Single amino acid mutations in the capsid switch the neutralization phenotype of porcine circovirus 2

Abstract

Porcine circovirus 2 (PCV2) is the causative agent of porcine circovirus-associated diseases in pigs. Previously, it was demonstrated that mAbs 16G12, 38C1, 63H3 and 94H8 directed against the PCV2 capsid protein recognize PCV2 strains Stoon-1010 (PCV2a), 48285 (PCV2b), 1121 (PCV2a), 1147 (PCV2b) and II9F (PCV2b), but only neutralize Stoon-1010 and 48285. This points to the existence of two distinct PCV2 neutralization phenotypes: phenotype a (mAb recognition with neutralization; Stoon-1010 and 48285) and phenotype b (mAb recognition without neutralization; 1121, 1147 and II9F). In the present study, amino acids that are important in determining the neutralization phenotype were identified in the capsid. Mutation of T at position 190 to A in strain 48285 (phenotype a) resulted in a capsid resembling that of strain 1147 (phenotype b) and caused a loss of neutralization (switch from a to b). Mutations of P at position 151 to T and A at position 190 to T in strain II9F (phenotype b) resulted in a capsid resembling that of strain 48285 (phenotype a) and gave a gain of neutralization (switch from b to a). Mutations of T at position 131 to P and of E at position 191 to R in Stoon-1010 (phenotype a) changed the capsid into that of 1121 (phenotype b) and reduced neutralization (switch from a to b). This study demonstrated that single amino acid changes in the capsid result in a phenotypic switch from a to b or b to a.

Retrospective Study of Porcine Circovirus Type 2a and 2b Between 1999 and 2016 in Taiwan

“…Mutations in ORF2 of PCV2 may also alter viral antigenicity which relates to 'immune escape', and may contribute to the switch of virus populations [24]. Therefore, genetic comparison of the ORF2 sequences of different groups may give insight into the diversity of the ORF2 which are closely associated with the potential of immune escape, vaccines development and disease control [2,24].…”

“…Porcine circovirus type 2 (PCV2) is a member of the genus Circovirus within the family Circoviridae [1,2]. PCV2 have non-enveloped icosahedral virion with a size of 17 nm and containing single-stranded circular deoxyribonucleic acid (DNA) genome of 1,767-1,768 nucleotides (nt) [1,2].…”

“…PCV2 have non-enveloped icosahedral virion with a size of 17 nm and containing single-stranded circular deoxyribonucleic acid (DNA) genome of 1,767-1,768 nucleotides (nt) [1,2]. PCV2 have three major open reading frames (ORF), ORF1-3 [1,2,3].…”

“…The ORF1 encodes two major replication associated proteins: the complete Rep, and the spliced form Rep, which has a frame shift Rep′ [1]. ORF2 encodes the capsid protein (Cap), which contains the immunodominant antigenic epitopes, and has been used as a target for vaccine development [2,4]. Interestingly, some variable amino acid residues located in the putative epitopes of ORF2 are exposed outside the virion, and these residues are suggested to be constantly under positive or negative selection forces due to constant exposure to high immunologic pressure [2,4].…”

“…ORF2 encodes the capsid protein (Cap), which contains the immunodominant antigenic epitopes, and has been used as a target for vaccine development [2,4]. Interestingly, some variable amino acid residues located in the putative epitopes of ORF2 are exposed outside the virion, and these residues are suggested to be constantly under positive or negative selection forces due to constant exposure to high immunologic pressure [2,4]. The ORF3 encodes a protein that has been implicated with cellular apoptosis in the porcine kidney PK-15 cell line, as well as in peripheral blood mononuclear cells [3].…”