Genetic analysis of echovirus 11 variability in adsorption to human erythrocytes

Two clusters of mutations map distinct receptor-binding sites of echovirus 11 for the decay-accelerating factor (CD55) and for canyon-binding receptors

In this study we present the comparative sequence analysis of the parental haemagglutinating (daf+) and mutant non-haemagglutinating (daf-) clones of echovirus 11 (EV11) isolated from the prototype strain Gregory. The sequence comparison revealed only a single amino acid substitution in the capsid protein VP2 of each mutant clone. These substitutions were located in the area of viral receptor-binding site for DAF. Since daf- mutants of EV11 did not interact with DAF, they used an alternative receptor for the cell entry. To elucidate the nature of the alternative receptor we used subvariant clones of EV11 adapted to human rhabdomyosarcoma (RD), human carcinoma (HEp-2) and African Green monkey kidney (BGM) cell lines. The usage of the subvariant clones with altered host range and the cell cultures of human and simian origin allowed us to map the amino acid substitutions associated with the adaptation of EV11 to the alternative cellular receptors. These amino acid substitutions were located on the surface of the virion in the canyon area. Hence the virus canyon may serve as the receptor-binding site for the alternative (in respect to DAF) cellular receptor(s).

Variations in the recognition of echovirus type 11 strains by a group-specific anti-VP1 monoclonal antibody

BACKGROUND

Mab 5-D8/1 is a monoclonal antibody (Mab) that was shown to be directed towards a conserved epitope of the capsid protein VP1 among the genus enterovirus. The use of this Mab for the routine detection of enteroviruses in clinical specimens led to the observation that several strains of echovirus type 11 (EV-11) could not be detected on spontaneously detached cells from 26-h cultures using a two-step immunofluorescence (IF) assay. Conversely, these strains were detected positive with the same Mab when tested on adherent or trypsinizated cells.

OBJECTIVES

The aim of this study was to understand the misrecognition of some strains of EV-11 by this Mab.

STUDY DESIGN AND RESULTS

IF tests at different times of the viral cycle brought evidence that the detection of a variant strain of EV-11 decreased rapidly with time, becoming undetectable 26 h post-infection, since the reference strain remained positive up to 46 h post-infection. The infective titres of the variant strains were shown to be high in comparison with those of well-recognised strains. Sequencing the Mab binding epitope confirmed that the variant strains exhibited no antigenic shift.

CONCLUSION

These results suggest that the poor recognition of some strains of EV-11 by Mab 5-D8/1 is due to a rapid decrease of the expression of the binding epitope in the cell, maybe in relation with the high lytic power of these strains. From a practical point of view, our data indicate that a negative result when Mab 5-D8/1 is used for enterovirus typing must be interpreted cautiously with highly replicative strains and that detached cells should not be used for enterovirus identification under these circumstances.