Variation in the lymphocyte transformation assay. Slope analysis of cell dose-response curves.

Blood samples from a single sheep were cultured at a number of different cell concentrations and stimulated with three lymphocyte mitogens, phytohaemagglutinin, concanavalin A and pokeweed mitogen. The response to stimulation, measured as log thymidine uptake (log cpm) was found to be a linear function of log cell concentration (log cell dose). Samples taken on different dates, varied significantly in the gradients of the log cpm: log cell dose plots. These alterations of gradient constituted the major source of variation of cpm in cultures at optimum cell concentration. It is concluded that the optimal mitotic response of lymphocyte cultures is determined more by the relative proportions of interactive cell types in the response than by the frequency of responder units. Also this proportion is subject to wide, spontaneous variation in the normal animal.