DEEP WORK

2.5.1 Pathogen recognition Once a pathogen succeeds in breaching the innate physical barriers, it is recognized by pattern recognition receptors on immune cells, this step being the first key factor in the triggering of all subsequent immune responses. These receptors are mainly present in DCs and macrophages, but also in other cell types, such as B lymphocytes or endothelial cells, and are acti..

2.4.3 Antimicrobial peptidesAntimicrobial peptides (AMPs) are small peptides (less than 100 amino acids) with low molecular weight and direct microbicidal activities. They are mostly cationic and amphipathic, although some anionic peptides are included among them. AMPs are synthesized as pre-pro-peptides, and, once the active peptides are released by cleavage, they interact directly with pathoge..

2.4.2 ComplementThe complement system is an ancient innate immune mechanism present in both vertebrate and invertebrate species. The mammalian complement system appears more developed and is composed of ∼30 different proteins, either plasma- or membraneassociated. The proteins and glycoproteins that constitute the complement system are synthesized by hepatocytes, but significant amounts are also..

2.4 Soluble mediators of immunityAn important array of regulatory mediators, highly toxic soluble molecules, degradative enzymes, and antimicrobial peptides provide strong immune humoral protection against a wide range of pathogens, orchestrate the majority of the immune mechanisms, and contribute to maintain the host homeostasis. These mediators, constitutively expressed or secreted upon induct..

2.3.2 Cells of the monocyte–macrophage lineage2.3.2.1 Monocytes and macrophagesMacrophages (and their precursors, monocytes) are the main phagocytic cells of the immune system. Tissue macrophages are present throughout the body and contribute to tissue homeostasis and immune surveillance. Upon tissue damage or infection, monocytes are rapidly recruited to the tissue where they differentiate into..

2.3 Cellular componentsThe different leukocyte types derived from the lymphoid and myeloid lineages known from mammals have also been recognized in fish, including cells morphologically and functionally equivalent to mammalian B and T lymphocytes, natural killer (NK) cells, monocytes, macrophages, neutrophils, eosinophils, mast cells, and thrombocytes (Secombes, 1996; Whyte, 2007), as well as th..

2.2 Organs, tissues, and general structures In higher vertebrates, the immune system consists of primary (lymphocyte-generating) and secondary (immune response-generating) lymphoid organs. The fetal liver, thymus and bone marrow constitute the primary lymphoid organs, while the spleen, lymph nodes, and mucosal-associated lymphoid tissue (MALT) comprise the secondary lymphoid organs.  Fish organi..

2.1 IntroductionFish are a wide and heterogeneous group of vertebrates that comprise about 40,000 species, divided into three classes: Agnatha (jawless fish represented by hagfish and lampreys), Chondrichthyes (cartilaginous fish comprising sharks, rays, and skates), and Osteichthyes (bony fish). Fish heterogeneity is based on many aspects of their biology and habitats. There are fish species ad..