Granulocytes are involved in non-specific defence mechanisms, i.e. they respond to the presence of foreign material in the body but do not recognise specific antigens. 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 the inflammatory response.
ORIGIN
Granulocytes are formed from embryonic cells called granuloblasts in the haemopoietic tissues of the kidney.
OCCURRENCE
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. Granulocytes are thought to account for 1-9% of the total white blood cells in juvenile Rainbow Trout (Oncorhynchus mykiss).
It should be noted that different authors have reported varying figures for the same species.