Granulocytes

GRANULOCYTES

  • Granulocytes may account for 4-60% of leucocytes in fish, and there is considerable variation in the numbers of granulocytes present in different species of fish.

Types

  • These cells have a distinctive structure and are referred to as Polymorphonuclear (PMN) leucocytes. The cytoplasm contains numerous fine granules. In fish, granulocytes are of three types: Neutrophils and eosinophils are the most common while basophils are much rarer. It is believed that basophilic granulocytes are not found in salmonids.
    • Neutrophils : A leucocyte having no affinity for acid or basic dyes, but stainable by neutral dyes. The most abundant type of leucocyte and are able to move out of the blood and into the tissues of the body to engulf bacteria wherever they invade.
    • Eosinophils : A special white blood cell (polymorphonuclear leucocyte) that can be stained with acid dyes such as eosin. These cells are involved in destruction of internal parasites and in the modulation of allergic inflammatory reactions.
    • Basophils : A substance or tissue element (e.g. white blood cell) showing an affinity for basic dyes; (e.g. granulocytes that can digest micro-organisms).

Function

Granulocytes are involved in non-specific defence mechanisms; these cells migrate to parts of the body where invasion occurs and destroy the foreign particles by phagocytosis or by direct killing known as the cytotoxic response. This process is termed as the inflammatory response.

  • Antigen : Any agent which can elicit an immune response. A given antigen usually contains a number of sites where combination with various antibodies may occur (determinants). An antigen may be soluble (e.g. microbial toxins, extracts) or particulate.
  • Inflammatory response : The reaction of the tissues to injury or presence of any antigen characterized clinically by heat, swelling, redness and pain and pathologically by vaso-dilation, hyperaemia, accumulation of leucocytes, and exudation of fluid and deposition of fibrin. This reaction is termed the inflammatory response.
  • Phagocytosis : The intracellular uptake of solid particles by cells, either for nutritional purposes (e.g. food), or in the case of phagocytes such as macrophages and granulocytes as a defence mechanism (foreign bodies).
Last modified: Wednesday, 2 February 2011, 10:49 AM