Characterization of the antigens used for immunization. (A) Schematic presentation of the viral envelope proteins. a, precursor envelope protein of KoRV (numbering according accession number AAZ99990.1), protease cleavage sites (PCS) are marked with arrow heads, SP-signal peptide. R-R peptide. b, recombinant gp70 as expressed using vector pET22b(+) with an N-terminal pelB leader sequence promoting translocation to the periplasma and a C-terminal His-tag. c, recombinant rp15E with N-terminal fused calmodulin binding protein (CBP) as expressed using the vector pCal-n, rp15E is the ectodomain of the transmembrane envelope protein, rgp70/rp52 is the entire surface envelope protein plus 25 amino acids from p15E. It is rp52 because it is not glycosylated. (B) SDS PAGE stained with Coomassie blue and Western blot (WB) analyses of the purified recombinant KoRV rp15E and rgp70/p52). KoRV proteins were detected using sera containing cross-reactive antibodies obtained by immunization of goats with recombinant rgp70/p52 and rp15E of PERV.