Expression of a truncated hepatitis E virus capsid protein in the protozoan organism Leishmania tarentolae and its application in a serological assay

Zoonotic infections with hepatitis E virus (HEV) genotype 3 are presumably transmitted via contaminated pig meat products, which raises the necessity for enhanced serological surveillance of pig herds. The aim of the study was to set up a novel protein expression system to overcome the well-known problems in (HEV-) protein expression using the standard Escherichia coli tools such as inclusion body formation and loss of protein conformation. A recombinant strain of the protozoan organism Leishmania tarentolae (L. tarentolae) was therefore established. A fragment of HEV ORF2 coding for a truncated capsid protein of a porcine HEV strain was cloned and parts of the plasmid DNA were introduced into the Leishmania genome, resulting in stably transformed cells. Via a C-terminal His-tag the recombinant HEVΔORF2 protein could be purified and concentrated directly from the medium, resulting in a total protein amount of approximately 1.4 mg/l Leishmania culture. The recombinant protein was coated on ELISA plates and was proven to be highly reactive and well-suited to be applied in a serological assay. By investigating 144 porcine sera, the in-house assay detected specific antibodies in 43.1% of the samples and demonstrated a higher sensitivity than a commercially available antibody test. Taken together, it was shown that L. tarentolae exhibits a remarkable alternative expression strategy for viral antigens with considerable advantages of a eukaryotic protein expression host.