Because of
these rapid fluctuations in amino acid composition, expected
from the quasispecies nature of FMDV (3, 4, 12), and because
a positive correlation between reactivity with n-mAb SD6
and some VP1 amino acids outside segment 133-156 was also
observed (compare Table 2), it was important to ascertain
that those amino acid changes at positions 138 and/or 147-
and not other alterations in VP1-were the direct cause of the
modified antigenicity.