The non-specific defense mechanisms of fish By Andrew G Challingsworth

The non-specific defense mechanisms of fish The organism needs to defend itself not only from pathogens that are outside the body, such as bacteria, viruses etc but also from abnormal cells within the body which can give rise to cancers. SQQ 737 Fish Health Management Topic 4, Defense Mechanisms.

Two defense systems have evolved in this respect. 1) The non-specific defense mechanism which we will take a closer look at in this short study. 2) The specific defense mechanism or the immune system.

Non-specific defense mechanism or the innate immune system. Much published work on the innate immune system in recent years. In reference too! 1)Disease resistance 2)Prophylactic measures 3)Environmental changes 4)Genetic trait

Recent Publication cont! 5)activity of macrophages 6)Cytotoxic cells 7)Complement components 8)Interferon 9)antibacterial peptides 10)Immunostimulants 11)Immunostimulants application Innate immunity of fish (overview)

Non-specific defense mechanisms or the innate immune system! Phylogenetically ancient mechanisms. Block entry of pathogens into the body. Eliminate them in a non-specific fashion.

Included in this category! Acute phase proteins I.e. C-reactive proteins Pentraxins C-reactive proteins (CRP) and Serum amyloid protein (SAP) are lectins. Present in the body fluids of vertebrates. Commonly associated with acute phase response.

Following significantly increased serum levels! Following tissue injury Trauma Infection (The acute phase response) Pentraxins take part in innate immune defense. Lectin type binding role. Activate the complement pathways recognition and clearance of apoptotic cells. Innate immune response (Overview)

Includes two lines of defense! First line of defense is external. Consisting of the skin, scales, and mucous membranes also secretions produced by fish. Second line of defense is internal. Triggered by chemical signals, employs antimicrobial proteins and phagocytic cells and the inflammatory response.

First line of defense Skin and mucous membranes! Skin provides barrier that cannot be penetrated by bacteria or viruses. But small abrasions can allow passage. Mucous membranes lining the digestive, respiratory and urinogenital canals act as: Barrier to microbes and is an effective non-specific defense.

Fish mucous contains immune parameters! Lectins Pentraxins Lysozyme Complement proteins Antibacterial peptides Igm

Limited pathogen recognition machinery although strength of innate defense against pathogens is impressive! Although sluggish (up to 12 weeks) Poiklothermic nature limited antibody repertoire affinity, maturation and memory. slow lymphocyte proliferation. Compared to the instant temperature of relatively independent innate immune response. Innate immune system is essential to the function of acquired immunity and determines the nature of the acquired response.

Phagocytic white blood cells! Phagocytosis ingestion of invading microbes by white blood cells (WBCs) Neutrophils 60-70% of all WBCs amoeboid movement, destruction of microbes. Monocytes 0.5% of (WBCs) stronger phagocytic response. Eosinophils limited phagocytic activity contain destructive enzymes. Natural killer cells destroying infected cells invaded by virus’s.

Antimicrobial proteins! Two important antimicrobial proteins complement and interferons. Complement Cooperating proteins several have a cascading effect, lysing invading pathogens. Also act as attractants or chemotaxis to draw in phagocytes to site of infection.

Interferons (IFN)! Substance produced which helps cells resist virus infection. Several types known Mass produced by recombinant DNA techniques. Inhibit replication of virus. They are not virus specific. Found mainly in the serum.

Natural haemolysins! Substances found in fish serum. Small molecular weight Capable of lysing foreign Red Blood cells. These chemicals have bactericidal properties.

Conclusion The importance of the non-specific defense mechanism is protection of the animal against disease which however varies in different groups. Being highest in invertebrates and lowest in man however having an intermediate response in fish is apparent.