Fig. 2.

The critical window of immunological development. The period between late gestation and weaning is depicted as a window in which natural and passive antibodies provide protection to the neonate and when colonization drives the development of adaptive immunity including oral tolerance. The dotted line indicates the period in which natural antibodies are considered important. Occurring in an orderly and regulated fashion, the events during this period create a state of immune homeostasis by the time of weaning (Butler et al., 2006; Butler and Sinkora, 2007).