Field isolates of porcine reproductive and respiratory syndrome virus (PRRSV) vary in their susceptibility to antibody dependent enhancement (ADE) of infection
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Abstract
Seventeen porcine reproductive and respiratory syndrome virus (PRRSV) field isolates,
including isolate ISU-P, were evaluated for their susceptibility to antibody dependent
enhancement (ADE) of infection mediated by antibodies raised against PRRSV isolate
ISU-P. Progeny virus yields of ISU-P and 4 of 16 field isolates in porcine alveolar
macrophages (PAM) were reduced following treatment with a concentration of antibody
that neutralized ISU-P (p < 0.01). In contrast, the yields of 12 of 17 field isolates
were enhanced (p < 0.01). Treatment of all isolates with a 10-fold lower concentration
of this antibody significantly (p < 0.01) increased virus yields of all isolates in
PAM. However, the degree of enhancement varied among the isolates when compared to
the enhancement of the yield of ISU-P. While no differences in enhancement were observed
among ISU-P and 9 field isolates, yield enhancement of 6 and 1 isolates were less
than and more than the yield enhancement of ISU-P, respectively (p < 0.05). The degree
of enhancement mediated by a high concentration of antibody raised against ISU-P was
inversely proportional to the ability of the antibody to neutralize the isolates (r
= 0.92). In contrast, no direct correlation (r = 0.32) was observed between the degree
of enhancement mediated by a low concentration of antibody and the ability of the
antibody to neutralize the isolates. These data suggest that the variability in the
susceptibility of PRRSV isolates to ADE arise from quantitative and/or qualitative
differences in the antigenic determinants associated with virus neutralization and/or
ADE. The antigenic diversity and the wide range in the susceptibility to ADE that
exists among field isolates indicate that ADE should be taken into consideration in
the development of effective immunization strategies for PRRS.