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

Immunological reactions of the Coxsackie viruses. I. The neutralization test; technic and application

The neutralization test is a reliable and useful procedure for following immunological reactions of the Coxsackie viruses (C virus). The standard procedure has been an incubation period of 1 hour at room temperature followed by subcutaneous inoculation into newborn mice. However, this time and temperature are not critical, for the virus in neutralized within 10 minutes of mixing with immune serum and remains neutralized for long periods. During the variable incubation periods used, the control virus remained active, even in dilute suspensions. The neutralization test is not affected by the presence or absence of complement. Neutralizing antibody is stable at 65°C. for 30 minutes, and immune serum has to be heated to 80°C. for 30 minutes before the antibody is no longer detectable. As the quantity of virus is increased, the quantity of serum required for neutralization likewise increases, but not in a regular or predictable fashion. Neutralized mixtures of the virus can be made infective again by simple dilution before inoculation. The neutralization test is a satisfactory means for typing Coxsackie viruses. At least seven antigenic types have been identified. Similar antigenic types have been found to be scattered over wide areas. Thus the Conn.-5 type was present in 1948 in Massachusetts, Connecticut, New York, and North Carolina. The Texas-1 type was present in 1943 in Connecticut and in 1948 in North Carolina and Texas. Further information on the specificity of the neutralizing antibody response has been obtained from a study of the occurrence and development of antibodies in 6 patients who contracted infections with one or another of the C viruses while working with them in the laboratory. From each patient a virus was isolated during the illness. No patient had detectable antibodies to his strain before his illness, but each soon thereafter developed antibodies to his own strain and to the prototype strain to which it was related. By means of the neutralization test, it has been shown that a family epidemic may include two different immunological types of virus. Neutralizing antibodies appear at the time of or soon after onset of illness, increase rapidly to titers of about 1:1000 which are maintained during the period of 1 to 3 months following infection, and are still present 2 years later, although at lower levels. Neutralizing antibodies are present in the normal population. In North Carolina, over 80 per cent of the children have antibodies at birth. The level falls rapidly to a minimum of 14 per cent at the age of 1, and then it quickly rises to reach the adult level at the age of 7. Gamma globulin collected in various parts of the United States between 1944 and 1949 and in Denmark in 1949 neutralizes at least four antigenically different Coxsackie viruses.

The biological, immunological, and physicochemical characterization of a transmissible agent capable of inducing DNA and thymine degradation in cultured human cells

Experiments designed to characterize an unidentified transmissible agent brought forth the following findings: The cytopathology consisted of the formation of intranuclear globules, collapse of the involved nuclei, and the extrusion of nuclear materials. The relatively dormant primary human amnion cells were less susceptible than the rapidly growing cell lines. Similarly, the slowly multiplying ribose variants were less susceptible than their corresponding parent cell lines. Interferon-like activity was released from infected cells. Infectivity was readily demonstrated following storage at 0–4°C for at least 8 months or at 37°C for at least 2 weeks. Freeze-thawing, however, markedly reduced or completely destroyed its infectivity. Infectivity was destroyed completely by ether and chloroform; partially by desoxycholate, and not affected by trypsin, papain, RNAse, DNAse, hyaluronidase, lysozyme, lecithinase, or pancreatic lipase. The rate of inactivation by 0.025 per cent formalin was much slower than that of vaccinia and herpes viruses. Its synthesis was suppressed by 5-fluorodeoxyuridine. This suppression was not reversed by thymidine and/or uracil. Heat-stable neutralizing antibody could not be demonstrated in 379 human and animal serums, in human gamma globulins, or in serums from animals "immunized" with this agent. Heat-labile inhibitors (lipoprotein-like) capable of inhibiting the infectivity of this agent were demonstrated in 154 of the 157 serums tested. Experimental evidence indicated the non-identity of this ubiquitous inhibitor and the properdin system. The non-infectious complex between this agent and the ubiquitous serum inhibitor may be dissociated (hence, become infectious) by simple dilution. Repeated attempts to reisolate a similar agent have not been successful. We have hypothesized that this agent is a virus consisting of DNA wrapped in a surface coat rich in lipid, and suggest that this virus be referred to tentatively as a lipovirus.

Physiologic role of the complement system in host defense, disease, and malnutrition

The role of the complement system as a system merging early-phase innate immunity with later-phase acquired immunity has been established. C3 is a key protein of the complement system. It is activated in four pathways: (1) the alternative pathway, (2) the mannan binding protein pathway, (3) the C-reactive protein pathway, and (4) the natural IgM pathway in innate immunity. It is also activated in (1) a classic pathway, i.e., through an antigen-antibody complex, and (2) by injured host cells in acquired immunity. Activation of C3 results in a variety of immunologic reactions such as immune adherence, phagocytosis, antibody response, cytolysis, inflammation, and killing of pathogenic microorganisms. Pathologic pictures of the complement system in various diseases were reviewed. Attention was focused on hypocomplementemia in the malnourished state. In humans and in experimental animals, reduced complement levels, especially of C3, were observed in relation to lowered host defense against infection. Hypocomplementemia improved after nutritional rehabilitation with a concomitant improvement of the clinical picture and recovery of host resistance. Enhancement of C3 levels in malnourished or well-nourished rats resulted in heightened resistance against bacterial infections. On the basis of these experimental and clinical observations, we obtained clues to prevent or treat a compromised host defense system in malnourished states.

Virulence of influenza A virus for mouse lung

The experimental infection of mouse lung with influenza A virus has proven to be an invaluable model for studying the mechanisms of viral adaptation and virulence. These investigations have identified critical roles for the haemagglutinin (HA) and matrix (M) genes of the virus in determining virulence for mouse lung. For the HA gene, the loss of glycosylation sites from the encoded polypeptide or changes which may affect the pH of HA-mediated endosome fusion have been observed following adaptation. These alterations also have the potential to impact on receptor specificity, beta inhibitor sensitivity and activation cleavage which may act in concert to account for the increased virulence of adapted strains. For the M gene, two specific changes in the M1 protein have been identified in strains adapted to, or virulent for, mouse lung. These changes are likely to affect pH-dependent association/dissociation of M1 with the viral ribonucleoprotein, and control virulence as well as growth. The role of other genes in mouse lung virulence remains unknown.

Isolation and characterization of conglutinin as an influenza A virus inhibitor

Normal horse and guinea pig sera contain alpha 2-macroglobulin which inhibits the infectivity and hemagglutinating activity of influenza A viruses of the H2 and H3 subtypes. On the other hand, normal bovine serum contains a component termed beta inhibitor that inhibits the infectivity and hemagglutinating activity of influenza A viruses of the H1 and H3 subtypes. To investigate the nature of the beta inhibitor of influenza A virus, we purified the conglutinin and examined its characteristics. First, we found a high correlation between the hemagglutination inhibition(HI) titer and conglutinin titer in several bovine sera (r = 0.906, p less than 0.005). The HI of bovine serum was mainly dependent on conglutinin because the HI activity was abrogated by N-acetylglucosamine but not by D-mannose. The conglutinin, purified from bovine serum, had neutralizing-activity as well as HI activity on influenza A viruses of the H1 and H3 subtypes. The HI activity of conglutinin was heat stable (56 degrees C, 30 min), Ca(++)-dependent, and resistant to both neuraminidase and periodate treatments. The HI activity of purified conglutinin was blocked by N-acetylglucosamine but not by D-mannose. The conglutinin was bound to hemagglutinin which had high mannose and complex sugar chains and its binding was inhibited by N-acetylglucosamine and dependent on divalent cations. These data indicate that the beta-like inhibitor activity of bovine serum is mainly dependent on conglutinin which inhibits hemagglutination and neutralizes the virus infectivity by its binding to a carbohydrate site at the HA.

Biological functions of monospecific antibodies to envelope glycoproteins of Newcastle disease virus

Monospecific antisera to HN and F glycoproteins of Newcastle disease virus were prepared, and their effects on the biological activities of the virus were investigated. Anti-HN serum inhibited hemagglutinating and neuraminidase activity, as well as hemolysis. Anti-F serum had no effect on hemagglutination or neuraminidase but inhibited hemolysis and virus-induced cell fusion. Anti-HN serum was highly neutralizing, while neutralization by anti-F serum was very inefficient in conventional plaque reduction tests, although both sera were estimated to contain comparable amounts of antibody reacting with the virus as indicated by complement fixation and immuno-diffusion tests. The neutralizing activity of anti-F serum was greatly enhanced by the addition of anti-IgG serum or fresh guinea pig serum, whereas that of anti-HN serum was little enhanced. Anti-HN serum incorporated in the agar overlay suppressed the development of plaques to some degree, while anti-F serum had little effect. The combination of anti-HN and anti-F sera resulted in a marked decrease in the number and size of plaques, demonstrating the synergistic effect of the two species of antibody in the containment of the spread of viral infection.

Epidemiology of mumps in the Netherlands

In a Dutch population group neutralizing antibodies against mumps virus were determined by a plaque reduction technique, which proved reproducible, sensitive and specific. The results with sera of about 800 suburban children show that mumps is acquired at an early age with peak acquisition rates between the ages of four and six years. Over 90% have acquired mumps before the age of 14 years. More than 95% of about 1000 adults (18--65 years) have neutralizing antibodies. The relatively constant median titre suggests that antibodies persist during life. During a family study 77 clinical and 18 subclinical cases were observed. In families with index cases the attack rate was 26/37 = 0.71. Eleven children (excluding six babies) escaped infection. The mean attack rate during the epidemic was 0.30. The mean titre of mumps neutralizing antibody is maximal during the first year after the disease but declines during childhood. Mothers exposed to mumps in the family occasionally showed a significant rise in titre. Some seronegative mothers remained seronegative after exposure.

Neutralization of animal viruses

Various aspects of the interaction of bacterial viruses and antibody were studied by Andrewes and Elford in England. Similar studies, as well as studies on animal viruses, were carried out in Australia by Burnet and his colleagues. One result of their extensive studies, which were summarized in great detail, was the conclusion that, with respect to their interaction with antibody, bacterial and animal viruses were basically different. Specifically, the difference resided in the stability of the union of virus and antibody, whereas bacterial viruses formed stable complexes, animal viruses formed complexes that tended to dissociate readily. The introduction of animal cell cultures as host systems greatly aided in the study of animal viruses, with respect to fewer and more readily controlled variables, and by the use of the plaque assay in enhanced quantitative reliability. In 1956, Dulbecco et al. described the interaction of two animal viruses with their respective antibodies. The results of these studies led these investigators to conclude, among other things, that animal viruses, at least the two they studied, reacted with antibodies to form complexes that did not dissociate spontaneously. This interpretation was challenged by Fazekas de St. Groth and Reid. As more animal virus-antibody systems were studied by many investigators, there seemed to be a greater accord for irreversible, rather than reversible, interaction. For this reason, in this chapter it is assumed that there are no differences between bacterial viruses, as one category, and animal viruses, as a separate category, concerning their interaction with antibodies. Rather, differences, when they exist, are considered to be related to the viruses per se. Although this chapter is intended to survey the neutralization of animal viruses, occasional reference is made to the studies on bacterial viruses when these studies are pertinent and illuminating to the topic at hand.

Immunological studies of heat-labile virus inhibitors. I. Specificity of absorption onto sensitive viruses and specific response after virus infections

Heat-labile virus inhibitor (HLI) in normal sera of various mammalian species capable of neutralizing variola (VRV) and Newcastle disease viruses (NDV) was studied immunologically. After sucrose density gradient centrifugation of guinea pig serum, the HLI activity against VRV and that against NDV were both demonstrated in the same region sedimenting fastor than IgM. Absorption with partially purified VRV or NDV removed the HLI activity on the homologous virus but not that on the other. Prior saturation of virions with specific antibody blocked the absorption of HLI, suggesting a specific competition for binding site (s) between specific antibody and HLI. The HLI level against variola virus was checked in connection with immunization with vaccinia virus. In human primary vaccination, the HLI level rose sharply within 4 weeks after vaccination, turning to decline gradually to settle at a level higher than that of the conventional neutralizing antibody (NA). In cases of human revaccination, a sharp rise of HLI started 4 days after vaccination and reached the highest level within 7 days, preceding the rise of conventional NA level which occurred about 3 days later. Three rabbits with negative HLI activity prior to vaccinia immunization obtained an HLI activity within 2 weeks, which showed a sharp rise up to 6-8 weeks. One rabbit with a positive prior HLI activity also showed a sharp rise of the HLI activity after immunization. In all rabbits the final HLI level was identical with that of conventional NA. Groups of guinea pigs were immunized with either VRV or NDV. Rises of the HLI level after immunization were observed in all animals, the activity being restricted to the homologous virus used in the immunization. Complement requiring NA was detected during the course of immunization but its behavior was different from that of HLI. The above observations were interpreted to suggest a ubiquitous presence of HLI as a specific reactive agent and its role at an earliest stage of immune response.

Interferon-Like Viral Inhibitor in Rabbits after Intravenous Administration of Endotoxin

Intravenous injection into rabbits of endotoxin or killed cells of Escherichia coli induced, in 1 hour, a viral inhibitor detectable in serum. The inhibitor disappeared from the serum in 7 to 24 hours, and was only active after incubation with rabbit cell cultures. Like interferon, it did not preferentially inactivate virus directly, was ineffective in chick cells, was inactivated by trypsin, and was not sedimentable. Unlike interferon, the inhibitor was heat labile. Nucleic acid or nucleotides apparently play no role in its induction.

STUDIES ON THE PATHOGENESIS OF FEVER WITH INFLUENZAL VIRUSES

Observations have been made on the fever-inducing properties of an endogenous pyrogen found in the circulation of rabbits after the intravenous inoculation of Newcastle disease virus (NDV). When endogenous pyrogen was given to a normal recipient, a biphasic fever was produced which simulated that seen with bacterial endotoxins. With the use of a technique of serial passive transfer, it has been shown that the "double-humped" response results from two separate actions of the injected pyrogen. The first of these appears to be a direct stimulation of the thermoregulatory centers. The second involves the release of further endogenous pyrogen in the normal recipient to cause, in turn, the second fever peak. Since the injection of endogenous pyrogen did not produce a significant change in the number of circulating leukocytes, it is inferred that this substance is different from either bacterial or tissue polysaccharides. In rabbits rendered tolerant by a previous injection of virus the second fever peak failed to appear and the response to endogenous pyrogen was monophasic. Evidence indicates that the absence of a second fever peak in the tolerant recipient was not due to rise in temperature on the preceding day of virus injection or to the development of either serum inhibitors or tolerance to virus itself. It is postulated that prior mobilization of endogenous pyrogen by virus may have modified the ability of the tolerant recipient to liberate further amounts of this substance in response to an injection of endogenous pyrogen.

The properdin system and immunity. VI. The inactivation of Newcastle disease virus by the properdin system

Detailed experiments are presented which indicate that the properdin system is an inhibitor of Newcastle disease virus. Viral inhibition required all known components of the properdin system: properdin, all four components of complement and magnesium; the removal of any one constituent resulted in a loss of inhibition; the replacement of the constituent restored antiviral effect. The inhibition of virus was temperature-dependent. The process of inhibition by serum resulted in a decrease in the amount of properdin available in the serum without any measurable effect on the components of complement. The prolonged incubation of inactive serum-virus mixtures with cation-exchange resin resulted in the restoration of some, but not all, of the hemagglutinating activity of the virus. The requirements of the properdin system and the implication of these findings were discussed.

The properdin system and immunity. V. The bactericidal activity of the properdin system

Methods for the preparation and standardization of reagents suitable for studies on the bactericidal action of the properdin system are described. The preparation and properties of serum free of properdin (RP(b)) are presented in detail because of the necessity for a suitable RP(b) in these studies. The properdin system is responsible for the bactericidal action of normal human serum against a variety of microorganisms. The present work shows that the removal of properdin from serum also removes bactericidal activity. Addition of properdin to properdin-deficient serum restores bactericidal activity. A quantitative relationship exists between the final properdin concentration and bactericidal activity against sensitive organisms. The possibilities of a bactericidal assay for properdin are discussed. It is demonstrated that, in addition to properdin, the four components of complement (present in RP(b)) are necessary for the destruction of properdinsensitive bacteria. If any component is missing, bactericidal activity is lost; when the component is replaced, bactericidal activity is restored. Magnesium is also necessary for the bactericidal activity of the properdin system. Maximal bactericidal activity is obtained with magnesium concentrations similar to that of normal human serum (10(-3) to 10(-4)M). The bactericidal activity of the properdin system occurs only at temperatures above 15 degrees . Resistant strains have been encountered in species of bacteria sensitive to the properdin system. Resistance or sensitivity is a characteristic of the individual strain and not of the species. The widespread occurrence of the properdin system in normal mammalian serum and the variety of bacteria destroyed by it suggest that the properdin system is a factor in natural resistance.