Cytokines and prevention of infectious diseases in poultry: a review

Cytokines are soluble, low molecular weight polypeptides and glycopeptides produced by a broad range of cell types of haematopoietic and nonhaematopoietic origin that have suppressive or enhansive effects on cellular proliferation, differentiation, activation, and motility. Like hormones, cytokines mediate cellular responses through autocrine, paracrine, and endocrine activities. Both inflammatory responses and specific immune responses to invasive microbes, which were evolved to protect the host from pathogens, are controlled by a complex network of cytokines. As regulators of the initiation and maintenance of host defenses, cytokines ultimately determine the type of response generated and the effector mechanisms generated to mediate resistance. As effector molecules, cytokines are produced transiently and locally to control the amplitude and duration of the response. Likewise, excessive or insufficient production of a cytokine or cytokines may contribute significantly to the pathophysiology of disease. Therefore, cytokines play pivotal but paradoxical roles in both in the regulation of inflammation and immunity. The use of exogenous cytokines against infectious agents in poultry medicine has centered on: (a) their use as adjuvants for vaccines, (b) their direct effects on inducing protection against infections and/or the undesired effects of immune responses elicited by pathogens, and (c) their ability to stimulate the ontogeny and activation of neonatal host defenses. This monograph will review what has been reported about the use of cytokines in poultry in these three main areas.