Neutrophils, Macrophages & Phagocytosis

  • There are two types on white blood cells:

    • Phagocytes

    • Lymphoocytes

  • Different types of phagocytes include: (part of Non-Specific defences)

    • Macrophages

      • Can destroy pathogens by phagocytosis

      • Antigen presentation

        • Same steps as the phagocytosis take place

        • After destroying the pathogen the glycoproteins from the cytoplasm move to the phagolysosome and bind to the antigen molecule

        • They are called major histocompatibility complex or MHC

          • When MHC binds to the antigens it forma an MHC-antigen complex.

        • MHC-antigen complex now moves to the cell surface membrane and the antigens are presented to the exterior of the cell.

        • This macrophage is called as an antigen-presenting cell or APC

        • APC play a critical role in the specific immune system by presenting antigens to lymphocytes

    • Neutrophils

      • They can rapidly engulf & destroy pathogens at the site of an infection.

  • Differnet types of lymphocytes include: (part of specific immune system)

    • B lymphocytes

    • T lymphocytes

  • Surface of pathogens are covered with chemicals which are not fund in human.

    • Incase of bacteria it is a component of the bacterial cell wall.

  • Blood contains special molecules which cna recognise these foreign chemicals and stick to them.

    • These molecules are called opsonins

  • By sticking to the pathogen opsonins tag teh pathogen as foreign.

  • Opsonins include antibodies as well as other molecules which are called complement.

  • Purpose of opsonins is to attach to foreign molecules & tag them as foreign

  • When a phagocytes engulfs a pathogen the phagocytes releases chemicals called cytokines

  • Cytokines signal to the phagocytes and other immune cells to move to the site of infection

  • Phagocytosis

  • Phagocytes such as neutroplis are attracted to molecules produced by pathogens

  • Receptors on the phagocyte membrane now attach to the opsonins and the phagocyte engulfs the pathogens.

  • The pathogens are now in a special vacuole called phagosome.

  • Lysosomes move towards the phagosome and fuse with it to form phagolysosome

  • Lysosomal enzymes now break down the pathogens and destroy it.