Acquired Immunity - Practice Questions & MCQ

• It is a pathogen-specific immunity.
• The immunity that an individual acquires after the birth is called acquired or adaptive or specific immunity. 
• It is specific and mediated by antibodies or lymphocytes or both which make the antigen harmless.
• It not only relieves the victim of the infectious disease but also prevents its further attack in future. 
• Thus acquired immunity consists of specialized В and T lymphocytes and antibodies.

Characteristic Features:

• Specificity: 
  • It is the ability to differentiate between various foreign molecules (for­eign antigens).
• Diversity: 
  • It can recognize a vast variety of foreign molecules (foreign antigens).
  • Discrimination between Self and Non-self: 
  • It can recognize and respond to foreign molecules (non-self) and can avoid response to those molecules that are present within the body (self) of the animal.
• Memory: 
  • When the immune system encounters a specific foreign agent, (e.g., a microbe) for the first time, it generates immune response and eliminates the invader. 
  • This is called the first encounter. 
  • The immune system retains the memory of the first encounter. 
  • As a result, a second encounter occurs more quickly and abundantly than the first encounter.

Components of Acquired Immunity:

• Acquired immunity has two components: 
  • humoral immunity or Antibody-mediated immune system (AMIS) 
  • cellular immunity or cell-mediated immune system (CMIS).
     

• Acquired immunity is of two types: active immunity and passive immunity.

Active Immunity:

• In this immunity person’s own cells produce antibodies in response to infection or vaccination. 
• Active immunity may be natural or artificial.
• A person who has recovered from an attack of smallpox or measles or mumps develops natural active immunity.
• Artificial active immunity is the resistance induced by vaccines. 

Passive Immunity:

• When ready-made antibodies are directly injected into a person to protect the body against foreign agents, it is called passive immunity. 
• It provides immediate relief.
• Passive immunity may be natural or artificial.
• Natural passive immunity is the resistance passively transferred from the mother to the fetus through the placenta. 
  • IgG antibodies can cross the placental barrier to reach the fetus.
  • Mother’s milk contains antibodies (IgA) that protect the infant properly by the age of three months.
• Artificial passive immunity is the resistance passively transferred to a recipient by the administration of antibodies.