EFFECT OF IN VITRO CULTIVATION ON THE PATHOGENICITY OF VENEZUELAN EQUINE ENCEPHALOMYELITIS VIRUS

Continued in vitro cultivation in a Maitland type medium resulted in a marked modification of the extraneural pathogenicity of the Venezuelan equine encephalomyelitis virus. The ability of the virus to induce lethal infections after peripheral inoculation was almost completely lost for mice 42 or more days of age, was somewhat reduced for mice 28 days of age, but was still retained for mice 21 or less days of age. The virulence of the virus by the cerebral route remained essentially unaffected for mice of any of the experimental age groups. Prolonged cultivation also resulted in almost complete attenuation of the virus for rabbits and guinea pigs by the intraperitoneal route

INTERFERENCE BETWEEN VIRUSES IN TISSUE CULTURE

The influence of one virus on the growth of another in tissue culture was investigated. The 17DD High strain of yellow fever virus was found capable of completely suppressing the growth of both the Asibi strain of the same virus and of the heterologous West Nile virus, even when these were added to the cultures in large amounts. The 17DD High strain of yellow fever virus and the West Nile virus produced either partial or complete suppression of growth of the Venezuelan equine encephalomyelitis virus, depending upon the quantity of the latter inoculated into the cultures. Owing to lack of methods for the detection of interference except in a single direction, reciprocal interference with these viruses could not be investigated. The 17DD High strain of yellow fever virus and the West Nile virus were able to suppress completely, or almost completely, the growth of influenza A virus added to the infected cultures in maximal amounts. Interference in the reverse direction, even with the use of small amounts of the neurotropic viruses, was not demonstrable. Cultures infected with the 17DD High strain of yellow fever virus were examined for the presence of neutralizing antibodies and non-specific antiviral substances; neither was found present

EFFECT OF IN VITRO CULTIVATION ON THE PATHOGENICITY OF WEST NILE VIRUS

The West Nile virus was cultivated in suspended cell culture media employing several different tissue components, and it has been observed to survive in culture for at least 32 days. Continued propagation of the virus in vitro resulted in a change in its pathogenicity. The change lay in a marked reduction or a complete loss of the ability of the virus to produce fatal infections in mice and in hamsters on peripheral inoculation, although there was no obvious simultaneous alteration in the lethal effect of the virus by the cerebral route. In mice, the extent to which invasiveness was lost depended upon the passage level of the virus and the age of the test animals. The younger (and more susceptible) the mice, the greater the number of passages which was required to diminish the virulence of the virus by peripheral routes; after 68 passages, the virus still retained its full capacity to kill 3-day-old mice, while its ability to kill 8-day-old mice was reduced and its ability to kill mice 14 or more days of age was essentially abolished. How soon the loss of pathogenicity occurs in hamsters has not been determined. Prolonged cultivation rendered the virus avirulent for hamsters by the intraperitoneal route

ELECTROPHORESIS OF THE COMPLEMENT-FIXING ANTIGEN OF HUMAN INFLUENZA VIRUS

1. An electrophoretic study has been made of normal mouse serum, influenza mouse serum, and influenza mouse lung suspension. The mobilities of the protein fractions present have been determined at various pH's by the optical method. 2. The pH-mobility curve of the soluble (complement-fixing) antigen present in the lung suspension has been determined analytically by sampling and application of the complement fixation test. The results show that the complement-fixing antigen has a mobility definitely smaller than that of serum albumin and close to that of a globulin, with an isoelectric point close to pH 5

NEUTRALIZATION OF INFLUENZA A VIRUS BY HUMAN SERUM

A linear relationship exists between the quantity of human serum used and the quantity of influenza A virus neutralized. By means of this relationship it is possible to determine the maximum quantity of virus which a given human serum can neutralize. This quantity, the neutralizing capacity, is a fixed value and, unlike the serum dilution end point, is independent of the amount of virus used in the neutralization test

THE SYNERGISM OF HUMAN INFLUENZA AND CANINE DISTEMPER VIRUSES IN FERRETS

The infections produced in ferrets by human influenza virus and canine distemper virus were studied. Cross immunity and cross neutralization tests showed that these two viruses were not related antigenically. Ferrets infected with influenza virus alone rapidly produced considerable quantities of neutralizing antibodies, and after the 6th day virus was not demonstrable in their lungs. Ferrets infected with both influenza and distemper viruses simultaneously produced but small amounts of neutralizing antibody, and influenza virus persisted in undiminished concentration in their lungs throughout the course of the infection

STUDIES ON INFLUENZA VIRUS : THE COMPLEMENT-FIXING ANTIGEN OF INFLUENZA A AND SWINE INFLUENZA VIRUSES

Influenza complement fixation tests designed for use with ferret serum are described. Complement-fixing antigens derived from influenza ferret lungs were unsatisfactory due to their low content of soluble antigen; those prepared from mouse lungs or developing chick embryo membranes proved to be better antigenically and were reliable when the various reagents in the test were properly adjusted to eliminate non-specific fixation of complement. The results of cross complement fixation tests indicated that the soluble antigens of the PR8 and W.S. strains of influenza A virus were closely similar, if not identical. They indicated also that the soluble antigen of swine virus possessed components present in the antigens of the human strains of virus

STUDIES ON EPIDEMIC INFLUENZA VIRUS : THE NATURE AND PROPERTIES OF THE COMPLEMENT-FIXING ANTIGEN

Evidence is presented which indicates that influenza virus elaborates a soluble antigen. The antigen is considerably smaller than the virus and can be separated from it, but the virus has not been washed free of antigen. The properties of the antigen suggest that it is an unstable protein of relatively large size

MODIFICATION OF THE HOMOTYPIC SPECIFICITY OF POLIOMYELITIS COMPLEMENT-FIXING ANTIGENS BY HEAT

Fluid obtained from HeLa cell cultures infected with poliomyelitis viruses served as a complement-fixing antigen. When used in the native state, i.e. untreated in any way, the fluids acted as homotypically specific antigens. When heated, however, the antigenicity was broadened and a high degree of heterotypic reactivity was encountered. Data are presented indicating that the observed group reactivity was apparently based on common antigens shared by the three immunologic types of poliomyelitis virus. This reactivity appeared to be specific for the poliomyelitis viruses. No evidence was obtained in preliminary experiments that heating of the antigens releases a "soluble" antigen responsible for the group reactivity

A COMPLEMENT FIXATION TEST FOR POLIOMYELITIS

A macroscopic (tube) complement fixation test for poliomyelitis, using infected tissue culture fluids, is described. The test was applied to 27 individuals with a clinical diagnosis of poliomyelitis. In 18 patients it was possible to make a laboratory diagnosis of poliomyelitis on the basis of a rise in complement-fixing antibody titer and in 4 others on the basis of a high stationary antibody titer. One individual gave a high and equal antibody response to two virus types, 3 others had no detectable antibody, and 1 appeared not to have poliomyelitis. Heterotypic reactions were encountered, but gave little difficulty in interpreting homologous responses. In those patients from whom a virus had been recovered, the serologic findings corresponded to the virus type recovered. The possible occurrence of dual infections with the viruses of poliomyelitis and Western equine and St. Louis encephalitis is discussed