THE NATURE OF NON-SPECIFIC INHIBITION OF VIRUS HEMAGGLUTINATION

The nature of the virus receptors of red cells; evidence on the chemical nature of the virus receptors of red cells and of the existence of a closely analogous substance in normal serum

The influenza virus receptors of fowl red cells and the influenza virus inhibitor of normal rabbit serum have the following attributes in common: They are stable at high temperatures and in solutions of pH as high as 10.0. They both resist destruction by a number of oxidizing agents but are readily destroyed by sodium periodate, trypsin, and influenza virus. These facts suggest that the red cell receptor and the normal serum inhibitor are either the same or analogous substances and that they may belong to the mucoprotein class of compounds.

Reactions between influenza virus and a component of allantoic fluid

Evidence is presented which shows that there is a component present in normal allantoic fluid, probably mucoprotein in nature, capable of combining with influenza A virus (PR8), and that following combination between this component and the virus only partial dissociation of the complex occurs. Evidence is also presented which strongly suggests that the component is present in virus-infected allantoic fluid in which it is in part combined with the virus and in part free although altered by viral action. The probability that the component is present as well in highly purified preparations of influenza virus, and its effect upon various reactions obtained with this agent are discussed.

The production of fever by influenzal viruses; factors influencing the febrile response to single injections of virus

The intravenous injection of the PR8 strain of influenza A virus, the Lee strain of influenza B, and the "B" strain of Newcastle disease virus produces fever in rabbits. This phenomenon has been studied in relation to certain in vitro properties of these viruses. Saline suspensions of virus prepared by centrifugation or elution from chicken erythrocytes produced fever. Fluids from which most of the virus particles had been removed were non-pyrogenic. Exposure to temperatures which destroyed the infectivity of the virus for chick embryos did not prevent fever. However, heating sufficient to destroy the hemagglutinin also rendered virus non-pyrogenic. The injection of erythrocytes onto which virus had been adsorbed produced fever. Heated virus adsorbed onto erythrocytes, which failed to elute, produced no elevation of temperature, although heated virus alone was pyrogenic. Neutralization of virus with specific immune serum prevented fever. Antipyrine was capable of abolishing the febrile response to virus. Certain differences between the febrile response in rabbits to the injection of viruses and that following bacterial pyrogens were noted. The period between injection and beginning of temperature rise is longer with virus than with bacterial pyrogens. Relatively low temperatures inactivate the fever-producing capacity of viruses, whereas bacterial pyrogens withstand prolonged autoclaving, and the neutralization of viral fever by specific immune serum contrasts sharply with the failure of antibody to affect the response to bacterial pyrogens. Certain previous observations on the lymphopenia produced in rabbits by the injection of influenzal viruses were confirmed. The capacity of virus preparations to induce fever in rabbits closely parallels their capacity to induce lymphopenia. It was concluded that the fever-producing property of influenzal viruses is closely associated with the capacity to agglutinate erythrocytes.

The production of fever by influenzal viruses; tolerance in rabbits to the pyrogenic effect of influenzal viruses

The mechanism of the fever caused by the intravenous injection of viruses of the influenza group in rabbits has been studied by observing the effect of repeated injections of the same or heterologous viruses. An initial injection of the PR8 strain of influenza A, the Lee strain of influenza B, or the "B" strain of NDV conferred tolerance to the pyrogenic effect of homologous virus administered on the following day. The period of tolerance lasted approximately 11 days. Prior injection of virus appeared also to protect against the lymphopenic action of homologous strains. These viruses were found to confer tolerance to the fever-producing effect of heterologous strains in an order corresponding to their positions in the receptor gradient of Burnet. Heated virus preparations appeared to confer tolerance in proportion to survival of hemagglutinin. Tolerance is probably unrelated to specific antibody formation since it is lost during a period of rapid immune response and heterologous strains exert a protective effect. No cross-tolerance was demonstrable between viruses and bacterial pyrogens and reticulo-endothelial blockade with thorotrast failed to modify the unresponsiveness of animals to 2nd day injections of homologous virus. Prevention of fever with antipyrine did not interfere with the protective effect of initial injections of virus. Arguments for and against a hypothesis that union of the virus particle with a receptor substance may play a part in the production of fever by these viruses are discussed.

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. 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.

A study in vitro of components in the transmission cycle of swine influenza virus

Swine lungworm extracts and suspensions of swine lungworms contain receptor-like substances capable of adsorbing influenza virus, a result consonant with the hypothesis (5–8) that the lungworm may be involved in the swine influenza cycle. Yet no evidence for multiplication of virus or even persistence of infectious virus in lungworms at undimished titer was found. Clearly much more information is needed, and it is hoped that the present demonstration of the practicality of studying the components of the transmission cycle proposed by Shope, will provide important tools requisite for further investigation of this problem. Studies on the role of the earthworm in the transmission of swine influenza suggest that, at best, that role would be a passive one.

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.