DISSOCIATION OF HEMAGGLUTINATING AND ANTIBODY-MEASURING CAPACITIES OF INFLUENZA VIRUS

Non-specific inhibitors of influenza viruses in normal sera

The presence of non-specific inhibitors in immune influenza sera may falsify the antibody pattern as shown by the haemagglutination-inhibition test, and it is consequently often necessary to pre-treat sera in order to inactivate these inhibitors. A number of different methods are in use for this purpose. It was therefore thought useful to compare the efficacy of the various methods with different representative influenza strains and normal sera from eight animal species and acute-phase human sera. Tests were carried out with simple heating at 56 degrees C, the use of receptor-destroying enzyme, the use of potassium periodate, and two methods involving the use of trypsin. No one technique was found to be universally applicable for all types of serum against all strains, and further testing with larger numbers of sera is advocated. It is felt that a combination of potassium periodate and trypsin with a change in concentration and times of action may be found advantageous.

STUDIES ON INHIBITORS OF INFLUENZA VIRUS HAEMAGGLUTINATION IN NORMAL RABBIT AND FERRET SERA

Inhibitors of influenza virus haemagglutination were completely removed from normal rabbit and ferret sera by purified and concentrated preparations of influenza viruses. Influenza A-prime strains absorbed only the Chu inhibitor and the B/Lee virus the Francis inhibitor. The heat or periodate inactivation of the viruses did not destroy their ability to combine with the inhibitor.The practical application of these experiments in the antibody absorption test for influenza antigenic studies is discussed.

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.

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.

The antigenic composition of influenza virus measured by antibody-absorption

The application of methods herein described for the absorption of antibody from sera by influenza virus adsorbed to erythrocytes has greatly facilitated absorption studies with this virus and has resulted in a more comprehensive demonstration of strain differences and relationships. It is now evident that there are at least 18 different antigenic components which can be measured in Type A strains of influenza virus. Utilization of quantitative absorption technics allows the simultaneous detection of variable quantities of several different antigens so that the antigenic composite of the strain is more clearly defined than was previously possible. The wide sharing of antigenic components leads to the conclusion that no completely new antigens have formed of late nor have the antigenic components of strains isolated several years ago disappeared. Some mechanisms for antigenic variation among strains are suggested, and the significance of the variation in antigenic components is discussed in relation to specifications for an effective vaccine.

Recent work on the intrinsic qualities of influenza virus; somatic and genetic aspects

The intrinsic qualities of influenza virus particles may be studied at the biological level from two points of view:(1) The surface structures associated with adsorption to the surface of the susceptible cell and entry into its substance are regarded as essentially somatic in character. Infection is possible only when these are present and functionally active.(2) The somatic qualities are controlled by a genetic mechanism composed of functional units equivalent to the genes of higher organisms. Recombination experiments based on multiple infection of a single cell can provide a technical approach to the genetic analysis of influenza virus.Work in these two fields is reviewed with special reference to that carried out in the Walter and Eliza Hall Institute of Medical Research, Melbourne.