The infectivity of chorio-allantoic membrane influenza virus and incomplete influenza virus by the six-hour soluble antigen productionl test

Abstract

1. After inoculation of eggs with a large dose (10^8·6 ID₅₀) of influenza virus, chorio-allantoic membranes harvested from the 3rd to at least the 21st hr. (but not at the 1st or 2nd hr.) gave rise to large amounts of soluble antigen in 6 hr. in the chorio-allantoic membranes of sub-inoculated eggs (6 hr. soluble antigen production test). These amounts were larger than resulted from inoculation of equivalent numbers of ID₅₀ of standard allantoic fluid virus. By the conventional 72 hr. test, the infectivity of the chorio-allantoic membranes increased 1 hr. later, at the 4th hr. after inoculation.2. Allantoic fluids and chorio-allantoic membranes harvested from passages of very large and of small amounts of influenza virus were tested by 6 hr. soluble antigen production. The relative amounts of soluble antigen formed by different seeds appeared to be determined by their ID₅₀: HA ratios, irrespective of whether they were allantoic fluid or chorio-allantoic membrane preparations. Larger amounts of soluble antigen were formed in 6 hr. per ID₅₀ inoculated by preparations having lower ID₅₀: HA ratios, i.e. containing larger amounts of ‘incomplete’ virus, and vice versa.3. It is suggested that high infectivity in the 6 hr. soluble antigen test per ID₅₀ inoculated is due to a content of ‘incomplete’ virus, or of virus precursors: possibly these are in fact the same.4. More particles of an incomplete virus preparation than of standard allantoic fluid virus must be inoculated to produce a given amount of soluble antigen in 6 hr. It is suggested that a process resembling multiplicity reactivation must occur in cells infected with more than one particle of ‘incomplete’ virus.