Virus-specific CD8⁺ T-cells detected in PBMC from horses vaccinated against African horse sickness virus.

African horsesickness (AHS) is an infectious but noncontagious viral disease affecting all species of Equidae. The recall immune response of AHSV naïve horses immunised with an attenuated African horsesickness virus serotype 4 (AHSV4) was characterised using immune assays including ELISPOT, real-time PCR (qPCR) and flow cytometry. The recall immune response detected in PBMC isolated from three inoculated horses showed an upregulation of circulating B lymphocytes that correlated with elevated IL-4 mRNA expression indicative of humoral immunity, but reduced frequency of CD4⁺ cells. In addition to the expected antibody response, an increase in CD8⁺ cells was also detected. Although these CD8⁺ cells may be CTL, the role of these cells in immunity against AHSV still has to be determined.