Immunoassay for serologic diagnosis of influenza type A using recombinant DNA produced nucleoprotein antigen and monoclonal antibody to human IgG

Molecular and phylogenetic analysis of human influenza virus among Iranian patients in Shiraz, Iran

Influenza is a viral respiratory pathogen responsible for frequent seasonal epidemics. There are currently three major human influenza viruses in global circulation namely A/H1N1, A/H3N2, and B. The objective of this study was to determine the human influenza virus genotypes in Shiraz, the capital of the Fars province of Iran. Three hundred patients suspected with human influenza virus infection were enrolled in this survey (2004-2005). The throat samples were cultured and titrated by hemagglutination (HA) assay. Typing and subtyping were performed by an in-house developed multiplex RT-PCR. Moreover, the phylogenetic analysis was carried out for HA gene. A total of 24 samples were found to be positive for human influenza virus infection, 17 H1N1 and 7 H3N2. These results were in agreement with the HI assay. The phylogenetic analysis results revealed that the Iranian H1N1 isolated were close to the A/New Caledonia/20/99 vaccine strain genetically and the Iranian H3N2 isolates were also related closely to the Fujian/411/021 and California/7/2004 vaccine strains. However, a slight genetic drift was found in these isolates. In conclusion, it was demonstrated that both influenza A subtypes A/H1N1 and A/H3N2 were dominant among Iranian patients in Shiraz during the 2004/5 winter season.

Advances in the diagnosis of respiratory virus infections

Background: Advances have been made in selecting sensitive cell lines for isolation, in early detection of respiratory virus growth in cells by rapid culture assays, in production of monoclonal antibodies to improve many tests such as immunofluorescence detection of virus antigens in nasopharyngeal aspirates, in highly sensitive antigen detections by time-resolved fluoroimmunoassays (TR-FIAs) and biotin-enzyme immunoassays (BIOTH-E), and, finally, in the polymerase chain reaction (PCR) detection of respiratory virus DNA or RNA in clinical specimens. All of these advances have contributed to new or improved possibilities for the diagnosis of respiratory virus infections.

Objectives and study design: This review summarizes our experiences during the last 15 years in the development of diagnostic tests for respiratory virus infections, and in use of these tests in daily diagnostic work and in epidemiological studies.

Results: Immunofluorescence tests based on monoclonal antibodies, all-monoclonal TR-FIAs, and biotin-enzyme immunoassays (EIAs) have about the same sensitivities and specificities. They compare well with the sensitivity of virus culture. PCR followed by liquid-phase hybridization is a sensitive method for detecting adenovirus DNA and enterovirus and rhinovirus RNA in clinical specimens. IgG EIA on paired acute and convalescent phase sera is the most sensitive serological test for respiratory virus infections and is a valuable reference method when evaluating the sensitivity of new diagnostic tests. The IgG avidity test can distinguish primary infections from re-infections at least in respiratory syncytial virus (RSV) infections. IgM antibody assays, on the other hand, had low sensitivities in our studies.

Conclusions: The choice of diagnostic methods for respiratory virus infections depends on the type and location of the laboratory, the number of specimens tested, and the previous experience of the laboratory. Virus culture, whenever possible, should be the basic diagnostic method; the results, including identification of the virus, should be available no more than 24 h later than the results of rapid diagnostic tests. In small laboratories, especially in hospitals where specimen transportation is well organized, immunofluorescence may be the best choice for antigen detection with the provision that an experienced microscopist and a good UV microscope are available. If the laboratory receives a large number of specimens and has previous experience with EIAs, then biotin-EIAs or TR-FIAs may be the most practical techniques. Their advantages include the stability of the antigens in clinical samples since intact, exfoliated epithelial cells are not required, treatment of specimens is practical, testing of large numbers of specimens is possible, and reading the printed test result is less subjective than reading fluorescence microscopy. The larger role of PCR in the diagnosis of respiratory virus infections depends on future developments such as practical methods to extract DNA or RNA and to purify the extracts from nonspecific inhibitors, plus further improvements to minimize cross-contamination. Group-specific detection of enteroviruses and rhinoviruses is an example of the potential for PCR technology. In experienced laboratories. EIA IgG antibody tests should be available. Recombinant antigens may be a useful part of such assays.

Use of recombinant nucleoproteins in enzyme-linked immunosorbent assays for detection of virus-specific immunoglobulin A (IgA) and IgG antibodies in influenza virus A- or B-infected patients

The nucleoprotein genes of influenza virus A/Netherlands/018/94 (H3N2) and influenza virus B/Harbin/7/94 were cloned into the bacterial expression vector pMalC to yield highly purified recombinant influenza virus A and B nucleoproteins. With these recombinant influenza nucleoproteins, enzyme-linked immunosorbent assays (ELISAs) were developed for the detection of influenza virus A- and B-specific immunoglobulin A (IgA) and IgG serum antibodies. Serum samples were collected at consecutive time points after the onset of clinical symptoms from patients with confirmed influenza virus A or B infections. Nucleoprotein-specific IgA antibodies were detected in 41.2% of influenza virus A-infected patients and in 66. 7% of influenza virus B-infected patients on day 6 after the onset of clinical symptoms. In serum samples taken on day 21 (influenza virus A-infected patients) or day 28 (influenza virus B-infected patients), nucleoprotein-specific IgA antibodies could be detected in 58.8 and 58.3% of influenza virus A- and B-infected patients, respectively. At the same time, IgG antibody rises were detected in 88.2% of influenza virus A-infected patients and in 95.8% of influenza virus B-infected patients. On comparison, hemagglutination inhibition assays detected antibody titer rises in 81.3 and 72.7% of patients infected with influenza viruses A and B, respectively. In contrast to the detection of nucleoprotein-specific IgG antibodies or hemagglutination-inhibiting antibodies, the detection of nucleoprotein-specific IgA antibodies does not require paired serum samples and therefore can be considered an attractive alternative for the rapid serological diagnosis of influenza.

A type-specific avian influenza virus subunit vaccine for turkeys: induction of protective immunity to challenge infection

The fraction NP/HA (nucleoprotein/haemagglutinin) obtained from n-octyl-beta-D-glucopyranoside-treated influenza A H5N2 virus was highly enriched for NP with residual haemagglutinin. This preparation was incorporated in ISCOMs. This potent 'immunostimulating complex' induced the production of high antibody titres in turkeys. The NP/HA ISCOMs preparation was found to protect turkeys from both homologous and heterologous challenge infection as shown by reduced viral titres in the lung and trachea of vaccinated turkeys. Clearance of the virus from trachea and lungs was seen at late stages of infection. The vaccine also induced a cellular immune response as measured by T-cell proliferation and a delayed-type hypersensitivity response. The results reported in this study demonstrate that the NP/HA ISCOM vaccine is capable of inducing type-specific immunity and that it has potential utility as a vaccine in turkeys.

Subtype specific ELISA for the detection of antibodies against influenza A H1N1 and H3N2 in swine

A subtype specific ELISA using purified hemagglutinin (HA) from influenza A H1N1 and H3N2 was developed to detect antibodies present in swine previously exposed to either H1N1 or H3N2 influenza viruses. The HA was extracted using the detergent octylglucoside followed by ion exchange chromatography. All HA preparations were free of contaminating nucleoprotein and matrix protein contamination. Monospecific swine anti-H1N1 and swine anti-H3N2 sera were used to demonstrate the subtype specificity of the assay. Monospecific rabbit anti-H1N1 or H3N2 was used to sterically block crossreacting determinants and thus enhance assay specificity. A linear relationship between single dilution point ELISA and the hemagglutination inhibition (HI) test was established. This enabled the accurate estimation of HI titer from ELISA. Further refinement of this ELISA based HI estimation system could allow it to replace the current HI procedures in instances where identification at the subtype level of specificity is acceptable. The substantial specificity requirements associated with the detection of strain specific antibody would still necessitate the use of the HI procedure.

Vaccinia virus expression and sequence of an avian influenza nucleoprotein gene: potential use in diagnosis

The nucleoprotein (NP) gene from avian influenza strain A/Shearwater/Aust/1/72 (H6N5) was cloned, sequenced, and expressed in vaccinia virus for the production of potent sera in immunised rabbits. The NP gene is 1565 bp and shares greater than 95% amino acid sequence identity with other NPs of the avian subtype. The recombinant NP expressed by vaccinia virus comigrated with endogenous A/Shearwater/Aust/1/72 NP by Western blot analysis. Polyclonal rabbit sera raised against recombinant NP was evaluated in an antigen capture ELISA system as a potential diagnostic tool for the detection of avian influenza. All type A strains, comprising several HA and NA subtypes, but not type B nor other avian viruses, were detected.