Neuroendocrine Regulation of Immune Function in Fish

Abstract

Immune defense mechanisms of fish have not been studied as extensively as those of mammals but they appear to share a number of structural and functional characteristics important in the humoral, cell-mediated and non-specific aspects of the immune response (Ellis, 1982; (Iwama and Nakanishi, 1996). The immune system of fish is influenced not only by environmental factors such as stress (Schreck, 1996; Narnaware et al., 1994a; Narnaware and Baker, 1996), temperature (Bly and Clem, 1992), pollution (Pulsford et al., 1995), environmental salinity (Narnaware et al., 1998b) but also by endogenous factors such as steroid hormones (Wang and Belosevic, 1994; 1995; Narnaware and Baker, 1996), neurotransmitters (Flory, 1990;Bayne and Levy, 1991 a,b; Narnaware et al., 1994a), products of the sympathetic nervous system (Flory, 1990) and cytokines and inter-ferons (Francis and Ellis, 1994; Tahir and Secombes, 1996;). Thus stimulation of fish immune responses through environmental and/or hormonal manipulation is of prime importance in protecting fish against diseases. In this chapter, we shall review the existing literature on the modulation of fish immune responses by peptide hormones, neurotransmitters, cytokine-like factors, and interferons. The relationship between the neuroendocrine and the immune system of fish will be discussed.