Avian inflammatory response: mediation by macrophages.

The inflammatory response is one of the best defined components of nonspecific immunity in birds. Introduction of an immunogen into the skin or peritoneal cavity results in a characteristic series of local and systemic responses. Initially, locally produced chemotactic substances cause heterophils and monocytes to emigrate from the blood through postcapillary venules to the site of immunogen. Monocytes and heterophils phagocytize the immunogen and monocytes can initiate specific immunity mediated by lymphocytes. Monocytes release a variety of hormone-like substances (monokines) that act locally to coordinate the localized inflammatory response and facilitate lymphocyte responses. These same monokines can gain entrance into the circulation and act systemically to orchestrate the acute phase response. Monokine activities characterized to date are similar to mammalian interleukin-1, interleukin-2, tumor necrosis factor, and granulocyte-stimulating factor. The inflammatory response is active in the embryo midway through incubation and is probably instrumental in protection of the embryo. Inappropriate or overexuberant inflammatory responses can lead to a variety of pathologies in the chicken, demonstrating the importance of precise regulation of the inflammatory response.