Current and Past Research
T Cell Research Expanded
T cells are an important part of our immune system and are distinctive because they carry out their function by interacting with other cells in a highly specific and directional manner. They can either secrete cytotoxins and kill other cells or they can secrete special growth factors and help other cells. In order to carry out these functions, T cells form a specialized junction with their target cell called an immunological synapse (IS). They subsequently move the microtubule organizing center (MTOC) close to the synapse and establish a specialized secretory zone. Finally, secretory vesicles accumulate in this zone and fuse with the membrane, allowing their contents to help or kill cells in the immediate area.
We have been studying how T cells polarize their cytoskeleton in response to antigenic target cells. Previously, we developed a new form of light microscopy called modulated polarization microscopy (MPM) that makes it possible to see cytoskeletal movements in living T cells. Studies using MPM provided important new insights into how this process works and gave us clues about how microtubules are anchored at the IS.
ADAP and Dynein Research
In particular, we have hypothesized that the dynein motor protein is anchored to the IS inside the T cell, where it can pull on microtubules, thus "reeling in" the MTOC. We have found that ADAP, a scaffolding protein, is anchored to the IS and forms a ring around its periphery. Our experiments have shown that dynein is anchored to the IS via its interaction with ADAP, and also forms a ring around the periphery of the IS. Cells in which ADAP is knocked down show a distinct lack of dynein polarization, and are deficient in MTOC translocation when activated.
Dynactin and Secretory Vessicles Research
Dynactin was initially thought to play a role in this process, due to its ability to regulate dynein function in other cellular processes, but T cells in which dynactin was knocked down showed no MTOC polarization failure. Current data suggest that dynactin is important for the movement of secretory vesicles along microtubules to the IS, and we are currently testing this theory.
Lis1 and Dynein Research
Another project in the lab focuses on Lis1 protein. Lis1 mutations cause the human disease lissencephaly, which is caused by neuronal migration failure and characterized by a smooth brain. Studies in neurons and other cells have shown that Lis1 is a microtubule- and dynein- binding protein that plays a significant role in dynein-mediated movements of the nucleus and the MTOC. Our initial studies in T cells have verified that Lis1 can bind to dynein (co-immunoprecipitation) and that Lis1 localizes largely to the IS in activated T cells. We are currently characterizing Lis1's role in T cell MTOC polarization.
Ethanol and Immunosupression Research
Another project in our lab is the study of ethanolic immunosuppression. Heavy drinkers often have depressed immune systems, and our research has shown that ethanol actually activates T cells. While initially counter-intuitive, we have found a model for this process. We have seen that intracellular calcium is slightly elevated in response to ethanol exposure. The transcription factor NFAT then migrates to the nucleus, but NFkB, another transcription factor active during T cell activation, does not migrate to the nucleus. This profile of activation may lead to T cell anergy, in which they are no longer responsive to external activation. We are currently exploring the signaling pathways used by ethanol, and we believe that lipid signaling plays a significant role.