Veterinary Immunology and Serology

EOSINOPHILS

• The second major polymorphonuclear granulocyte and it is named so because its cytoplasmic granules stain intensely with eosin.
• Eosinophils originate from bone marrow and leave bone marrow in a relatively immature state to spleen where they mature.
• Life span is short.
• In blood circulation half life is about 30 minutes then enter into tissues where they have half life of about 12 days.
• Tissue Eosinophils are about 500 times more than as observed in blood.
• Eosinophils are slightly larger then neutrophil with bilobed nucleus.

Eosinophils of different species

	Eosinophils contain pink cytoplasmic granules of variable size
	Rod shaped granules, partially cover the nucleus.
	Eosinophils are characterized by small, round eosinophilic granules in the cytoplasm.
	Large round irregular sized orange red stained granules. (Pomegranate seeds like).

 

• Cytoplasm contains two major types of granules 
  • Primary granules - contain arylsulfatase,peroxidase and acid phosphatase
  • Crystalloid granules- have a core of major basic protein surrounded by a matrix containing eosinophil cationic protein, eosinophil peroxidase and eosinophil-derived neurotoxin.

Function

• Although eosinophills can phagocytose small prticles, but they are more suited for the extracellular killing of parasites by the process of antibody dependent cellular cytotoxicity (ADCC).
• Since it contain Fc receptors specific for Ig E, it can kill IgE coated parasites especially helminths by the process of ADCC. Helminths are relatively resistant to lysosomal enzymes of neutrophils and macrophages. Eosinophils release major basic protein and cationic protein which are toxic to the parasites.
• They participate in type I– hypersensitivity reaction mediated by IgE antibody and cause tissue damage.