Ability of the human body to resist and fight all types of organisms and toxins is called Immunity.

3 layers of Immunity

  1. Barrier Immunity
  2. Innate Immunity
  3. Acquired Immunity or Adaptive Immunity

Barrier Immunity

  • Skin is a physical barrier which prevents an organism to enter into the body. Skin also provides a chemical and a biological barrier. Skin cells produce antimicrobial proteins which kill the microorganism. Skin also contains immune cells.
  • Shedding of skin or desquamation helps to remove the bacteria which might have adhered to the skin surface.
  • Similar immunity is provided by surface lining of respiratory, gastrointestinal, genitourinary system, nose and pharynx.
  • Respiratory system – this have cilia which remove foreign material. It also has chemicals which act as antimicrobials like mucus and surfactants.
  • Stomach – release acids which kills bacteria. (destruction of swallowed organisms by gastric juices)
  • Eyes – tears kills microbes.

Innate Immunity

In (inside) Nate (born) – something one is born with.

It is present from birth. It is not specific. It is made up of various cells and complement system.

Cells of innate immune system.

  • Neutrophils
  • Basophils
  • Eosinophils
  • Monocytes
  • Macrophages
  • Mast cells – reside in connective tissue and mucous membrane. They contain heparin and histamine.
  • Dendritic cells – present in skin, lining of nose, stomach and intestines. They are a type of antigen presenting cells. They present it to the lymphocytes. They are also called Langerhans cells.
  • Natural Killer cells – these destroy our own cells which have become defective such as virus cells and tumour cells.

Complement System – Complements the action of antibodies and other cells in destroying bacteria.

Acquired (Adaptive) Immunity

  • This develops after a pathogen has attacked the body. It takes weeks to months to develop this immunity.
  • First Exposure – very low response. It keeps a memory.
  • Second Exposure – A lot of antibodies are produced.
  • Much of the immunity is acquired

Components of Adaptive Immunity

  • B Cells
  • T Cells

Humoral Immunity – is due to B lymphocytes. B lymphocytes produce antibodies. On second exposure, antibodies recognise a pathogen and coat it. Neutrophils are then attracted to these which phagocytose them.

Cellular Immunity – is due to T lymphocytes. It includes Helper T Cells (CD4) and Killer T Cells (CD8). It directly kills cells.

  • Helper T Cells – secrete growth factors and cytokines which help with maturation of other immune cells including CD8 cells.
  • AIDS kills CD4 cells which cripples the whole immune system.

immune response