Number Of Infectious Centers Research Articles

Rous sarcoma virus production in mixed cultures of mammalian Rous sarcoma cells and chick embryo cells.

AbstractThe induction of Rous sarcoma virus (RSV) production was analyzed in mixed cultures of mouse or hamster Rous sarcoma cells and chick embryo cells treated with ultraviolet inactivated hemagglutinating virus of Japan (UV‐HVJ). The pre‐treatment of UV‐HVJ with a certain concentration of anti‐HVJ serum increased the yield of infectious RSV in mixed cultures enabling a quantitative analysis of this phenomenon to be made. RSV‐inducing ability of a mixture of HVJ and anti‐HVJ serum was affected by the concentration of anti‐HVJ serum and showed changes in parallel with the cell fusion activity of the mixture. The effect of UV‐HVJ on RSV induction was not achieved by incubation of the cell mixture at 0° C as it was after shaking at 37° C. These findings suggest that the production of infectious RSV in mixed cultures may be initiated in heterokaryons of mammalian Rous sarcoma cells and chick embryo cells. The number of infective centers in mixed cultures was, however, as small as 1% of that of heterokaryons. It is possible that only a small fraction of the heterokaryon population is productive of infectious RSV.

The Growth of Echovirus 1 in HEp-2 Cells Treated with Antibody to the Host Cells

Summary Antibody prepared against HEp-2 cells inhibited the replication of echovirus 1. The number of infective centres was reduced and the cells which were infected produced less virus per cell than control cells. The attachment of virus to cells was not affected. The inhibition was reduced by increasing the multiplicity of infection. Application of antibody 5 min. after virus adsorption at 4° reduced the inhibition and there was little inhibition when it was applied 10 min. after adsorption. The antiserum had no inhibitory effect when infection was initiated by virus RNA; the antiserum may act by preventing uncoating of the virus.

The effect of polycations on the interaction of viral RNA with mammalian cells: studies on the infectivity of single- and double-stranded poliovirus RNA.

Abstract A wide variety of polycations augment the infectivity of single- and double-stranded poliovirus RNA. Several mechanisms of action may be involved, depending upon the polycation and the form of RNA in question, but it is clear that the stimulation of infectivity is not solely a consequence of improved adsorption and penetration. In the range of 50–50,000 RNA molecules per host cell, there is a linear relationship between quantity of RNA and number of infectious centers. However, larger excesses of RNA result in a sharply reduced yield of infectious centers and a concomitant reduction in the cloning efficiency of the host cells. The maximum proportion of a cell population that could be infected in the experiments reported was 2–4% in the case of single-stranded RNA, 0.5% in the case of double-stranded RNA. The adsorption and penetration of double-stranded RNA is complete within 2–3 minutes, whereas that of single-stranded RNA occurs more slowly. The present data, and those from previously reported experiments, indicate differences between the initial events of the growth cycles of single- and double-stranded RNA.

Suppression of growth of herpes simplex virus in chick embryo fibroblasts at 40 degrees C.

Four strains of herpes simplex virus tested all showed inability to form plaques in chick embryo fibroblasts (CEF) at 40 C, while no such suppression of growth was observed with WEE, vaccinia or JE virus in the same cells. The suppression was not due to a complete inhibition of viral growth, because virus-infected CEF bottle cultures consistently showed a small but definite increase of virus titer in 24 hr. When CEF monolayers adsorbing herpes virus were placed at 40 C, the number of infective centers decreased gradually; however, this decrease was much slower than the degradation of free virus at this temperature. Transfer of virus-infected CEF bottle cultures from 35 C to 40 C at any time during a one step growth cycle promptly slowed down subsequent virus replication. When virus-infected CEF bottles were incubated first at 40 C for 24 hr and then transferred to 35 C, a new increase in virus titer took place following a short lag. What stage of virus replication is suppressed at 40 C remains yet to be determined.

Comparison of ultraviolet sensitivity of Bacillus subtilis bacteriophage SPO2 and its infectious DNA

Deoxyribonucleic acid extracted from a clear plaque mutant of the temperate phage, SPO2, was infectious when incubated with competent cultures of Bacillus subtilis 168 M . The relationship between numbers of infectious centers and DNA concentration was linear. The sensitivity of the infectious DNA to ultraviolet light was much greater than that of the free phage when B. subtilis 168 M was used as host. Acriflavin, which inhibits host cell reactivation, increased the rate of ultraviolet inactivation of the free phage so that it approached the inactivation rate of the phage DNA. Acriflavin had little effect on the survival curves of the infectious DNA. Non-host reactivating mutants (hcr−)† of B. subtilis 168 M were isolated. The survival curves of SPO2 phage were much steeper when the hcr− mutant was used as a host than those obtained when the hcr+ parental strain was used as a host. Ultraviolet sensitivity of the phage DNA was still greater than that of the free phage even when B. subtilis hcr− was used as host, but the difference in sensitivity was much less than the difference obtained with B. subtilis hcr+ as a host. Possible explanations for the greater ultraviolet sensitivity of the infectious DNA are discussed.

Inhibition of Sendai virus by N-1-isobutylbiguanide hydrochloride as studied by immunofluorescent staining.

SummaryIn the presence of a non-toxic concentration of N1-isobutylbiguanide hydrochloride, HA production in L cells infected with Sendai virus was reduced to 1/16 of the control. The effect of the compound was reversible, and the presence of the compound through the entire course of infection was necessary and essential for the inhibition. The number of infectious centers was not reduced even when the cell was treated with the compound all through infection, indicating that the compound did not affect the processes of adsorption or penetration of the virus. However, the infected cells remained in the first stage of antigen development in the presence of the compound, i.e., the accumulation of antigens was limited to the juxta-nuclear region of cytoplasm and not extended to the entire cytoplasm. It is concluded that the effect of the compound is on the inhibition of the late maturation mechanism of Sendai virus synthesis.

Behaviour of an Attenuated Strain of Foot-and-mouth Disease Virus in Culture

IN previous articles1,2 it was reported that differences were found between virulent and attenuated strains of foot-and-mouth disease virus in surviving cultures of calf tongue epithelium. The attenuated strains (a) gave rise to a lower number of infective centres after adsorption, (b) were less efficiently titrated in the epithelial cultures, (c) multiplied to a lower titre, but (d) produced more interferon, and (e) were more sensitive to interferon action than the virulent strains. From the findings it was suggested that at the most only 5 per cent of the attenuated strain was competent, that is, was able to initiate infection and the further production of virus. The other 95 per cent was thought to enter the cell, inducing cellular resistance and the production of interferon. As a result of successive multiplication cycles of competent virus there was a build-up of non-competent virus and of interferon, which, in turn, inhibited the growth of competent virus. Hence there was a failure of lesion development in animals but still sufficient antigen production to stimulate immunity.

Chemical changes in chick embryo cells infected with Rous sarcoma virus in vitro

The content of nucleic acid (RNA and DNA), acid-soluble nucleotides, and proteins, and the mean cell volume were determined over a period of 7 days in chick embryo fibroblasts infected in vitro with RSV. The essential findings were the following: Normal cells subcultured for 24 hours, in which the virus reproduces most rapidly, had a high metabolic activity and accumulated RNA and acid-soluble nucleotides. From the time of infection to the third day, the average total RNA (RNA plus acid-soluble nucleotides) per infected cell remained the same as in the control cells. Later, the total RNA increased and the excess reached 75% of the control value by the seventh day. From the second day after infection until the end of the experiments, cells of cultures in which all cells released virus contained 40–70% more RNA than normal cells, which is about twenty times the quantity of viral RNA released by infected cells in 24 hours. The acid-soluble nucleotides increased from the fourth day, when 50–100% of cells registered as infective centers and both the cell count and the number of infective centers became stationary. The proteins and the mean volume of infected cells increased in parallel from the second day after infection until the end of the experiments, reaching values double those in controls. The quantity of DNA in infected cells remained unaltered. Infected cells grew more slowly than noninfected cells after 2 days; from the study of cell multiplication and mean cell volume, it appears that the contact between cells may inhibit the growth of infected as well as of control cells.

THE INFLUENCE OF HYDROSTATIC PRESSURE AND URETHANE ON THE THERMAL INACTIVATION OF BACTERIOPHAGE

In Difco nutrient broth, containing 0.5 per cent NaCl, pH 6.6, Escherichia coli phages T1, T2, and T5 were inactivated at 66 degrees C., and T7 at 60 degrees C., at nearly the same rate. In each case the rate of destruction was not uniform but more or less decreased with time of heating. With T2 there was an initial increase in number of infective centers after heating for several minutes at 66 degrees C. Hydrostatic pressures up to 10,000 pounds per square inch retarded the thermal destruction of T1, T2, and T5, but accelerated that of T7, while small concentrations of urethane accelerated the rate of each. The rate of inactivation was increased by the addition of 0.005 M phosphate, and was decreased by 0.005 M MgCl(2) in all but T7, whose rate was unaffected by this amount of Mg. The influence of Ca was similar to that of Mg. The addition of 0.005 M MgCl(2) to the broth medium resulted in a first order rate of destruction of T5 at either normal or increased pressure, and with as well as without urethane. Analysis of data obtained under these conditions indicated that the thermal inactivation proceeds with a volume increase of activation of 113 cc. per mol, and with a heat and entropy of 170,000 calories and 425 E. U., respectively, in the rate-limiting reaction. In the presence of 0.1 M urethane the heat and volume change of activation are apparently slightly greater. The relation between concentration of urethane and the amount of acceleration in rate of destruction at normal pressure and 66 degrees C. indicated that the total rate involves at least two first order rate processes: the thermal inactivation itself and a urethane-catalyzed reaction, the latter involving the combination of an average of 2.3 molecules of urethane in the activated state of the bacteriophage molecule whose destruction results in loss of phage activity.

CHEMICAL STUDIES ON HOST-VIRUS INTERACTIONS

5-methyl tryptophane inhibited the multiplication of E. coli B without apparently affecting the rate of its oxygen utilization or R. Q. in a synthetic medium. E. coli B, under conditions of inhibition in the presence of this compound, was infected with the bacterial viruses T2 or T4. Infected organisms, in the presence of this compound, were unable to reproduce virus, assayable by the plaque method. Indeed, the number of infectious centers disappeared at a logarithmic rate in the presence of 5-methyl tryptophane, although the compound did not reduce the titers of B, T2, or T4, when the bacteria or viruses were exposed separately to the agent. In contrast to the irreversibility of the interference effects induced by viruses, the effects induced by short exposures to 5MT appear to be reversible on removal of the compound.