ACQUIRED OR ADAPTIVE IMMUNE SYSTEM

Acquired or Adaptive Immune System

  • Acquired immunity is the immunity acquired through encounters with pathogens over a lifetime.

  • The adaptive immune system is effective but takes several days to become fully active, utilizing antigens and antibodies.

  • It is capable of adaptation and learning against various pathogens.

  • The adaptive immune system divides into two primary types:

    • Antibody-mediated immunity (humoral immunity):

      • Involves B-lymphocytes that differentiate into plasma cells and memory B cells.

      • Plasma cells produce antibodies specific to encountered antigens.

      • Memory B cells store copies of antibodies for future reinfection.

      • Effective against bacterial cells, parasites, toxins, viral agents, and fungal infections.

    • Cell-mediated immunity:

      • Involves T-lymphocytes, differentiating into helper T cells, cytotoxic T cells, suppressor T cells, and memory T cells.

      • Cytotoxic T cells (killer T cells) bind to specific antigens and release perforins to destroy infected cells.

      • Helper T cells release interferons and interleukins, assisting immune responses.

      • Memory T cells restock the immune library for future encounters.

      • Suppressor T cells regulate and down-tune the immune response.

Attributes of Adaptive Immunity

The adaptive immunity possesses several key attributes:

  1. Antigen Specificity: Highly specific, targeting unique antigens of each microbe.

  2. Immunologic memory: Memory cells (T and B cells) from the first encounter help respond to subsequent infections.

  3. Diversity: Responsive to a wide variety of antigens, despite requiring time to develop.

  4. Specific receptors: Host cell receptors are specifically tailored for microbial antigens.

Types of Acquired Immunity

Acquired immunity types are classified into:

  • Active Immunity:

    • Immunity developed by the individual’s active participation in eliminating pathogens.

    • Developed through:

      • Natural Active Immunity: Results from natural infections, leading to memory cell production.

      • Artificial Active Immunity: Achieved through vaccinations, which provoke immune responses without severe effects (e.g., MMR vaccine).

  • Passive Immunity:

    • Immunity where antibodies are introduced into the body without active involvement.

    • Antibodies can be:

      • Natural Passive Immunity: Acquired from mother to child via placenta or breast milk (e.g., colostrum).

      • Artificial Passive Immunity: Injection of pre-formed antibodies (gamma globulin) into the body, offering quick but temporary immunity (e.g., rabies antiserum).

Summary of Immune Responses

  • Active Immunity: Body’s immune response is active in creating defenses and memory cells.

  • Passive Immunity: Ready-made antibodies are introduced; no memory cells formed, short-lived response.