Natural variation of equine infectious anemia virus Gag protein cytotoxic T lymphocyte epitopes

Two defined cytotoxic T lymphocyte (CTL) epitopes from equine infectious an emia virus (EIAV)-infected horses, equine leukocyte alloantigen (ELA)-A5.1 -restricted epitope 18a, and ELA-AS-restricted epitope 28b-1 were evaluated for conservation among three wild-type EIAV strains. Epitope 18a variation occurred in all three wild-type EIAV strains, while epitope 28b-1 varied i n one strain. Further, 12% amino acid changes occurred in the Gag proteins of a recently isolated wild-type strain, documenting a much greater Gag pro tein variation than previously reported. Evaluation of epitope 18a among tw o virus isolates from sequential disease episodes in a single horse, H513 ( ELA-A5.1/A8), demonstrated that no variation that affected CTL recognition occurred. H513 PBMC had CTLm to epitope 18a before the occurrence of diseas e episodes caused by viruses expressing epitope 18a; however, the frequenci es were low (5-15/10(6) PBMC). Later in infection there was an absence of d isease episodes associated with an increase in CTLm frequency to EIAV(WSU5) -infected targets, but not epitope 18a-pulsed targets. Therefore, if CTLm t o EIAV epitopes were involved in maintaining the carrier state in H513, the y recognized epitopes Other than 18a. (C) 1999 Academic Press.