Analysis of lymphocyte aggregation using digital image analysis.

We present the development and testing of a novel assay of lymphocyte adhesion based on time-resolved morphological measurements of intercellular aggregation. Homotypic lymphocyte aggregation is induced according to various protocols and monitored for several hours using video microscopy and time-lapse recording. Digital images of the aggregating cell population are acquired and analyzed to obtain the size distribution and the shape of cell aggregates. By following the temporal evolution of the size distribution of aggregates, the rates of aggregation events can be accurately quantified and compared. In addition, an analysis of the two- and three-dimensional structures of the aggregates using appropriately defined shape factors allows comparisons of mechanical binding strengths and cytoskeletal activity. To demonstrate the capabilities of the assay, we present results from a series of aggregation experiments with Jurkat cells treated with 33B6, 19H8, IC9, and 20E4 monoclonal antibodies. These monoclonal antibodies bind to various epitopes of known adhesion molecules and induce aggregation phenomena that proceed at different rates. Our results show that the assay has small repeatability error and is sensitive enough to compare aggregation events induced through distinct molecular epitopes. Used in conjunction with current biochemical detection assays and adhesion pathway modulation experiments, the developed assay will facilitate the study of cellular adhesion and aggregation mechanisms.