Absence of ‘Incomplete’ Virus Production in certain Influenza Strains

Abstract

CONCENTRATED allantoic inocula of PR8 (influenza A) virus give rise to particles having the antigenic make-up, hæmagglutinating power and enzymic activity of the seed, but lacking infectivity. Since it bears some resemblance to interference by an unrelated virus, the phenomenon was named ‘auto-interference’¹. The use of this term was rather unfortunate: partly because Ziegler et al. ² had previously proposed it to describe the behaviour of old virus preparations containing a large proportion of non-viable particles, as first observed by Henle and Henle³; and partly as it led to the belief that incomplete virus was produced by cells infected by more than one virus particle. Indeed, extensive theoretical predictions have been based on this assumption⁴. Experiments, however, soon revealed that, whatever its mechanism, multiplicity of infection cannot be implicated to account for the facts, as incomplete virus was produced when only 1 per cent of the cells had been infected⁵. This piece of negative evidence brought forward by Cairns and Edney is in itself sufficient to invalidate the hypothesis; here positive proof is furnished that certain strains of influenza virus do not produce incomplete particles even under conditions of multiple infection.