Antigenic characterization
By cross hemagglutination inhibition (HI) assays (Table 4) reaction
patterns of sera directed against clone 30 (2.II) or Ulster (2.I.2) and
the Egyptian isolates of genotype 2.II were indistinguishable.
Reactivity even with a phylogenetically distant class 1 APMV-1 isolate
(R2919/06) was in the range of 2 log2 steps. In
contrast, reactivity of a serum raised against another genotype
2.VII.1.1 virus (R1468/12) was considerably lower with genotype 2.II and
2.I viruses (3 log2) as well as with the class 1 virus (4 log2).
However, genotype 2.VII.1.1 specific serum did not distinguish between
Egyptian genotype 2.VI and 2.VII.1.1 viruses. In addition, a serum
raised against classical PPMV-1 virus (R151/94) assigned to genotype
2.VI did show equal reactivity to both genotype 2.XXI chicken isolates,
but reactivity was decreased to genotype 2.II and 2.I and class 1 virus
and to a lesser extent to genotype 2.VII.1.1 viruses. Reactivity
profiles obtained by HI with a panel of mAbs, further highlighted
antigenic differences between PPMV-1 and other genotype 2.XXI strains
(R1973/2011-cl 4 and R1954/2011-cl 6). A second set of mAbs, reactive
with vaccine type genotype 2.II viruses varied in their reactivity
profile: whereas mAb U85 recognized genotype 2.II, 2.I and R1468/12
(2.VII.1.1) viruses, mAb 7D4 was specific only for vaccine type 2.II
viruses, and mAb 10 recognized an epitope present in genotype 2.II and
2.I viruses. These data strongly suggested, that epitope specific
difference existed, but that they were of minor importance for
recognition by polyclonal sera that comprise antibodies directed against
multiple epitopes.