Immune protection of the hatchling.

Abstract

It has become clear that, although their immune responses are impoverished compared with those of adults, neonates are capable of mounting adaptive immune responses, which are dependent on the conditions of antigen exposure. Whilst embryonic vaccination of chicks can successfully induce adaptive immunity, the precise mechanisms whereby this is generated in the face of immune unresponsiveness remain to be elucidated. This chapter reviews existing data and further describes the ontogeny of humoral and Th1 cytokine responses in neonatal chicks and their enhancement through manipulation of the immune system. Neonatal chicks are capable of producing age-related Th1 cytokine profiles following parasitic infection. This contrasts with the mammalian system, in which neonates mount Th2-biased cytokine responses following antigen challenge. However, humoral responses are slow to develop, only being detected in juvenile birds from 18 days post-hatch in response to T-dependent non-replicating antigen. We suggest that the immaturity of this response is due to a defect in the neonatal B-cell population. The manipulation of immune function during the neonatal period, a time when chicks are uniquely vulnerable to infection, offers the prospect of improved methods for prevention and treatment of disease.