B and T lymphocytes are two important classes of cells of the immune system that function in the identification of foreign antigens and their clearance from the host. The outer envelope of lymphocytes, or the plasma membrane, is the site of a myriad of events that are essential for the viability of lymphocytes and their response to foreign antigen. In cell pathology, the plasma membrane is also the site of cell invasion by foreign pathogens, such as HIV in T lymphocytes, and their exit from the cell. The plasma membrane therefore represents an important structural and functional element of lymphocytes and the immune system as a whole, and it represents the principal object of our studies. As such, our research provides a better understanding of the mechanisms underlying immune cell activation and response, and will lead to discoveries that serve to benefit our ultimate goal of a better health for mankind.

Much of our research is dedicated towards deciphering how the structure of the membrane functions in translating extracellular cues into physiological events inside the cell. This process, termed signal transduction, leads to activated T and B lymphocytes following binding of foreign peptides to their surface antigen receptors. Importantly, our research and that of others have shown that specialized regions of the plasma membrane called membrane domains, or membrane rafts, are essential for efficient transduction of signals from the antigen receptors. Although there are many different types of membrane domains in cells, it is the glycolipid-enriched class of domains that have been shown to be most important for signal transduction.

In the past, scientists have studied glycolipid-enriched membrane (GEM) domains by taking advantage of their unique resistance to certain types of detergents. Although this has proven to be a very informative approach to studying GEM domains, at the same time it is disruptive to cells, and therefore makes measurement of specific physical and biological properties of GEM domains difficult or even impossible. Accordingly, to study GEM domains in situ with minimum disruption of cells, we have developed tools that allow us to visualize the domains in intact, viable cells. Specifically, we have engineered genes that encode the fluorescent molecule green fluorescent protein (GFP) fused to a signal that targets the molecule to GEM domains. Thus, cells that express our gene are fluorescent, and the fluorescence is concentrated in GEM domains of the plasma membrane. Importantly, the fluorescent labeling of the domains allows us to measure GEM domains using fluorescence microscopy, including their properties during signal transduction.

Fluorescence imaging is only one avenue that we take in studying membrane domains and their role in signal transduction. We also use "classical" approaches of membrane fractionation, which consists of disrupting membranes followed by separating components by their density. Molecular genetic approaches are also proving to be a valuable approach in measuring the role of GEM domains in specific biochemical events, and we foresee continuing in this avenue as well. In summary, methods both new and old are being applied to questions related to membrane domains and signal transduction in immune cells. The outcome of these studies is a more complete understanding of the elements of cell membranes that function in the regulating lymphocyte growth and activation in the human immune system.