We are interested in identifying soluble protein factors in blood which can either promote or inhibit stem cell activity in the brain. Through a previous aging study and the transfer of blood from young to old mice and vice versa we had identified several proteins which correlated with reduced stem cell function and neurogenesis in young mice exposed to old blood. Over the past year we studied two factors, CCL11/eotaxin and beta2-microglobulin in more detail in tissue culture and in mice. We could demonstrate that both factors administered into the systemic environment of mice reduce neurogenesis in a brain region involved in learning and memory. We have also begun to test the effect of these factors on human neural stem cells and we started experiments to try to identify protein factors which can enhance neurogenesis.