Alick Isaacs

Virus interference. II. Some properties of interferon

Interferon could be titrated by the amount of interference induced in fragments of chorio-allantoic membranes challenged with influenza A virus. Over a ten-fold range, inverse proportion between interferon concentration and haemagglutinin titre reached by the challenge virus was observed. Interferon proved stable at 2°C for 2 weeks. Marked inactivation took place after 1 h at 60°C. Interferon was not measurably sedimented by 100 000 g for ½ h. It was held back by gradocol filters of a. p. d. 0.6 μ. It was not dialyzable. Interferon was active against influenza A, Sendai, Newcastle disease and vaccinia viruses. It was not neutralized by anti-MEL rabbit serum and only slightly inhibited by pooled human serum rich in complement-fixing antibody to influenza A soluble antigen.

Particle Counts and Infectivity Titrations for Animal Viruses

Publisher Summary The principles of measuring the concentration of virus particles are based on the techniques evolved for counting bacteria. In this chapter, the principles are discussed along with their application to certain animal viruses. Three aspects of this subject are discussed: (1) measurement of the infectivity titer of a preparation, (2) measurement of the total number of virus particles in a preparation, and (3) calculation of the ratio of the infectivity titer to the virus particle count and the significance of different ratios. There are three types of method used for measuring virus infectivity: direct method, all-or-none response method, and indirect methods. Measurement of the total number of virus particles in a preparation includes those methods in which the particles can be seen and counted directly in the electron microscope such as calculations from the mass, volume, and density. Direct methods (including electron microscopic enumeration) and indirect methods (dosage–response curve) are used. It is suggested that virus particle counting techniques may be useful in searching for incomplete forms of other viruses, and in trying to elucidate which properties of the virus particles and which cell constituents are important in determining what will be the end result of the virus-cell interaction.

Interferon production by different viruses

Abstract Viruses with an optimal temperature of growth of 35° in chick embryo fibroblasts generally gave good yields of interferon in these cells. Viruses with higher optimal temperature of growth (39–42°) gave much lower yields of interferon. When production of interferon was measured at different temperatures in a single cycle of virus growth, the highest yields of interferon were found at temperatures above the optimal temperature for virus growth. Newcastle disease virus showed contrasting behavior in primary cultures of chick and human cells. In chick cells it produced plaques, good yields of infective virus and hemagglutinin, but poor yields of interferon. In human thyroid cells it did not produce plaques, nor did it show any increase of infective virus or hemagglutinin, but it produced good yields of interferon. The findings provide some evidence to favor the suggestion that poor production of interferon may be one factor in virus virulence.

Optimal temperature for growth and sensitivity to interferon among different viruses.

Abstract Eleven viruses have been studied for their optimal temperature for producing plaques in chick embryo fibroblasts. This was found to vary between 32° and 42°, and a good correspondence was found between the optimal temperature for growth and the sensitivity of these viruses to interferon in the same type of plaque assay. Interferon assays carried out at 35° or 39° did not give significantly different results. A relationship between these two properties and the virulence of these viruses for the chick embryo was found, but two exceptions to this relationship were noted.

The influence of oxygenation on virus growth: II. Effect on the antiviral action of interferon

Abstract A good correspondence has been found between the depth to which viruses will grow in tubes filled with agar and their sensitivity to the antiviral action of interferon; viruses sensitive to interferon had a high oxygen requirement. When cultures were prepared in the presence of interferon the viruses did not grow to the same depth, showing that the action of interferon was more pronounced in the deeper parts of the tube. Reduction in the available oxygen, either by addition of sodium thioglycolate or by increasing the depth or the concentration of agar in the overlay, caused an increase in the inhibiting titer of interferon. Increase in the available oxygen, either by incubating cultures in an atmosphere of oxygen or by using a very thin overlay, caused a decrease in the inhibitory titer of interferon. The results are consistent with the hypothesis that interferon inhibits an oxidative process which provides energy needed for viral synthesis.

An Inhibitor of the Production of Interferon ("Blocker ").

Abstract Certain preparations of crude chick interferon had earlier been found to inhibit interferon production as well as virus growth. This inhibition is now shown to be due, not to interferon, but to an inhibitor for which the name “blocker” is proposed. Blocker was found in the allantoic fluid of eggs infected with fowl plague, Newcastle disease virus and B/England/939/59 influenza virus, but not so far in four other strains of influenza virus. Blocker resembles interferon in a number of properties: heat stability, nondialyzability, lack of sedimentation at 105,000 g for 2 hours, stability at pH 2, absence of neutralization by viral antiserum and presence in greater amount in the infected allantoic fluid than in the chorioallantoic membrane. However, blocker differs from interferon in two main ways. Firstly, on partial purification of interferon, blocker becomes gradually separated from interferon. Secondly, on treatment with trypsin there was either no change or a small rise in the activity of blocker, and on treatment with pepsin there was a clear rise. Blocker may be considered as a repressor of the synthesis of interferon.

The Influence of Oxygénation on Virus Growth. I. Effect on Plaque Formation by Different Viruses.

Abstract When tubes containing infected cell cultures were partly filled with agar-containing overlay medium, viral plaques appeared over a limited depth below the surface, but the size and number of plaques approached zero as the depth increased. That this effect was dependent on oxygen concentration is shown by earlier-appearing and deeper plaques when the oxygen tension was raised, and by retarded, shallower plaques when the oxygen tension was lowered. Oxygen requirement for viral growth was influenced by the contents of the overlay medium and the type of host cell. Viruses which were either unrelated or closely related to one another differed in their oxygen requirements and a correlation between oxygen requirement and interferon sensitivity was suggested.

The nucleic acid content of influenza virus

Abstract 1. 1. Three strains of influenza virus have been purified by adsorption on to and elution from aluminium phosphate, followed by differential centrifugation. 2. 2. The total virus was submitted to the Schmidt-Thannhauser hydrolytic procedure and the resulting ribonucleotide mixture was analysed by ion-exchange chromatography. Paper ionophoresis was not satisfactory in the presence of protein. 3. 3. The ribonucleic acid content of the two spherical A strains (WS and MEL) was just over 1%, and there was a very much smaller proportion of deoxyribonucleic acid. The partly filamentous Persian strain contained only about 0.4% of ribonucleic acid. 4. 4. The results as regards spherical strains differed slightly but significantly from those of Ada and Perry 2 . In the present work the ratio of 6-amino/6-oxo bases was approximately 1, and the purine/pyrimidine ratio was unusually low.

Action of interferon on the growth of sublethally irradiated virus

Abstract A strain of influenza and one of fowl plague virus when treated with sublethal doses of ultraviolet irradiation were found to be more sensitive to the action of interferon than was unirradiated virus.