Acquired Immunity (also known as Specific or Adaptive Immunity)
- Definition: Acquired immunity is the immune system that is pathogen specific, and is not genetically conferred. It is obtained either from the development of antibodies (AB) in response to exposure to an antigen (Ag), from vaccination, or transmission of antibodies (e.g., mother to foetus).
- It is the capability of multicellular organisms to resist harmful microorganisms.
- It develops later than innate immunity, acquired through previous experience with a foreign agent.
- It provides a specific response to the inducing antigen.
- It develops after a latent period of 1-2 weeks.
- Immune memory develops, leading to stronger responses in subsequent infections.
- Consists of two groups of lymphocytes: B and T cells.
- Includes Humoral immunity (mediated by antibodies produced by B cells) and Cell-mediated immunity (defends against microorganisms by T cells).
Types and Forms of Acquired Immunity
Acquired immunity can be classified into two main types: Active and Passive.
- 1. Active Immunity:
- Definition: Immunity which results from the production of antibodies by the immune system in response to the presence of an Antigen. It involves the activation of B cells (which produce antibodies) and T cells (which destroy infected cells and support B cells).
- It is based on the principle that the secondary immune response is stronger than the primary immune response thanks to the presence of memory B- and T-cells that develop in response to the primary stimuli. Immune memory ensures that subsequent infections by the same pathogen are controlled more quickly.
- This type of immunity provides long-lasting protection through the development of immune memory.
- Forms of Active Immunity:
- Natural Active Immunity: This occurs when a person is exposed to a live pathogen and develops a primary immune response. It is not induced by deliberate exposure. For example, when an individual is infected with a virus, their immune system responds by producing specific antibodies and remembers the pathogen for more effective future responses.
- Artificial Active Immunity: This immunity is induced by a vaccine, a substance that contains antigens. Vaccines contain weakened or inactivated forms of pathogens (or parts of them), stimulating the immune system to generate an adaptive immune response without causing the disease itself.
- 2. Passive Immunity: