Persistent antigenic variation of influenza A viruses after incomplete neutralization in ovo with heterologous immune serum

Characteristics of virulent, attenuated, and avirulent Mycoplasma pneumoniae strains

Homologous pairs of virulent and attenuated or avirulent Mycoplasma pneumoniae strains were derived and compared in an effort to elucidate the mechanisms of virulence. These related strains were found to vary in growth, glycolysis, protein electrophoretic patterns, peroxide formation, morphology, and cytadsorption. Variations in the last two characteristics closely correlated with avirulence. This enables understanding of one stage in the pathogenic sequence and provides a convenient marker for avirulence. The derivation of infectious avirulent strains may make possible their use as live vaccines against M. pneumoniae disease.

Independent variation in nature of hemagglutinin and neuraminidase antigens of influenza virus: distinctiveness of hemagglutinin antigen of Hong Kong-68 virus

Antigenic variations of the two virus-coded surface proteins of influenza virus-hemagglutinin and neuraminidase-were examined in seven strains of influenza A(2) virus (including the Hong Kong/68 strain) isolated from 1957 to 1968. Changes in the two antigens were found to occur independently in nature, resulting in new viruses which differ from older strains more with respect to one antigen than the other. The Hong Kong/68 strain is markedly different from previous A(2) strains in its hemagglutinin antigen but possesses neuraminidase indistinguishable antigenically from that of recent strains. Immunization experiments in mice provided evidence that only the neuraminidase component of an earlier A(2) strain provided protection against Hong Kong virus challenge. Segregation of hemagglutinin and neuraminidase antigens through recombination of each of the seven strains of influenza A(2) virus with A(0)/NWS virus made it possible to investigate antigenic variation of the two dissociated surface proteins independently in a common plaque assay system. Comparison of these hybrid viruses with the parent A(2) strains provided evidence that all the cross-reactivity of the Hong Kong strain with previous A(2) viruses is explicable on the basis of its similar neuraminidase component. It is proposed that the taxonomy of influenza A viruses must take into account differences in neuraminidase as well as hemagglutinin antigens.

Studies of base-sequence homology among some cytoplasmic deoxyriboviruses of vertebrate and invertebrate animals

Relationships among some cytoplasmic deoxyriboviruses were investigated by deoxyribonucleic acid/ribonucleic acid hybridization experiments. Evidence of base-sequence homology between nucleic acids of different viruses was found within, but not between, the poxvirus and iridescent virus groups. Viruses of the vaccinia subgroup of poxviruses were 30 to 100% related, and the degree of relatedness was correlated with serological relatedness. Relationships within the iridescent virus group depended on the laboratory of origin and passage history of the virus strains used. None of these viruses was related to a superficially similar virus of frogs.

Genetic differentiation by nucleic Acid homology I. Relationships among Mycoplasma species of man

Reich, Paul R. (National Institutes of Health, Bethesda, Md.), Norman L. Somerson, Carol J. Hybner, Robert M. Chanock, and Sherman M. Weissman. Genetic differentiation by nucleic acid homology. I. Relationships among Mycoplasma species of man. J. Bacteriol. 92:302-310. 1966.-Genetic relatedness among human mycoplasmas was evaluated by measuring the amount of nucleic acid hybrid retained on a membrane filter. Hybrids were formed from deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) derived from representative strains of seven serologically distinct human Mycoplasma species. The results indicate that serologically distinct human Mycoplasma species can also be distinguished by the homology techniques. Low-level cross-reactivity was observed among nucleic acids derived from the seven species. Genetic heterogeneity was demonstrated among three strains of M. salivarium and between two strains of M. orale type 2. In contrast, comparison of three strains and three passage levels of M. pneumoniae revealed them to be indistinguishable. M. pneumoniae appears to be the most distinct of all human mycoplasmas, as shown by both homology and the high buoyant density value of its DNA. Nucleic acids from mycoplasmas which had identical buoyant densities were in some cases differentiable. Mycoplasmas with different DNA buoyant densities were invariably distinguishable by the homology technique.

Genetic relatedness among mycoplasmas as determined by nucleic acid homology

Reich, Paul R. (National Institutes of Health, Bethesda, Md.), Norman L. Somerson, James A. Rose, and Sherman M. Weissman. Genetic relatedness among mycoplasmas as determined by nucleic acid homology. J. Bacteriol. 91:153-160. 1966.-A sensitive membrane filter method to detect nucleic acid homology was used to determine genetic relatedness among mycoplasma isolates. Deoxyribonucleic acid (DNA) was isolated from mycoplasmas and used as a primer for synthesis of tritium-labeled, complementary ribonucleic acid (RNA) by the enzyme RNA polymerase. DNA from each mycoplasma isolate tested was reacted separately with complementary RNA synthesized with homologous or heterologous DNA as primer. The quantity of DNA-RNA hybrids formed was assayed by the nitrocellulose membrane filter method. The amount of radioactivity bound to the membrane filter was used to measure the degree of homology between the nucleic acids. The three mycoplasma isolates from human oral cavities (DC 63, V2785, Botteicher) and the prototype strain PG21 placed in the Mycoplasma hominis type 1 group by gel diffusion and complement-fixation testing were investigated with this technique. Analysis of the data confirmed their immunological grouping with the M. hominis type 1 and their distinction from other human mycoplasmas. In contrast to the data from immunological studies, none of the four isolates tested appeared to be identical to any other. Preliminary experiments with DNA from four other mycoplasma isolates from tissue cultures inoculated with human material revealed them to be closely related, and possibly identical. The advantages of this nucleic acid homology technique for the study of relatedness among mycoplasmas are described.

Association of Canine Adenovirus (Toronto A 26/61) with an Outbreak of Laryngotracheitis ("Kennel Cough"): A Preliminary Report

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Observations on a poliovirus variant

1. Some of the biological and physical properties of one member (FES) of an inter-related group of viruses were examined and compared with the Saukett strain of poliovirus Type 3.

2. The accumulated data of particle size, immunological relationship, and host tissue and cell tropism indicates that this is a naturally occurring non-neurotropic strain of poliovirus Type 3. It shows a slight immunological difference from Saukett, and also differs from it in temperature stability.

3. The significance of four different isolations of this agent in a brief period is discussed.

Immunological strain specificity within type 1 poliovirus

The demonstration of immunological differences between poliovirus strains of any one type is a valuable procedure in epidemiological research as it may allow a virus strain to be identified as derived from or unrelated to a given possible source of infection. It is obviously of particular importance in connexion with live poliovirus vaccination campaigns. Both kinetic tests and conventional neutralization and complement-fixation techniques have been used to this end, the former involving a more complicated test procedure and the latter demanding greater nicety in the pre-standardization of reagents. The present paper reports on attempts to establish a simplified technique.Neutralization titres of sera obtained by immunization of guinea-pigs with three strains of type 1 poliovirus (including one isolated from a patient in the 1958-59 epidemic in Léopoldville described in the two preceding papers) indicated a degree of strain specificity sufficient to permit the design of a simple screening method for the purpose of a rough immunological classification.Preliminary observations on isolates from persons fed attenuated virus indicate that antigenic changes may occur in the course of multiplication of the virus in the human intestinal tract.

Antigenic variants of influenza A virus (PR8 strain). II. Serological and immunological characteristics of variants derived from variants

Four successive generations of antigenic variants of influenza PR8-S virus, each derived from the previous one by serial passage in the lungs of mice immunized with the homologous agent, were compared with the original parent PR8-S virus with respect to their serological and immunological character. It was demonstrated by means of H.I., complement-fixation and in ovo-neutralization tests that the variants exhibited a progressively decreasing reactivity with the parent PR8-S antiserum while retaining the ability to elicit antibody to PR8-S influenza virus and to their respective predecessors. Accompanying these changes was a progressive reduction in antigenicity without any significant changes in pathogenicity for mice. Experimental evidence was presented which indicates that the serological changes observed with the variants are not related to the P-Q phenomenon. Antibody absorption tests showed that the variants share antigens with PR8-S virus but differ from it by the presence of specific antigenic components; these increase in quantity with each successive variant while the amount of related antigens shows a progressive decrease. The importance of evaluating the significance of antigenic changes of influenza viruses with active immunity tests was emphasized by the fact that PR8-S vaccine protected mice against fatal infection with lethal doses of the variant strains although the latter had a progressively decreasing serological reactivity with PR8-S antiserum. The inheritable character of the new antigenic properties of the variant strains was demonstrated by their persistence in the absence of thea selective environment following 18 to 24 serial intranasal passages with large inocula in normal mice and following limiting dilution passage in fertile eggs.

Evidence for genetic interaction between non-infectious and infectious influenza A viruses

Influenza virus rendered non-infectious by ultraviolet irradiation retained ability to "exchange" genetic traits with related virus, resulting in recombined forms. Sedimentation studies indicated association of recombinining activity with particles approximately the size of influenza virus. Genetic activity was not demonstrated when virus was more severely disrupted in attempts to observe phenomena analogous to bacterial transformation. Irradiated virus was also shown to remain capable of genetic exchange for at least 4 days after inoculation into embryonate eggs. In contrast infectious virus becomes insusceptible to genetic exchange after 1 hour incubation in eggs. The importance of this delayed recombination phenomenon to processes of virus evolution and influenza strain variation was discussed.

Propagation of influenza virus in immune environments

INFLUENZA VIRUS CAN SURVIVE, AND CAN BE PROPAGATED IN IMMUNOLOGICAL ENVIRONMENTS INDUCED IN MICE BY VACCINATION WITH THE HOMOLOGOUS STRAIN OF VIRUS: survival was associated with the emergence of variants which differed from the parent strain in antigenic characteristics. The data concerning hemagglutinating activity of the variants, on the one hand, and of the antigenicity, on the other, are compatible with the concept that the structure of the influenza virus includes a surface arrangement which is distinct from the inner virus bulk. The points (a) that propagation was accomplished with difficulty whenever the immunological environment was altered, and (b) that once established, passage was continued without difficulty, are interpreted to indicate that the mechanism of variation may involve a rearrangement of the basic hereditary mechanism.

The influenza virus: its morphology, immunology, and kinetics of multiplication

The morphology of influenza virus is described, and the properties of its two components, the elementary body and the soluble substance, differentiated. The relationship between the filamentous and spherical structures observed in the infected allantoic fluid is still obscure, but the filaments are thought to represent either a form of influenza virus or a stage in its multiplication.The antigenic constitution of A and B viruses is discussed and variations in the pattern of individual strains over the past two decades described. The author outlines his speculations on the origin and mechanism of these variations. Other differences in serological behaviour, such as non-specific inhibition and the avidity effect, are discussed.The results of experimental investigation, with various animal hosts, of the kinetics of influenza virus multiplication are reviewed, and the effects of such factors as incubation temperature and concentration of the seed virus considered. The bearing of these studies of enzymatic virus/host-cell interactions on the chemotherapeutic control of influenza is emphasized.