Comparison of human respiratory syncytial virus A2 and 8/60 fusion glycoprotein gene sequences and mapping of sub-group specific antibody epitopes.

The fusion glycoprotein, F, of human respiratory syncytial virus is a principal target of neutralising antibodies and an important protective immunogen. Among sub-group A strains of the virus the F gene is highly conserved. A comparison of F gene sequences of two sub-group B strains, 8/60 and 18537, indicates that the gene also is conserved within this sub-group. However, both limited sequence variability and antigenic variation occurs between F genes from different virus sub-groups. Such variability may be important in the failure of natural- and vaccine-induced immunity and it is thus important to identify the variable epitopes. Three anti-F MAbs exhibiting sub-group specific neutralisation and binding to recombinant F glycoprotein were studied. Comparison of A2 and 8/60 F gene sequences revealed 64 predicted variant amino acids. In order to map the variant amino acids responsible for sub-group specific binding, three sets of chimaeric genes, in which different domains of A2 and 8/60 F were exchanged, were created and expressed. Sub-group specificity mapped to the N-terminal region of F1 for two MAbs (RS2B8 and RS348) and to the C-terminal region for the third. By using site-directed mutagenesis, sub-group specific binding of MAbs RS2B8 and RS348 was attributed to a predicted loop region between residues 200 and 216. This loop carried four residues variant between the sub-groups. Change of at least two was necessary to abrogate MAb binding.

Comparison of cytotoxic T-lymphocyte responses to hepatitis C virus core protein in uninfected and infected individuals.

Cytotoxic T lymphocytes have been implicated in the control of hepatitis C virus (HCV) infection. Recognition by cytotoxic T lymphocytes of epitopes within HCV core protein has been defined previously by in vitro stimulation with synthetic peptides. The aim of this study has been to examine cytotoxic T-lymphocyte responses generated against peptides produced naturally following intracellular processing of viral protein. Antigen-specific cytotoxic T-lymphocyte lines were generated from both HCV uninfected and infected individuals by culturing CD8+ T cells with autologous dendritic cells loaded intracytoplasmically with recombinant HCV core protein. Analysis of the epitopes recognized by core protein-specific cytotoxic T lymphocytes used synthetic peptides that were selected based on their predicted binding to HLA-A*0201 molecules. Core protein-specific cytotoxic T lymphocytes derived from HCV uninfected and infected individuals were able to lyse autologous target cells pulsed with each of 5 predicted epitopes. Generation of HCV-specific cytotoxic T lymphocytes using dendritic cells as antigen presenting cells provides a method of comparing the potential repertoire of cytotoxic T-lymphocyte responses to the responses that occur in chronically infected individuals. No evidence of a qualitatively different response by patient cytotoxic T lymphocytes was apparent which might explain persistence of the virus.

New monoclonal antibodies to oestrogen and progesterone receptors effective for paraffin section immunohistochemistry.

Assessment of oestrogen and progesterone receptors (ER and PgR) in breast cancer is widely used for the prediction of response to endocrine therapy and as a prognostic marker. Cytosolic assays have been replaced in many centres by immunochemical techniques, which have many advantages including applicability to small samples, simplicity, and cost-effectiveness. This study describes the generation and characterisation of two novel murine monoclonal antibodies recognizing ER and PgR, designated NCL-ER-6F11 and NCL-PGR respectively, which are effective in heat-treated formalin-fixed, paraffin-embedded tissue. The antibodies have been characterized by Western blotting and by immunohistochemistry on normal and pathological breast and other tissues. NCL-ER-6F11 has been shown to compare favourably with a currently available ER antibody. These antibodies may prove of value in the assessment of hormone receptor status in human breast cancer.

Hepatitis C virus density heterogeneity and viral titre in acute and chronic infection: a comparison of immunodeficient and immunocompetent patients.

BACKGROUND: Heterogeneities in the buoyant density of hepatitis C virus RNA have been reported in different groups of patients, and have been attributed to differential binding of viral particles to beta-lipoproteins and IgG, and the presence of hepatitis C virus nucleocapsids in circulation. It may be that hepatitis C virus density heterogeneity correlates with the severity of liver disease, hepatitis C virus RNA titre, and the immunocompetence of the patient. METHODS AND RESULTS: We have analysed five immunodeficient patients (one with hypogammaglobulinaemia and selective IgA deficiency, one with X-linked agammaglobulinaemia, three with common variable immunodeficiency) who have been acutely infected with the same batch of intravenous immunoglobulin contaminated with hepatitis C virus (genotype 1a). The course of hepatitis C virus infection in these patients was compared to one immunocompetent patient who presented with acute hepatitis C virus and progressed to chronic disease, and seven immunocompetent patients with chronic hepatitis C. Serum samples were analysed by differential flotation ultracentrifugation in NaCl solution (density 1.063 g/ml). The high and low density fractions were tested for the presence of RNA by RT-PCR. Serum samples were also quantified for hepatitis C virus RNA (Amplicor HCV Monitor kit, Roche Diagnostic Systems). Three quarters of the acutely infected patients analysed presented with low density hepatitis C virus. Low density hepatitis C virus was absent in most chronic infections but persisted in two patients with common variable immunodeficiency. High density hepatitis C virus was detected in the chronic phase in all acutely infected patients in whom the disease persisted, and was present in all samples from PCR-positive patients with chronic infection. Immunodeficient patients had significantly higher hepatitis C virus RNA titres on presentation than immunocompetent patients, but there was no correlation between titre and clinical course of infection. CONCLUSIONS: Heterogeneities in the buoyant density of hepatitis C virus RNA have been identified in the patient groups studied. Low density hepatitis C virus is detected more often in acute infection and high density hepatitis C virus is detected more often in chronic infection. Despite acute infection via the same route of infection with the same hepatitis C virus strain, the five immunodeficient patients studied all followed a different clinical course.

Identification of DEBS 1, DEBS 2 and DEBS 3, the multienzyme polypeptides of the erythromycin-producing polyketide synthase from Saccharopolyspora erythraea.

The ery A region of the erythromycin biosynthetic gene cluster of Saccharopolyspora erythraea has previously been shown to contain three large open reading frames (ORFs) that encode the components of 6-deoxyerythronolide B synthase (DEBS). Polyclonal antibodies were raised against recombinant proteins obtained by overexpression of 3' regions of the ORF2 and ORF3 genes. In Western blotting experiments, each antiserum reacted strongly with a different high molecular weight protein in extracts of erythromycin-producing S. erythraea cells. These putative DEBS 2 and DEBS 3 proteins were purified and subjected to N-terminal sequence analysis. The protein sequences were entirely consistent with the and DEBS 3 proteins were purified and subjected to N-terminal sequence analysis. The protein sequences were entirely consistent with the translation start sites predicted from the DNA sequences of ORFs 2 and 3. A third high molecular weight protein co-purified with DEBS 2 and DEBS 3 and had an N-terminal sequence that matched a protein sequence translated from the DNA sequence some 155 base pairs upstream from the previously proposed start codon of ORF1.

6-Deoxyerythronolide-B synthase 2 from Saccharopolyspora erythraea. Cloning of the structural gene, sequence analysis and inferred domain structure of the multifunctional enzyme.

Sequencing of the eryA region of the erythromycin biosynthetic gene cluster from Saccharopolyspora erythraea has revealed another structural gene (ORF B), in addition to the previously characterised ORF A, which appears to encode a component of 6-deoxyerythronolide-B synthase, the enzyme that catalyses the first stage in the biosynthesis of the polyketide antibiotic erythromycin A. The nucleotide sequence of ORF B, which lies immediately adjacent to ORF A, has been determined. The predicted gene product of ORF B is a polypeptide of 374417 Da (3568 amino acids), which is highly similar to the product of ORF A and which likewise contains a number of separate domains, each with substantial amino acid sequence similarity to components of known fatty-acid synthases and polyketide synthases. The order of the predicted active sites along the chain from the N-terminus is 3-oxoacyl-synthase--acyltransferase--acyl-carrier-protein-- 3-oxoacyl-synthase--acyltransferase--dehydratase--enoylreductase-- oxoreductase--acyl-carrier-protein. The position of the dehydratase active site has been pinpointed for the first time for any polyketide synthase or vertebrate fatty-acid synthase. The predicted domain structure of 6-deoxyerythronolide-B synthase is strikingly similar to that previously established for vertebrate fatty-acid synthases. This analysis of the sequence supports the view that the erythromycin-producing polyketide synthase contains three multienzyme polypeptides, each of which accomplishes two successive cycles of polyketide chain extension. In this scheme, the role of the ORF B gene product is to accomplish extension cycles 3 and 4.

An unusually large multifunctional polypeptide in the erythromycin-producing polyketide synthase of Saccharopolyspora erythraea.

Erythromycin A, a clinically important polyketide antibiotic, is produced by the Gram-positive bacterium Saccharopolyspora erythraea. In an arrangement that seems to be generally true of antibiotic biosynthetic genes in Streptomyces and related bacteria like S. erythraea, the ery genes encoding the biosynthetic pathway to erythromycin are clustered around the gene (ermE) that confers self-resistance on S. erythraea. The aglycone core of erythromycin A is derived from one propionyl-CoA and six methylmalonyl-CoA units, which are incorporated head-to-tail into the growing polyketide chain, in a process similar to that of fatty-acid biosynthesis, to generate a macrolide intermediate, 6-deoxyerythronolide B. 6-Deoxyerythronolide B is converted into erythromycin A through the action of specific hydroxylases, glycosyltransferases and a methyltransferase. We report here the analysis of about 10 kilobases of DNA from S. erythraea, cloned by chromosome 'walking' outwards from the erythromycin-resistance determinant ermE, and previously shown to be essential for erythromycin biosynthesis. Partial sequencing of this region indicates that it encodes the synthase. Our results confirm this, and reveal a novel organization of the erythromycin-producing polyketide synthase, which provides further insight into the mechanism of chain assembly.