Class I MHC molecules on many cell types are clustered in patches of perhaps 25 molecules and most are mobile. MHC I clusters or for immobilizing MHC molecules, and are studying the way in which dispersion or immobilization affects antigen presentation to cytolytic T cells. It is thought that membrane proteins and lipids are not randomly distributed in the fluid lipid bilayer. Rather, both proteins and lipids may asociate to form domains. Most of the evidence for these domains is indirect.
Many domains are smaller than the resolution of the light microscope.
Using this microscope we plan to image the patchiness of surfaces of living cells, and to follow changes in this patchiness when cells present antigen. A particular type of lipid domain, a 'lipid raft', has been suggested as important for trafficking of some membrane lipids and proteins, and for the assembly of signaling complexes after surface receptors bind their ligands. We are probing for these rafts using fluorescence resonance energy transfer. Lateral diffusion in the presence of barriers and vesicle traffic. Gershfeld N.L. A singular state of membrane lipids at cell growth temperatures.