Arch Virol (1999) 144: 525–546
Antigenic and genetic variations of the 15 kD nucleocapsid protein
of porcine reproductive and respiratory syndrome virus isolates
, K.-J. Yoon
, J.-H. Lee
, J. J. Zimmerman
K. M. Harmon
, and K. B. Platt
Department of Veterinary Microbiology and Preventive Medicine,
Iowa State University, Ames, Iowa, U.S.A.
Department of Veterinary Diagnostic and Production Animal Medicine,
College of Veterinary Medicine, Iowa State University, Ames, Iowa, U.S.A.
Department of Entomology, College of Agriculture, Iowa State University,
Ames, Iowa, U.S.A.
National Veterinary Services Laboratories, United States Department
of Agriculture, Ames, Iowa, U.S.A.
Accepted September 22, 1998
Summary. The antigenic variability of the 15 kD nucleocapsid protein of porcine
reproductive and respiratory syndrome (PRRS) virus was characterized with a
panel of 24 monoclonal antibodies (MAbs) raised against the American PRRS
virus isolate ISU-P. Five continuous epitopes designated EpORF7-A through E
were revealed by the reactivity pattern of these MAbs with 67 American ﬁeld
isolates, two modiﬁed-live vaccine viruses, and the European Lelystad virus as
determined by the indirect immnoﬂuorescence assay and Western immunoblot-
ting and conﬁrmed by additivity and blocking enzyme-linked immunosorbent
assays. The reactivity pattern of isolates in the IFA permitted their subdivi-
sion into 4 American antigenic groups which represented 84.1, 11.6, 2.9 and
1.4% of viruses tested. The antigenic variation among isolates was correlated to
single, group speciﬁc nucleotide substitutions and mediated by a combination of
at least 4 of the 5 epitopes. EpORF7-A was conserved in all American isolates and
the Lelystad virus which constituted a separate antigenic group. Consequently,
monoclonal antibodies speciﬁc for EpORF7-A may prove useful as the antigenic
basis for a universal diagnostic test for the PRRS virus. EpORF7-C, D and E were
only present in the American isolates tested.
Porcine reproductive and respiratory syndrome (PRRS) is a major disease of
swine throughout the world. Clinical manifestations are characterized by repro-