Apparent multiplication of the Lansing poliomyelitis virus in cortisone treated chick embryos.

Cortisone has been found by Schwartzman (Proc. Soc. Exptl. Biol. Med., 75, 835, 1950) and by Kilbourne and Horsfail (Proc. Soc. Exptl. Biol. Med., 76, 116, 1951) to increase the susceptibility of the host to certain viruses. Studies were undertaken therefore to determine whether the administration of cortisone might render chick embryos susceptible to infection with the Lansing strain of poliomyelitis virus. Suspensions of infected mouse brains were injected into the allantoic cavity of chick embryos that had been treated with cortisone by injecting 5 mg into the yolk sac. Passages were made with allantoic fluid every 7 days. In one of several attempts to establish the virus, allantoic fluid from the third, fourth, and fifth transfers produced typical paralysis in mice. Other tests have shown that without cortisone the virus persists only for 4 days in the allantoic cavity in sufficient concentration to produce paralysis in mice. The 5 egg passages covered a period of 34 days. In 13 titrations performed on mouse brains infected with the stock virus, only 8 per cent of the mice that received the 10dilution became paralyzed while none of those injected with the 10-7 suspensions developed paralysis. The dilution of the original inoculum brought about by 5 egg transfers was slightly greater than 10-7. Neutralization tests on the virus recovered from the fifth egg passage, using Lansing antiserum kindly furnished by Dr. Jonas E. Salk, identified it as the Lansing strain. When the virus was mixed with saline, it produced paralysis in all of 12 mice in an average of 8.5 days, but when mixed with the antiserum only 2 of 20 mice developed paralysis and this was delayed to an average of 28 days. Further tests showed that this Lansing antiserum does not give a cross reaction with the virus of mouse encephalomyelitis, strain FA, thus excluding the possibility that this virus had been picked up inadvertently and passed in eggs. This note is submitted, as the results indicate that it may be possible by the method employed or by improved procedures to establish the Lansing strain in chick embryos.