Learning Objectives: By the end of this lesson, students should be able to explain how innate and adaptive immunity collaborate to fight infections, describe the sequence of immune activation, and understand the mechanisms of immunological memory and effector function.
Introduction
The innate and adaptive arms of the immune system work together to stop infections.
- Innate immunity responds immediately after a pathogen breaches physical and physiological barriers.
- If the pathogen is not contained, adaptive immunity is activated in an antigen-specific manner.
This collaboration ensures efficient clearance of pathogens and establishes long-term protection through immunologic memory.
Sequence of Immune Response
- Innate Immune Response
- Activated within minutes to hours after pathogen entry
- Phagocytes recognize pathogens via PAMPs using pattern-recognition receptors (PRRs)
- Phagocytosis and antigen processing help contain infection and prepare for an adaptive response
- Adaptive Immune Response
- Activated 1–2 weeks after primary infection if innate immunity fails to clear the pathogen
- Antigen presentation by phagocytes stimulates T lymphocytes, which release cytokines
- B lymphocytes differentiate into plasma cells, produce antibodies, and undergo isotype switching
- Effector functions:
- Antibodies: opsonization, complement activation, antibody-dependent cellular cytotoxicity
- Cytotoxic T cells: kill infected cells
- Helper T cells: enhance phagocyte activity
- Positive Feedback Between Innate and Adaptive Immunity
- Phagocytes stimulate T lymphocytes through antigen presentation
- T cells enhance the microbicidal activity of phagocytes
- Cytokines drive B lymphocyte differentiation and antibody production
- Both arms coordinate to eliminate pathogens efficiently
- Immunologic Memory
- After infection is cleared:
- Effector cells and antibodies persist temporarily
- Memory B and T cells provide long-term protection against subsequent infections
- After infection is cleared:
