Reactions between influenza virus and a component of allantoic fluid

INFLUENZA : I. THE HEMAGGLUTINATION AND INFECTIVITY TITRE CURVES OF PR8 INFLUENZA VIRUS CULTIVATED IN EMBRYONATED EGGS AT DIFFERENT TEMPERATURES

Groups of embryonated eggs infected with the PR8 strain of influenza virus A were incubated at 34°, 37.5°, and 40°C. At frequent intervals, for periods ranging up to 96 hours, pooled allantoic fluids were tested simultaneously for infectivity and hemagglutination. After about 12 hours of virus growth, fluids often showed infectivity titres greater than 10^–5, but were incapable of causing hemagglutination. At later time intervals, marked disagreement between the two tests for viral activity was noted at all temperatures, but most strikingly at 40°C. Hemagglutination titres were highest and best sustained in eggs incubated at 34°C., while incubation at 37.5°C. resulted in the highest and best sustained infectivity titres. Hemagglutination titre determinations do not reflect accurately the rate of influenza virus multiplication. Possible reasons for the lack of correspondence between hemagglutination and infectivity are discussed.

The multiplication of influenza viruses in the fertile egg: A Report to the Medical Research Council

Hoyle & Fairbrother (1937) showed that tissues infected with influenza virus contained two distinct particles, the infective virus elementary body, and a smaller particle, the soluble antigen, which could be demonstrated by complement-fixation tests.

A labile component of normal serum which combines with various viruses; neutralization of infectivity and inhibition of hemagglutination by the component

A labile component present in the serum of human beings, guinea pigs, and rabbits neutralizes the infectivity of mumps, Newcastle disease, influenza A and B viruses. The labile component of these sera and of mouse serum also inhibits hemagglutination of chicken RBC by these viruses. The component is inactivated by heating at 56 degrees C. for 30 minutes and upon storage at 4 degrees C. for periods longer than 2 weeks. The virus-neutralizing and hemagglutination-inhibiting properties result from serum component-virus combination in the presence of calcium. The combination is stable, and does not undergo spontaneous dissociation. Partial separation of virus can be brought about by heating mixtures held for 24 hours or by removal of calcium ions with sodium citrate. The labile serum component appears to be distinct from hemolytic complement.

The associative reactions of pneumonia virus of mice and influenza viruses; the effects of pH and electrolytes upon virus-host cell combinations

Combination between PVM and erythrocytes as well as between the influenza viruses and erythrocytes is inhibited at low electrolyte concentrations. Combination between PVM and lung particles as well as between the virus and erythrocytes can be dissociated in solutions of low electrolyte concentration. The rate of elution of influenza virus is decreased under similar conditions. PVM can combine with and be dissociated from erythrocytes repeatedly without affecting the combining capacity of the ceils and does not possess an enzyme-like activity similar to that of the influenza viruses. Because dissociation depends on electrolyte concentration and pH, it appears that the PVM-cell component complex may be in the nature of a weak salt.

Studies on host-virus interactions in the chick embryo-influenza virus system; adsorption and recovery of seed virus

Upon injection of active influenza A or B virus into the allantoic cavity of the developing chick embryo, an average of only 70 per cent of the agent was adsorbed onto the tissue, as measured by the difference between the quantity of virus injected and that found free in the allantoic fluid of the injected eggs during the constant period. The degree of adsorption was similar, regardless of whether 10⁹ or 10² ID₅₀ of active virus was injected. Attempts to demonstrate the adsorbed virus in suspensions of the infected tissue met with partial success only in that not more than 1 to 5 per cent of the amount calculated to be adsorbed was actually found. All efforts to increase the yield of virus have failed. These results led to the suggestion that the seed virus, which participates in the propagation, becomes altered in such a way that it no longer may be demonstrated by infectivity titrations, whereas the active virus found represents superficially adsorbed virus, which does not multiply.

A mucoprotein derived from human urine which reacts with influenza, mumps, and Newcastle disease viruses

A mucoprotein, present in normal human urine, has been isolated and obtained in a state of a high degree of purity. A number of the biological, chemical, and physicochemical properties of the substance have been studied. From the results obtained in the present investigation and those reported in succeeding papers (34, 35) it appears that the mucoprotein has a high molecular weight, i.e., of the order of 7.0 x 10⁶, consists of thread-like molecules which have axial ratios of approximately 100, and is specifically antigenic. This substance, which appears to be free of contaminating material, possesses in extraordinary degree the capacity to react with influenza, mumps, and Newcastle disease viruses. At equilibrium, with influenza virus, the minimal amount of the substance capable of giving a demonstrable reaction with one hemagglutinating unit of virus appears to be about 0.0003 µg. The mucoprotein is altered by preparations of influenza viruses and its capacity to react with these agents or others is lost. The kinetics of the inactivation process brought about by influenza viruses is in accord with those of well known enzyme-substrate systems. With the exception of the capacity to react with viruses, altered mucoprotein did not differ from the native substance relative to any of the properties examined in the present study. That certain physicochemical properties of the altered mucoprotein are different from those of the native substance is demonstrated in succeeding papers (34, 35).

Studies on host-virus interactions in the chick embryo-influenza virus system. VI. Evidence for multiplicity reactivation of inactivated virus

Evidence has been presented that influenza viruses both of type A and B partially inactivated by ultraviolet irradiation may regain their capacity to propagate in the allantoic membrane of the chick embryo. In using such irradiated preparations as inocula for growth curve experiments it could be shown that the development of hemagglutinins as well as of infectivity preceded at rates resembling those noted with more than 10 times the amount of infective virus actually found in the irradiated seed. Partial inactivation of the inocula by heating to 56°C. gave similar results. The phenomenon was observed only with seed irradiated for short periods of time so that the virus particles sustained only few hits of radiation. On prolonged exposure resulting in numerous hits per virus particle the capacity of reactivation was lost. Likewise, an irradiated preparation capable of reactivation in the allantoic membrane, could not be diluted more than about 30-fold and still clearly produce this phenomenon. This indicated that reactivation is obtained only when one host cell adsorbs more than one non-infective virus particle but not upon adsorption of a single particle. These data are in striking agreement with the phenomenon of "multiplicity reactivation" observed in the bacteriophage-E. coli system by Luria and Dulbecco.

Studies on host-virus interactions in the chick embryo-influenza virus system. IV. The role of inhibitors of hemagglutination in the evaluation of viral multiplication

The role of inhibitors of hemagglutination in the evaluation of host-virus interactions in the chick embryo-influenza virus system has been analyzed. Comparisons were made between materials (allantoic fluids and membrane suspensions) derived from in vivo (growth curve) experiments at hourly intervals after inoculation, and from in vitro tests in which normal allantoic fluids and membrane suspensions were incubated with virus at 37°C. for various periods of time. In both instances large amounts of virus were added to the systems, resulting in comparable concentrations of the agent. The seeds employed were either fully active or irradiated by ultraviolet light to the extent that the virus lost its capacity to increase but kept its interfering and hemagglutinating properties. The various materials were assayed for (a) the hemagglutinating titers of the virus present in the systems before and after heating to 56°C.; (b) the concentration of inhibitor in the materials at various stages of incubation after heating to 70°C. for 30 minutes as measured by the hemagglutination-inhibition reaction with native or heated test virus (30 minutes 56°C.); and (c) the degree of adsorption of the hemagglutinins present in the materials onto chicken red cells at 0°C. and their subsequent elution at 37°C. The effects of receptor-destroying enzyme (RDE), treatment with sodium periodate, or high speed centrifugation on the inhibitory activities were studied in some of the tests. The essential results which indicate certain sources of error in the evaluation of host-virus interactions as well as means for studying virus activity at the early stages of the infectious process, were as follows: 1. Though some inhibitory effects on hemagglutination were noticeable in the allantoic fluid during the 1st hour after inoculation they were, as a rule, no longer apparent after this interval, and treatment with RDE did not increase the hemagglutinin titers. Thus, the interpretation of growth curve data concerning allantoic fluids hardly seems to be affected by inhibitor. On the other hand, striking effects were noted with the membrane suspensions of growth curve experiments in that RDE shortened the latent period to 2 hours and the titers in the first few positive samples (4 to 5 hours) increased) whereas in later harvests no such effect was noted. Under these conditions complement-fixation antigens and hemagglutinins made their appearance in the tissues simultaneously and not as previously reported the former prior to the latter. However, the infectivity showed increments only several hours after these two activities had become measurable. Thus the hypothesis of the stagewise development of influenza virus is still supported by these data. 2. Using the inhibition of hemagglutination technic it was found that the inhibitor in allantoic fluid rapidly decreased as a result of the action of active and irradiated virus, but destruction was never complete. In the membranes of the in vivo series only active seed led to loss of inhibitor, again without complete destruction, beginning at the time complement-fixing antigen and hemagglutinins became measurable. Irradiated seed was without effect in vivo whereas, in the in vitro tests it equalled the activity of the active virus. The implications of this difference in the effectiveness of active and irradiated seed in vivo with regard to the understanding of the mode of viral multiplication are discussed. 3. Although many factors may influence the shape of adsorption-elution curves it is felt that at 0°C. the extent of adsorption is directly related to the amount of inhibitor present in the systems. In the early hours after inoculation the degree of adsorption was relatively small but it increased gradually with the time of incubation. The inhibitor of adsorption was destroyed by RDE and NaIO₄ and was only partially sedimentable by high speed centrifugation. In every respect studied its properties corresponded with the findings obtained with inhibitors in the hemagglutination-inhibition technic. Although the difference in the rapidity of inhibitor destruction as measured by the various technics might suggest a multiplicity of inhibitors it is felt that it rather denotes a greater sensitivity of the adsorption technic as compared to the others.

DECREASE OF BOUND SIALIC ACID AND INHIBITOR IN CHORIOALLANTOIC MEMBRANES INFECTED WITH INFLUENZA VIRUS

Tess, Bernard R. (University of Illinois at the Medical Center, Chicago) and J. Emerson Kempf . Decrease of bound sialic acid and inhibitor in chorioallantoic membranes infected with influenza virus. J. Bacteriol. 86: 239–245. 1963.—During the adsorption period after the inoculation of chick embryos with the PR8 strain of influenza A virus, bound sialic acid (BSiA) in the chorioallantoic membranes decreased, presumably as a result of cleavage of surface glycoprotein by the viral neuraminidase. A further decrease occurred between 1 and 6 hr after infection, indicating that cleavage of the surface glycoprotein was continuing, and that the enzyme may have begun to act upon intracellular glycoprotein. Decreased levels of BSiA continued until 48 hr after infection, possibly as a result of continued intracellular enzyme activity plus destruction of glycoprotein as virus was released from the surface of the cells. BSiA began to increase 48 hr after infection, presumably because of regeneration of glycoprotein and its decreased destruction by the viral enzyme, since the process of infection was largely completed. Heat-stable hemagglutination inhibitor did not begin to decrease until 8 hr after infection; thereafter, the levels of BSiA and inhibitor appeared to be related.

Studies on host-virus interactions in the chick embryo-influenza virus system. XIV. The relation between tissue-bound and liberated virus materials under various conditions of infection

Studies have been reported concerning the relationships between virus materials found in the allantoic membranes and media of eggs deembryonated after injection of Standard (ST), heat-inactivated (37 degrees C.) standard (DeltaST), and undiluted passage (UP) seeds. It was found that the membranes always contained relatively more non-infectious hemagglutinins (NIHA) than the media and, correspondingly, the ratios between infectious virus and hemagglutinin units (ID(50)/HA) in the tissues were up to 1.5 log(10) units lower than in the liberated progeny. These differences were seen not only following inoculation of undiluted ST, DeltaST, and UP seeds, the progenies of which always contain considerable proportions of NIHA, but also when dilute ST inocula were employed which lead to the liberation of only infectious virus. Essentially similar differences in the ID(50)/HA ratios were observed also in the allantoic membranes and fluids obtained from growth curve experiments in the intact chick embryo employing the various types of seeds. In correlating the liberated virus materials in the media of deembryonated eggs to those in the membranes it was noted that in any given 2 hour interval during the phase of nearly constant production and release up to 10 times the quantity of infectious virus was shed as was present in the tissues at the onset of that period. In contrast, only about (1/4) of the hemagglutinins were released during the same time. The viral (V) and soluble (S) complement-fixing antigens were found in the tissues but no detectable quantities were released during any 2 hour interval. The NIHA in the membranes apparently is located within the cells since it could not be released by the action of RDE. Intracellular inhibitors of hemagglutination were readily inactivated following inoculation of undiluted ST, DeltaST, or UP seeds but not when ultraviolet-inactivated virus was used. The inhibitor activity decreased in proportion to the hemagglutinins produced. Transfer of infected deembryonated eggs to the cold room after production and liberation of progeny were well under way immediately halted further release but in the tissues the status quo was maintained and release was resumed on return to the 37 degrees C. incubator. The addition of potassium cyanide to the medium of deembryonated eggs at 37 degrees C. during the period of nearly constant production and release of virus material reduced immediately and to comparable extents the ID(50) and HA titers in the tissues and liberation decreased in proportion. On removal of the cyanide 2 hours later, both titers in the tissues gradually returned to those of the untreated control eggs with a corresponding increase in liberation. The ID(50)/HA ratios were not affected by these manipulations. It is concluded that the NIHA in the membranes forms part of a dynamic process. An attempt has been made in the discussion to integrate the present results with previous observations concerning the formation of incomplete forms of virus and their nature and role in the infectious process.

Influenza virus and its mucoprotein substrate in the chorioallantoic membrane of the chick embryo. I. Characterization and quantitative assay of soluble substrate and studies on its relation to allantoic cells

As a preliminary to a study of the fate of mucoprotein substrate in tissues infected with influenza virus, some characteristics of soluble hemagglutination inhibitors (HI) extracted from chorioallantoic membranes (CAM) have been investigated. The inhibitory material was found to be heat-stable, precipitable with cold ethanol, and subject to progressive inactivation by active viruses or by receptor-destroying enzyme (RDE). Certain changes in the slope of titration curves obtained with precipitated and non-precipitated fractions upon alcohol fractionation suggested that the HI in heated CAM extracts was heterogeneous. Alcohol in low concentration precipitated preferentially the more efficient (longer?) HI leaving the "weak" component in the non-precipitated fraction. With higher concentrations of alcobol, "strong" HI were converted to "weak" ones, either by denaturation or as result of reduced solubility. These changes in slope of titration curves were reflected in significant discrepancies when densitometric titers (HI(50)) of fractions were compared with their titers in pattern tests. The action of active viruses on HI, on the other hand, did not induce qualitative changes in the composition of the inhibitory principle: Titration curves retained parallel slopes even when their position was markedly displaced from that of control curves. In its essential properties, the HI from the CAM appeared to be similar to inhibitors isolated from various other biological sources which have been identified as mucoprotein in nature. Standards for reproducibility of inhibitory titers obtained by the densitometric method of Hirst and Pickels have been presented. The relation of HI to the allantoic epithelium has been analyzed. It has been concluded that the HI is a normal constituent and secretion product of these cells. Under physiological conditions, i.e. in the intact egg, the HI contained in the mucoid outer layer of allantoic cells appears to be protected from enzymatic action from without, although adsorption of viral particles may be temporarily impeded. In deembryonated eggs, or in excised membranes, a reduction in total inhibitory substrate as a result of the action of RDE has been observed. It has been shown in experiments on adsorption of active or heat-inactivated virus on the allantoic membrane that prevention of adsorption by RDE may require the synergistic action of the active viral enzyme itself. It has been concluded that the maintenance or restoration of a normal supply of mucoprotein substrate is a function of the ability of allantoic cells to maintain homeostatic conditions under stress.

Inhibition of Theiler's encephalomyelitis virus (GDVII strain) of mice by an intestinal mucopolysaccharide. I. Biological properties and mechanism of action

A mucopolysaccharide has been obtained from intestinal tissue of adult mice which inhibits both infectivity and hemagglutination of Theiler's GDVII strain of encephalomyelitis virus of mice. The inhibitor is inactive against the FA and TO strains of Theiler's virus and against the Lansing strain of poliomyelitis virus. In the adult mouse, large amounts of the inhibitor are found only in the small intestine. The small intestine of infant mice, however, contains a considerably smaller amount of inhibitor. Inhibition, both in vivo and in vitro, appears to be the result of an interaction between virus and inhibitor. The intestines of man, monkey, rabbit, rat, cotton rat, hamster, sheep, cow, and pig contain relatively little inhibitor whereas guinea pig intestine contains as much as adult mouse intestine. An enzyme was found in the feces of mice, and several other animals, which is capable of destroying the inhibitory activity of the mucopolysaccharide with the liberation of reducing sugars.

Studies on host-virus interactions in the chick embryo-influenza virus system. VII. Data concerning the significance of infectivity titration end-points and the separation of clones at limiting dilutions

Equal mixtures of influenza A (PR8) and B (Lee) viruses, based on predetermined ID(50) values of the individual preparations, were titrated in closely spaced steps near the 50 per cent infectivity end-point. Typing of the hemagglutinins found in the allantoic fluids after incubation of the eggs for 72 hours showed an approximately equal distribution between types A and B, when less than 2 ID(50) of the mixed seed had been injected. With larger inocula influenza A became dominant because it reproduces at a faster rate than the influenza B virus. While this result agreed with expectations, it was found that passage of the allantoic fluids revealing influenza A agglutinins in mixture with anti-A serum, and of B agglutinins with anti-B, yielded the heterologous virus in many instances, even when only one-half of an ID(50) of mixed seed had been administered in the original titration. "Negative" fluids obtained from embryos injected with as little as one-eighth of an ID(50) upon passage yielded on occasion virus of one or the other type. Similar closely spaced titrations near the 50 per cent end-point of single strains (PR8) indicated that if hemagglutinins were found after incubation of 72 hours they were of high titer, as a rule. However, in some embryos hemagglutinins became detectable only between the 3rd and 4th days of incubation. In addition, negative allantoic fluids removed from embryos 72 hours after injection yielded on occasion virus on passage, yet no hemagglutinins were found in some of these eggs after an additional incubation period of 24 hours, or a total of 96 hours. None of the possible explanations for these various observations, which have been discussed in detail, is completely satisfactory. However, the data indicate that in infectivity titrations the ID(50) end-point obtained at 72 hours, or even after 96 hours, does not reflect the total amount of virus present in the material titrated. The data also denote that separation of variants, or mutants or "genetic recombinants" by the limiting dilution technic, although possible, does not represent an absolutely safe procedure.