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J Vet Sci 2018; 19(3): 358-367  https://doi.org/10.4142/jvs.2018.19.3.358
Phenotypic and genotypic analyses of an attenuated porcine reproductive and respiratory syndrome virus strain after serial passages in cultured porcine alveolar macrophages
Seung-Chul Lee1,4, Sunhee Lee2, Gun-Woo Yoo1, Hwan-Won Choi1, Yun-Hee Noh1, Chang Eon Park3, Jae-Ho Shin3, In-Joong Yoon1, Shien-Young Kang4,*, Changhee Lee2,*
1Choongang Vaccine Laboratory, Daejeon 34055, Korea
2Animal Virology Laboratory, School of Life Sciences, BK21 Plus KNU Creative BioResearch Group, and 3School of Applied Biosciences, College of Agriculture and Life Sciences, Kyungpook National University, Daegu 41566, Korea
4College of Veterinary Medicine, Chungbuk National University, Cheongju 28644, Korea
Correspondence to: Tel: +82-53-950-7365; Fax: +82-53-955-5522; E-mails: changhee@knu.ac.kr (C Lee), sykang@cbu.ac.kr (SY Kang)
Received: October 20, 2017; Revised: January 24, 2018; Accepted: January 30, 2018; Published online: May 31, 2018.
The porcine reproductive and respiratory syndrome virus (PRRSV) is a globally ubiquitous swine viral pathogen that causes major economic losses worldwide. We previously reported an over-attenuated phenotype of cell-adapted PRRSV strain CA-2-P100 in vivo. In the present study, CA-2-P100 was serially propagated in cultured porcine alveolar macrophage (PAM) cells for up to 20 passages to obtain the derivative strain CA-2-MP120. Animal inoculation studies revealed that both CA-2-P100 and CA-2-MP120 had decreased virulence, eliciting weight gains, body temperatures, and histopathologic lesions similar to those in the negative control group. However, compared to CA-2-P100 infection, CA-2-MP120 yielded consistently higher viremia kinetics and enhanced antibody responses in pigs. All pigs inoculated with CA-2-MP120 developed viremia and seroconverted to PRRSV. During 20 passages in PAM cells, CA-2-MP120 acquired 15 amino acid changes that were mostly distributed in nsp2 and minor structural protein-coding regions. Among these changes, 6 mutations represented reversions to the sequences of the reference CA-2 and parental CA-2-P20 strains. These genetic drifts may be hypothetical molecular markers associated with PRRSV macrophage tropism and virulence. Our results indicate that the PAM-passaged CA-2-MP120 strain is a potential candidate for developing a live, attenuated PRRSV vaccine.
Keywords: attenuated vaccines, macrophage tropism, porcine reproductive and respiratory syndrome virus, virulence, whole genome sequencing

© 2018 The Korean Society of Veterinary Science.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.