Veterinary Immunology and Serology

RECOGNITION OF MICROBES BY NEUTROPHILS AND MACROPHAGES

• Neutrophils and macrophages express surface receptors that recognize microbes in the blood and tissues and also these receptors activate cells to produce cytokines and microbicidal substances that help in phagocytosis of microbes.
• There are several classes of phagocyte receptors, which bind microbes and mediate their internalization.
• Mannose binding receptors
  • The mannose binding receptor on macrophage surface bind with the terminal mannose and fructose residues of glycoproteins and glycolipids present in the bacterial cell walls.
• Receptors for opsonins
  • Opsonins are various blood proteins, which coat the microbes and helps in phagocytosis, and this process is called opsonization. Opsonic index is the ratio of the amount of opsonin in the blood of a disease affected animal to the amount of opsonin in the blood of a healthy animal.
• Other phagocyte receptors,which activate the phagocytes but do not participate directly in endocytosis: Example
• Toll like receptors (TLRs)
  • TLRs are a family of membrane proteins found in cell membranes of phagocytes and other cell types. They serve as pattern recognition receptors for a variety of microbe derived molecules and stimulate innate immune response.