Active and Passive Immunity
Depending on how the body acquires its defense mechanisms, the acquired immune system is further classified into two distinct types:
- Active Immunity and
- Passive Immunity.
Understanding the difference between the two is crucial for immunology and public health.
Active Immunity
Active immunity develops when a person’s own immune system is stimulated to produce antibodies and memory cells in response to a foreign antigen.
1.Mechanism:
- The host body actively participates in the defense process. B-cells and T-cells are engaged, and immunological memory is successfully created.
2.Speed and Duration:
- Because the body has to manufacture the antibodies from scratch, active immunity takes time (days or weeks) to develop. However, once developed, it provides long-lasting or even lifetime protection due to the presence of memory cells.
3.Types of Active Immunity:
- Natural Active Immunity: Occurs when a person catches a disease naturally (e.g., suffering from chickenpox), fights it off, and recovers. The body naturally remembers the pathogen for the future.
- Artificial Active Immunity: Achieved through vaccination. A harmless, dead, or weakened version of a pathogen is deliberately injected into the body. This forces the immune system to actively produce antibodies and memory cells without causing the actual disease (e.g., the BCG vaccine for Tuberculosis or the Covishield vaccine for COVID-19).
Passive Immunity
Passive immunity occurs when ready-made, fully formed antibodies are directly introduced into the body to provide immediate protection against an infection.
1.Mechanism:
- The host’s immune system remains completely passive.
- It does not actively produce any antibodies itself, nor does it create any memory cells for future use.
2.Speed and Duration:
It provides immediate, rapid relief and protection. However, because the introduced antibodies degrade over time and no memory cells are formed, passive immunity is strictly short-lived (lasting only a few weeks or months).
3.Types of Passive Immunity:
- Natural Passive Immunity: Antibodies are naturally transferred from a mother to her child.
- Artificial Passive Immunity: Used in medical emergencies where the patient’s body does not have enough time to mount an active immune response. Doctors inject highly concentrated, artificially synthesized antibodies directly into the patient’s bloodstream.
- Examples: Anti-tetanus serum (ATS) given after a rusty nail injury, or Anti-venom injections administered immediately after a poisonous snakebite.
Significance of Mother’s Milk (Colostrum)
The natural transfer of immunity from mother to infant is one of the most critical aspects of early human survival. A newborn baby’s immune system is highly immature and cannot immediately produce its own antibodies.
- Placental Transfer: During pregnancy, certain maternal antibodies, specifically IgG, cross the placenta and enter the fetal bloodstream, protecting the baby for the first few months after birth.
- Colostrum: This is the thick, yellowish milk produced by the mother during the initial few days of lactation immediately following childbirth. Colostrum is exceptionally rich in the secretory antibody IgA.
- Health Impact: Consuming colostrum provides the infant with robust natural passive immunity, protecting the newborn’s vulnerable digestive and respiratory tracts from various environmental infections. Promoting early breastfeeding is a major focus of India’s maternal and child health programs, such as the MAA (Mothers’ Absolute Affection) Programme.
