Transforming growth factor beta: a matter of life and death.

A wide variety of functions, many of which represent opposing activities, have been attributed to TGF-beta, a molecule implicated in embryogenesis, development, and immune and inflammatory processes. This paradoxical behavior of promoting or inhibiting cell growth and function, while important in normal physiology and homeostasis, can contribute to or interrupt pathologic sequelae, making TGF-beta a particularly intriguing molecule for study. New transgenic mouse models displaying targeted alterations in TGF-beta 1 expression offer novel and unique opportunities to determine the essential function(s) of TGF-beta.