Non- specifc immune mechanism

NON-SPECIFIC IMMUNE MECHANISM

  • It includes
    • Physical barrier like mucus, skin (dermis and epidermis), scales and chemical defenses – mucus, lysozyme and immunoglobulins
    • Humoral factors
    • Cellular factors

Physical barriers of fish immune system

  • The mucus and epidermis are the first line of defense in fishes. Protection by these barriers is extremely effective. The mucus, generated by the epidermal mucosal cells is the outermost line of defense of the fish. The mucus is continuously replenished and it contains factors which inhibit the growth and establishment of parasites on the external surface areas. It also contains proteolytic enzymes and maintains unfavourable pH levels for pathogen growth
  • Scales: The base of the fish scales reaches down into the dermal connective tissue and extends to the outer skin surface, which protects the fishes against the pathogens in the water.
  • Epidermis: Under the mucus lie the layers of the epidermis. The outer layer is composed of flattened squamous cells differing from their mammalian counterparts by not having the corneous dead cells on the surface. Below this, the epidermis has a layer made up of fusiform cells. Both of these top two layers are interspersed with bulbous, mucous-secreting cells. The third layer’s cells are more rounded, and finally the lower-most layer has the extended, columnar-shaped cells which rest on a basement membrane. Throughout the whole epidermis, occasional neutrophilic migrating cells may be observed. A feature distinguishing the fish epidermis from the mammalian example is that throughout the epidermal layer of the fish, mitosis is usually seen in the lower layer. This is because mammals require hardened layers of skin to prevent dehydration, whereas in the aquatic environment the fish has no need for such protection.
  • Dermis: The dermis, another protective barrier of the skin, lies under the basement membrane. This layer of the skin is composed of fibrous connective tissue interspersed with melanocytes, the black pigment cells.

Humoral factors of fish immune system

  • Non-specific humoral molecules include

Molecule

Composition

Mode of action

Lectins

Specific sugar binding proteins

Recognition, precipitation, agglutination

Lytic enzymes

Catalytic proteins lysozyme, etc

Hemolytic and antibacterial activity

Transferrin/ lactoferrin

Glycoprotein

Iron binding

Ceruloplasmin

Acute-phase protein

Copper binding

C-reactive protein

Acute-phase protein

Activation of complement

Interferon

Protein

Resistance to viral infection

Cellular factors of fish immune system

  • Inflammation: At the site of injury, whether it be caused by a wound or an invasive pathogen, an immediate reaction or inflammatory response develops. The inflammatory response, is an alarm system which is activated after a violation has been committed in order to repair the initial damage and prevent further harm. The release of histamines and other defensive factors by the damaged cells activates a chain of events which eventually seals the damaged area and begins restoration to a normal condition.
Last modified: Sunday, 18 September 2011, 5:35 AM