Neutrophils of animals
Neutrophils of animals are produced in the bone marrow from the extravascular neutrophilic myelocytes. They are numerously found in the blood of most animals.
The nucleus of mature cells is divided into lobes, usually five lobes and are stained blue or purple by Leishman’s stain. They have abundant and fine granular cytoplasm which take up the neutral stain.
These granules store lysosomes, which contfain hydrolytic enzymes, proteolytic enzymes and lipases to digest the invading organisms.
The oxidative enzymes of the lysosome produce hydrogen peroxide, which attack the bacterial cell wall to cause bactericidal effect.
Neutrophils are highly motile, responds to chemotaxis and actively phagocytic, thus serve as a first line of defence against invading organisms, (bacteria, viruses and cellular remnants).
At the onset of infection neutrophils produce pyrogens which act on thermo-regulator centre of the brain results in fever. This rise in body temperature slows the reproduction process of bacteria and viruses
Immature forms of neutrophils are characterized by unsegmented or less number of nuclear lobes and are referred to as juvenile or band cells. Pseudo neutrophils and heterophils are comparable to neutrophils, which are present in rabbit and poultry respectively.
Heterophils contain large rod or spindle shaped granules, which are acid in reaction and stain red or pink with eosin.
Abnormalities of Neutrophils
Neutrophilia
It indicates more number of neutrophils in the circulation. Physiological neutrophilia occur in conditions like exercise, emotion, pregnancy, lactation and parturition.
Abnormal or pathological neutrophilia may be due to acute inflammation following injury, surgery, burns, arthritis and acute infection by pyrogenic bacteria.
Shift to left is a term used to describe an increase in the number of immature neutrophils (Band cells) in the circulation which is characteristic of bacterial infections. The shift to left is clinically helpful in diagnosis of traumatic reticulopericarditis (TRP).
Neutropenia
It indicates reduction in neutrophils in the circulation, which is very common in viral infections and chronic infections like TB, brucellosis and protozoal and fungal infections. Injection of antiinflammatory drugs (cortisol) and antibacterial drugs (chloramphenicol and sulphanamides) may result in neutrophilia.