Comparison of Antigenicity among Various Subgroups of Classical Swine Fever Virus

Classical swine fever (CSF), also known as hog cholera, is caused by classical swine fever virus (CSFV) and is an economically important and highly contagious disease of pigs. Analysis of the E2 sequences of CSFVs from field outbreaks in Taiwan during 1993 to 2001 showed that the viruses could be divided into historical subgroup (subgroup 3.4) and exotic subgroup (subgroup 2.1). Analysis also showed that, in the field conditions, there has been a switch in CSFV populations from subgroup 3.4 to 2.1 after 1996. To further investigate whether the differences of antigenicity among various CSFVs subgroups were the reasons for this switch, antigenicities of E2 glycoprotein from various subgroups isolated in Taiwan were analyzed. In this study, E2 glycoprotein from subgroups 1.1, 2.1 and 3.4 were expressed by using baculovirus expression system. The twelve recombinant baculoviruses were titrated with indirect fluorescent assay (IFA) and X-gal staining, showing that the titers obtained by both tests were located within a range of 107.3~108.1 TCID50/ml. The one-step replication curves of these recombinant viruses also showed that the replication characteristics of these viruses were similar. Proteins expressed in infected insect cells were detected by IFA and Western blot. The antigenicity of various domains in E2 from three subgroups was analyzed by using five MAbs against different epitopes and strains showing that these expressed proteins could be differentiated by their variable intensities of fluorescence.