The percentages of fluorescent plaques derived from brain
lysates from PKO mice inoculated with rLm-gp33 or rLmnp118
were calculated as described above for B6 mice. Of
plaques derived from rLm-np118-inoculated mice, 78% (31 of
40) were fluorescent and of those derived from rLm-gp33-
inoculated mice, 89% (74 of 83) were fluorescent. Thus, consistent
with the lack of protection in PKO mice, there was not
an enrichment for viruses with deletions in the EGFP coding
region and thus not for gp33. This strongly supports the notion
that it is the immune pressure that drives the selection of
epitope escape mutants.