TISSUE-CULTURE ADAPTATION OF FOOT-AND-MOUTH-DISEASE VIRUS SELECTS VIRUSES THAT BIND TO HEPARIN AND ARE ATTENUATED IN CATTLE

Isolates of foot-and-mouth disease virus (FMDV) exist as complex mixtu res of variants, Two different serotype O1 Campos preparations that we examined contained two variants with distinct plaque morphologies on BHK cells: a small, clear-plaque virus that replicates in BHK and CHO cells, and a large, turbid-plaque virus that only grows in BHK cells, cDNAs encoding the capsids of these two variants were inserted into a genome-length FMDV type A12 infectious cDNA and used to produce chimer ic viruses that exhibited the phenotype of the original variants, Anal yses of these viruses, and hybrids created by exchanging portions of t he capsid gene, identified codon 56 in VP3 (3056) as the critical dete rminant of both cell tropism and plaque phenotype, Specifically, the C HO growth/clear-plaque phenotype is dependent on the presence of the h ighly charged Arg residue at 3056, and viruses with this phenotype and genotype were selected during propagation in tissue culture, The gene tically engineered Arg 3056 virus was highly attenuated in bovines, bu t viruses recovered from animals inoculated with high doses of this vi rus had lost the ability to grow in CHO cells and contained either an uncharged residue at 3056 or a negatively charged Glu substituted for a Lys at a spatially and antigenically related position on VP2 (2134), Comparison of these animal-derived viruses to other natural and engin eered viruses demonstrated that positively charged residues are requir ed at both 2134 and 3056 for binding to heparin, Taken together, these results indicate that in vitro cultivation of FMDV type O selects vir uses that bind to heparin and that viruses with the heparin-binding ph enotype are attenuated in the natural host.