Frequency of memory cytotoxic T lymphocytes to equine infectious anemia virus proteins in blood from carrier horses.

This research explores how horses with Equine Infectious Anemia Virus (EIAV) might keep the disease in check due to cytotoxic T lymphocytes (CTL), particularly memory CTL. Researchers specifically investigate CTL in carriers with low viral loads and analyze how they respond to the EIAV virus proteins.

Methodology and Initial Findings

The study began by igniting in vitro stimulation of peripheral blood mononuclear cells (PBMC) from four carrier horses with autologous EIAV-infected PBMC and human IL-2. The aim was to determine the presence and frequency of memory cytotoxic T lymphocytes (CTLm), which are believed to ‘remember’ pathogens and viruses. Three out of four horses had detectable CTLm; one of them also had low-level effector CTL (CTLe).

The CTLm were restricted by equine lymphocyte alloantigen-A (ELA-A) locus-encoded MHC class I molecules found on autologous equine kidney (EK) target cells, signifying a specific immune response to the virus. Notably, the researchers found no expression of MHC class II molecules on EK cells.

Evaluation of CTLm Frequency in Inapparent Carriers

Subsequent steps involved determining the frequency of CTLm in PBMC from five carrier horses that had been infected with EIAV for 22 to 50 months. The team achieved this by using limiting dilution analysis.

• The researchers collected the PBMC, diluted, and stimulated them.
• They tested the stimulated PBMC on EK cell targets that were infected with EIAV and recombinant vaccinia viruses expressing EIAV Env or Gag/Pr proteins.

Outcomes

All five horses had demonstrable CTLm in response to EIAV-infected targets. Four out of five horses demonstrated CTLm reaction to the targets expressing the EIAV Env protein and four horses also showed CTLm response to Gag/Pr-expressing targets. The frequency of CTLm ranged from 60 to 468 per million PBMC for the EIAV-infected targets, 4 to 286 for the Env-expressing targets, and 25 to 190 for the Gag/Pr-expressing targets.

Implications of the Study

These results could provide significant insights that may facilitate the identification of epitopes recognized by dominant CTLm from horses controlling lentivirus infection that can serve as potential vaccines or therapeutic targets for EIAV.