PubMed1975
The aim of the study was to establish the relationship between mouse-virulence and affinity of influenza A2-viruses to certain naturally occurring mucoprotein receptor substances. Mouse adaptation of 4 egg adapted cloned H2N2-strains, sensitive to RDE-resistant horse serum inhibitor (PSI), and RDE-sensitive chick serum inhibitor (HSI) in the haemagglutination inhibition and neutralisation test (E+-strains) resulted in mouse virulent strains with diminished PSI-sensitivity (M+-strains, (Table 2). Sensitivity to HSI and to the RDE sensitive fraction of PSI was comparatively less affected (Tables 3, 4). In contrast to the original egg-adapted strains there were only minor differences in inhibitor sensitivity between different M+-strains (Tables 2, 3). 4 mouse virulent strains, derived from 3 egg-adapted strains resistant to PSI and HSI (E--strains), either remained unchanged (2) or gained inhibitor sensitivity (2), (Tables 2, 3). Mouse adapted strains resistant to HSI and PSI could also be selected from M+-strains by passage with PSI in embryonated eggs. In general, properties related to mucoprotein affinity of these strains correspond to those of M--strains derived from E--strains. During selection of M--strains by passage with PSI, strains insensitive to PSI but with considerable residual sensitivity to HSI were encountered (Tables 5, 6). Evidence is presented, that strains of intermediate sensitivity can consist of essentially homogenous populations (Figure 1). While egg adapted inhibitor-sensitive strains showed a high, insensitive strains a low affinity to the human erythrocyte membrane, the reverse was true for mouse adapted strains (Figure 2, Talbes 7, 8). On the other hand all inhibitor-insensitive strains proved to have a higher affinity to the mouse and bovine erythrocyte membrane than sensitive strains (Table 9). PSI-sensitivity of one PSI-sensitivity of one PSI-sensitive Hong Kong/1/68 (H3N2)-strain did not change during mouse adaptation. In a second line, passed in suckling mice, PSI-sensitivity decreased below HSI-sensitivity. Changes in respect to erythrocyte affinity were similar to those of H2-strains.