The mechanism of active cerebral immunity to equine encephalomyelitis virus; the local antigenic booster effect of the challenge inoculum

The mechanism of active cerebral immunity to equine encephalomyelitis virus; influence of the rate of viral multiplication

Continued serial brain-to-brain passage of strains of W.E.E. virus in mice has yielded variants which kill mice with increased rapidity. Their rate of multiplication in the mouse brain has been found to be correspondingly increased. At 1 hour after intracerebral inoculation of various amounts of W.E.E. virus, only 3.5 to 10 per cent of the expected amount of virus was recovered from the infected brains. In infected mouse brains, the period of active viral multiplication was preceded by a latent phase which lasted a considerably shorter time in the case of a "fast" than in that of a "slow" variant. In brains inoculated with various amounts in excess of minimal lethal doses the rates of multiplication tended to converge with the result that the maximum titer was reached after about the same period of time. After inoculation of smaller amounts, the rates of viral multiplication tended to parallel each other. Vaccinated mice may be fully resistant to maximal intracerebral doses of a slowly multiplying strain while they are not at all or only partly protected against a rapidly multiplying one derived from it. This difference is demonstrable even though fast and slow variants are, as far as can be tested, serologically identical. The difference in response may be masked if animals are immunized with relatively large doses of vaccine. The bearing of these findings on certain practical problems has been pointed out.

The pathogenesis of infection with a virulent (CG 179) and an avirulent (B) strain of Newcastle disease virus in the chicken. II. Development of antibody

Circulating antibody appeared in the convalescing NDV-infected chicken concomitantly with the disappearance of virus from the tissues. The antigenic response to the CG 179 and B strains was demonstrated to be approximately equal. The neutralization test in the embryo and the hemagglutination inhibition technique yielded parallel results in the measurement of antibody early in convalescence, but late in convalescence the hemagglutination inhibition titers were relatively lower. This disparity indicates the possible duality of the antibodies. There was a wide ratio between the neutralizing antibody titers found in the brain and in the serum after an asymptomatic infection with NDV. The antibody level in the brain appeared to be related to the extent of virus growth and damage in the central nervous system. It appeared likely that a major factor in determining the virulence of the CG 179 strain was the more rapid attainment in the central nervous system of high virus concentration which outstripped the defense mechanisms of the host.

The pathogenesis of infection with a virulent (CG 179) and an avirulent (B) strain of Newcastle disease virus in the chicken. I. Comparative rates of viral multiplication

The comparative growth rates of a virulent (CG 179) and an avirulent (B) strain of NDV in the chicken were analyzed. Following intramuscular inoculation, the CG 179 and B strains both increased at the same rate in the extraneural tissues, i.e. the blood, lung, rectum, and spleen, but the CG 179 strain showed an accelerated growth rate in the brain. The CG 179 strain also multiplied more rapidly in the brain than the B strain following intracerebral administration of minimal inocula. Recovery with the B strain was associated with a decline in virus titer, first in the circulating blood, then in the visceral organs, and lastly in the central nervous system. Certain neuropathological observations were correlated with the pattern of virus growth.

The mechanism of cross-protection afforded by dengue virus against West Nile virus in hamsters

The protection afforded by similar concentrations of different dengue virus serotypes against a subsequent challenge of West Nile virus was studied in hamsters. The New Guinea C strain of dengue 2 virus gave the best protection. It was found that the anamnestic neutralizing antibody response induced by the challenge West Nile virus against West Nile virus in hamsters, previously immunized with dengue 2 virus, might play a major role in the cross-protection observed in this system.

Immunosuppression and experimental virus infection of the nervous system

This chapter describes the current views of the pathogenesis of virus infections of the nervous system, with particular attention to certain aspects of virus-host interactions. Following invasion of the central nervous system, infection can follow a variety of patterns, as to number and distribution of neuronal and non-neuronal cells involved. There is a corresponding diversity in the pathological lesions of the central nervous system (CNS) produced by acute virus infection. Infection can be pictured as a race between virus and host defenses, where many factors, acting through different mechanisms, can influence the outcome. Outcome is always determined by multiple virus and host variables, although single variables can be independently studied under experimentally controlled conditions in the laboratory. The chapter demonstrates that in many virus-host combinations, the immune response plays an important role in recovery from primary infections. It mentions that an immunopathological process mediates the disease which follows certain CNS virus infections.