IONIC CONDUCTANCES AND CD4 LYMPHOCYTE DIFFERENTIATION

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Antigen-mediated calcium signaling is a critical determinant of lymphocyte gene expression and has been associated with functional responses to T-cell receptor (TCR) stimulation including proliferation, anergy, apoptosis and memory. Because the outcome to stimulation of naive cells is not predetermined, elements that regulate the calcium response, have the capacity to regulate peripheral T cell differentiation in vivo. We have identified profound modulation in the expression of voltage- dependent (Kv) channels that correlates with each functional response to antigen in vivo. Kv channels have been previously shown to regulate calcium signaling in vitro. The unique Kv channel phenotypes of each subpopulation of differentiating T cells has led us to hypothesize that Kv channels may be important determinants of the calcium responses and the function of differentiating lymphocytes. T cell differentiation, therefore may be controlled by the unique balance between antigen and receptor, the constituents in the immune microenvironment, which regulated Kv channel activity, and also upon the repertoire of Kv channels expressed by an individual cell. Any shift in the balance of these factors could affect the membrane potassium permeability, shift the electrical potential across the lymphocyte membrane, alter calcium signaling, and the cells capacity to produce and secrete cytokines, respond to external factors, express cell surface molecules, and differentiated. If calcium does direct alternative functional responses of T cells, it is unlikely to result from simple changes in its steady-state concentration. Rather, the outcome to stimulation is more likely to be encoded in features such as the latency, duration and frequency of calcium oscillations. Kv channels help to define the frequency and duration of calcium oscillations to the extent that changes in the potassium permeation of Kv channels result in parallel changes in the membrane potential, and calcium concentration within mitogen stimulated human lymphocytes. It is not known, however whether antigen- mediated calcium signaling is regulated differently at each stage of T cell differentiation, or if voltage-dependent potassium channels regulate calcium signaling in vivo. Although potassium channels are not the sole determinants of calcium oscillations, given the role of potassium channels in setting the membrane potential and the dependence of calcium influx in the membrane electrical potential difference, modulation of potassium channel expression and permeation, would likely have a significant impact upon calcium signaling and T cell functions in vivo. The central hypothesis of this proposal is that the TCR-mediated calcium response regulates CD4plus lymphocyte differentiation, and that Kv channel regulate the secondary responses of differentiated cells to antigen.