Defining critical windows in the development of the human immune system.

Identifying critical windows in immune system development is crucial for determination of either safety or vulnerability to exposure to specific agents during rapidly changing phases of ontogeny. These phases in the human range from postconception early gestation through adolescence. A detailed understanding of these windows will facilitate avoidance of environmental toxins as well as allow improved planning for unavoidable exposures. Critical windows of immune development will be influenced by concomitant development, maturation and growth of other organ systems, thus the influence of potentially toxic exposures must be determined within a co-ordinated multisystem and multidisciplinary approach.