The immune system

The Basics of the Immune System

  • The immune system consists of a network of cells, tissues, and organs that work together to protect the body against harmful microorganisms and diseases.
  • The immune system differentiates between the body’s own cells (self) and foreign cells (non-self) through the identification of antigens, which are protein markers on the surface of cells.

Cells Involved in the Immune System

White Blood Cells (Leukocytes)

  • One main type of immune system cell is the leukocyte or white blood cell, which combats disease and infection.
  • Leukocytes are produced and stored in many locations in the body, including the bone marrow, spleen, and thymus.

Macrophages

  • Macrophages are leukocytes that engulf, digest, and destroy microorganisms through a process called phagocytosis.
  • They also help to stimulate other cells in the immune system to respond to the pathogen.

B-Cells and T-Cells

  • Both B-cells and T-cells play crucial roles in the immune response.
  • B-cells produce antibodies that can bind to the antigens on pathogens and neutralise them.
  • T-cells can directly destroy infected cells and can also help to stimulate B-cells to produce antibodies.

The Immune Response

Primary Immune Response

  • The first time the immune system encounters a specific pathogen, it mounts a primary immune response.
  • This response is generally slow because there aren’t many B-cells that can produce the specific antibody that the pathogen requires.

Secondary Immune Response

  • If the immune system encounters the same pathogen again, it mounts a faster and stronger secondary immune response.
  • Memory cells, created during the primary response, quickly recognise the specific antigen and produce the necessary antibodies.

Active and Passive Immunity

Active Immunity

  • Active immunity occurs when the body’s own immune system produces antibodies in response to an infection or vaccination.
  • This type of immunity is usually long-lasting because memory cells are produced.

Passive Immunity

  • Passive immunity occurs when a person is given antibodies rather than producing them.
  • This immunity is temporarily as the body doesn’t produce memory cells against these antigens. Examples include antibodies passed from mother to baby during breastfeeding.