Physics & Astronomy ETDs

Publication Date



This dissertation explores the dynamics and distribution of immunoglobulin E receptors (FceRI) on mast cells by drawing on the techniques of experimental and theoretical physics. The motivation for these investigations is provided by a considerable interest in the transmembrane signaling mechanisms of immunoreceptors, especially when triggered with membrane-bound ligands. Experimental investigations quantify the spatiotemporal dynamics of the redistribution of FceRI due to membrane-bound monovalent ligands, using total internal reflection fluorescence microscopy and single-particle tracking. When mast cells contact such substrates, receptor clusters form at cell-substrate contact points. The initial rate of accumulation of receptors into these contact points or cell protrusions is consistent with diffusion-limited trapping. Over longer timescales (>10 s), individual clusters move with both diffusive and directed motion components and eventually coalesce to form a large central receptor patch surrounded by a receptor cluster depletion zone. Detailed analysis of single-particle trajectories show that receptors maintain their diffusivity when confined within receptor clusters, and increase their diffusivity (above that of monomeric unliganded FceRI) in central patches. To study the kinetics of central patch formation, a new coalescence theory described by a melding process, which is not instantaneous, was developed. In these theoretical investigations, the difficult problem of moving boundaries is encountered. To handle the complexity, which stems from boundary growth due to particle melding, the study is divided into three parts. The first is about stationary trapping problems investigated by the standard defect technique, and the second is about a validity study of an adiabatic approximation for moving boundaries. In the last part of this dissertation, a new coalescence theory is developed, which is based on a completely self-consistent approach. Here, the time dependence of the moving boundary is not prescribed but obtained through feedback. Comparison of experiment and theory shows that observed biological cluster coalescence is delayed at early times and occurs at a faster rate at later times than predicted by a simple theory. The incompatibility at early times is addressed by a generalization of the theory to incorporate a time-dependent melding process by a memory concept, which quantitatively explains the observed delay.

Degree Name


Level of Degree


Department Name

Physics & Astronomy

First Committee Member (Chair)

Thomas, James L

Second Committee Member

Kenkre, Vasudev N

Third Committee Member

Prasad, Sudhakar

Fourth Committee Member

Lidke, Diane S

Project Sponsors

Army Research Office Grant W911NF0510464, National Institute of Biomedical Imaging and Bioengineering T32EB009414, National Institutes of Health P50GM085273




Immunoglobulin E--Receptors, Mast cells--Immunology, Cellular signal transduction.

Document Type