Rescue of a H3N2 influenza virus containing a deficient neuraminidase protein by a hemagglutinin with a low receptor-binding affinity

Abstract

Influenza viruses possess at their surface two glycoproteins, the hemagglutinin and the neuraminidase, of which the antagonistic functions have to be well balanced for the virus to grow efficiently. Ferraris et al. isolated in 2003-2004 viruses lacking both a NA gene and protein (H3NA- viruses) (Ferraris O., 2006, Vaccine, 24(44-46):6656-9). In this study we showed that the hemagglutinins of two of the H3NA- viruses have reduced affinity for SAα2.6Gal receptors, between 49 and 128 times lower than that of the A/Moscow/10/99 (H3N2) virus and no detectable affinity for SAα2.3Gal receptors. We also showed that the low hemagglutinin affinity of the H3NA- viruses compensates for the lack of NA activity and allows the restoration of the growth of an A/Moscow/10/99 virus deficient in neuraminidase. These observations increase our understanding of H3NA- viruses in relation to the balance between the functional activities of the neuraminidase and hemagglutinin.

Figure 1. Affinities of the HAs of the H3NA- viruses for sialylglycopolymers.

Binding curves were fitted with the two models MM and MM2 for A/Moscow/10/99, A/Lyon-CHU/26430/03 and A/Reunion/586/04 viruses with 6′SLN receptors (A) and 3′SL receptors (B). The values of the dissociation constant (K_d) of the three viruses for 6′SLN receptors (C) and 3′SL receptors (D) calculated from the two models (MM and MM2) are indicated. The values correspond to the mean +/– standard deviation calculated from three independent assays. The Bayesian Information Criterion (BIC) is indicated for each regression.

Figure 2. Kinetics of virus growth experiments in MDCK cells.

P2 MDCK viruses were used to infect MDCK cells at a m.o.i of 0.001. Supernatants were harvested at the indicated times. The TCID₅₀/50 µl values correspond to the mean +/– standard deviation calculated from two independent assays.