RESUMEN
Separation of null cell fraction from the other cellular components of human peripheral blood obtained from normal healthy individuals was effected through the Ficoll-Hypaque density gradient centrifugation, carbonyl iron phagocytosis-magnet application, E-rosette forming and binding to 19S-EAC respectively. The null cells were used as effector cells in the cytotoxic assay. The spontaneous cell-mediated cytotoxicity assay was employed and the highly NK-sensitive K562 labelled with Na251 CrO4 were used as targets. The null cell fraction was divided into several portions to allow for normal control, diluent control and tests. The test portions were those exposed to the various antimalarial drugs employed. It was observed that the T cell, B cells and null cell fractions accounted for 72%, 18% and 10% of the total lymphocyte population respectively. The mean cytotoxicity generated by the natural killer subset was 63%. The antimalarial drugs/drug combination used were chloroquine, quinine, pyrimethamine and sulfadoxine/pyrimethamine combination. Concentrations used were their respective minimal inhibitory concentration (MIC) and corresponding 5 X MIC. The inhibitory effects on natural killer cell activity of these drugs were observed. The possible reasons for these observations are discussed.