Porcine endogenous retrovirus transmission characteristics of an inbred herd of miniature swine

Abstract

Here we report the identification of inbred miniature swine that failed to produce human-tropic replication-competent porcine endogenous retroviruses (HTRC PERVs), using in vitro coculture assays. When HTRC PERVs were isolated from transmitting animals, all were recombinant viruses, with the receptor-binding domain of PERV-A combining with PERV-C-related sequences.

FIG. 1.

Alignment of pre-VRA (A) and VRA (B) regions of the env genes of HTRC PERV. Only those nucleotides that vary between the PERV-A (shaded boxes) and PERV-C (unshaded boxes) reference sequences are indicated. HTRC PERV loci were PCR amplified from PERV-infected 293 cells using oligonucleotides designed to match LTR sequences conserved between the three infectious classes of PERV (5′-CCTGGTGGTCTCCTACTGTCG-3′ and 5′-GCTTTTATGGGGTTCACAACAAA-3′) with TaKaRa DNA polymerase (Intergen). The sequences were divided into three families as defined by the position at which their nucleotide sequence underwent transition between PERV-C and PERV-A. Representative members of each family are presented. A nucleotide substitution that did not correlate with either reference sequence was identified at base 192 in sequence T6E5 (black box).

FIG. 2.

PCR analysis of miniature swine genomic DNA indicating that PERV-A-PERV-C TM recombinants are not present in miniature swine genomic DNA but develop during tissue culture. The sense primer specific for PERV-A is located in the VRA region, and the PERV-C specific antisense primer is located in the TM region. Samples are as follows: water control (lane 1), DNA from miniature swine (nontransmitting animals, lanes 2 and 3; transmitting animals, lanes 4 and 5), 293 cells infected with HTRC-PERV (lanes 6 to 8), 293 cells (lane 9), and a plasmid-positive control of a cloned HTRC-PERV env gene (lane 10). Control amplifications of cytochrome b sequences were successful and comparable from each sample (data not shown).