11.3 - Types of Immunity

Classification of Immunity

• Active immunity: Lymphocytes produce their own antibodies in response to stimulation by antigens.
• Passive immunity: The body receives antibodies from an external source.
• Both types can be acquired naturally or artificially.

Active Immunity

• Antibodies are produced naturally by lymphocytes.
• Remains for a long period.
• Natural active immunity:
  • Pathogens stimulate lymphocytes to produce antibodies.
  • Recovery gives permanent immunity to the disease.
  • Memory cells rapidly produce antibodies if the same pathogen attacks again.
• Artificial active immunity:
  • Immunisation stimulates immunity against a specific disease through vaccine injections.
  • A vaccine is a suspension of weakened, dead or non-virulent pathogens.
  • The first injection usually produces an antibody level below the level of immunity.
  • A booster dose raises antibody production above the level of immunity.
  • Memory cells enable lymphocytes to produce enough antibodies immediately when the actual pathogen infects the body.
  • Examples: Salk vaccine for poliomyelitis, BCG vaccine for tuberculosis and HPV vaccine for cervical cancer.

Passive Immunity

• The body does not produce its own antibodies; antibodies come from an external source.
• Gives immediate, short-term and temporary protection.
• Natural passive immunity:
  • Maternal antibodies diffuse through the placenta into the foetal blood flow.
  • Antibodies in breast milk or colostrum protect the baby for the first few months after birth.
• Artificial passive immunity:
  • An antiserum injection provides specific antibodies against a specific antigen.
  • Protection is immediate but short-lived.
  • Examples: Antitetanus, anti-rabies and antiserum for poisonous snakes.

Comparison of Active and Passive Immunity Graph Characteristics

Graphs of Active Immunity (Vaccination)

• The first vaccine injection raises the antibody level slowly but below the level of immunity.
• The second injection, or booster dose, raises the antibody level above the level of immunity.
• Antibody production by lymphocytes gives long-lasting immunity.

Graphs of Passive Immunity (Antiserum Injection)

• The first antiserum injection raises the antibody level immediately above the level of immunity.
• The antibody level then decreases; immunity is temporary.
• A second injection is given only if the antibody level falls below the level of immunity while the person is still infected.

Differences between Vaccine and Antiserum

• Similarities: Both protect against infectious diseases and involve antigen-antibody interactions.
• Vaccine: Contains weakened, dead or non-virulent pathogens; used for prevention; does not protect immediately; produces long-lasting immunity; injected before infection; stimulates lymphocytes to produce antibodies; requires a booster dose to raise antibodies above the level of immunity.
• Antiserum: Contains specific antibodies; used for treatment or immediate protection; protects immediately; produces temporary immunity; injected when infected, before infection if risk is high, or immediately after infection; requires another injection only if antibody level falls below the level of immunity while infection persists.