Abstract
The complement-fixation test has been increasingly employed in the identification of virus infections of the central nervous system. With one exception all complement-fixing antigens thus far employed with equine encephalomyelitis have been prepared from animal brain tissue, usually that of the mouse. 1 - 7 Mohler, 8 using a formolized antigen prepared from chick embryos inoculated with the virus of Western equine encephalomyelitis, reported complement fixation with serum from convalescent or immunized horses.
Because of its size a single infected chick embryo contains many times as much virus as an infected mouse brain and in view of the greatly decreased incubation period for maximal production of virus further investigation of this source of antigen was suggested.
Equine encephalomyelitis antigen. A strain of Eastern virus obtained from Dr. A. B. Sabin and the McMillan strain of Western virus received from Dr. J. Casals were employed. The viruses had been maintained at high titer by continued intracerebral passage through mice. They were then subjected to 13 rapid passages in hens′ eggs containing 10-day-old embryos by inoculation of 0.1 cc of 1:100 suspension of infected embryonic tissue onto the chorioallantoic membrane. The embryos were removed after 18-24 hours and suspended in physiological salt solution to give a concentration of 20% by weight. The suspension was centrifuged at 2,500 r.p.m. for 15 minutes and the supernatant removed and stored at −70°C. Before use as antigen the virus suspension was thawed and centrifuged at 3,000 r.p.m. for 15 minutes. The clear supernatant was diluted with an equal volume of physiological salt solution. The preparations, still infectious for mice in titers of 10-8 with Eastern virus and 10-6 with Western virus, were then tested in order to determine their complement fixing ability in the presence of immune serum.
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