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.
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.