Fish immunology has achieved great progress in recent years. While before 1990s, most researches focused on the fish systematic immunity, and the mucosal immunity of fish had not been given enough attention. Indeed, it has been shown that fish mucosal immunity plays an important role in disease defense. Fish mucosal immunity research has made some exciting progress in this decade. This review will focus on such progress: Constitution of mucosal-associated tissues and distribution of different immune cells, including T/B lymphocytes, granules, monocytes, macrophages, goblet cells, etc, in these sites have been well described with the development of some monoclonal antibody to these cells and associated techniques. Non-specific immune response mechanism of mucosal tissues reported these years, such as secretion of non-specific anti-bacteria and anti-fungi substances in mucus, the respiratory burst, enzyme activity of immune cells and so on, is believed important for fish disease defense. The specific immunity of mucosal tissues also attracts much interest and makes great achievement in antigen presenting, MHC genes, antibody producing and antibody secreting cells, comparison of serum and mucus immunoglobulin, relationships of immune response between different mucosal immune tissues. Whether mucosal immune system is independent of systematic immune system is another interesting question and causes great concern. In recent years, some evidences from phyletic evolution and ontogenesis show that mucosal immunity is prior to systematic immunity in evolution. Dynamics of antibody producing of mucosal tissues and serum in immersion or oral vaccines immunized fish also shows immune response can be elicited in mucosal tissues independent of systematic immune system. Some researchers also begin to pay attention to factors involved in mucosal immune regulations, for instance, neuromodulators and cytokines. The level of these factors changes in fish immune response process but the mechanisms of regulation still remain unknown.
A central component of fish growth coordination is the Growth hormone-Insulin-like Growth Factor-Ⅰ(GH-IGF-Ⅰ) axis.The GH-IGFⅠ axis begins with GH production in the pituitary gland under the control of multiple hypothalamic hormones,including somatostatin(SS).SS have been proved to possess a variety of biological functions with widely distribution in the central nervous system and peripheral tissues.It plays roles in the physiological process of the central nervous system,modulating growth,development and metabolism processes.Research results on mammalian SS have been applied to produce new medicines.Research on fish somatostatin have lasted for over 25 years,and it has received more and more attentions.Fish is an important animal model and one of the important protein source of human,research on fish SS can help to understand the physiology roles of SS and to regulate fish growth and other physiologic processes.Mammalian SS exists as two predominant biologically active forms, SS14 peptide and its N-terminal extensions of 14 amino acids,SS28.Both SS14 and SS28 are encoded by a common gene and processed from a single precursor,PSSI.SS14 is highly conserved in all known vertebrate species,including several mammalian species,chicken,frog and fishes,with the same amino acid sequence.In addition to having PSSI,Fish possess one or two other different forms of somatostatin(SS),PSSⅡ and PSSⅢ.The PSSⅡ molecule is thought to be processed to a large form of SS(SS28 or SS25) with [Tyr7,Gly10]-SS14 at its C-terminus,while the PSSⅢ would produce a SS14 variant-SS14.All the three types of PSS genes had been cloned both in goldfish and Orange-spotted grouper.PSSs are widely distributed throughout the central nervous system(CNS) and peripheral tissues. PSS are differentially expressed,both in terms of the distribution among tissues and in terms of the relative abundance within a tissue.SS exerts diverse inhibitory actions through binding to specific membrane-bound G-protein-coupled receptors.There are different types
