The nature of the virus receptors of red cells; the effect of partial heat inactivation of influenza virus on the destruction of red cell receptors and the use of inactivated virus in the measurement of serum inhibitor

Role of the p38/AKT Pathway in the Promotion of Cell Proliferation by Serum Heat Inactivation

Serum is a common biomaterial in cell culture that provides nutrients and essential growth factors for cell growth. Serum heat inactivation is a common treatment method whose main purpose is to remove complement factors and viruses. As serum contains many heat-labile factors, heat inactivation may affect cell proliferation, migration, differentiation, and other functions. However, the specific mechanism of its effect on cell function has not been studied. Thus, we investigate the exact effects of heat-inactivated FBS on the viability of various cells and explore the possible molecular mechanisms. We treated HCT116, HT-29, and HepG2 cell lines with heat-inactivated (56 °C for 30 min) medium, DMEM, or fetal bovine serum (FBS) for different times (0, 10, 15, 30, 60, or 90 min); we found that heat-inactivated FBS significantly promoted the viability of these cells, whereas DMEM did not have this effect. Moreover, heat-inactivated FBS stimulated cells to produce a small amount of ROS and activated intracellular signaling pathways, mainly the p38/AKT signaling pathway. These results indicate that heat-inactivated FBS may regulate the p38/AKT signaling pathway by promoting the production of appropriate amounts of ROS, thereby regulating cell viability.

STUDIES OF THE HEMOLYSIS OF RED BLOOD CELLS BY MUMPS VIRUS : II. THE RELATIONSHIPS OF HEMAGGLUTINATION, VIRUS ELUTION, AND HEMOLYSIS

The relationship between hemagglutination and hemolysis by the mumps virus has been studied under conditions which affect (a) the receptors of chicken red cells and (b) the adsorption and subsequent elution of the virus from these cells. The results show that the hemolytic action of the virus appears to involve some of the same receptor areas of erythrocytes that are implicated in hemagglutination. Materials such as allantoic fluid, egg white, and red cell extract, which inhibit the agglutination of chicken red cells by mumps virus, also interfere with its hemolytic activity. Of these inhibitors, egg white and red cell extract, which are readily destroyed by the virus during incubation at 37°C., exert a greater antagonistic effect on hemagglutination than on hemolysis. Heated mumps virus or unheated influenza virus interferes with the hemolysis of red cells by untreated mumps virus. Though hemolysis takes place during elution of the virus after its adsorption on the red cell, the processes are apparently distinct. The hemolytic activity is easily affected by certain conditions of pH and temperature which have no effect on the ability of mumps virus to adsorb on and elute from red cells.

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.

Purification of an influenza virus substrate, and demonstration of its competitive antagonism to apple pectin

A substance was demonstrated in erythrocytes which antagonized the inhibiting effect of apple pectin on influenza virus hemagglutination. This substance was purified and found to be a water-soluble material, rather labile, and with some properties which suggested that it contained a polysaccharide. It was destroyed in vitro by highly purified preparations of the virus. It occurred in greatest amount in human erythrocytes and to a lesser extent in the red cells of species not susceptible to the virus. It was also found in normal rabbit serum. Calcium ions were found to be essential to the action of apple pectin in causing inhibition of virus hemagglutination. A second substance was purified from an alkaline extract of erythrocytes, and shown likewise to have an effect antagonistic to that of pectin. However, this latter material was not destroyed by the virus, and seemed to owe its effect to the binding of calcium ions.

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.

The nature of the virus receptors of red cells; partial purification of the virus agglutination inhibitor in human plasma

A substance (VHI) exists in human plasma which inhibits the agglutination of red cells by influenza virus and is distinct from influenza antibody. When plasma is fractionated by alcohol in the cold the VHI comes out mainly with a mixture of lipid-free alpha and beta globulins (fraction IV-4). On further fractionation the activity comes out with a fraction consisting mainly of beta₁ globulin (fraction IV-7). Boiling fraction IV-4 or IV-7 after considerable dilution brings about a large increase in the amount of VHI, much more than can be detected in the original plasma. A similar VHI has been extracted from the ghosts of fowl red cells.

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).

Reactivation of non-infective virus in a cortisone-injected host

The administration of cortisone to chick embryos inoculated with large quantities of inactive influenza B virus results in a rate of viral increase greater than is concommittantly observed with inocula of comparable infectivity which are devoid of inactive particles. Thus, more than a mere negation of autointerference is effected. It is concluded that in the presence of cortisone reactivation has occurred of non-infective virus to a state in which it can participate in viral synthesis. Cortisone-induced viral reactivation is dependent upon a high partide/cell ratio and is thus analogous to the previously described phenomenon of "multiplicity reactivation." Cortisone does not influence either homologous or heterologous viral interference unless reactivation of the inactive interfering virus occurs. Virus reactivable with cortisone possesses both interfering and enzymatic properties. Reactivation of virus with cortisone cannot be effected in vitro but is mediated by the host cell. Two hypotheses concerning the action of cortisone are presented.

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.