Veterinary Immunology and Serology

NEUTROPHILS

• Neutrophils are considered as the first line of defense against pathogenic microorganismsm and called as martyrs of immune system.
• Neutrophils are attracted to the site of invasion by chemotactic signals and they engulf and kill the invading organisms.
• About 5-6 hours later macrophages are attracted to the site of infection.
• Neutrophils are the major cell type of myeloid system.
• They originate from bone marrow and their development in bone marrow takes about two weeks time.
• During their development (stem cells to myelocytes), they acquire cytoplasmic granules hence they are called polymorphonuclear (PMN) leucocytes.
• Mature neutrophils circulate in the blood for a short period of 10-12 hours later move in tissues.
• Total life span is only a few days.
• Neutrophils do not have capacity to multiply or replicate.
• In blood, neutrophils are about 12 µm in diameter, nucleus is segmented and cytoplasm contains many granules.
• When viewed under electron microscope, two types of granules are there.

Neutrophils of different species

	Segmented neutrophils have an irregularly lobed nucleus without the true formation of filaments connecting the lobs.
	Segmented neutrophils similar to those of canine ,having an irregular nuclear membrane with only occasional cells having distinct filament formation.
	Neutrophils of mature type having filaments connecting the lobes,although many segmented neutrophils are identified only by an indentation of neucleus.
	Segmented neutrophils, nuclear chromatin arrangements characterized by the presence of dark staining plaques that make the nucleus appear almost granular.

• Primary granules((azurophilic granules) - contain defensins and bactericidal enzymes such as myeloperoxidase and lysozyme; neutral proteases such as elastase; acid hydrolases such as b -glucuronidase and cathepsin B.
• Secondary granules (specific granules) - contain lysozyme, collagenase and lactoferrin (iron binding protein), gelatinase etc.
• Neutrophils also contain a small Golgi apparatus, some mitochondria and very few ribosome or rough endoplasmic reticulum. Because of this they can not synthesize large amount of proteins. Neutrophils constitute 60-75% of blood leucocytes in carnivores; 20-30% in ruminants and 50% in horse.

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