Classical swine fever virus (CSFV) envelope glycoprotein E2 containing one structural antigenic unit protects pigs from lethal CSFV challenge

Envelope glycoprotein E2, formerly called E1 or gp51-54, of classical swine fever virus (CSFV) expressed in insect cells protects swine from classical swine fever. Monoclonal antibodies directed against epitopes of domains B and C and subdomain Al are neutralizing. The domains are located on two structural antigenic units in a proposed model of the antigenic structure of E2. One unit consists of nonconserved antigenic domains B and C and the other contains highly conserved antigenic domain A. We produced several mutant E2 proteins by use of the baculovirus expression system. Two selected mutants were E2 proteins in which one of the two structural antigenic units, unit B/C or unit A, was deleted. The protective capacity of the mutant E2 proteins was investigated in an immunization experiment in pigs. Titres of the neutralizing responses in pigs immunized with mutant E2 proteins were all comparable with that of intact E2. These vaccinated pigs were protected against an intranasal lethal CSFV challenge, indicating that the immune response induced by one structural antigenic unit of E2 can protect pigs against classical swine fever.