Final Activity Report Summary - CFSE (Developing quantitative methods for estimating birth and death rates of immune cells using CFSE label) Due to the development of several important experimental techniques, immunology is rapidly becoming more and more quantitative. It is now possible to track the immune responses specific to various viruses and bacteria in vivo, and more and more data are becoming available on the interactions of different types of immune cells during an immune response. Despite the widespread use of techniques of molecular biology, we are still at the beginning of our understanding of how immune responses are generated, how they are maintained and how various environmental factors may affect the rates of cell proliferation and death during an immune response. In particular, relatively little is known about the rates of proliferation and death of lymphocytes in various settings in vivo and in vitro. This research project was aimed at filling this gap. We have formulated a novel approach that can be used to estimate the rates of proliferation and death of lymphocytes in different conditions in vitro and in vivo. The approach is based on application of mathematical models of different levels of complexity to data that enumerate the number of divisions that cells in the population have undergone (CFSE data). Application of the novel mathematical models to data available via a collaboration with the laboratory of Dr Phillip Hodgkin (Walter and Elisa Hall Institute of Medical Research, Melbourne, Australia) revealed several interesting unexpected results. We have found that despite the commonly held belief, cytokine interleukin 2 (IL-2) does not affect the speed at which activated CD4+ T cells divide. However, IL-2 does affect the fraction of cells that are stimulated to participate in the response, and most importantly, IL-2 regulates how activated cells are dying during the immune response. We find that lower IL-2 concentration lead to faster rates of death of activated cells. These results challenge the widely spread view that IL-2 or T-cell growth factor regulates expansion of T cell populations by regulating cell proliferation. Similar predictions have also been generated in other experimental systems including CD8 T cells. Overall, our work forms a basis for the analysis of CFSE data, widely produced in immunology, and generates guidelines for thorough analysis of such data. We are developing tools to be used for the analysis of CFSE data; these tools are made freely available to the general public.
