CTL from EIAV carrier horses with diverse MHC class I alleles recognize epitope clusters in Gag matrix and capsid proteins

Abstract

Cytotoxic T lymphocytes (CTL) are important for controlling equine infectious anemia virus (EIAV). Because Gag matrix (MA) and capsid (CA) are the most frequently recognized proteins, the hypothesis that CTL from EIAV-infected horses with diverse MHC class I alleles recognize epitope clusters (EC) in these proteins was tested. Four EC were identified by CTL from 15 horses and 8 of these horses had diverse MHC class I alleles. Two of the eight had CTL to EC1, six to EC2, five to EC3, and four to EC4. Because EC2-4 were recognized by CTL from >50% of horses with diverse alleles, the hypothesis was accepted. EC1 and EC3 were the most conserved EC and these more conserved broadly recognized EC may be most useful for CTL induction, helping overcome MHC class I polymorphism and antigenic variation.

Fig. 1

Identification of peptides containing CTL epitopes. PBMC from EIAV-infected horse H596 were stimulated with EIAV_WSU5 and evaluated. Target cells were pulsed first with peptide pools (A), then with two peptides (B), and finally with individual peptides (C). Asterisks on top of columns indicate a % specific lysis that was significantly different (defined in Materials and methods) from target cells with no peptide (NP). The error bars on the columns are 1 SE.

Fig. 2

Gag MA (A) and CA (B) peptides recognized by CTL from EIAV-infected horses. All peptides recognized by CTL from horses H507, H513, H521, H529 and H540 are from a previous study (Zhang et al., 1998), whereas the remaining peptides are from this study. EC1–4 is shadowed. Epitope-lacking regions are shadowed and boxed. Peptide sequences and horse numbers in boxes indicate fine-mapped epitopes. The underlined peptides were recognized by CTL from eight horses with unique MHC class I alleles.

Fig. 3

Amino acid sequence variation of EC1–4 in 79 EIAV proviral clones and plasma virus variants from GenBank. Only variable sequences are presented with the dots indicating aa identical to those in EIAV_WSU5 and the dashes indicating amino acid deletions.