Echovirus 6 strains derived from a clinical isolate show differences in haemagglutination ability and cell entry pathway

Two echovirus 6 (EV6) strains were isolated from a clinical sample after successive sub-cultures in PLC (human hepatocellular carcinoma) and HeLa (human cervical adenocarcinoma) cells. The first strain retained its haemagglutinating capacity (HAEV6) while the second became non-haemagglutinating (NHAEV6). Virus binding assay showed that HAEV6 was capable of binding to DAF-expressing cells but not NHAEV6 confirming the role of DAF in EV6 haemagglutination. The lack of competition between the two viral strains during coinfections suggested that each strain used a different cell entry pathway. We provide evidence showing that HAEV6 used preferentially the lipid raft-dependent caveolae pathway, whereas NHAEV6 followed the clathrin-mediated pathway. Comparison of the sequences of HAEV6 and NHAEV6 revealed five amino acid changes in the VP1, VP2 and VP3 capsid proteins distributed in domains which are known to be highly immunogenic or suggested to be involved in receptor binding, virion stability and pathogenicity.