The Development of Functionally Responsive T Cells

This chapter provides an overview of the properties of mature thymus-derived (T) cells, including both the molecules they use for recognition and the molecules they use in responses. The diversity of characteristics that are loosely considered “T cell specific” allows tackling critically the issue of the way they are coordinated in development. T lymphocytes play central roles in immune responses and in the regulation of cell growth for several hematopoietic lineages. The importance of these cells is derived from their unique integration of specific antigen recognition with an impressively versatile, highly regulated array of possible effector functions. T cell development is divided into four phases. First is an expansion phase prior to T cell receptor (TCR) rearrangement, which appears to be correlated with programming of at least some response genes for inducibility. Second is a controlled phase of TCR gene rearrangement. Third is the complex process of selection. Whereas peripheral T cells can undergo forms of positive selection and negative selection, neither is exactly the same phenomenon that occurs in the thymic cortex. The fourth stage is the reconversion of the positively selected TCR αβ cell into a responsive effector cell