Current Research

The leukocyte adhesion cascade is a sequence of adhesion and activation events that ends with extravasation of the leukocyte, whereby the cell exerts its effects on the inflamed site. At least five steps of the adhesion cascade are capture, rolling, slow rolling, firm adhesion, and transmigration. Each of these five steps appears to be necessary for effective leukocyte recruitment, because blocking any of the five can severely reduce leukocyte accumulation in the tissue. These steps are not phases of inflammation, but represent the sequence of events from the perspective of each leukocyte.

T lymphocytes display a remarkable ability to evaluate differences in MHC-peptide complexes. Alteration of a single amino acid in an antigenic peptide has significant and distinct biological effects on the T cell recognition. Current research proposes all these events are governed by the TCR-MHC interactions. Using well developed micropipette and confocal microscope techniques, as well as relative cellular and mouse model,   specific experiments will be conducted to find the common mechanism of the TCR-MHC interaction by quantitatively measuring the binding kinetics and comparing with corresponding biological effects, thereby providing a basis for rational design of immunotherapy.

As a model system, we study the interactions of L-selectin, expressed on leukocytes, and P-selectin, expressed on activated platelets and endothelial cells, with their common leukocyte ligand, P-selectin glycoprotein ligand-1 (PSGL-1).. These rapidly reversible interactions mediate rolling adhesion of leukocytes on vascular surfaces during inflammation. L- and P-selectin bind to the same N-terminal region of PSGL-1 but with different affinities in 3D assays. Here, we use the thermal fluctuation method to directly compare the 2D association and dissociation rates for interactions of L- and P-selectin with PSGL-1.

Researchers have long speculated that integrins might display this unusual behavior, but experiments measuring the forces that disrupt integrin–ligand interactions failed to find any evidence of catch bonds. Kong et al. took a slightly different approach. They used atomic force microscopy to measure how long individual bonds between {alpha}5β1 integrin and fibronectin lasted when pulled apart with constant forces. As the pulling force increased, the {alpha}5β1–fibronectin association lasted longer, indicating that the molecules do form catch bonds.

The interaction of circulating platelets with the vessel wall involves a process of cell catch and release, regulating cell rolling, skipping, or firm adhesion and leading to thrombus formation in flowing blood. In this regard, the interaction of platelet glycoprotein Ibα (GPIbα) with its adhesive ligand, vWF, is activated by shear force and critical for platelet adhesion to the vessel wall. Our studies reveal molecular mechanisms regulating GPIbα-vWF bond formation and platelet adhesion under shear stress.

AFM is used to study mechanical regulation of molecular interactions, conformational changes, and proteolysis. Using AFM, we demonstrated catch bonds selectin/ligand,  GPIb/VWF, and integrin/ligand interactions. Catch bonds are counter-intuitive behaviors where force prolongs lifetimes of molecular bonds, which is oppsite to the ordinary behavior of slip bonds where force shortens lifetimes.

BFP uses a red blood cell as a force transducer, which can provide a much softer spring (0.3 pN/nm) to probe single molecule interactions with higher force resolution (~1 pN).

Micropipette-aspirated red cell is utilized to detect adhesion events and measure adhesion probability. The 2D binding kinetics and affinity of the specific molecular interaction are determined by comparing data to a probabilistic kinetics model.

Molecular dynamics (MD) are used to simulate receptor-ligand interactions and to induce conformational changes. Simulations provide insights to structure-based molecular mechanisms.

Biosensors are used to visualize activities of kinase molecules following cell receptor engagement that triggers signaling.