The non-specific defense mechanisms of fish

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The non-specific defense mechanisms of fish

• By Andrew G Challingsworth

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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.

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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.

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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

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Recent Publication cont!

• 5)activity of macrophages
• 6)Cytotoxic cells
• 7)Complement components
• 8)Interferon
• 9)antibacterial peptides
• 10)Immunostimulants
• 11)Immunostimulants application

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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.

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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.

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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.

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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.

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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.

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Fish mucous contains immune parameters!

• Lectins
• Pentraxins
• Lysozyme
• Complement proteins
• Antibacterial peptides
• Igm

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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.

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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 viruss.

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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.

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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.

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Natural haemolysins!

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

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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.