ANTIGENIC CHARACTERIZATION OF BRAZILIAN BOVINE VIRAL DIARRHEA VIRUS ISOLATES BY MONOCLONAL-ANTIBODIES AND CROSS-NEUTRALIZATION

Nineteen Brazilian isolates of bovine viral diarrhea virus (BVDV) were characterized antigenically with a panel of 19 monoclonal antibodies (mAbs) (Corapi WV, Donis RO and Dubovi EJ (1990) American Journal of V eterinary Research, 55: 1388-1394). Eight isolates were further charac terized by cross-neutralization using sheep monospecific antisera. Ana lysis of mAb binding to viral antigens by indirect immunofluorescence revealed distinct patterns of reactivity among the native viruses. Loc al isolates differed from the prototype Singer strain in recognition b y up to 14 mAbs. Only two mAbs - one to the non-structural protein NS2 3/p125 and another to the envelope glycoprotein E0/gp48 - recognized 1 00% of the isolates. No isolate was recognized by more than 14 mAbs an d twelve viruses reacted with 10 or less mAbs. mAbs to the major envel ope glycoprotein E2/gp53 revealed a particularly high degree of antige nic variability in this glycoprotein. Nine isolates (47.3%) reacted wi th three or less of 10 E2/gp53 mAbs, and one isolate was not recognize d by any of these mAbs. Virus-specific antisera to eight isolates plus three standard BVDV strains raised in lambs had virus-neutralizing ti ters ranging from 400 to 3200 against the homologous virus. Nonetheles s, many antisera showed significantly reduced neutralizing activity wh en tested against heterologous viruses. Up to 128-fold differences in cross-neutralization titers were observed for some pairs of viruses. W hen the coefficient of antigenic similarity (R) was calculated, 49 of 66 comparisons (74.24%) between viruses resulted in R Values that anti genically distinguish strains. Moreover, one isolate had R Values sugg esting that it belongs to a distinct serologic group. The marked antig enic diversity observed among Brazilian BVDV isolates should be consid ered when planning diagnostic and immunization strategies.