Showing papers on "Influenza A virus published in 1989"

Avian-to-human transmission of the PB1 gene of influenza A viruses in the 1957 and 1968 pandemics.

Abstract: We determined the origin and evolutionary pathways of the PB1 genes of influenza A viruses responsible for the 1957 and 1968 human pandemics and obtained information on the variable or conserved region of the PB1 protein. The evolutionary tree constructed from nucleotide sequences suggested the following: (i) the PB1 gene of the 1957 human pandemic strain, A/Singapore/1/57 (H2N2), was probably introduced from avian species and was maintained in humans until 1968; (ii) in the 1968 pandemic strain, A/NT/60/68 (H3N2), the PB1 gene was not derived from the previously circulating virus in humans but probably from another avian virus; and (iii) a current human H3N2 virus inherited the PB1 gene from an A/NT/60/68-like virus. Nucleotide sequence analysis also showed that the avian PB1 gene was introduced into pigs. Hence, transmission of the PB1 gene from avian to mammalian species is a relatively frequent event. Comparative analysis of deduced amino acid sequences disclosed highly conserved regions in PB1 proteins, which may be key structures required for PB1 activities.

Emergence and apparent transmission of rimantadine-resistant influenza A virus in families

Abstract: To determine whether rimantadine can protect family members from acquiring influenza A viral illness and to assess the possible selection of drug-resistant strains of virus, we conducted a randomized, double-blind, placebo-controlled study in three communities during two influenza seasons. When influenza A occurred in a family, the members (including the index patient) were given either rimantadine (adult oral dose, 200 mg per day) or placebo for 10 days. The presence of illness was monitored by daily recording of symptoms and temperature measurements; infection was determined by isolation of the virus and by serologic studies. Among households with documented influenza A infections, symptomatic illness occurred in one or more contacts in 10 of 28 families treated with rimantadine and in 10 of 29 families treated with placebo. Asymptomatic secondary influenza A infections were found in five families assigned to receive rimantadine and in four families assigned to receive placebo. Rimantadine-resi...

Genes and Proteins of the Influenza Viruses

Abstract: This chapter describes the structure of the genes of influenza A, B, and C viruses Influenza viruses contain a segmented single-stranded RNA genome that has been called negative stranded because the viral messenger RNA (mRNAs) are transcribed from the viral RNA segments. A great deal of new knowledge has been obtained about influenza A, B, and C viruses, since the last major multiauthored reviews of the genetics, molecular biology, and structural biology of influenza viruses (Palese and Kingsbury, 1983). The complete nucleotide sequence of the 8 RNA segments of the influenza A and B viruses has been obtained, and significant progress has been made with the sequencing of the influenza C virus genome. Other major developments include the following: 1. The three-dimensional structure of both major surface antigens, hemagglutinin and neuraminidase, has been determined from X-ray studies of crystallized proteins, and the structure of a neuraminidase—antibody complex has been obtained. In addition, the structure of the influenza virus hemagglutinin complexed with its receptor sialic acid has been elucidated, which may provide a basis for the rational design of antiviral drugs that would block viral attachment to cells. 2. In both influenza A and B viruses, previously unrecognized small integral membrane proteins, M2 and NB, respectively, have been identified and extensively characterized. 3. The influenza A virus N9 neuraminidase has also been found to exhibit hemagglutinating activity. 4. Influenza C virus glycoprotein exhibits both hemagglutinating and neuraminate-O-acetyl esterase activity.

Purified influenza virus hemagglutinin and neuraminidase are equivalent in stimulation of antibody response but induce contrasting types of immunity to infection.

Abstract: BALB/c mice immunized with graded doses of chromatographically purified hemagglutinin (HA) and neuraminidase (NA) antigens derived from A/Hong Kong/1/68 (H3N2) influenza virus demonstrated equivalent responses when HA-specific and NA-specific serum antibodies were measured by enzyme-linked immunosorbent assays (ELISAs). Antibody responses measured by hemagglutination inhibition or neuraminidase inhibition titrations showed similar kinetic patterns, except for more rapid decline in hemagglutination inhibition antibody. Injection of mice with either purified HA or NA resulted in immunity manifested by reduction in pulmonary virus following challenge with virus containing homologous antigens. However, the nature of the immunity induced by the two antigens differed markedly. While HA immunization with all but the lowest doses of antigen prevented manifest infection, immunization with NA was infection-permissive at all antigen doses, although reduction in pulmonary virus was proportional to the amount of antigen administered. The immunizing but infection-permissive effect of NA immunization over a wide range of doses is in accord with results of earlier studies with mice in which single doses of NA and antigenically hybrid viruses were used. The demonstrable immunogenicity of highly purified NA as a single glycoprotein without adjuvant offers a novel infection-permissive approach with potentially low toxicity for human immunization against influenza virus.

Interleukin-2 production used to detect antigenic peptide recognition by T-helper lymphocytes from asymptomatic HIV-seropositive individuals.

Abstract: T LYMPHOCYTES from mice1 and healthy humans2 immunized against the human immunodeficiency virus (HIV) envelope have recently been shown to recognize two antigenic regions of the gp160 HIV-envelope protein which have been located on the basis of amphipathicity3–6. In HIV-infected humans, T-cell proliferative responses are lost soon after infection7,8. Here we demonstrate that interleukin-2 production is often retained even when proliferative activity is absent, and that it can be used to monitor T-helper cell responses by HIV-seropositive donors. We use this approach to investigate the T-helper cell response of 42 asymptomatic HIV-seropositive patients to four synthetic gp160 peptides and to influenza A virus, an antigen requiring intact CD4 T-helper cell function. As many as 67% of the HIV-seropositive donors who retain responsiveness to influenza A virus respond to a single peptide, and 85–90% responded to at least one of the peptides.

Acute otitis media and respiratory virus infections.

Abstract: We studied the association of acute otitis media with different respiratory virus infections in a pediatric department on the basis of epidemics between 1980 and 1985. Altogether 4524 cases of acute otitis media were diagnosed. The diagnosis was confirmed by tympanocentesis in 3332 ears. Respiratory virus infection was diagnosed during the same period in 989 patients by detecting viral antigen in nasopharyngeal mucus. There was a significant correlation between acute otitis media and respiratory virus epidemics, especially respiratory syncytial virus epidemics. There was no significant correlation between outbreaks of other respiratory viruses and acute otitis media. Acute otitis media was diagnosed in 57% of respiratory syncytial virus, 35% of influenza A virus, 33% of parainfluenza type 3 virus, 30% of adenovirus, 28% of parainfluenza type 1 virus, 18% of influenza B virus and 10% of parainfluenza type 2 virus infections. These observations show a clear association of respiratory virus infections with acute otitis media. In this study on hospitalized children Haemophilus influenzae strains were the most common bacteriologic pathogens in middle ear fluid, occurring in 19% of cases. Streptococcus pneumoniae was present in 16% and Branhamella catarrhalis in 7% of cases. There was no association between specific viruses and bacteria observed in this study.

The systemic and mucosal immune response of humans to influenza A virus.

Abstract: Influenza A virus contains a negative-sense, single-stranded RNA genome which consists of 8 segments that code for 7 structural and 3 non-structural proteins (Murphy et al. 1985). In nature, the virus undergoes antigenic changes, referred to as antigenic drift and shift, that permit it to escape from immunity induced by prior infection with related influenza A viruses (Murphy et al. 1985). Common to both types of antigenic change are alterations in the surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA) (Murphy et al. 1985). Antibodies to the HA glycoprotein neutralize the infectivity of the virus, and antibodies to the NA prevent efficient release of virus from infected cells (Askonas et al. 1982; Becht et al. 1971). Passive transfer of monoclonal antibodies to the HA or NA glycoprotein protects mice from experimental challenge with wild type influenza virus whereas those to the membrane (M) protein or nucleoprotein (NP) fail to protect (Askonas et al. 1982). Clearly, the surface glycoproteins constitute the major protective antigens against which an immune response is directed. Immunization of animals with purified NP or with NP expressed by a vaccinia virus induces partial resistance to lethal wild type virus challenge, but the level of resistance is considerably less than that induced by immunization with HA (Andrew et al. 1986; Wraith et al. 1986). It is thought that the resistance induced by immunization with NP is mediated primarily by histocompatibility class I restricted cytotoxic T-cells, but is not limited to this T-cell subset (McDermott et al. 1987; Taylor et al. 1986).

Resistance of Influenza A Virus to Amantadine and Rimantadine: Results of One Decade of Surveillance

Abstract: All clinical isolates of influenza A viruses from patients in Huntington, West Virginia, during the decade 1978-1988 were tested, and 65 of 65 H1N1 and 176 of 181 H3N2 viruses were susceptible to the antiviral action of amantadine and rimantadine The five resistant viruses were obtained from three members of a family undergoing therapy or prophylaxis with rimantadine Resistant influenza emerged during treatment with rimantadine and spread to two family contacts, causing typical influenza with fever, myalgia, and cough of 5 days' or less duration Genetic characterization of the resistant viruses when compared to the susceptible virus isolated on day 1 from the index case revealed a single amino acid change in the transmembrane portion of the M2 protein In vitro studies showed that rimantadine was significantly more active than amantadine against both H1N1 and H3N2 viruses Although this resistant influenza was transmitted and caused illness in one family, the absence of naturally occurring resistant viruses suggests that the emergence of new strains of influenza A each few years may prevent the widespread emergence of resistant influenza A virus

Efficacy of Inactivated Influenza A Virus (H3N2) Vaccines Grown in Mammalian Cells or Embryonated Eggs

Abstract: Influenza virus (H3N2) host cell variants isolated from a single infected individual were compared for their protective efficacies when used as formalin-inactivated purified whole virus vaccines in ferrets. A/Mem/12/85 virus grown in embryonated chicken eggs (egg-grown), which differs from A/Mem/12/85 grown in mammalian Madin-Darby canine kidney cells (MDCK-grown) by a single amino acid substitution in the hemagglutinin molecule, was shown to be distinguishable by immune ferret serum. Ferrets were immunized intramuscularly with intact inactivated MDCK- or egg-grown virus and were subsequently challenged with infectious virus grown in either host cell type. MDCK-grown-virus vaccine induced higher mean serum hemagglutination-inhibiting (HAI) and neutralizing antibody titers than did egg-grown-virus vaccine and induced superior protection of ferrets against subsequent challenge with infectious virus grown in either host cell type. These results suggest that human influenza viruses that are antigenically and structurally similar to viruses grown in mammalian cells may be more efficacious as vaccines than some variants selected in eggs.

Biologic potential of amantadine-resistant influenza A virus in an avian model.

Abstract: Amantadine has been accepted for both the treatment and prophylaxis of influenza A virus infections. Although amantadine-resistant mutants have been shown to be readily generated both in the laboratory and in children treated with rimantadine, little is known about their biologic properties, such as genetic stability, transmissibility, or pathogenicity, compared with the parental virus. This study examined these properties using an avian influenza virus, A/chicken/Pennsylvania/1370/83 (H5N2). Variants that were amantadine-resistant, virulent, and capable of competing with wild-type virus for transmission to susceptible hosts in the absence of the drug were selected. These amantadine-resistant variants were also genetically stable, showing no reversion to wild-type after six passages in birds over a period of greater than 20 d. Thus, these virus variants had no detectable biologic impairment. The mutations conferring drug resistance were in the M2 polypeptide and were identical to mutations previously described in human amantadine-resistant virus. These results suggest that resistant mutants may have the potential to threaten the effective use of amantadine and rimantadine for the control of epidemic influenza.

Mice immunized with recombinant vaccinia virus expressing dengue 4 virus structural proteins with or without nonstructural protein NS1 are protected against fatal dengue virus encephalitis.

Abstract: We have constructed vaccinia virus recombinants expressing dengue virus proteins from cloned DNA for use in experimental immunoprophylaxis. A recombinant virus containing a 4.0-kilobase DNA sequence that codes for three structural proteins, capsid (C), premembrane (pre-M), and envelope (E), and for nonstructural proteins NS1 and NS2a produced authentic pre-M, E, and NS1 in infected CV-1 cells. Mice immunized with this recombinant were protected against an intracerebral injection of 100 50% lethal doses of dengue 4 virus. A recombinant containing only genes C, pre-M, and E also induced solid resistance to challenge. Deletion of the putative C-terminal hydrophobic anchor of the E glycoprotein did not result in secretion of E from recombinant-virus-infected cells. Recombinants expressing only the E protein preceded by its own predicted N-terminal hydrophobic signal or by the signal of influenza A virus hemagglutinin or by the N-terminal 71 amino acids of the G glycoprotein of respiratory syncytial virus produced glycosylated E protein products of expected molecular sizes. These vaccinia virus recombinants also protected mice.

RNA-binding properties of influenza A virus matrix protein M1

Abstract: The matrix protein (M1) of influenza A virus, which has a critical role in viral assembly and can inhibit the viral transcriptase complex, has the ability to bind RNA. The RNA-binding property of M1 is specific for single-stranded RNA, like that of influenza nucleoprotein (NP) and shows similar sensitivity to pH and to salt concentration. M1:RNA complexes are stable, once formed, to competition from excess single-stranded RNA. The possible location of the RNA-binding regions in the M1 protein is discussed.

Growth restriction of influenza A virus by M2 protein antibody is genetically linked to the M1 protein.

Abstract: The M2 protein of influenza A virus is a 97-amino acid integral membrane protein expressed at the surface of infected cells. Recent studies have shown that a monoclonal antibody (14C2) recognizes the N terminus of M2 and restricts the replication of certain influenza A viruses. To investigate the mechanism of M2 antibody growth restriction, 14C2 antibody-resistant variants of strain A/Udorn/72 have been isolated. Most of the variant viruses are not conventional antigenic variants as their M2 protein is still recognized by the 14C2 antibody. A genetic analysis of reassortant influenza viruses prepared from the 14C2 antibody-resistant variants and an antibody-sensitive parent virus indicates that M2 antibody growth restriction is linked to RNA segment 7, which encodes both the membrane protein (M1) and the M2 integral membrane protein. Nucleotide sequence analysis of RNA segment 7 from the variant viruses predicts single amino acid substitutions in the cytoplasmic domain of M2 at positions 71 and 78 or at the N terminus of the M1 protein at residues 31 and 41. To further examine the genetic basis for sensitivity and resistance to the 14C2 antibody, the nucleotide sequences of RNA segment 7 of several natural isolates of influenza virus have been obtained. Differences in the M1 and M2 amino acid sequences for some of the naturally resistant strains correlate with those found for the M2 antibody variant viruses. The possible interaction of M1 and M2 in virion assembly is discussed.

Transcription-inhibition and RNA-binding domains of influenza A virus matrix protein mapped with anti-idiotypic antibodies and synthetic peptides.

Abstract: We have undertaken by biochemical and immunological experiments to locate the region of the matrix (M1) protein responsible for down-regulating endogenous transcription of A/WSN/33 influenza virus. A more refined map of the antigenic determinants of the M1 protein was obtained by binding of epitope-specific monoclonal antibodies (MAbs) to chemically cleaved fragments. Epitope 2-specific MAb 289/4 and MAb 7E5 reverse transcription inhibition by M1 protein and react with a 4-kilodalton cyanogen bromide fragment extending from amino acid Gly-129 to Gln-164. Anti-idiotype serum immunoglobulin G prepared in rabbits immunized with MAb 289/4 or MAb 7E5 mimicked the action of M1 protein by inhibiting transcription in vitro of influenza virus ribonucleoprotein cores. This transcription-inhibition activity of anti-MAb 7E5 immunoglobulin G and anti-MAb 289/4 immunoglobulin G could be reversed by MAb 7E5 and MAb 289/4 or could be removed by MAb 7E5-Sepharose affinity chromatography. Transcription of influenza virus ribonucleoprotein was inhibited by one of three synthetic oligopeptides, a nonodecapeptide SP3 with an amino acid sequence corresponding to Pro-90 through Thr-108 of the M1 protein. Of all the structural proteins of influenza virus, only NP and M1 showed strong affinity for binding viral RNA or other extraneous RNAs. The 4-kilodalton cyanogen bromide peptide (Gly-129 to Gln-164), exhibited marked affinity for viral RNA, the binding of which was blocked by epitope 2-specific MAb 7E5 but not by MAbs directed to three other epitopes. Viral RNA also bound strongly to the nonodecapeptide SP3 and rather less well to anti-idiotype anti-MAb 7E5; these latter viral RNA-binding reactions were only slightly blocked by preincubation of anti-MAb 7E5 or SP3 with MAb 7E5. These experiments suggest the presence of at least two RNA-binding sites, which also serve as transcription-inhibition sites, centered around amino acid sequences 80 through 109 (epitope 4?) and 129 through 164 (epitope 2) of the 252 amino acid M1 protein of A/WSN/33 influenza virus. A hydropathy plot of the M1 protein calculated by free-energy transfer suggests that the two hydrophilic transcription-inhibition RNA-binding domains are brought into close proximity by an alpha-helix-forming intervening hydrophobic domain.

Interplay between carbohydrate in the stalk and the length of the connecting peptide determines the cleavability of influenza virus hemagglutinin.

Abstract: The ability of many viruses to replicate in host cells depends on cleavage of certain viral glycoproteins, including hemagglutinin (HA). By generating site-specific mutant HAs of two highly virulent influenza viruses, we established that the relationship between carbohydrate in the stalk and the length of the connecting peptide is a critical determinant of cleavability. HAs that lacked an oligosaccharide side chain in the stalk were cleaved regardless of the number of basic amino acids at the cleavage site, whereas those with the oligosaccharide side chain resisted cleavage unless additional basic amino acids were inserted. This finding suggests that the oligosaccharide side chain interferes with HA cleavage if the number of basic amino acids at the cleavage site is not adequate to nullify this effect. Similar interplay could influence cleavage of other viral glycoproteins, such as those of human and simian immunodeficiency viruses and paramyxoviruses.

Suppression of immunity to influenza virus infection in the respiratory tract following sleep disturbance.

Abstract: The extent to which sleep deprivation interferes with immunity in the respiratory tract to influenza virus has been assessed in mice. Mice were orally immunized with influenza virus on two occasions separated by a one week interval and challenged intranasally one week later. Some animals were deprived of sleep for a 7 h period immediately following challenge. Three days after challenge, virus clearance and virus specific antibody were determined in lungs of sleep deprived and normally sleeping mice and the results compared with unimmunized mice subjected to the same protocol. Whereas immunized, normal sleep mice achieved total virus clearance, sleep deprivation in immunized mice completely abrogated this effect such that sleep deprived animals behaved as though they had never been immunized. There was no difference in viral clearance in unimmunized mice whether sleep deprived or not, indicating that sleep deprivation did not itself have a direct effect on viral replication. The data reported here support the concept that sleep is a behavioral state which is essential for optimal immune function in the presence of a respiratory tract pathogen.

Natural or vaccine-induced antibody as a predictor of immunity in the face of natural challenge with influenza viruses.

Abstract: A study of influenza in residential schools provided the opportunity to assess the significance of antibody as a predictor of immunity. Five hundred and fifty-six pupils from 8 schools were included in the investigations, and the outcome for these children in 27 naturally occurring outbreaks of influenza was analysed. The outbreaks comprised 5 caused by strains of influenza A H3N2, 10 caused by strains of influenza A H1N1, and 12 caused by strains of influenza B. On 8 occasions a second outbreak of the same serotype occurred in a school. There was a general correlation between the presence of antibody to the outbreak strain and protection from infection. For each of the three influenza virus serotypes the infection rate in those with no detectable antibody was approximately 80%. Those with past experience of the virus but no antibody to the outbreak strain experienced lower infection rates (62% overall) but the infection rates were lowest in those with intermediate and high level antibody to the challenge strain (18% overall). Vaccine was used by three of the schools. The effect of antibody derived from recent experience, either natural or vaccine-induced, on subsequent challenge with a drifted strain i.e. one showing antigenic drift away from the previous strain, was compared. Intermediate or high level antibody to the challenge strain in those who had experienced a recent natural infection was associated with a low infection rate (9%). A similar level of antibody produced in response to vaccination was associated with a significantly higher infection rate (23%: P less than 0.025).(ABSTRACT TRUNCATED AT 250 WORDS)

An outbreak of influenza a/taiwan/1/86 (h1n1) infections at a naval base and its association with airplane travel

Abstract: In late October 1986, an outbreak of influenza-like illness was detected at the Naval Air Station in Key West, Florida. Between October 10 and November 7, 1986, 60 active duty personnel reported experiencing a respiratory illness characterized by fever, cough, sore throat, and myalgia. Influenza A/Taiwan/1/86 (H1N1) virus was recovered from three symptomatic patients. Forty-one (68%) of 60 case-patients belonged to a 114-person squadron that had traveled to Puerto Rico for a temporary assignment from October 17-28, 1986. Among squadron members, the attack rate for persons previously vaccinated with the 1986-1987 trivalent influenza vaccine and for those unvaccinated was the same (37%). Transmission of infection among squadron personnel appeared to have commenced in Key West and continued in a barracks in Puerto Rico and aboard two DC-9 aircraft that transported the squadron back to Key West on October 28. There was no evidence that the outbreak spread to the surrounding civilian communities in Puerto Rico or Key West. This was the first reported outbreak of respiratory illness due to influenza A/Taiwan/1/86 (H1N1) in the continental United States in the 1986-1987 influenza season.

Systemic and local antibody responses in elderly subjects given live or inactivated influenza A virus vaccines.

Abstract: Intranasal live attenuated cold-adapted (ca) influenza A/Kawasaki/9/86 (H1N1) reassortant virus and parenteral inactivated influenza A/Taiwan/1/86 (H1N1) virus were given alone or in combination to 80 ambulatory elderly subjects. An enzyme-linked immunosorbent assay was used to measure hemagglutinin-specific (HA) antibodies in serum and nasal wash specimens collected before vaccination and 1 and 3 months later. Serum immunoglobulin G (IgG) and nasal wash IgA HA responses were elicited in 56 and 20%, respectively, of 25 inactivated-virus vaccinees and in 67 and 48%, respectively, of 27 recipients of both vaccines but in only 36 and 25%, respectively, of 28 vaccinees given live virus alone. Inactivated virus, administered alone or with live virus vaccine, induced higher titers of serum antibody than did the live virus alone. In contrast, nasal IgA HA antibody was elicited more often and in greater quantity by the vaccine combination than by either vaccine alone. Despite these differences, the peak titers of local antibody mounted by each group of vaccinees were similar. By 3 months postvaccination, serum IgG and nasal IgA HA antibody titers remained elevated above prevaccination levels in 50 and 17%, respectively, of the inactivated-virus vaccinees and in 46 and 23%, respectively, of recipients of both vaccines but in only 19 and 7%, respectively, of the live-virus and systemic antibodies, if vaccinees. The finding that live ca influenza A virus induced short-lived local and systemic antibodies, if confirmed, suggests that live virus vaccination may not be a suitable alternative or adjunct to inactivated virus vaccination for the elderly.

Identification and characterization of T helper epitopes in the nucleoprotein of influenza A virus.

Abstract: By using a series of overlapping synthetic peptides that cover more than 95% of the amino acid sequence of nucleoprotein (NP) of influenza A/NT/60/68 virus, five Th cell epitopes in B10.S (H-2s), BALB/c (H-2d), CBA (H-2k), and B6 (H-2b) mice have been identified. The specificity of Th cell recognition of epitopes is largely dependent on the H-2 haplotype of the responding mouse strain. However, two out of the five Th epitopes defined could be recognized by mice of more than one haplotype, implying that the primary sequence of protein antigens could also influence the selection of dominant T cell epitopes by the immune system. Immunization of B10.S mice with peptide 260-283 generated strong Th cell response against type A influenza viruses. In the other three strains of mice tested, priming with helper peptides induced a stronger antipeptide than antiviral T cell response. However, the low responsiveness to virus in these mice could be partially overcome by immunization with a mixture of several helper peptides. The Th epitopes are defined by the ability of the peptides to stimulate class II MHC restricted CD4+ T cells to proliferate and to produce IL-2 in vitro. When compared with the known epitopes on NP recognised by class I restricted CD8+ cytotoxic T cells, it appears that Th and cytotoxic T cell epitopes are nonoverlapping. The AMPHI and Motifs methods were employed to analyze the sequence of NP and predict the potential dominant sites in the molecule. The predictions are compared with the experimental data obtained and the implications discussed.

The immunoglobulin G subclass responses of mice to influenza A virus: the effect of mouse strain, and the neutralizing abilities of individual protein A-purified subclass antibodies.

Abstract: The IgG subclass responses to cold-adapted (ca) influenza A/Queensland/6/72 virus and purified haemagglutinin H3 was assessed in C57BL/6 and BALB/c mice. In BALB/c mice IgG2a was present as the major subclass in serum, lung and salivary secretions after two doses of ca virus. In contrast, the serum response in C57BL/6 mice was predominantly IgG1 after primary and secondary inoculations of ca virus. However, in lung and salivary secretions no specific subclass was dominant. When purified H3 was used as the inoculum, serum responses were dominated by IgG1 in BALB/c mice after two inoculations whereas all four subclasses were present at equal levels in C57BL/6 mice. Overall the lung and salivary responses detected in C57BL/6 mice were lower than those observed in BALB/c mice with all four subclasses contributing equally to the response in BALB/c mice. The neutralizing and haemagglutination inhibition abilities of the four Protein A-Sepharose-purified IgG subclasses differed between the BALB/c, C57BL/6 and CBA/CaH mice strains. IgG1 and IgG2a were most effective in BALB/c mice and in C57BL/6 and CBA/CaH mice, IgG2a and IgG2b. These results are discussed in terms of the differing abilities of replicating and non-replicating virus to stimulate differential responses in mice and the TH1 and TH2 helper cell concept.

The use of intravenous ribavirin to treat influenza virus-associated acute myocarditis.

Abstract: We studied three patients with influenza virus-associated fulminant myocarditis; one was infected by type B and the others by type A influenza virus. In one patient, dissemination of type A (H1N1) virus to the myocardium was demonstrated, and viremia complicated the clinical course despite the use of oral amantadine HCl and ribavirin aerosol. All patients were treated with iv ribavirin, two initially and the third after viremia was detected during hyperacute rejection of a cardiac transplant. No significant adverse effects could be directly attributed to therapy, and viral shedding abruptly terminated coincident with its use; however, both patients treated shortly after onset of myocarditis died. The third required support by an artificial heart, and died 8 mo later. Immunotyping of myocardial tissues in two cases revealed an initial predominance of T helper cells. Serial endomyocardial biopsies available from one of these demonstrated a subsequent marked decrease in the T helper cell population as inflammation and necrosis subsided during and following therapy.

Antigenic Conservation of H1N1 Swine Influenza Viruses

Abstract: Summary Influenza viruses of the H1N1 subtype have been continually circulating in pigs in the U.S.A. for at least 50 years. To examine the level of antigenic variation in these swine viruses, a panel of 60 monoclonal antibodies (MAbs) to the haemagglutinin (HA) of recent swine isolates was prepared. Evaluation of neutralization escape mutants selected with these MAbs defined four antigenic sites on the HA, two of which overlap. Swine viruses isolated over 24 years in an enzootic area in Wisconsin were examined by ELISA and haemagglutination inhibition (HI) with these MAbs and the results indicated that the antigenic sites defined by these MAbs were highly conserved in these viruses. In comparing recent H1N1 viruses from pigs, turkeys, ducks and humans, changes in the antigenic sites were detected on the basis of HI reactivity. However, results of ELISA with these viruses clearly showed that the antigenic sites were still present on almost all H1N1 viruses of swine origin; thus, altered reactivity of these viruses in HI tests with MAbs was not a reflection of changes in the antigenic sites defined by the MAbs. It seems likely that the variation detected in these viruses occurs by a mechanism other than immune selection.

Virulent avian influenza A viruses: their effect on avian lymphocytes and macrophages in vivo and in vitro.

Abstract: To investigate the pathogenesis of virulent avian influenza A viruses, the effect of A/turkey/Ont/7732/66 (H5N9) (Ty/Ont), A/tern/South Africa/1961 (H5N3) (Tern/S.A.) and A/chicken/Pennsylvania/1370/83 (H5N2) (Ck/Penn) on avian lymphoid cell populations was examined in vivo. Previous studies have shown that infection of chickens with Ty/Ont resulted in the extensive destruction of lymphoid tissues. In this study, other virulent avian H5 influenza viruses, Tern/S.A. or Ck/Penn, had little or no effect on lymphoid tissues of infected chickens. Therefore the effect of Ty/Ont on lymphoid tissue is a specific activity of this virus only and not of other virulent avian H5 influenza strains. To examine the role of viral replication in the destruction of lymphocytes, in vitro cultures of avian macrophages and lymphocytes were inoculated with Ty/Ont. Macrophages supported the synthesis of viral proteins whereas lymphocytes produced small, but detectable amounts of viral protein; however, infectious virus was not produced by either cell type. Furthermore inoculation of chicken spleen cells with Ty/Ont in vivo and in vitro had a profound effect on the proliferative response of lymphocytes to concanavalin A. These results suggest that Ty/Ont infects macrophages as well as lymphocytes in the chicken, and the effects of the virus on both cell types may well contribute to lymphoid necrosis.