Veterinary Immunology and Serology

BIOLOGICAL BARRIERS

Circulating Phagocytes and NK cells

• Neutrophils and macrophages (monocytes in blood) identify, ingest and destroy the microbes.
• Neutrophils are also called polymorphonuclear leukocytes and each circulated in the blood only for 6 hours.
• Neutrophils are recruited at the site of infection within a few hours of infection otherwise they undergo programmed cell death and usually phagocytosed by resident macrophages in the liver and spleen.
• Macrophages and their circulating precursors, the monocytes play important role in both innate and adaptive immunity.
• Macrophages have a single rounded nucleus and they are phagocytic, hence they are called mononuclear phagocytes.
• All the cells of the mononuclear phagocytic system arise from the bone marrow stem cells and develop into circulating monocytes.
• Macrophages show variation from their basic structure.
  • Connective tissue macrophages - histiocytes,
  • Macrophages in liver - kupffer cells, 
  • Brain - microglial cells, 
  • Lungs - alveolar macrophages, 
  • kidney - mesangial cells, 
  • Spleen and lymph node - macrophages.
• All they form reticuloendothelial (RE) system.