Mathematical Biology Seminar Peter Kim University of Utah Wednesday Jan. 21, 2009 3:05pm in LCB 215 "Questioning the T cell proliferation program " Abstract: We propose a mathematical model for the dynamics of the primary killer T cell response. While the currently accepted paradigm is that the response can be explained by assuming that activated T cells follow a proliferation program, our model is based on the hypothesis that adaptive regulatory T cells are the main mediators of a timely T cell contraction. We formulate two mathematical models for programmed T cell responses: a model in which cells undergo a fixed number of divisions and a model in which cells live for a fixed time. Our results show that programmed responses cannot exhibit robust behavior, because they scale with respect to precursor frequencies, a quantity that is highly variable. As an alternative approach, we hypothesize that primary T cell expansion may be controlled by the appearance of regulatory cells. Accordingly, we formulate a mathematical model and show that the regulated response is robust to a variety of parameters including precursor frequencies. This response is thus shown to be governed by emergent group dynamics rather than by autonomous programs.