FIG. 1.

Passage history of serotype C FMDV variants analyzed in this study. Plaque-purified FMDV C-S8c1 (▪) passaged once cytolytically in BHK-21 cells (○) was further propagated in BHK-21 cells either in cytolytic or in persistent infections. C-S8c1-derived populations p100 and p213 were obtained after 100 and 213 serial cytolytic passages, respectively. Clones c1 and c10 were isolated from C-S8c1 p100 (37). RGG and MARLS are two mutants resistant to MAb SD6 (3, 37). FMDV MARLS was subjected to 10 rounds of selection and amplification (b○) with heparin-Sepharose binding and infection of BHK-21 cells, to eliminate viruses with high affinity for heparin. This led to the isolation of clones MARLS/hs⁻ c1, c2, c3, and c4 (bottom right). Procedures for cytolytic infections and isolation of virus from single plaques are described in Materials and Methods. Persistent FMDV infections and the R100 population were described previously (8, 9, 21).