Learning Objectives: By the end of this lesson, students should be able to describe the components of adaptive immunity, explain its key characteristics (specificity, diversity, memory, self-tolerance), and understand how adaptive immunity collaborates with innate immunity to defend against pathogens.
Introduction
Adaptive immunity provides specific and long-lasting defense against pathogens. Its components include B and T lymphocytes and their effector cells. Unlike innate immunity, adaptive immunity is antigen-specific, diverse, and capable of immunologic memory.
Key Characteristics of Adaptive Immunity
- Specificity: Each B and T lymphocyte recognizes a particular antigen.
- Diversity: The population of lymphocytes collectively recognizes a wide variety of antigens.
- Immunologic memory: Responses are enhanced upon repeated exposure to the same antigen.
- Self vs Non-self discrimination: Adaptive immunity distinguishes host cells from pathogens.
- Self-limitation: Responses are terminated after a challenge to conserve energy and prevent uncontrolled cell proliferation.
Functional Significance:
- Specificity & memory: protects against persistent or recurring pathogens.
- Diversity: ensures defense against as many pathogens as possible.
- Effector specialization: mounts appropriate responses for each pathogen.
- Self-tolerance: prevents autoimmunity.
- Self-limitation: prevents overactivation that can cause leukemia or lymphoma.
Innate vs Adaptive Immunity
| Characteristic | Innate Immunity | Adaptive Immunity |
|---|---|---|
| Specificity | For PAMPs | For specific microbial and non-microbial antigens |
| Diversity | Limited | High |
| Memory | No | Yes |
| Self-reactivity | No | No |
| Components | Skin, mucosa, normal flora, phagocytes, granulocytes, NK cells, complement, cytokines | Lymph nodes, spleen, mucosal-associated lymphoid tissues, B & T lymphocytes, antibodies |
| Function | Immediate defense | Specific defense, memory formation, and coordination with innate immunity |
Integration with Innate Immunity
The adaptive immune response collaborates with innate immunity to stop infections. Once pathogens breach physical and physiological barriers, the innate immune system responds immediately, while adaptive immunity mounts a targeted, specific response and forms long-term memory.
