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Background: Thymidine analogue resistance mutations (TAMs) selected under treatment with nucleoside analogues generate two distinct genotypic profiles in the HIV-1 reverse transcriptase (RT): (i) TAM1: M41L, L210W and T215Y, and (ii) TAM2: D67N, K70R and K219E/Q, and sometimes T215F. Secondary mutations, including thumb subdomain polymorphisms (e.g. R284K) have been identified in association with TAMs. We have identified mutational clusters associated with virological failure during salvage therapy with tenofovir/emtricitabine-based regimens. In this context, we have studied the role of R284K as a secondary mutation associated with mutations of the TAM1 complex., Results: The cross-sectional study carried out with > 200 HIV-1 genotypes showed that virological failure to tenofovir/emtricitabine was strongly associated with the presence of M184V (P < 10-10) and TAMs (P < 10-3), while K65R was relatively uncommon in previously-treated patients failing antiretroviral therapy. Clusters of mutations were identified, and among them, the TAM1 complex showed the highest correlation coefficients. Covariation of TAM1 mutations and V118I, V179I, M184V and R284K was observed. Virological studies showed that the combination of R284K with TAM1 mutations confers a fitness advantage in the presence of zidovudine or tenofovir. Studies with recombinant HIV-1 RTs showed that when associated with TAM1 mutations, R284K had a minimal impact on zidovudine or tenofovir inhibition, and in their ability to excise the inhibitors from blocked DNA primers. However, the mutant RT M41L/L210W/T215Y/R284K showed an increased catalytic rate for nucleotide incorporation and a higher RNase H activity in comparison with WT and mutant M41L/L210W/T215Y RTs. These effects were consistent with its enhanced chain-terminated primer rescue on DNA/DNA template-primers, but not on RNA/DNA complexes, and can explain the higher fitness of HIV-1 having TAM1/R284K mutations., Conclusions: Our study shows the association of R284K and TAM1 mutations in individuals failing therapy with tenofovir/emtricitabine, and unveils a novel mechanism by which secondary mutations are selected in the context of drug-resistance mutations.

The genotypic determination of HIV tropism to guide the use of maraviroc, the first CCR5 antagonist with specific antiviral activity against CCR5 (R5)-tropic HIV variants, has been widespread in the last two years. Retrospective analyses from maraviroc clinical trials (MOTIVATE and MERIT) demonstrated that specific genotypic tools and the phenotypic assay TrofileTM are comparable in predicting virologic response to maraviroc. Moreover, recent studies performed in cohorts of patients outside clinical trials have reported overall rates of virologic response to maraviroc up to 82% in patients harboring HIV R5-tropic variants according to genotypic tools. Specific technical requirements as well as recommendations for proper HIV tropism determination in the clinical setting have been improving, according to new data reported in several studies related with this issue. This review updates clinical and methodological recommendations for genotypic determination of HIV tropism to guide therapeutic decisions using CCR5 antagonists, considering the most recently reported data.

Objectives: To describe the results of a voluntary reporting system for adverse events in a Patient Safety Program of an occupational injuries mutual insurance company., Method: In 2008 a system of notification and registration of adverse events (actual or potential) was introduced in 2008 by the Union de Mutuas, an occupational injuries insurance company with 36 health centres, and provides coverage for 259,922 workers. The reporting questionnaire covers all areas of health care provided by the mutual company. Access to the questionnaire was conducted through the intranet, was voluntary and anonymous. The notifications registered between 1 January 2009 and 31 December 2010 are analysed., Results: A total of 16 questionnaires were completed, with a total of 205 incidents. The profile of the reporter was first-level health care (57.7%), and seniority in their job for 5-10 years. Of all the notifications, a health care cause of the incident was seen in 43.5% of cases, of which 85.9% of the incidents were preventable. Of all reported events, 71.7% were related to an ambulatory care medical centre, and only 2.4% was related to a surgical procedure., Conclusions: Most of the notifications were preventable incidents, and recorded by first-level medical care. The reporting questionnaire was shown to be a valid tool in our work environment for the detection of adverse events in the care process., (Copyright © 2011 SECA. Published by Elsevier Espana. All rights reserved.)

The RNA interference pathway is a mechanism to regulate gene expression that acts in mammalian antiviral immunity as a complement of interferon- and cytokine-based innate immunity. RNA interference has been proposed as an ancient mechanism against viruses since several components of this system show an effect against viral replication. In fact, protein effectors of this pathway, as well as synthesized microRNA, act against HIV-1, exerting a partial control over HIV-1 latency and replication. Conversely, HIV-1 may counteract this antiviral cell response through two major lines of attack: first, its main regulator Tat suppresses the cellular RNA interference pathway; and second, the virus synthesizes viral microRNA that alter specific cellular functions to enhance HIV-1 replication. As a result of this complex interaction, the microRNA profile in an HIV-1-infected cell is deeply modified. One key application of all this knowledge is the development of pharmacological treatment since microRNA expression can be manipulated and artificial small interference RNA can be delivered into the infected cell to inhibit viral replication. This strategy, combined with current antiretroviral therapy, could be valuable in controlling HIV-1 replication in infected cells.

A double-blinded, controlled study of vaccination of untreated patients with chronic human immunodeficiency virus type 1 (HIV-1) infection with 3 doses of autologous monocyte-derived dendritic cells (MD-DCs) pulsed with heat inactivated autologous HIV-1 was performed. Therapeutic vaccinations were feasible, safe, and well tolerated. At week 24 after first vaccination (primary end point), a modest significant decrease in plasma viral load was observed in vaccine recipients, compared with control subjects (P = .03). In addition, the change in plasma viral load after vaccination tended to be inversely associated with the increase in HIV-specific T cell responses in vaccinated patients but tended to be directly correlated with HIV-specific T cell responses in control subjects.

Despite extensive efforts, a preventive HIV vaccine has not yet been obtained and remains the main challenge in the field of AIDS research. Empirical approaches which have proved successful for many vaccines are not sufficient to tackle HIV-1 and new strategies to design effective preventive AIDS vaccines are critical. To this aim, further understanding of the mechanisms of action of neutralizing antibodies is required. In this review we summarize our current knowledge on the structure of the gp160 viral envelope and the dynamics of viral entry, the evolution of humoral response in HIV-infected patients and the mechanisms of viral escape. Finally, we describe the few neutralizing antibodies with activity against a broad spectrum of circulating HIV strains and their relevance in the design of new candidates to HIV-1 vaccines.

Transcriptional activation of HIV-1 gene expression is partially controlled by the interaction between viral and cellular transcription factors acting at HIV-1 long terminal repeat (LTR) sequences. HIV-1 subtyping at LTR region and nucleotide LTR variability from clinical samples in 48 subjects carrying different HIV-1 subtypes (9A, 5C, 3D, 3F, 21G, 2H, 3J and 2 undefined) at the protease (PR) gene, were performed. LTR sequences from each HIV-1 clade were cloned in luciferase-expression vectors to determine basal and Tat-induced transcriptional activities in the presence and absence of PMA stimulation. A high number (37.8%) of recombinants at LTR/PR regions were identified. All HIV-1 promoters presented low basal transcriptional activity that was nevertheless induced by Tat and PMA. LTR activity was similar across the majority of HIV-1 variants in response to Tat and cell activation. Only subtype C and CRF01&#95;AE LTRs presented higher basal and induced-PMA transcription activities than HXB2 clade B promoter. No basal or Tat/PMA induced activity was found in those promoters presenting G to A hypermutation compared to the wild type promoter activities. G to A hypermutation at some important transcription binding-factor sites within LTR compromised the activity of the viral promoter, decreasing the in vitro viral transcription of the luciferase gene., (Copyright © 2010 Elsevier B.V. All rights reserved.)

The approval of maraviroc (Selzentri®), the first CCR5 antagonist, with specific antiviral activity against CCR5 (R5)-tropic HIV variants, has promoted the determination of HIV coreceptor usage in the clinical setting. The phenotypic assay Trofile™, which is based on recombinant virus technology, has been the most widely used diagnostic test, given that it was the only assay which provided tropism information in the pivotal maraviroc clinical trials. However, this method displays logistical and technical limitations that make it far from convenient as a diagnostic test in clinical practice. Genotypic methods based on V3 genotyping represent a more feasible alternative and progressively are replacing phenotypic assays. Even though their sensitivity to detect X4-tropic variants is lower compared to Trofile™, recent studies have demonstrated that specific genotypic tools (geno2pheno and PSSM) are comparable to Trofile™ and ES-Trofile™ in predicting virologic response to maraviroc. This review summarizes clinical and methodological recommendations for the genotypic determination of HIV tropism to guide therapeutic decisions with CCR5 antagonists in HIV therapeutics.

Once HIV-1 enters the target cell, the first goal in the viral cycle is to integrate into the cellular chromosomes. The irreversible integration as a provirus allows HIV-1 to persist in the infected cell in a quiescent or latent stage that leads to viral escape from immune response and current antiviral treatment. HIV-1 replication is absolutely dependent on different cellular and viral factors that initiate viral expression, acting at the long terminal repeat of the integrated provirus. Accordingly, HIV-1 induces changes in the cellular environment to make possible an efficient replication and production of viral progeny. One main instigator of HIV-1 replication is the viral regulator Tat, which is absolutely required for efficient transcription and elongation of viral transcripts. For this purpose, Tat recruits several cellular proteins to make the chromatin structure accessible for the transcription machinery, to acquire the posttranslational modifications essential for its function, and to produce efficient viral replication. However, the host cell has also several antiviral mechanisms that may act at different steps of the viral cycle to thwart HIV-1 replication. To level the match, HIV-1 encodes accessory proteins, such as Vif and Vpu, which play important roles in HIV-1 pathogenesis by counteracting cellular antiviral factors. The increasing knowledge of viral protein interactions with host cell factors will be essential for the discovery of new targets that could be used to design new therapeutic strategies.

Objective: To investigate the molecular phenotype of the AIDS-onset delaying polymorphism in CXCL12beta 3'UTR (rs1801157)., Methods: The 3 UTRs of the CXCL12beta isoform containing the A or G polymorphic variants were cloned downstream of the Luciferase gene under the control of the CXCL12 promoter. The plasmids were transfected in U373 and LC5 cells and the polymorphism phenotype was evaluated in terms of Luciferase activity and mRNA stability., Results: The 3'A genotype compared to 3'G leads to an increased luciferase activity in unstimulated and PMA+Ionomycin treated cells both in astrocytes (p = 0,0002, p = 0,02) and fibroblasts (p = 0,002, p = 0,03). The mRNA containing the 3'A variant have two-fold longer half-life compared to the 3'G variant (p = 6,99E(-7))., Conclusions: CXCL12beta 3'A polymorphism, previously associated with resistance to AIDS progression and other diseases, leads to increased levels of CXCL12 mRNA, the results presented here demonstrate that this effect is a consequence of an enhanced mRNA stability. Our data contribute to characterize the CXCL12 as a potential pharmacological target in AIDS, autoimmune diseases and cancer.

Although C-MYC is overexpressed in a number of tumors, the mechanisms governing its expression in normal or tumor cells are not completely understood. Recruitment of the Retinoblastoma protein family members to gene promoters by E2F factors has a dominant negative effect on their activity during the G(0) and G(1) phases of the cell cycle. Despite the presence of an E2F-binding site on the C-MYC promoter, it escapes the repressive effect of E2F-Retinoblastoma complexes through unknown mechanisms during exit from quiescence. We hypothesized that occupancy of E2F elements by factors distinct from E2F might account for this escape. To test this hypothesis, we investigated whether the E2F element in the C-MYC promoter is regulated differently than E2F elements in promoters that are activated at the G(1)-S transition. Employing gel shift analysis, the E2F element from the C-MYC promoter was found to form a unique non-E2F complex, referred to as E2F C-MYC Specific (EMYCS), which is not observed with E2F elements from several other promoters. The DNA contact residues for EMYCS are distinct but overlapping with residues required for binding of E2F proteins. Finally, the approximate estimated molecular weight of the DNA-binding component of EMCYS is 105 kDa. Functional studies indicate that EMYCS has transcriptional transactivation capacity and suggest that it is required to activate the C-MYC promoter during exit from quiescence.

There has been a significant increase in research activity into infectious diseases in Spain in the last few years. The Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC) currently has ten study groups, with the cooperation of infectious diseases specialists and microbiologists from different centres, with significant research activity. The program of Redes Temáticas de Investigación Cooperativa en Salud (Special Topics Cooperative Health Research Networks) is an appropriate framework for the strategic coordination of research groups from the Spanish autonomous communities. The Spanish Network for Research in Infectious Diseases (REIPI) and the Network for Research in AIDS (RIS) integrate investigators in Infectious Diseases from multiple groups, which continuously perform important research projects. Research using different experimental models in infectious diseases, in numerous institutions, is an important activity in our country. The analysis of the recent scientific production in Infectious Diseases shows that Spain has a good position in the context of the European Union. The research activity in Infectious Diseases carried out in our country is a great opportunity for the training of specialists in this area of knowledge.

Research carried out on human immunodeficiency virus (HIV) infection illustrates the speed in the transfer of knowledge obtained from basic research to the treatment of patients. Due to studying the viral life cycle and structure and function of HIV proteins, there are currently more than 20 drugs available to treat infected patients. In this article a review is carried out on the biological cycle of HIV, highlighting those steps that represent preferential targets for pharmacological intervention. In the second part of the article, the characteristics of the main antiretroviral families that form the basis of classic antiretroviral treatment are summarised as well as reviewing the recently introduced drugs which are directed at new targets. Finally, an assessment is made of the new prototypes that are in the pre-clinical development phase and which will strengthen the future therapeutic arsenal against HIV infection.

This monograph discusses most important aspects Maraviroc, the development and application perspectives of this drug, as well as main questions raised in its use. Maraviroc is the first CCR5 antagonist approved for treating HIV infection. Its imidazopyridine structure interacts with CCR5 and induces a co-receptor conformation that prevents glycoproteins binding to the viral envelope. It has powerful antiviral activity and acts on a wide spectrum of viruses with affinity for this receptor. This situation means that a tropism test has to be done before treatment to define whether the patient is a carrier of R5 variants. Maraviroc is indicated in HIV infected patients who have received previous antiretroviral treatment. It has a low toxicity and, according to preliminary data, a high genetic barrier. The resistance mechanism is associated with changes in the V3 region which allow the virus to recognise the CCR5 co-receptor bound to the Maraviroc molecule. The main cause of treatment failure is the selection of pre-existing X4 strains not detected by the reference test. Maraviroc can be combined with any other antiretroviral on the market or in clinically advanced development. The indication of Maraviroc in the early phases of the infection is not currently recommended and will depend whether it is shown to be inferior when compared other treatments or a benefit in other pathogenic aspects, such as recovery of CD4 lymphocytes or a reduction in viral reservoirs.

Background: In HIV-infected T lymphocytes, NF-kappaB/Rel transcription factors are major elements involved in the activation of LTR-dependent transcription from latency. Most NF-kappaB heterodimer p65/p50 is sequestered as an inactive form in the cytoplasm of resting T lymphocytes via its interaction with I kappaB inhibitors. In these cells, both absolute HIV latency and low level ongoing HIV replication have been described. These situations could be related to differences in the balance between NF-kappaB and I kappaB alpha ratio. Actually, control of I kappaB alpha by cellular factors such as Murr-1 plays a critical role in maintaining HIV latency in unstimulated T lymphocytes. Formerly, our group demonstrated the presence of nuclear I kappaB alpha in T cells after PMA activation. Now we attempt to determine the dynamics of NF-kappaB/I kappaB alpha nucleocytosolic transport in absence of activation as a mechanism to explain both the maintenance of latency and the existence of low level ongoing HIV replication in resting CD4+ T lymphocytes., Results and Conclusion: We show that the inhibition of the nuclear export by leptomycin B in resting CD4+ T cells resulted in nuclear accumulation of both I kappaB alpha and p65/RelA, as well as formation of NF-kappaB/I kappaB alpha complexes. This proves the existence of a rapid shuttling of I kappaB alpha between nucleus and cytosol even in absence of cellular activation. The nuclear accumulation of I kappaB alpha in resting CD4+ T lymphocytes results in inhibition of HIV-LTR dependent transcription as well as restrains HIV replication in CD4+ T lymphocytes. On the other hand, basal NF-kappaB activity detected in resting CD4+ T lymphocytes was related to low level HIV replication in these cells.

The long terminal repeat (LTR) region of HIV-1 promotes and modulates proviral transcription. LTR genetic variability might influence viral replication and disease progression. Proviral LTR sequences from 32 HIV-1-infected individuals showing different rates of disease progression were examined. Non-progressors (NP, n = 11) were individuals with high and stable CD4 counts and persistently low or undetectable plasma HIV-RNA. Slow progressors (SP, n = 6) were subjects with minimal CD4 decays over time and low plasma HIV-RNA. Typical progressors (TP, n = 15) were individuals with chronic infection showing CD4 counts repeatedly below 500 cells/mul. The mutation frequency within distinct LTR functional regions involved in HIV-1 transcription were compared in these three groups of patients. No significant differences were observed in the mutation frequency in most LTR regulatory sites when comparing the three groups. However, changes in USF regulatory binding sites were more frequent in TP than in SP/NP, while changes in Sp1 binding sites were less common in the former. This is the first study examining the genetic variability of the HIV-1 LTR region in long-term non-progressors showing further divergent outcomes.

Objective: The expansion of an aggressive population of fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA) synovium occurs despite their expression of functional death receptors and exposure to death receptor ligands. FLS can survive Fas challenge because of the constitutive expression of FLIP apoptosis inhibitor. We investigated whether Fas signaling plays a pathogenetic role by activating a nonapoptotic proinflammatory program in RA FLS., Methods: Cultured RA FLS were stimulated with an agonistic anti-Fas antibody in the presence or absence of the caspase inhibitor Z-VAD-FMK or after RNA interference with a short hairpin RNA expression plasmid directed against FLIP. NF-kappaB and activator protein 1 (AP-1) activation was studied by electrophoretic mobility shift assays and p65 immunofluorescence analysis, and expression of messenger RNA (mRNA) for monocyte chemoattractant protein 1, interleukin-8, IkappaB alpha, and matrix metalloproteinases (MMPs) 1, 9, and 13 was examined by reverse transcription-polymerase chain reaction. Chemotactic activity of Fas-activated FLS-conditioned media was studied in Transwell migration assays., Results: Fas stimulation activated NF-kappaB and AP-1, and this response required caspase activity, since Z-VAD-FMK inhibitor precluded it. FLIP was processed to p43 protein after Fas stimulation in a caspase-dependent manner, and inhibition of FLIP expression resulted in reduced Fas-triggered NF-kappaB activation. Fas stimulation increased expression of mRNA for IkappaB alpha, MMPs, and chemokines, and Fas-activated RA FLS displayed increased chemotactic activity for monocytic cells., Conclusion: Fas triggering may contribute to the proinflammatory features of RA FLS by activating NF-kappaB and AP-1 and by expression of relevant target genes, such as MMPs and chemokines. Fas proinflammatory signaling is dependent upon caspase activity and FLIP expression. These data implicate FLIP as a potentially important molecular switch that turns the Fas signaling away from apoptosis and toward induction of a proinflammatory phenotype in RA FLS.

Therapeutic immunization with autologous monocyte-derived dendritic cells (DCs) loaded with heat-inactivated autologous human immunodeficiency virus type 1 (HIV-1) in 12 patients with chronic HIV-1 infection who were receiving highly active antiretroviral therapy (HAART) was feasible, safe, and well tolerated. Virus was obtained during an initial interruption of HAART (hereafter, "stop 1") so that DCs could be pulsed. After immunization and a second interruption of HAART (hereafter, "stop 2"), set-point plasma viral load (PVL; 24 weeks after stop 2) decreased > or =0.5 log(10) copies/mL relative to baseline PVL in 4 of 12 patients. We observed a significant lengthening in mean doubling time of PVL rebound and significant decreases in the area under the curve and the mean peak of PVL rebound after stop 2, compared with those after stop 1. This response was associated with changes in HIV-1-specific CD4(+) lymphoproliferative and CD8(+) T cell responses. These changes were not observed in a group of nonimmunized control patients.

The progressive and irreversible destruction of the immune system represents the hallmark of HIV infection. Even though this process is directly related to the infection of CD4 lymphocytes, the destruction of this lymphocyte population observed along infection is not solely due to a direct cytopathic effect elicited by HIV replication. AIDS immune pathogenesis is an extremely complex phenomenon involving different mechanisms which are not fully understood yet. In this article the mechanisms involved in HIV infection and destruction of target cells and the immune response elicited by HIV are analysed. Finally, viral escape mechanisms to host immune response are considered.

The main goal of this study was to assess the role of mycophenolate mofetil (MMF) during interruption of highly active antiretroviral therapy (HAART). Seventeen patients with early-stage chronic HIV type 1 infection were treated with HAART for 12 months. They were then randomized (day 0) to receive MMF (HAART-MMF group, n = 9) or to continue the regimen (HAART group, n = 6) for 120 additional days. At day 120 in the HAART-MMF group, HAART was discontinued, and MMF administration was continued. The primary end point of the study was the number of individuals maintaining a plasma viral load (VL) set point of <200 copies/mL after at least 6 months off HAART. At day 120, all patients in both groups had undetectable plasma VLs. After 6 months off HAART, 5 of 9 patients in the HAART-MMF group versus 1 of 6 patients in the HAART group maintained a plasma VL of <200 copies/mL (P = 0.28). According to the ability of their plasma to inhibit cellular proliferation, patients were reclassified and divided into an inhibition group (n = 6) and a no inhibition group (n = 9). The doubling time of VL rebound was significantly higher in the inhibition group (mean +/- SE, 10.22 +/- 1.3) than in the no inhibition group (mean +/- SE, 4.6 +/- 1.6; P = 0.03). Moreover, 5 of 6 patients in the inhibition group maintained a plasma VL of <200 copies/mL versus 1 of 9 patients in the no inhibition group (P = 0.005) after 6 months off HAART. We found that combining MMF and HAART delayed VL rebound and improved control of viral replication without HAART but only when inhibition of lymphocyte proliferation was achieved.

The double-stranded RNA (dsRNA)-dependent protein kinase PKR activates NF-kappa B via the I kappa B kinase (IKK) complex, but little is known about additional molecules that may be involved in this pathway. Analysis of the PKR sequence enabled us to identify two putative TRAF-interacting motifs. The viability of such an interaction was further suggested by computer modeling. Here, we present evidence of the colocalization and physical interaction between PKR and TRAF family proteins in vivo, as shown by immunoprecipitation and confocal microscopy experiments. This interaction is induced upon PKR dimerization. Most importantly, we show that the binding between PKR and TRAFs is functionally relevant, as observed by the absence of NF-kappa B activity upon PKR expression in cells genetically deficient in TRAF2 and TRAF5 or after expression of TRAF dominant negative molecules. On the basis of sequence information and mutational and computer docking analyses, we favored a TRAF-PKR interaction model in which the C-terminal domain of TRAF binds to a predicted TRAF interaction motif present in the PKR kinase domain. Altogether, our data suggest that TRAF family proteins are key components located downstream of PKR that have an important role in mediating activation of NF-kappa B by the dsRNA-dependent protein kinase.

Plasma stromal cell-derived factor (SDF)-1 levels, SDF1-3'A polymorphism, and CXCR4(+) T lymphocytes in relation to resistance to human immunodeficiency virus (HIV)-1 infection and its progression were investigated in a study of HIV-positive patients, exposed but uninfected (EU) subjects, and healthy control subjects, all lacking CCR5 Delta 32 homozygosity. SDF1-3'A homozygosity was associated with low plasma SDF-1 levels in uninfected persons and was not related to long-term nonprogression. HIV-1 infection involved increased plasma SDF-1 levels, which were not attributable to any kind of chronic viral infection, because all EU hemophiliacs were hepatitis C virus-positive but had normal SDF-1 levels. High plasma SDF-1 levels and low CXCR4 expression on T lymphocytes was associated with long-term nonprogression, whereas in advancing disease expression of CXCR4 increased, accompanied by a decrease in plasma SDF-1 during the more advanced stages of HIV-1 infection. EU subjects with sexual exposure to HIV-1, but not EU hemophiliacs, showed an underpresentation of SDF1-3'A allele frequency, which was coupled with high plasma SDF-1 levels and low CXCR4 expression.

Molluscum contagiosum virus (MCV) is a human poxvirus that causes abnormal proliferation of epithelial cells. MCV encodes specific molecules to control host defences, such as MC159L, which as previously shown prevents apoptosis induced by death receptors. However, unlike most poxviruses, MCV lacks a homologue to the E3L and K3L proteins of vaccinia virus, which are involved in the control of the key antiviral and pro-apoptotic dsRNA-dependent protein kinase, PKR. In this study, we analysed the relationship of MC159L to PKR. We found that MC159L is not a direct inhibitor of PKR since it does not associate with PKR and cannot block PKR-induced phosphorylation of eIF-2alpha. However, expression of MC159L inhibits apoptosis triggered by PKR through death receptor-mediated pathways. In addition, MC159L inhibits NF-kappaB activation induced in response to PKR. Expression of MC159L cannot counteract the PKR-mediated antiviral action in the context of a poxvirus infection, despite its ability to affect these signalling events. These findings show that MC159L is able to interfere with downstream events triggered by PKR in the absence of a direct physical interaction, and assign a role to MC159L in the control of some PKR-mediated biological effects.