POSITIVE SELECTION OF EQCD8(-ACTIVATED KILLING() PRECURSORS INCREASESEQUINE LYMPHOKINE)

Lymphokine activated killing (LAK) is an example of natural cytotoxici ty, and as such is a critical means of defense against diseases such a s viral infection and neoplasia, Despite this important role, the spec ific molecular interactions involved in LAK or other forms of natural cytotoxicity are only partially understood. In some species, cells cap able of mediating natural cytotoxicity express the CD8 molecule, altho ugh no specific role has been demonstrated for CD8 in non-MHC restrict ed 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 pe rformed using equine lymphocyte populations enriched or depleted for E qCD8 expression by positive or negative selection, The results indicat e 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.