Characterizing MHC-I Delivery to Cell Plasma Membrane: A Spatiotemporal Study

In our work, we aim at characterizing the delivery of Class I Major Histocompatibility Complex (MHC-I) molecules to the plasma membrane. Three aspects of MHC-I dynamics were investigated: delivery rate, position of delivery
events and synthesis and delivery of new molecules. Using Total Internal Reflection Fluorescence Microscopy (TIRFM) in combination with image analysis, we quantify the delivery rate of MHC-I to the plasma membrane. Furthermore, we demonstrate that inhibition of Dynamin reduces MHC-I delivery rate, a result that leads to the important conclusion that MHC-I molecules are primarily trafficked by Clathrin-coated vesicles. We find that MHC-I molecules are transported to specific, non-random locations on the plasma membrane, with possible implication on the interaction of MHC-I with their receptors on T lymphocyte cell membranes. Finally, comparing experimental Fluorescence Recovery After Photobleaching (FRAP) data with simulated recovery, we show that fluorescence recovery cannot be ascribed to lateral diffusion alone, and has an additional component originating in the delivery of newly synthesized MHC-I to the plasma membrane. These results may shed new light on the rates of synthesis and delivery of MHC-I molecules.