Breed Differences in PCV2 Uptake and Disintegration in Porcine Monocytes

Abstract

Porcine circovirus type 2 (PCV2) is associated with various diseases which are designated as PCV2-associated diseases (PCVADs). Their severity varies among breeds. In the diseased pigs, virus is present in monocytes, without replication or full degradation. PCV2 entry and viral outcome in primary porcine monocytes and the role of monocytes in PCV2 genetic susceptibility have not been studied. Here, virus uptake and trafficking were analyzed and compared among purebreds Piétrain, Landrace and Large White and hybrid Piétrain × Topigs20. Viral capsids were rapidly internalized into monocytes, followed by a slow disintegration to a residual level. PCV2 uptake was decreased by chlorpromazine, cytochalasin D and dynasore. The internalized capsids followed the endosomal trafficking pathway, ending up in lysosomes. PCV2 genome was nicked by lysosomal DNase II in vitro, but persisted in monocytes in vivo. Monocytes from purebred Piétrain and the hybrid showed a higher level of PCV2 uptake and disintegration, compared to those from Landrace and Large White. In conclusion, PCV2 entry occurs via clathrin-mediated endocytosis. After entry, viral capsids are partially disintegrated, while viral genomes largely escape from the pathway to avoid degradation. The degree of PCV2 uptake and disintegration differ among pig breeds.

Changes on the viral capsid surface during the evolution of porcine circovirus type 2 (PCV2) from 2009 till 2018 may lead to a better receptor binding

“…2010). Interestingly, previous work from our laboratory demonstrated that monocytic cells, known as scavenger cells and being responsible for cleaning up foreign material in the body, can indeed take up PCV2 virions and disintegrate viral capsids, but have problems with degrading/digesting PCV2 DNA (Wei et al. 2018).…”

“…To amplify the ORF2 gene, a conventional PCR assay was performed using two primer pairs (ORF2-fw: 5′-gcgcacttcttttcgttttcag-3′, ORF2-rev: 5′-gaatgcggccgcttatcacttcgtaatggtttttattattca-3′; pgPCV2-fw: 5′-ggctgtggcctttgktac-3′, pgPCV2-rev: 5′-tgtrgaccacgtaggcctcg-3′) (Lefebvre et al. 2008; Wei et al. 2018).…”

“…It is thought that the use of Piétrain boars for the production of hybrid fattening pigs forms the basis of this low susceptibility. Recent work has demonstrated a more efficient uptake and disintegration of PCV2 by monocytes from purebred Piétrain than those from purebred Landrace and Large White, which may in part explain this better resistance (Wei et al. 2018).…”

Conformational Changes and Nuclear Entry of Porcine Circovirus without Disassembly

“…The reverse and transient binding failure of MAb 3F6 alone was thus mostly due to PCV2 capsid conformational changes. The inhibition of endosome-lysosome acidification increases PCV2 infection in porcine epithelial cells (20), while PCV2 requires an acidic environment in 3D4/31 cells (18) and colocalizes with the lysosomes in primary porcine monocytes (33). The motor-driven transport of vesicles through the cytoplasm might be actin dependent in 3D4/31 cells (34).…”

A Heterologous Viral Protein Scaffold for Chimeric Antigen Design: An Example PCV2 Virus Vaccine Candidate

“…PCV2 belongs to the Circovirus genus of the Circoviridae family, conformed by PCV1, PCV2, and PCV3 [15], and has the greatest geographical distribution [16]. PCV2 infects the cells of the immune system, such as the dendritic cells, monocytes, and macrophages [17,18], negatively modulating the regulatory cytokine pattern of the immune response, which causes lymphocyte depletion and immunodeficiency in infected pigs [19][20][21]. This immunodeficiency allows the infection with other concomitant pathogens, which provokes the death of infected animals [22].…”