Position-dependent cell survival and the microcytotoxicity assay

Abstract For microcytotoxicity, when numbers of effector or target cells are limited, the method of Takasugi and Klein (1970) is at present the most convenient way of assessing cytotoxicity. In this procedure, target cell survival is affected by minor variations in culture conditions or washing vigour and the variations may be greater in some areas of the plate than in others, notably at the sides and especially the corners. A randomized block design for allottment of treatments to the plate is less affected by these position effects than the conventional row by row design. Statistical significance of acquired data may then be assessed by two-way analysis of variance, which is more sensitive than Student's t test in these circumstances. The use of the randomized procedure for the microcytotoxicity assay is strongly recommended.