Modeling of early events in T cell signal transduction after controlled T cell activation by peptide major histocompatibility complex

Calcium signaling was observed in murine T cells over time, starting at a p recise moment of contact with a layer of fibroblasts expressing a stimulato ry major histocompatibility class II-peptide complex. The contact was contr olled by a film-thinning apparatus. Intracellular calcium levels were follo wed with the ratiometric dye, Fura-2. The calcium response was highly synch ronized and well fitted by a mathematical model. The model includes three c omponents: a sequence of reactions occurring after T cell receptor (TCR) tr iggering, InsP(3)-mediated calcium release from intracellular stores (Meyer and Stryer, Proc. Natl. Acad. Sci. USA 85: 5051-5055, 1988); and slow chan ges in levels phospholipase C-gammal (PLC gammal) reflecting a decrease in receptor triggering rate. Each component in the model controls a different part of the response-the initial delay, the sharp rise. and the slow decay, respectively. Kinetic parameters determined from curve fitting were the in itial delay in calcium signaling defined as the time when [PLC gammal] reac hed its half of its maximum (76 s), the coefficient characterizing calcium efflux from endoplasmic reticulum (ER) (2.86 muM s(-1), expressed per liter of cell volume), and a rate constant characterizing the diminishing yield of production of PLC gammal (0.00046 s(-1)) by active TCR. Only the paramet er representing PLC gammal production varied much from cell to cell. (C) 20 01 Biomedical Engineering Society.