Characterization of polyclonal antibodies against the capsid proteins of Ljungan virus

Ljungan virus (LV) is a suspected human pathogen isolated from voles in Sweden and North America. To enable virus detection and studies of localization and activity of virion proteins, polyclonal antibodies were produced against bacterially expressed capsid proteins of the LV strain, 87-012G. Specific detection of proteins corresponding to viral antigens in lysates of LV infected cells was demonstrated by immunoblotting using each one of the generated polyclonal antibodies. In addition, native viral antigens present in cell culture infected with LV strains 87-012G or 145SLG were detected in ELISA and by immunofluorescence using the antibodies against the VP0 and VP1 proteins. The anti-VP3 antibody did not react with native proteins of the LV virion, suggesting that the VP3 is less potent in evoking humoral response and may have a less exposed orientation in the virus capsid. No activity of the antibodies was observed against the closely related human parechovirus type 1. The polyclonal antibody against the VP1 protein was further used for detection of LV infected myocytes in a mouse model of LV-induced myocarditis. Thus, polyclonal antibodies against recombinant viral capsid proteins enabled detection of natural LV virions by several different immunological methods.