Dealing from the Evolutionary Pawnshop

Cell fate decisions are made throughout the embryogenesis of higher vertebrates in order to pattern a complex multicellular organism. In the adult organism, cell fate decisions are continually made by lymphocytes to ensure homeostasis in the uninfected individual and during defense against pathogenic microorganisms. Helper T cells make numerous decisions during ontogeny, postdevelopmental circulation in lymphoid organs, and immune response. The decision concerning which type of effector cell to become upon antigenic challenge has been reexamined closely in the past year. The results of these findings will serve as a model of what has become an increasingly exciting area of complex, developmentally regulated gene expression. It is hoped that this speculative and hypothetical portrait of lymphocytes will help focus further discussion and investigation about the evolution of cellular decision making in higher species.