Neutralization of Vaccine Virus by Immune Serum

Abstract

Summary and Discussion Experiments have been performed with a view to gaining information on the protection afforded by immune serum against vaccinal infection of mice, and in order to correlate the protective potency of serum against virus introduced intracerebrally in mice with that introduced intracutaneously in rabbits. It was learned that virus could be titrated satisfactorily by intracerebral inoculation of mice, and that with the strain of virus used the estimates of potency agreed well with those derived from the results of rabbit-inoculation. This was taken to mean that the virulence of this strain of virus for mouse and rabbit was essentially the same. Addition of immune serum to the viral suspensions protected mice from infection. The moderate irregularity of the titration-curve which was found when virus was injected alone was found to be considerably increased, but not to such an extent as to make the use of the “50 per cent point” an invalid one for measuring viral titer. It will be recalled that a similar observation was made when virus was titrated on the rabbit skin in the presence of immune serum, and furthermore that the degree of irregularity of results seemed to be proportional to the concentration of immune serum. The fact that a similar condition obtains in the mouse suggests that it is fundamentally related to the protective activity of immune serum. It was found that on dilution of the immune serum its protective capacity fell off regularly, as was found to be the case when titrations were made in the rabbit. It seemed, however, that the power of serum to protect the intracerebrally injected mouse from fatal infection was greater than its capacity to protect against the development of a cutaneous lesion. In evaluating this observation it must, of course, be borne in mind that we were not in a position to recognize the development of a minimal lesion in the brain. However, fatal infection of mice, and cutaneous lesions in rabbits, appeared to follow the introduction of equivalent amount of the original viral suspension of this strain. Further speculation must await fuller information.