Enhancement of Influenza Virus Multiplication by Chicken Serum

Abstract

Summary Chicken serum increases the yield of influenza B (Lee) virus several-fold in suspension cultures of chorioallantoic membrane (CAM) in vitro. The mean increase in virus yield at a serum concentration of 23% is 550%. Serum allows the production of an additional amount of 300 to 450 hemagglutinating units (HAU) of virus per 3.8 cm2 of CAM in membranes whose yield in the absence of serum varies from 25 to 160 HAU/3.8 cm2. The percent increase in yield in the presence of serum is inversely related to the yield of virus in untreated controls. The extent of enhancement of virus yield is similar in CAM from 7- and 10-day-old embryonated eggs, but in CAM from 13-day-old eggs and older, chicken serum inhibits viral multiplication. The enhancing activity is approximately 50% dialyzable, and is inactivated to the extent of 40% by heating at 65°C for 30 min. The activity is not inactivated by treatment with trypsin, chymotrypsin, papain, pronase, or deoxyribonuclease I. In some chicken sera there is present a heat labile inhibitor of Lee virus multiplication. Inhibition of virus multiplication by such sera may be slight or marked. After heating at 65°C for 30 min, such sera enhance the multiplication of virus.