A STATISTICAL-THEORY FOR FLOW-CYTOMETRY PROFILES IN TERMS OF THE BINDING OF LIGANDS TO CELL-SURFACE RECEPTORS AND CHANGES IN GENE-EXPRESSION

Flow cytometry analysis is a technique used for obtaining light scatte ring and fluorescence intensity data in order to characterise a chosen cell line. From a sample of the data obtained, it is desired to infer the distribution of cell size, cell granularity and occupancy of cell surface receptors, by constructing histograms for the variables of in terest. Often an attempt is made, for instance, to account for the cha nges in shape of these histograms in terms of alterations in gene expr ession, etc. In this paper we analyse the way that changes in the samp le histograms can be interpreted in three frequently encountered situa tions, namely (a) when there is one cell line exposed to alterations i n chemical potential of ligand, (b) when there are two cell lines expo sed separately to saturating concentrations of the same ligand, and (c ) when two ligands are added in saturating amounts, first separately, then together, to the same cell line. We demonstrate that, under a wid e range of assumptions, the change in histogram shape can be accounted for in terms of a proportionate and absolute component and examples a re given to illustrate this. Finally, a computer program to analyse ex perimental data in terms of estimated shift and stretch parameters is described.