Identification of regions of poliovirus 2BC protein that are involved in cytotoxicity

The expression of poliovirus 2BC protein in yeast and mammalian cells leads to a number of metabolic and morphological alterations, such as growth inhibition, intracellular membrane proliferation, blockade of the exocytic pathway, and enhanced membrane permeability. Yeast cells that express poliovirus 2BC in an inducible manner were used to identify the regions of 2BC implicated in the modifications of these cellular functions. Several 2BC deletion mutants were generated to define the minimal portion of 2BC required to alter these activities. Additional deletion mutants that were obtained by random mutagenesis followed by selection in yeast cells provided new insights into the structure and mechanism of action of 2BC. The activity responsible for membrane proliferation is located in 2C, while the activities responsible for membrane permeabilization and inhibition of the exocytic pathway are located in 2B. Several regions of 2B and 2C required for the different functions of 2BC were identified. Thus, the integrity of the N termini of both 2B and 2C is necessary for 2BC-induced cytotoxicity. It is also possible to separate the different cellular alterations provoked by 2BC by the use of several 2BC variants. Deletion of amino acids 52 to 65 in 2B generates a 2BC deletion variant, 2bC deltaAvrII, that still blocks yeast growth but is unable to enhance membrane permeability or to inhibit the exocytic pathway. On the other hand, 2Bcl28*.32b and 2Bcl28*.3c, which contain only 73 and 77 amino acids of 2B, interfere with yeast division and enhance membrane permeability but affect the exocytic pathway only weakly and do not induce membrane proliferation. Our findings indicate that Saccharomyces cerevisiae represents a useful model system to analyze the functions of poliovirus 2BC and show the feasibility of separating the activities assigned to this protein.

Prognostic factors in primary gastrointestinal non-Hodgkin's lymphoma: a multivariate analysis of 76 cases

OBJECTIVE

To present our experience with the treatment of primary gastrointestinal (GI) non-Hodgkin's lymphoma, evaluate prognostic factors, and give our recommendations for treatment.

DESIGN

Retrospective study.

SETTING

Teaching hospital, Spain.

SUBJECTS

76 patients (47 men and 29 women, mean age 51 years) treated over the 15 years 1980-1994.

INTERVENTIONS

52 patients had radical resections, 19 palliative resections, and 5 biopsy alone. 42 (55%) also had adjuvant chemotherapy and 20 (26%) radiotherapy.

RESULTS

Patients with primary intestinal lymphoma were slightly but not significantly younger than those with gastric lymphoma (43 compared with 56 years). 43 Patients (57%) had tumours in the stomach, 26 (34%) in the small bowel, and 7 (9%) in the colon. At presentation 34 had stage I disease, 25 stage IIE1 disease, and the remaining 17 stage IIE2; 14 were classified as low grade, 41 as intermediate, and 21 as high grade. 60 (79%) had a B-cell phenotype. Overall 5-year survival was 53%. Of the 11 variables tested by univariate analysis for their prognostic effect only abdominal mass (p < 0.001), clinical stage (p < 0.001), type of operation (p < 0.001), tumour size (p < 0.05), and histological grade (p < 0.05) achieved significance, but when Cox's multivariate analysis was applied only clinical stage was significant (p < 0.01).

CONCLUSION

Operation is the treatment of choice, but chemotherapy and radiotherapy may have a role though as yet there are no standard guidelines for their use.

Immunohistochemical characterization of hepatic lesions associated with Elaeophora elaphi parasitism in red deer (Cervus elaphus)

This study was based on the immunohistochemical characterization of hepatic lesions caused by Elaeophora elaphi in 15 red deer. In eight animals filariae were found in branches of the portal vein. "Web-like" endophlebitis (15 cases), lymph nodule-like thrombi associated with filarial debris (12 cases) and fibrinous thrombi (three cases) were also observed in the portal vein. Multifocal granulomatous hepatitis (six cases) and lymph nodule-like tissue (three cases) were found in the liver parenchyma. The distribution of CD3 antigen, IgG-lambda light chains, and S-100 protein in lymphoid tissue in the portal vein thrombi and hepatic parenchyma was similar to that found in the cortex of the lymph nodes. In these lesions, lymphoid follicles with large germinal centres (mainly composed of IgG+ B lymphocytes, with occasional S-100+ follicular dendritic cells) predominated over interfollicular lymphoid tissue (mainly composed of CD3+ T lymphocytes and S-100+ interdigitating cells). This suggested that the local humoral immune response was more important than the cellular response in this parasitic disease. The presence of interdigitating and follicular dendritic cells confirmed the high degree of organization of the abnormal lymphoid tissue and suggested that antigen presentation to T and B lymphocytes and the subsequent proliferation of the latter was particularly efficient in such tissue. The latter may therefore be superior to diffuse granulomatous infiltrate in terms of the production of a local immune response.

Effect of nitric oxide on poliovirus infection of two human cell lines

The role of nitric oxide after poliovirus infection of the human HeLa (carcinoma) and U937 (promonocytic) cell lines has been analyzed. Both types of cells produced detectable levels of nitric oxide after poliovirus infection. However, this production was not sufficient to limit viral productivity. On the other hand, pretreatment with the nitric oxide donor glycerine trinitrate lengthened the course of poliovirus infection.

Thrombocytopenia associated with apoptotic megakaryocytes in a viral haemorrhagic syndrome induced by a moderately virulent strain of African swine fever virus

A viral haemorrhagic syndrome was induced in 14 pigs by inoculation with an African swine fever (ASF) virus strain of moderate virulence, to determine changes in megakaryocyte (MK) numbers and morphology and thus to assess the role of these cells in the thrombocytopenia characteristic of subacute ASF. The strain tested induced changes in the proportion of different types of MK (typical nucleated MKs, apoptotic MKs and immature MKs); it also caused subcellular lesions over the first 7 days post-inoculation (dpi). At 7 dpi, severe thrombocytopenia was observed. There was a statistically significant increase in apoptotic MK numbers. The MKs showed three stages in the course of the disease: a compensatory stage, represented by cytoplasmic projections, a hypermaturity stage, represented by apoptotic MKs, and a regenerative stage, represented by clusters of immature MKs. These changes, especially the presence of numerous apoptotic MKs, may explain the early and transitory thrombocytopenia detected in subacute ASF. The large number of apoptotic MKs observed may be associated with the accelerated maturation of these cells, resulting from the action of cytokines, or peripheral platelet consumption, or both.

High-resolution ultrasound associated with aspiration biopsy in the follow-up of patients with differentiated thyroid cancer

OBJECTIVE: To assess the value of ultrasound in the follow-up of patients undergoing surgery for differentiated thyroid carcinoma.

SUBJECTS: The study included 89 patients (70 women and 19 men) with differentiated thyroid carcinoma (76 papillary and 13 follicular cancer).

METHODS: High-frequency ultrasound (US) was used in the evaluation of 89 subjects who underwent surgery for thyroid carcinoma. Fine-needle aspiration was performed in cases with positive US. In addition, determinations of thyroglobulin (Tgb) in serum, scintigraphy with 131I, and cervical palpation were evaluated. We determined sensitivity, specificity, and overall accuracy for each of these diagnostic methods.

RESULTS: Ultrasonography was positive in 22 subjects, 16 in the nodal area and 6 in the thyroid bed. Twenty-two subjects received fine-needle aspiration with US control; 13 (59%) of 22 were positive for cancer. The results of the US for detecting neoplastic disease showed a sensitivity of 65%, specificity of 86%, and overall accuracy of 82%. The overall accuracy for scintigraphy was 88% and for Tgb, 91%.

CONCLUSION: We concluded that US can be included in the follow-up protocol for patients undergoing surgery for differentiated cancer of thyroid, as a valuable tool to localize the recurrence. This technique is particularly useful in the evaluation of patients who are found to have elevated Tgb levels.

The treatment of differentiated thyroid cancer includes surgery and, in some cases, the ablation of residual thyroid tissue with therapeutic doses of iodine 131I. 1 The posttreatment search for recurrence or metastases is based on periodic body scanning with 131I and determination of serum thyroglobulin (Tgb) levels. 2,3

High-resolution ultrasound (US; 10 MHz) has been found to have a high sensitivity in diagnosing nonpalpable cervical masses. 4–6 Thus the possibility exists that including it in the protocols for follow-up of differentiated thyroid cancer may be valuable.

The aim of our study was to assess the value of high-resolution US (associated with directed fine-needle aspiration [FNA] biopsy) in the follow-up of patients undergoing surgery for papillary and follicular thyroid cancer.

Equine pulmonary mycosis due to Aspergillus niger and Rhizopus stolonifer

Invasive pulmonary mycosis caused by Aspergillus niger and Rhizopus stolonifer is reported in a 2-year-old horse, one of three that died after being housed in a disused, uncleaned stable. Lesions were characterized by thrombosis of the blood vessels with haemorrhage and tissue necrosis. Fungal hyphae were observed both in thrombosed vessels and in adjacent necrotic tissue. In culture media inoculated with lung samples and samples from the bedding hay, two types of colony were recorded and identified as A. niger and R. stolonifer. This study is the first description of equine pulmonary mucormycosis and of A. niger as an aetiological agent in the horse.

Membrane permeability changes induced in Escherichia coli by the SH protein of human respiratory syncytial virus

The small hydrophobic (SH) protein of human respiratory syncytial virus (HRSV) has been efficiently expressed in Escherichia coli. In analogy to small hydrophobic proteins encoded by other RNA viruses, membrane permeability changes to low-molecular-weight compounds were detected in bacteria expressing HRSV SH protein. These changes implied, at least, the entry of both the protein synthesis inhibitor hygromycin B and the beta-galactoside substrate o-nitrophenyl-beta-d-galactopyranoside and the exit of preloaded [3H]uridine from bacterial cells. Site-directed mutagenesis indicated that the C-terminal end of SH is needed for induction of membrane permeability changes. In addition, amino acid substitution at residue 32 (Ile to Lys) abolished that activity. This was correlated with a drastic increase in SH electrophoretic mobility and a decrease of the predicted values of alpha-helix for all residues of the SH transmembrane domain. Other sequence changes have either partial effect or no effect on the membrane permeability changes induced by the SH protein. However, none of the mutations abrogated the association of SH protein with bacterial membranes, indicating that incorporation of SH protein to membranes is not sufficient to induce the observed changes. Membrane permeability changes then might provide a useful test for the identification of key amino acid residues in this unique HRSV gene product.

Poliovirus protein 2BC increases cytosolic free calcium concentrations

Poliovirus-infected cells undergo an increase in cytoplasmic calcium concentrations from the 4th h postinfection. The protein responsible for this effect was identified by the expression of different poliovirus nonstructural proteins in HeLa cells by using a recombinant vaccinia virus system. Synthesis of protein 2BC enhances cytoplasmic calcium concentrations in a manner similar to that observed in poliovirus-infected cells. To identify the regions in 2BC involved in modifying cytoplasmic calcium levels, several 2BC variants were generated. Regions present in both 2B and 2C are necessary to augment cellular free calcium levels. Therefore, in addition to inducing proliferation of membranous vesicles, poliovirus protein 2BC also alters cellular calcium homeostasis.

Abnormal antler growth associated with testicular hypogonadism in red deer

A wild 5-yr-old red deer (Cervus elaphus) was eulled from a privately owned herd because of deformed antlers, retained velvet and bilateral symmetrical testicular hypogonadism. The clinical and pathological changes seen in this deer were most consistent with congenital hypoplasia, but testicular atrophy was an alternative possibility for the etiology of their condition.

Cleavage of p220 by purified poliovirus 2A(pro) in cell-free systems: effects on translation of capped and uncapped mRNAs

Poliovirus protease 2A(pro) has been obtained in soluble form as a fusion protein with maltose binding protein (MBP). Addition of MBP-2A(pro) to rabbit reticulocyte cell-free systems gives rise to efficient cleavage of the initiation factor of translation p220 (eIF-4G). Translation of capped mRNA encoding the influenza virus NP protein is severely impaired in lysates in which p220 has been proteolytically cleaved. This inhibition is dependent on the concentration of mRNA added to the lysate. Thus, increasing the concentrations of mRNA substantially overcomes the blockade of NP synthesis after p220 cleavage. Notably, translation of uncapped NP mRNA is also compromised in p220-deficient rabbit reticulocyte lysates, suggesting that p220 participates in the translation of both capped and uncapped NP mRNAs. The effects of p220 proteolysis by poliovirus 2A(pro) have also been assayed on luciferase mRNA translation. Three types of mRNAs encoding for luciferase have been examined: capped, uncapped, and mRNA bearing the poliovirus 5' leader region (leader luc mRNA). Synthesis of luciferase directed by any of these mRNAs was inhibited after cleavage of p220 in rabbit reticulocyte lysates. Interestingly, supplementation of the lysate with HeLa cell extracts stimulates leader luc mRNA translation by poliovirus 2A(pro). These results indicate that activation of translation of mRNAs bearing the poliovirus leader region promoted by this poliovirus protease requires a factor present in HeLa cell extracts. These findings agree well with recent experiments implicating p220 not only in protein synthesis directed by capped mRNAs but also in the translation of naturally uncapped mRNAs.

Focal mesangial-sclerosing glomerulonephritis and acute-spontaneous infectious canine hepatitis: structural, immunohistochemical and subcellular studies

The glomerular alterations observed in a dog with acute spontaneous infectious canine hepatitis (ICH) are described. Histologic changes of the glomeruli were enlargement of the mesangium with presence of intranuclear inclusion bodies and without proliferation of mesangial cells. Electron microscopy revealed adenovirus replication sites in glomerular mesangial cells and in endothelial cells of glomerular capillaries, as well as a focal mesangial-sclerosing glomerulonephritis associated with electron dense deposits which were closely related with extracellular ICH viral particles and immunohistochemically reactive for immunoglobulin (Ig) G, IgA, IgM and C3c complement components.

Poliovirus infection and expression of the poliovirus protein 2B provoke the disassembly of the Golgi complex, the organelle target for the antipoliovirus drug Ro-090179

Infection of Vero cells with poliovirus results in complete disassembly of the Golgi complex. Milestones of the process of disassembly are the release to the cytosol of the beta-COP bound to Golgi membranes, the disruption of the cis-Golgi network into fragments scattered throughout the cytoplasm, and the disassembly of the stacked cisternae by a process mediated by long tubular structures. Transient expression of the viral protein 2B in COS-7 cells also causes the disassembly of the Golgi complex by a process preceded by the accumulation of the protein in the Golgi area. Vero cells infected for 3 h show no recognizable Golgi complexes at the ultrastructural level and display an enormously swollen endoplasmic reticulum (ER) with extensive areas of its surface heavily coated. Ro-090179 (Ro), a flavonoid isolated from the herb Agastache rugosa, provokes the specific swelling and disruption of the Golgi complex and strongly inhibits poliovirus infection. Ro provokes the swelling and the disruption of the stacked cisternae and trans-Golgi elements without affecting the cis-most Golgi cisternae much. Moreover, Ro inhibits the fusion of the Golgi complex with the ER in cells treated with brefeldin A and provokes the accumulation of the intermediate compartment membrane protein p58 into ERD2-positive Golgi elements but has no effect on the anterograde transport involved in protein secretion. Our results indicate that the secretory pathway and specifically the Golgi complex are preferential targets of poliovirus.

Cefminox versus Cefoxitin in Hysterectomy Prophylaxis : Clinical Efficacy and Serum and Tissue Concentrations

This phase III, prospective, randomised, open, controlled clinical trial compared the efficacy of single-dose cefminox (2g) versus triple-dose cefoxitin (2g every 4 hours) as antibiotic prophylaxis in 112 women undergoing gynaecological surgery (vaginal or abdominal hysterectomy). Peak, intraoperative and trough serum concentrations were determined for both antibiotics, as well as their concentrations in myometrial tissue in a subset of patients from the study (22 patients from the cefminox group and 18 from the cefoxitin group). Clinical response was satisfactory in all women treated with cefminox (59 of 59) and in 52 of 53 patients treated with cefoxitin. Fever-related morbidity, hospital stay and adverse reactions were similar in both groups. Peak serum concentrations were 132.3 mg/L for cefminox and 82.2 mg/L for cefoxitin. 12-hour concentrations were 2.82 mg/L for cefminox and 2.17 mg/L for cefoxitin, and were higher than the respective minimum inhibitory concentrations (MICs) for pathogens commonly associated with this pathology. Uterine tissue concentrations were 24.5 and 41.6 mg/L for cefminox and cefoxitin, respectively, and also clearly exceeded MIC. It was shown that the use of a single preoperative dose of cefminox was similar in efficacy to 3 doses of cefoxitin administered every 4 hours, and that the serum and tissue concentrations attained provide adequate antibiotic coverage. In view of the general trend towards the use of a single dose for prophylaxis, cefminox offers a new alternative for antibiotic prophylaxis in gynaecological surgery.

The N-terminal Arg-rich region of human immunodeficiency virus types 1 and 2 and simian immunodeficiency virus Nef is involved in RNA binding

Comparison of the amino acid sequences of human immunodeficiency virus (HIV) Nef protein and several RNA-binding proteins shows similarities in some regions of these proteins. Thus, poliovirus protein 2C, an RNA-binding protein, shares with Nef the sequence YXQQ...MDD...DXXD. In addition, both proteins contain an Arg-rich motif that, in the case of poliovirus 2C, is involved in RNA-binding activity. Moreover, the RNA-binding, anti-terminator N proteins of lambda, phi21 and P22 phages show sequence similarities with HIV Nef at the Arg-rich motif. To assess the significance of this motif, native and deletion variants of Nef protein were assayed for RNA-binding activity. The N-terminal 35 amino acids of HIV-1 Nef that comprise the Arg-rich motif are sufficient for RNA binding. Point mutations engineered at the Arg-rich motif of HIV-1 Nef revealed that basic amino acid residues are essential for RNA-binding activity. The Nef proteins from HIV-2 and SIV can also interact with RNA, while the same proteins with the N-terminal Arg-rich domain truncated fail to interact with RNA. These findings indicate that all three Nef proteins from HIV-1, HIV-2 and simian immunodeficiency virus belong to the RNA-binding family of proteins. The three proteins contain an Arg-rich region at the N-terminus which is necessary to interact with RNA.

The yeast Saccharomyces cerevisiae as a genetic system for obtaining variants of poliovirus protease 2A

The inducible expression of poliovirus protease 2A (2Apro) blocks the growth of Saccharomyces cerevisiae. A number of yeast colonies that grow after 2Apro induction have been isolated. The majority of these clones express 2Apro to control levels, suggesting that their ability to divide is not due to the loss of 2Apro gene inducibility. The sequences of the 2Apro genes isolated from 22 clones were determined. Most of the 2Apro sequences from these colonies contain point mutations in the poliovirus protease. The different variant protease sequences were transferred to an infectious poliovirus cDNA clone. Translation of genomic RNA obtained from these poliovirus mutants in cell-free systems revealed that some of them had defects in their ability to cleave P1-2A in cis. In addition, several of these variants cleaved the translation initiation factor eIF-4G inefficiently. Transfection of the RNA generated from the full-length poliovirus genomes mutated in 2Apro yielded five viable polioviruses with a small plaque phenotype. These five polioviruses efficiently cleaved p220 but showed defects in viral protein synthesis, transactivation of a leader-luciferase mRNA, and 3CD cleavage to 3C' and 3D'. All 2Apro mutant sequences, including those that did not yield viable viruses, were cloned in pTM1 vector under a T7 promoter. Only the 2Apro variants that have activity to cleave 3CD produced viable poliovirus. Our findings indicate that S. cerevisiae represents a useful system for obtaining poliovirus 2Apro variants that may provide further insight into the role of this protease during the poliovirus replication cycle.

Ultrastructural changes related to the lymph node haemorrhages in acute African swine fever

In order to determine the pathogenic mechanisms involved in lymph node haemorrhages in acute African swine fever (ASF), eight pigs were inoculated with ASF virus, strain Malawi'83. Lymph node haemorrhages were observed from three days post infection (dpi) onwards, coinciding with ASF virus replication in monocytes and macrophages adjacent to stimulated endothelial cells, phagocytic stimulation of capillary and small-vessel endothelial cells, increase in the number of fenestrations of endothelial cells, and endothelial cell loss, as well as clusters of blood cells and necrotic material beneath the endothelium. Vascular lumina were blocked by platelet plugs and fibrin microthrombi. These phenomena became more marked as the disease progressed. At five dpi, virus replication was also found in circulating neutrophils. At seven dpi, lesions were more intense and were accompanied by virus replication in sinus and capillary endothelial cells, and in other cell populations including pericytes, fibroblasts, smooth muscle fibres and reticular cells. The results obtained in this study suggest that lymph node haemorrhages are related to endothelial stimulation and the onset of disseminated intravascular coagulation. Virus replication in vessel wall cells occurs only in the final stages of the disease and plays a secondary role.

Permeabilization of mammalian cells to proteins: poliovirus 2A(pro) as a probe to analyze entry of proteins into cells

Two hybrid protein molecules containing the poliovirus protease 2A (MBP-2A(pro)) (maltose-binding protein-2A(pro) and MBP-Pseudomonas exotoxin A-2A(pro)) have been constructed and purified. Both hybrid proteins efficiently cleave the translation initiation factor eIF-4G when they are co-internalized into cells with adenovirus particles. Almost no intact eIF-4G can be detected in cells incubated with these proteins following this method. Reovirus infectious subviral particles also promote the delivery of MBP-2A(pro) into cells, although less efficiently than adenovirus particles. None of the other methods employed to permeabilize cells to MBP-2A(pro) achieves the degree of eIF-4G cleavage observed with adenovirus particles. By comparison about 30% of cells electroporated with MBP-2A(pro) still contain intact eIF-4G. More drastic electroporation conditions lead to a significant decrease of cell survival. Osmotic lysis of pinocytic vesicles resulted in 30% of the eIF-4G being cleaved in cells treated in suspension. Delivery of MBP-2A(pro) by pH-sensitive liposomes leads to poor hydrolysis of eIF-4G. Taken together our results indicate that permeabilization of cells with adenovirus particles is the most efficient method for introducing MBP-2A(pro) into cells.

Ultrastructural findings in natural canine hepatozoonosis

The ultrastructure of several stages of Hepatozoon canis found in dogs with clinically and histologically diagnosed infections was determined using transmission electron microscopy. Merozoites, macro- and microschizonts and gamonts were found in spleen, liver, kidneys and lungs. Macro- and micromeronts were characterized by their size and by the presence of intracytoplasmic amylopectin granules. Gamonts, which provide the basis for clinical diagnosis of the disease, were observed within mononuclear cells (monocytes/macrophages); they were butterfly-shaped and exhibited varying electron densities. On the basis of the microscopic observations reported here, it is clear that the life cycle of H. canis is a complex one.

African swine fever virus infection of bone marrow: lesions and pathogenesis

The effects of African swine fever (ASF) virus infection on bone marrow hematopoiesis and microenvironment were determined by studying the sequential development of ultrastructural lesions of bone marrow and blood cell changes. Eight pigs (two pigs/infected group) were inoculated by intramuscular route with 10(5) 50% hemadsorbing doses (HAD50) of the Malawi'83 ASF virus isolate. Two uninfected pigs were used as controls. Ultrastructural changes developed by day 3 postinoculation (PI), persisted through day 7 PI, and were characterized by activation of macrophages. From day 5 PI, viral replication was observed in monocytes/macrophages, reticular cells, immature neutrophils, and promonocytes. Also viral replication was detected in megakaryocytes, endothelial cells, and pericytes at day 7 PI. Vascular alterations consisted of activation of sinusoidal endothelial cells, intravascular coagulation, and fibrin strands interspersed among microenvironment and hematopoietic cells. No significant changes were observed in total white blood cells counts, percentage of monocytes, and platelet counts; however, severe lymphopenia and neutrophilia were detected from day 3 PI. Results of this experiment indicate that there is increased hematopoiesis in bone marrow during acute ASF, coinciding with macrophage activation. Neither vascular changes nor viral replication in different bone marrow cell populations gave rise to impaired bone marrow function. Increased hematopoiesis would exert a positive influence by preventing the early onset of thrombocytopenia and would exert a negative influence by stimulating the spread of the virus via neutrophils. Increased hematopoiesis would be unable to compensate for the lymphopenia.

Entry of Semliki forest virus into cells: effects of concanamycin A and nigericin on viral membrane fusion and infection

Semliki forest virus (SFV) was biosynthetically labeled with pyrene phospholipids and used to investigate two alternative routes of entry of SFV into BHK-21 cells: (1) receptor-mediated endocytosis followed by fusion of the viral envelope with the endosomal membrane and (2) direct fusion of SFV with the plasma membrane induced by low pH treatment. The selective inhibitor of the vacuolar proton-ATPase, concanamycin A, abolished fusion and subsequent infection only when the virus utilized the endocytic route to enter cells. The inhibitory effect of this macrolide antibiotic was bypassed by low pH treatment of cells. However, the ionophore nigericin was inhibitory irrespective of the route used by the virus to infect cells, suggesting the necessity of a transmembrane pH gradient for the entry process. According to our results, concanamycin A emerges as a suitable tool for selectively investigating the involvement of endosomal function in animal virus entry.