor of CIITA transcription. BLIMP-I represses the B cell-specific promoter of the human gene that encodes CIITA (MHC2TA) in a binding site-dependent manner. Decreased CIITA correlates with increased BLIMP-I during plasma cell differentiation in cultured cells. Ectopic expression of BLIMP-I represses endogenous mRNA for CIITA and the CIITA targets, class II MHC, invariant chain and H2-DM (the murine equivalent of HLA-DM) in primary splenic B cells as well as 18-81 pre-B cells. Thus, the BLIMP-I program of B cell differentiation includes loss of antigen presentation via extinction of CIITA expression.

A novel lipopolysaccharide inducible C-C chemokine receptor related gene in murine macrophages

To identify genes induced in activated macrophages, we screened a cDNA library prepared from the lipopolysaccharide (LPS)-treated cell line, RAW264, using the suppression subtractive hybridization technique. One of the clones isolated was dramatically induced by LPS in macrophages. The predicted protein sequence of this gene contains the domain unique to seven transmembrane receptors, and shows similarity with mouse C-C chemokine receptor 5 (CCR5). Therefore, we designated it LPS inducible C-C chemokine receptor related gene (L-CCR). Northern blot analysis revealed that L-CCR was specifically expressed in differentiated macrophages after LPS stimulation. These results show that L-CCR is a novel C-C chemokine receptor related gene induced by LPS in macrophages and may play an important role in inflammatory responses.

Identification of Distinct Regions of 5′ Flanking DNA That Mediate Constitutive, IFN-γ, STAT1, and TGF-β-Regulated Expression of the Class II Transactivator Gene

Class II transactivator (CIITA) is a master regulator required for constitutive and IFN-γ-inducible expression of class II MHC genes. Although the role of CIITA is greatly appreciated, the mechanisms underlying constitutive and IFN-γ-induced expression of CIITA are not understood. The study of CIITA induction is extremely important, but has been fraught with difficulty. This study describes for the first time a large (7-kb) fragment of 5′ flanking sequences that mediates the B cell-specific, IFN-γ-induced, and TGF-β-suppressed expression of CIITA. This pattern of expression matches the authentic expression of the endogenous gene. Within the 7-kb fragment, sequences that lie between nucleotides −545 and −113 relative to the transcriptional start site are critical for constitutive promoter expression in B cells. In contrast, inducible activation of CIITA by IFN-γ requires sequences contained in an additional 4 kb of upstream DNA. This region mediates an IFN-γ response when linked to either the endogenous CIITA promoter or a heterologous promoter. A role for STAT1 in regulation of the CIITA promoter is shown by the rescue of IFN-γ induction by expression of STAT1 in STAT1-defective U3A cells. TGF-β significantly inhibits IFN-γ-mediated induction of the CIITA promoter in 2fTGH fibroblasts, which indicates that the promoter is a target for TGF-β. This inhibition is achieved by suppression of the basal promoter. This study provides a focal point for understanding the mechanism of B cell-specific, IFN-γ-induced, and TGF-β-suppressed expression of CIITA.

Molecular analysis of G1B and G3A IFN gamma mutants reveals that defects in CIITA or RFX result in defective class II MHC and Ii gene induction

Class II major histocompatibility complex (MHC) genes and the invariant (Ii) gene are inducible by interferon-gamma (IFN gamma) but not by interferon-alpha and interferon-beta. The promoter regions of these genes contain three regulatory elements that mediate constitutive and IFN gamma-induced expressions; however, none of the DNA-binding proteins that interact with these elements are regulated by IFN gamma. Recently, a gene coding for a transactivator (CIITA) of class II MHC genes that complements a HLA-DR-negative immunodeficiency has been isolated. Using one IFN gamma mutant cell line (G3A) that is selectively defective in HLA-DR and Ii induction, four lines of evidence are presented to show that CIITA mediates the IFN gamma induction of HLA-DR and Ii genes. Analysis of another mutant line, G1B, indicates that the lack of DRA and Ii gene induction by IFN gamma is correlated with the lack of RFX DNA binding activity, thus providing the link between RFX and an IFN gamma response.

HLA class II molecules (HLA-DR, -DP, -DQ) on cells in the human CNS studied in situ and in vitro

Human leucocyte antigen (HLA) class II molecules expressed by antigen-presenting cells (APC) are major restriction elements in the interaction between APC and T cells of the CD4+ subtype. To explore the immune accessory function of cells in the central nervous system (CNS), we studied the expression of HLA-DR, -DP, and -DQ molecules on CNS cells in situ and in vitro. Reactive microglia and perivascular cells in multiple sclerosis lesions expressed all three HLA class II molecules, whereas microglia in the normal CNS expressed HLA-DR only. All three HLA class II molecules were up-regulated on cultured microglia after stimulation with interferon-gamma (IFN-gamma). Microglial stimulation of allogeneic CD4+ T cells in a mixed lymphocyte reaction (MLR) was effectively blocked using anti-HLA-DR monoclonal antibodies (mAb) but not using anti-HLA-DQ mAb. HLA class II-positive astrocytes and endothelial cells were not identified in normal or diseased CNS. Cultured astrocytes stimulated with IFN-gamma could, however, be induced to express HLA class II antigens of all subtypes, although great variability was observed between different donors. Our results indicate that although both microglia and astrocytes are capable of expressing all HLA class II subtypes in vitro, subtype expression differs between normal and pathological states in situ. Such selective expression may be associated with functional properties.

Consensus interferon induces peak mRNA accumulation at lower concentrations than interferon-alpha 2a

The biological activity of a novel recombinant interferon, r-metIFN-con1, which represents a consensus sequence of the most commonly appearing amino acids at each locus of 14 naturally occurring IFN-alpha s, was assessed and compared to that of IFN-alpha 2a. The increase in cellular mRNA levels for three IFN-inducible genes served as a quantitative measure of the effectiveness of the stimulation by each of the IFNs. Three cell lines were treated with equimolar amounts of two IFNs encompassing a 5 log range and mRNA was extracted at five different times after treatment. In all cases, r-metIFN-con1 produced mRNA increases at lower concentrations than IFN-alpha 2a. HLA-DR alpha mRNA, which is not affected by IFN-alpha in ME180 or Daudi cells, was also not affected by r-metIFN-con1. However, in Eskol cells, both IFNs effected an increase in HLA-DR alpha mRNA to similar levels. The r-metIFN-con1 was effective at approximately 10-fold lower molar concentrations. At effective concentrations (10-fold lower molar dose of r-metIFN-con1), both IFNs produced similar kinetics of accumulation of all three mRNAs tested. r-metIFN-con1 is therefore more effective than IFN-alpha 2a at the level of mRNA regulation as well as the antiviral and antiproliferative activities that have been reported previously.

Current concepts in DRA gene regulation

The purpose of this review is to provide an interpretative view of work from our laboratory on the DRA gene, and incorporate it with work from other laboratories. Specially, we will deal with: (a) the functional roles of transcription factors in DRA gene regulation; (b) the mechanisms of DRA induction by cytokines; (c) the analysis of DRA gene control in primary untransformed cells, and (d) interactions among transcription factors critical for DRA gene expression.

Enhanced expression of HLA-class II molecules on activated human T lymphocytes following treatment with tumor necrosis factor alpha

Many factors induce or enhance expression of major histocompatibility complex class I and class II molecules on various cell types. Human T lymphocytes are class II negative in the resting state but show expression of class II molecules following activation. We analyzed the modulating capacity of the lymphokines recombinant interferon gamma (rIFN-gamma), interleukin-4 (IL-4), and recombinant tumor necrosis factor alpha (rTNF-alpha) on class II expression in subsets of alloactivated human T lymphocytes. The activated CD4+ T cells expressed all three class II isotypes (DR, DQ, and DP), whereas the cytotoxic CD8+ T-cell lines expressed DR and DP molecules but failed to bind DQ-specific monoclonal antibodies significantly. Treatment with rIFN-gamma and IL-4 had no effect on class II expression on any of the T-cell lines or clones, whereas rTNF-alpha enhanced class II expression in both subsets. rTNF-alpha could modulate expression of all three class II isotypes but, in principle, it appears only to affect ongoing class II synthesis as de novo synthesis of class II molecules with a resultant change in the class II phenotype from DR+ DQ- DP+ to DR+ DQ+ DP+ in the CD8+ T lymphocytes was not observed. No synergic effects of rINF-gamma and rTNF-alpha were observed; this results from the fact that activated T cells express few, if any, receptors of rIFN-gamma.

HLA-class-I and -class-II expression on renal tumor xenografts and the relation to sensitivity for alpha-IFN, gamma-IFN and TNF

In this study we evaluated the usefulness of the histocompatibility leucocyte antigen (HLA) class-I and class-II expression on renal-cell carcinoma (RCC) xenografts as predictive markers for response to cytokine therapy. Eight different RCC xenografts growing in BALBC nu/nu mice were treated with 0.5 or 5.0 ng/g recombinant human alpha- or gamma-interferon (IFN), or 500 ng/g recombinant human tumor necrosis factor (TNF). Modulation of HLA class-I, -II expression was evaluated immunohistochemically using the monoclonal antibodies (MAbs) W6.32 and B8.11.2 and at the mRNA level using the plasmids pDP001 and DR alpha 120. HLA class-I expression in all lines was upregulated by alpha- and gamma-IFN and was highest in the high-IFN-dose-treated tumors. TNF also stimulated HLA-class-I expression and up-regulated class-I expression still further when combined with IFN. Highest up-regulation of HLA-class-I in all tumors was measured in the alpha-IFN-5.0/TNF-500-ng/g-treated mice, although this was not necessarily the treatment regimen resulting in the most pronounced effect on tumor growth. Hence, maximum upregulation of class-I antigens at a given regimen was not always indicative for the highest achievable anti-tumor effect. HLA-class-II expression which was present on only 3 of the untreated tumors was up-regulated by both alpha and gamma-IFN. TNF itself did not up-regulate class-II expression but enhanced the class-II expression on the alpha-IFN-treated tumors but not on the gamma-IFN-treated tumors. Irrespective of the basic expression level, inducibility of both HLA-class-I and -class-II antigens appear to be correlated to the direct effects on growth of renal-tumor xenografts towards alpha-IFN, gamma-IFN and TNF. Modulation of HLA antigens was studied in the nude mouse, hence T-cell-mediated effector mechanisms cannot explain the good correlation between inducibility and response. Nonetheless, our studies indicate that the extent of modulation of HLA-class-I and -II can serve as predictive marker for response to cytokine therapy, which may serve as a valuable criterion for inclusion of patients in cytokine treatment regimens.

Radio-immunoassay detection of interferon-gamma in urine after intravesical Evans BCG therapy

Our previous studies suggested that interferon-gamma (IFN gamma) was produced in the local immune response to intravesical BCG. To confirm this we modified a commercially available radio-immunoassay for detection of this lymphokine in urine. The urinary levels of IFN gamma were compared in serial urine samples taken from six patients undergoing treatment with Evans strain BCG and seven patients receiving intravesical mitomycin C/epirubicin. IFN gamma was detected consistently in response to BCG with levels reaching a peak (mean 67.1 U/ml., range 7.9 to 155.9 U/ml.) four to six hours post-instillation whereas after other intravesical agents no IFN gamma was detectable after seven of 13 instillations. After the remaining six instillations lower levels were detected (mean 7.4 U/ml., range 0.6 to 22.4 U/ml.). The difference in peak levels between the two groups was statistically significant (p less than 0.001 Mann Whitney U test). These results are further evidence of specific cellular immune activity in response to intravesical BCG therapy and suggest anti-tumour mechanisms similar to allograft rejection and autoimmunity.

Primary hypothyroidism associated with interleukin-2 and interferon alpha-2 therapy of melanoma and renal carcinoma

Four patients out of twenty with renal cancer and melanoma undergoing cancer immunotherapy with interleukin 2 (IL-2) and interferon alpha-2 (IFN-alpha 2) had laboratory evidence of hypothyroidism starting at cycle three to six, with a decline in serum thyroxine below normal and, in three cases, a rise in serum thyrotropin and thyroglobulin. One hypothyroid patient had elevated serum antimicrosomal antibody titres before the start of treatment and two others responded similarly during therapy. Three of the sixteen euthyroid patients also developed elevated titres of this antibody. Partial or complete remission was observed in seven of the patients--three of the four with hypothyroidism showed tumour regression. Thus IL-2 and IFN-alpha 2 can cause hypothyroidism, presumably via induction or exacerbation of autoimmune thyroid reactions. The occurrence of hypothyroidism may be mediated by high-dose IL-2 (rather than by LAK cell therapy as previously suggested) and potentiated by IFN-alpha 2.

Further evidence for a human B cell activating factor distinct from IL-4

Supernatants from activated human T cell clones were previously shown to contain B cell-activating factor (BCAF), an activity which results in polyclonal resting B cell stimulation. In the present study, we investigate the relationship between this activity and human interleukin-4 which was also shown to act on resting B cells. The supernatant of the T cell clone TT9 contains IL-4 but anti-IL-4 antiserum does not affect the response of B cells as measured by thymidine uptake or cell volume increase. Furthermore, IL-4 induces Fc epsilon-receptor (CD23) expression on 30% of unstimulated human B cells, whereas BCAF-containing supernatants from clone P2, that do not contain detectable amounts of IL-4, promote B cell proliferation without inducing CD23 expression. Our results therefore establish that IL-4 and BCAF are distinct activities and suggest that they trigger different activation pathways in human B cells. In addition, culture of B cells with T cell supernatants for 72 hr induces a three- to fourfold increase in the expression of HLA-DR, -DP, and -DQ antigens in 50% of B cells. The addition of inhibiting concentrations of anti-IFN-gamma, LT, or IL-4 antisera to the cultures does not change these results. Finally, 30% of B cells cultured with T cell supernatants leave the G1 phase of the cell cycle and 20% reach mitosis. Taken together, our findings further support the existence of a B cell-activating factor responsible for the activation of resting human B cells.

Gamma interferon-like immunoreactivity in the rat nervous system

The presence of gamma interferon-like immunoreactivity in the peripheral nervous system and in some central nervous system neurons is described. The immunohistochemical evidence is based upon labeling of neurons with five different monoclonal antibodies against rat gamma interferon and one polyclonal antiserum. Immunoreactive material was abundantly present in the peripheral nervous system including small primary sensory neurons in dorsal root ganglia and postsynaptic neurons of the sympathetic and parasympathetic nervous system. Large neurons in dorsal root ganglia were not stained. Neurites stained with DB1 antibody against rat gamma interferon were found in most organs examined such as the gastrointestinal tract, heart, lungs, kidney, sexual organs and skin. In contrast, staining was weak in the central nervous system and restricted to a few neurons in the hypothalamus and in the midbrain. It is speculated that this newly discovered system containing a gamma interferon-like neuropeptide could be involved in the neuronal control of immunological processes in its target organs.

Human interferon gamma receptor 1 (IFNGR1) gene maps to chromosome region 6q23-6q24

The human interferon gamma receptor (IFNGR1) gene has been localized by in situ hybridization to chromosome 6 at q23-q24. This chromosomal region is often deleted in lymphoid cell malignancies.

Regulation of MHC gene expression during the differentiation of bone marrow-derived macrophages

The ability of the macrophage to express class II MHC gene products appears to arise from both T-dependent and T-independent mechanisms. One mechanism by which macrophages express Ia-antigens in the absence of T-lymphocytes is postulated to be controlled by differentiation. By using a liquid bone marrow culture system, we have studied both class I and class II surface expression and mRNA accumulation during macrophage differentiation in vitro. The results demonstrated that Ia expression increased until 7 days in culture and then slowly declined. In contrast, class I expression appeared to steadily increase throughout the differentiation period. Northern blot analysis of RNA isolated from bone marrow-derived macrophages (BMDM) at various periods during culture, using E alpha, A alpha, and class I cDNA probes, correlated well with the results of Ia and H-2K surface expression. Further analysis demonstrated that the expression of Ia-antigens on BMDM was not the result of T-helper lymphocytes. This was determined by demonstrating (1) that bone marrow cultures were devoid of mature T-lymphocytes, (2) the absence of interferon (IFN)-gamma transcripts in both adherent and nonadherent populations of bone marrow cells, and (3) that the addition of anti-IFN-gamma monoclonal antibody (mAb) to the bone cultures did not alter the percentage of Ia-positive BMDM. Moreover, the addition of anti-tumor necrosis factor-alpha mAb to the bone marrow cultures had no effect on Ia expression by BMDM. Taken together, these results allow us to conclude that Ia expression by BMDM is probably not mediated via exogenous signals but rather results from an intrinsically controlled process.

Trypsin inhibitors inhibit induction by interferon-gamma of HLA-DR antigen expression on human skin cells

Serine protease inhibitors with a specificity for trypsin inhibit interferon-gamma (INF-gamma)-induced HLA-DR expression on a hybrid human epidermal cell line (H12), dermal fibroblasts, and primary keratinocytes. Protease inhibitors with a specificity for chymotrypsin or papain fail to inhibit IFN-gamma. The inhibitory effect of the trypsin inhibitors is similar to that of glucocorticoids in that it is a transient event, fading with length of exposure to IFN-gamma, and is reversed by the addition of dibutyryl cyclic AMP (dbcAMP) and phospholipase C(PLC) from Clostridium perfringens. In H12 cells, dbcAMP and PLC enhance the IFN-gamma induction of HLA-DR, but do not induce in the absence of INF-gamma. Evidence suggests that the protease inhibitors, as well as dbcAMP and PLC, may modulate HLA-DR expression at a post-translational site as well as during IFN-gamma signal transduction. These results suggest that trypsin-like protease activity may be required for cellular HLA-DR antigen expression following exposure to IFN-gamma.

In vivo effects of combination treatment with recombinant interferon-gamma and -alpha in metastatic melanoma

The toxicity and therapeutic efficacy of the combination of recombinant interferon gamma (rIFN-gamma) and alpha (rIFN-alpha) was investigated in 15 patients with metastatic melanoma. Patients were treated with an escalating dose of rIFN-gamma and a fixed dose of rIFN-alpha administered s.c. 3 times a week. The maximum dose was well tolerated. The median survival time of the patients was 7 months; no clinical remissions were observed. In the majority of cases, expression of HLA class-I and -II antigens on the patients' peripheral blood lymphocytes and monocytes increased markedly during treatment. An increase in HLA-DR expression of peripheral blood T lymphocytes was correlated with a longer survival time. This suggests that activation of T lymphocytes may have a favourable influence on the course of metastatic disease. The in vitro anti-proliferative activity of IFNs on melanoma cell lines isolated from melanoma metastases during treatment of 3 patients was determined. In contrast to the lack of in vivo anti-tumour effect in patients, both rIFN-gamma and rIFN-alpha inhibited DNA synthesis of these melanoma cell lines in vitro, combined IFNs acting synergistically. Anti-proliferative activity observed in vitro occurred at IFN concentrations below the peak serum levels achieved in vivo.

Interleukin-2 alone and in combination with other cytokines in melanoma: the investigational approach at the University of Texas M.D. Anderson Cancer Center

The clinical data that have been accumulated so far suggests a significant influence of IL-2 dose and schedule on the immunobiological effects and clinical toxicities observed with this cytokine. Consequently, the series of Phase I and Phase II clinical trials conducted at the University of Texas M. D. Anderson Cancer Center in patients with advanced malignant melanoma investigating the use of IL-2 in combination with other cytokines, monoclonal antibodies, or ex vivo activated effector cells have used a common dose and schedule of IL-2 administration for which abundant immunobiological information already exists. This approach allows cross-trial comparison of experience with toxicities, immunobiological observations and clinical activity by a group of investigators within a single institution, and more rapid and valid evolution towards combination biological therapy, which preclinical data suggest will have greater activity than single agent therapy.

A gamma-interferon-induced factor that binds the interferon response sequence of the MHC class I gene, H-2Kb

Transcription of class I genes of the major histocompatibility complex (MHC) can be induced by interferons. Treatment of HeLa cells with interferon-gamma induces a DNA-binding factor, IBP-1, specific for a site within the interferon response sequence (IRS) of the H-2Kb promoter. The mol. wt of IBP-1, as estimated by photoactivated protein-DNA crosslinking analysis, is approximately 59 kd. Point-mutation of this binding site abolishes IBP-1 interaction and the ability of the MHC promoter to respond to interferon. Induction of this binding activity is rapid and closely parallels the previously reported time course of transcriptional activation of endogenous MHC class I genes. Treatment of cells with cycloheximide, a protein synthesis inhibitor, blocked the induction of the DNA-binding activity. An oligonucleotide derived from the virus- and double-stranded RNA-inducible promoter of the interferon-beta 1 gene is able to bind IBP-1. Sequences similar to the IBP-1 binding site are found upstream of many interferon-responsive genes.

Expression of HLA-DR mRNA in T cells following activation is early and can precede DNA synthesis

The stimulation of T cells is accompanied by the appearance of a number of activation antigens not found on resting T cells. We have studied the expression of one group of such antigens, the HLA class II antigens (DR, DQ and DP), following stimulation with PHA and PMA. Immunofluorescence studies using monoclonal antibodies indicated that cell surface class II determinants were detectable as little as 30 minutes following stimulation, and that their levels remained constant for about 24 hours, after which they began to increase. Studies on the molecule level demonstrated an increase in the steady state levels of mRNA for DR beta by 15 minutes. Immunoblot analysis of resting T cell lysates using a monoclonal antibody reactive with DR detected a polypeptide of approximately 28 KDa, which agrees with the known molecular mass of the light chain of class II molecules on SDS-PAGE, suggesting that the rapid surface expression might have been due to the presence of pre-formed class II polypeptides. These results demonstrate 1) that T cells defined as resting by conventional criteria contain class II polypeptides and 2) that increases in steady state levels of class II mRNA is a very early event which precedes the initiation of DNA synthesis.

The expression of I-A correlates with the uptake of interferon-gamma by macrophages

The current studies were designed to examine some of the requirements for I-A expression when macrophages (M phi) were treated with interferon-gamma (IFN-gamma). In order to define the minimum time required for IFN-gamma to induce surface expression of I-A antigen on bone marrow-derived M phi, cells were incubated with IFN-gamma for varying lengths of time, washed and thereafter incubated for 72 h before assaying I-A surface expression. Using saturating amounts of IFN-gamma (300 IRU/ml), we found that between 0 and 30 min of IFN-gamma treatment there is a direct correlation between the length of treatment and the level of I-A surface expression. When the steady state level of RNA for the I-A beta gene was assayed, a low level of I-A beta RNA was seen in cells treated for 10 min with saturating amounts of IFN-gamma (300 IRU/ml) while a 30-min or 60-min exposure of cells to the same concentration of IFN-gamma resulted in a steady increase in the level of I-A beta RNA. Similar results were found when we measured the levels of RNA for the tumor necrosis factor and C3 complement genes, both of which are induced by IFN-gamma in M phi. M phi treated with low amounts of IFN-gamma (3 IRU/ml) for 30 min do not express cell surface I-A. Cells incubated continuously for 72 h with 3 IRU/ml of IFN-gamma expressed a level of I-A on the surface equivalent to the level of I-A expressed on cells treated for only 30 min with 300 IRU/ml of IFN-gamma. Based on the observed correlation between either the IFN-gamma concentration or the length of time the cells were exposed to IFN-gamma, or the level of I-A expression on M phi, we conclude that the expression of I-A correlates with the uptake of IFN-gamma.

Regulation of class II MHC gene expression by macrophages from Bcgr and Bcgs mice

The presence of class II mRNA was determined following stimulation of macrophages from Bcgr and Bcgs mice with rIFN-gamma. Despite the continuous expression of surface I-A glycoprotein by macrophages from Bcgr mice, class II mRNA was no longer present. The transient expression of I-A by macrophages from Bcgs mice, however, was accompanied by the disappearance of class II mRNA from the cells. Restimulation of macrophages from Bcgs mice, with rIFN-gamma resulted in the reappearance of class II mRNA and surface I-A expression. The reappearance of class II mRNA and the surface expression of I-A glycoprotein was inhibited by PGE2. These results indicate that differences in I-A expression by macrophages from Bcgr and Bcgs are not at the level of class II gene expression.

IFN-induced modulation of histocompatibility antigens on human cells. Background, mechanisms and perspectives

IFN proteins are a family of lymphokines with anti-viral effects. Several other effects of IFNs have also been described, including enhancement of natural killer (NK) cell activity, enhancement of cytotoxic T-lymphocyte activity, and enhancement of the expression of major histocompatibility complex (MHC) antigens. The latter effects have been characterized as immunomodulatory, whereas the well-known inhibition of growth of malignant cells has been termed anti-proliferative. This review summarizes the current knowledge of the enhancement of MHC products by IFNs. Whereas the basic methodologies for demonstrating the enhancement are simple and reliable, especially when using flow cytometry (FCM), the biological relevance of this reaction is largely unknown. Based on recent findings, however, we have hypothesized that the above-mentioned diverse effects of IFNs are all - in some way or other - related to the classical anti-viral mechanism. This concept proposes that the MHC-enhancing effect of IFNs is a vital part of the immunological defense against virus infections and an integral part of the anti-viral effects of IFN proteins.

Interferon-gamma in vivo. Induction and loss of class II MHC antigens and immature myelomonocytic cells in rat organs

The effects of recombinant rat interferon-gamma on class II major histocompatibility complex antigen expression in vivo were studied by immunohistology in LEW rats after continuous intravenous infusion for three days. Interferon-gamma administration led to a systemic induction of class II molecules in previously negative parenchymal and stromal cells. The induction patterns observed were highly reproducible, but not closely dose dependent within a 25-fold dose difference tested. However, the effect of interferon infusion differed profoundly in individual cell types, and appeared to be related to the differentiation stage of each cell population. Thus, epithelial cells like duct epithelia, urothelium or basal ear skin keratinocytes as well as endothelia in big vessels were strongly and easily induced for class II antigen expression. Parenchymal cells like cardiomyocytes and hepatocytes showed intermediate reactivity, while capillary endothelia, neurons in the brain, straight proximal kidney tubules or endocrine pancreatic islet cells did not express class II antigens. The induced expression was rapidly lost from most cells within one or two days after interferon withdrawal; the only exception occurred in keratinocytes. Long-term alterations were, however, still found 14 days after infusion. Interstitial class II-positive dendritic-shaped cells were increased in the organs and hepatic Kupffer cells carried class II antigens. On conventional histology all organs appeared perfectly normal at this date. After three days of interferon, cells of an immature myelomonocytic phenotype occluded medium-sized and small veins in all organs and occurred in granuloma-like lesions in the liver. Although these cells quickly disappeared after interferon withdrawal they might have been at least partially responsible for single deaths on day three. Our study provides a basis for testing the immunological in vivo function of parenchymal class II antigen expression and its differentiation-specific regulation.

Regulation of the expression of class II genes of the human major histocompatibility complex in tumor cells

The control of expression of human class II MHC genes has been studied in lymphoid and melanoma cells. Specific unmethylation of all restriction sites nearby the promoter regions has been detected in all cell lines and tissues studied, irrespective of their ability to express class II MHC products. The main functional role of DNA methylation appears, on the contrary, to be the regulation of a fraction of the nucleotide polymorphism of class II MHC genes. Constitutive expression of these genes can be modified by recombinant IFN-gamma and by the demethylating agent 5-azacytidine. Both the modifiers differentially regulate the levels of class II MHC and invariant chain products. In melanoma cells IFN-gamma derepresses transcription of a 1.2-Kb HLA-DR alpha mRNA, but does not affect the levels of a 0.8-Kb HLA-DR alpha specific mRNA. These molecular changes are triggered by IFN-gamma through a protein-synthesis-dependent pathway.

Regulation of cell growth by interferon

Interferons can regulate growth and differentiation in a wide range of cell types. These mechanisms are currently being examined. Interferons inhibit the growth of tumour cells and are thus potential anti-cancer agents. They can also inhibit normal cell growth in vitro, and stimulate tumour cell growth in vitro. They may also be involved in some autoimmune diseases. This review examines the effect of interferons on cell proliferation, function, and growth, focusing primarily on in vitro cell systems.

Differential expression of the HLA-DR genes in various melanoma cell lines treated with interferon-gamma: methylation of the HLA-DR alpha gene in these lines is not correlated with its expression

Melanoma cell lines treated with or without interferon-gamma were tested for the presence of DR alpha mRNA and protein. The six lines examined fell into three general categories: two that expressed high levels of DR alpha mRNA and protein before and after interferon-gamma treatment, one that expressed very low levels before treatment with interferon-gamma, but was induced to express high levels after interferon-gamma treatment, and three that expressed very low levels before treatment, and were only slightly inducible after treatment with interferon-gamma. The presence of DR-alpha protein on the melanoma cell surface was always positively correlated with the presence of DR alpha mRNA in the cells. Furthermore, in the cell line that was interferon-gamma-inducible, the time at which DR alpha mRNA and protein appeared and the doses of interferon-gamma needed to induce this appearance were directly correlated. Methylation patterns of the DR alpha gene in these cell lines were also studied in order to determine whether the degree of DR alpha gene methylation among the lines correlated with expression of the gene. Digestion of DNA with the restriction enzyme MspI, which recognizes the sequence 5'CCGG3' and 5'CmCGG3', led to the appearance of a 3.1 kb band from all lines tested. Hpa II digestion, which recognizes 5'CCGG3', but not 5'CmCGG3', led to the appearance of 3.1, 4.4, and 6.7 kb bands in all lines tested except for DUMEL 8, which showed only the 3.1 kb band. Interestingly, DUMEL 8 expressed very low levels of DR alpha mRNA and protein before and after interferon-gamma treatment. We conclude that interferon-gamma has a regulatory effect on DR alpha genes of various melanoma cell lines to varying degrees. This may reflect an effect of interferon-gamma on certain subpopulations of melanocytes in vivo. Our data also indicate that partial methylation of the DR alpha gene does not inhibit its expression. Furthermore, interferon-gamma does not appear to induce expression of the DR gene by altering methylation patterns within the region recognized by our probe.

Immunohistochemical study of HLA class 1 antigens on the hepatocytes of patients with chronic hepatitis B

In order to evaluate the role of histocompatibility antigen (HLA) class 1 antigens in the pathogenesis of liver cell necrosis, HLA class 1 antigens on hepatocytes were studied in the liver biopsy materials from 20 patients with chronic hepatitis B by the peroxidase-labeled antibody method using a monoclonal antibody to human HLA-A, B, C (Cappel Laboratories). Both increased expression of HLA class 1 antigens on the hepatocytes and decreased distribution of intrahepatic hepatitis B core antigen (HBcAg) were observed in patients with an exacerbation of the inflammatory activity. These findings suggest that expression of HLA class 1 antigens on the hepatocytes may be increased when an exacerbation of inflammatory activity develops, and may be compatible with the concept that expression of these antigens plays and important role for the lysis of hepatitis B virus (HBV)-infected liver cells by cytotoxic T cells. Furthermore, in seven patients, expression of HLA class 1 antigens was studied in the liver before and after treatment with human lymphoblast interferon (IFN)-alpha, recombinant IFN-alpha or IFN-beta. Increased expression of HLA class 1 antigens was observed in patients with decreased intrahepatic HBcAg and DNA-P in sera after IFN treatment. These results also suggest that the increase of HLA class 1 antigens by IFN may be related to the immune mechanism for the effective elimination of HBV.

Molecular biology of the H-2 histocompatibility complex

The H-2 histocompatibility complex of the mouse is a multigene family, some members of which are essential for the immune response to foreign antigens. The structure and organization of these genes have been established by molecular cloning, and their regulation and function is being defined by expression of the cloned genes.

Qualitative differences in effects of recombinant alpha-, beta- and gamma-interferons on human peripheral blood leukocytes in vitro

The in vitro effects of bacteria-produced human interferons alpha 2, beta and gamma on several properties of peripheral blood leukocytes from different healthy donors were compared. Treatment with HuIFN-alpha 2 or HuIFN-beta resulted in inhibition of the proliferative response to phytohaemagglutinin and in closely parallel induction of 2'-5'-oligoadenylate synthetase activity. In contrast, HuIFN-gamma had no significant effect on these two activities. However, all three HuIFN were able to enhance natural killer cell cytotoxicity and the expression of HLA-DR surface antigens, with only quantitative variations from donor to donor. Similar results were observed with glycosylated recombinant hamster-cell-derived HuIFN-gamma and with natural HuIFN-gamma. These data demonstrate qualitative differences in the effects of HuIFN-gamma compared to those of HuIFN-alpha 2 or -beta on cells of the immune system.

Expression of extracellular and intracellular human IFN-gamma in mouse L cells transformed with the human IFN-gamma cDNA gene

Cotransformation with a plasmid containing a thymidine kinase gene (pTK2) and a plasmid encoding human IFN-gamma (pTG11) has been used to establish murine L cell lines expressing human IFN-gamma. The HuIFN-gamma gene was present in 30% of the tk+ cell lines and some of these secreted low levels of IFN into the culture medium. Two of the clones obtained after transformation were selected for detailed analysis. Clone 1-12 constitutively secreted very low levels of HuIFN-gamma in the culture medium. This antiviral activity was characterized by its species specificity and antigenicity as authentic human IFN-gamma In contrast, clone 3-47 produced a HuIFN-gamma activity which could only be detected intracellularly. This clone was resistant to infection both by Vesicular stomatitis (VSV) and Mengo viruses and contained increased levels of enzymes known to be induced by interferon. Our results suggest that clone 3-47 produces a non-secreted HuIFN-gamma like molecule which is able to trigger an antiviral state in the murine cell independent of the interaction with a specific IFN-gamma surface receptor.

Control of Ia antigen expression on phagocytic cells of the thymic reticulum by interferon-gamma and prostaglandins

Phagocytic cells of the thymic reticulum (P-TR) spawned in the microenvironment of primary thymic stroma cultures express class II antigens on their membranes. We can show that Ia-antigen expression is regulated by the local secretion of interferon-gamma (IFN-gamma): (a) early primary culture supernatants contain IFN as tested by a cytopathogenic inhibition test after concentration of IFN activity; (b) the addition of a specific anti-IFN-gamma antiserum to primary cultures reduces Ia expression on P-TR suggesting that IFN-gamma produced in situ is implicated in Ia expression; (c) the percentage of Ia+ cells declines as primary cultures age. This phenomenon parallels the disappearance of thymocytes which are the supposed candidate for IFN-gamma secretion. (d) When isolated from their stromal environment and replated in secondary cultures, P-TR lose their membrane Ia antigen which can be re-expressed in the presence of recombinant IFN-gamma, but not IFN-alpha/beta. The decline of Ia expression on P-TR during the aging of primary cultures may be delayed by the inhibition of prostaglandin secretion.