THE CYTOTOXICITY PATHWAY OF NATURAL KILLER CELLS IN CORD BLOOD COMPARED TO PERIPHERAL BLOOD

( The cytotoxic activity of natural killer cells is usually tested by radioactive assay ⁵¹Cr release assay), which detects the release of cytoplasmic contents after plasma membrane disintegration of dying cells. In contrast to this indirect evaluation of cytotoxicity, the assessment of cell damage by flow cytometry aims to provide a more exact characterization of the death pathway via detection of the percentage of apoptosis and necrotic cells. Annexin V-FITC (Axv -FITC) can be used to label cells in the early apoptotic state, while propidium iodide (PI) indicates late apoptosis or necrosis. The NK cytotoxicity of cord blood (CB) and peripheral blood (PB) was determined after 4 hours of incubation in the absence of cytokines. After 4 hours in vitro incubation, co-staining with Annexin V-FITC (Axv-FITC) and propidium iodide (PI) permitted discrimination between viable, early apoptotic and necrotic cells. As we would expect, the cytotoxicity pathway in PB mononuclear cells (MNCs) consists of both apoptosis and necrosis pathways but in CB MNCs it almost consists of early apoptosis; and necrosis is negligible. With escalating E: T (effector: target) ratio changes in the percentage of apoptotic cells in PB samples were significantly higher than CB samples. The mechanism(s) of the low cytotoxicity of resting cord NK cells is not well understood. Complementary research in this field is recognized to elucidate the phenotypical and functional properties of CB cells and how they relate to maturational stages. CB studies are important for transplantation research and ma! y provide insight to the suppressive mechanism by which the host -recipient could evade GVHD and rejection.

Keywords
Peripheral Blood, Cord Blood, Natural Killer Cells, Apoptosis, Necrosis, Flow Cytometry.