Positive selection of EqCD8+ precursors increases equine lymphokine-activated killing

Lymphokine activated killing (LAK) is an example of natural cytotoxicity, and as such is a critical means of defense against diseases such as viral infection and neoplasia. Despite this important role, the specific molecular interactions involved in LAK or other forms of natural cytotoxicity are only partially understood. In some species, cells capable of mediating natural cytotoxicity express the CD8 molecule, although no specific role has been demonstrated for CD8 in non-MHC restricted cytotoxicity. In this study the role of the EqCD8 equine homolog of CD8 in LAK cell activity was examined. A series of LAK assays were performed using equine lymphocyte populations enriched or depleted for EqCD8 expression by positive or negative selection. The results indicate that positive selection of LAK precursors using an anti-EqCD8 (CVS8) antibody greatly increases LAK cytotoxicity. The implications for the role of the EqCD8 molecules in LAK are discussed.