Overview
This lecture explains how the adaptive (acquired) immune system, particularly the humoral response and B cells, protects the body against pathogens through antibody production and memory formation.
Adaptive Immune System: Basics
- The adaptive immune system targets specific pathogens after recognizing them as threats.
- It acts slower than the innate immune system because it must first encounter the pathogen.
- Adaptive immunity has memory, allowing for faster responses upon future exposures.
- It is systemic, capable of protecting the entire body.
Humoral Immunity and Antibodies
- Humoral immunity uses antibodies produced by B lymphocytes to target pathogens in body fluids.
- B cells originate and mature in bone marrow.
- Mature B cells develop immunocompetence (ability to recognize antigens) and self-tolerance (avoid attacking self).
- Each B cell displays unique membrane-bound antibodies, each specific to a particular antigen.
B Cell Activation and Response
- B cells are activated when they bind to their matching antigen, usually in lymph nodes or spleen.
- Activated B cells clone themselves, creating effector (plasma) cells and memory cells.
- Plasma cells produce large quantities of antibodies to neutralize and mark antigens.
- Memory cells ensure a quicker secondary immune response if the same pathogen returns.
Antibody Actions
- Antibodies neutralize pathogens by blocking their binding sites.
- Agglutination lets antibodies bind multiple antigens, clumping them for easier removal by macrophages.
- Antibodies attract phagocytes and other immune cells to destroy marked pathogens.
Types of Humoral Immunity
- Active immunity: body produces its own antibodies after exposure to antigen, naturally (infection) or artificially (vaccination).
- Vaccines use weakened or dead pathogens to prime the body for future attacks.
- Passive immunity: body receives antibodies from another source, like from mother's placenta or via antibody-rich serum.
Limitations and Adaptations
- Some pathogens, like flu viruses, frequently change antigens, so immunity may not last.
- Passive immunity is temporary, as it doesn't create memory cells or long-lasting antibodies.
Key Terms & Definitions
- Adaptive Immune System — immune defense that specifically targets and remembers pathogens after exposure.
- Humoral Immunity — branch of adaptive immunity using antibodies in bodily fluids to fight pathogens.
- B Lymphocyte (B Cell) — white blood cell that produces antibodies.
- Antigen — molecule that triggers an immune response.
- Antibody — protein produced by B cells that binds to specific antigens.
- Effector/Plasma Cell — activated B cell that mass-produces antibodies.
- Memory Cell — long-lived B cell that retains information for faster future responses.
- Active Immunity — immunity developed by the body producing its own antibodies.
- Passive Immunity — temporary immunity from receiving external antibodies.
Action Items / Next Steps
- Review how vaccinations provide active immunity.
- Prepare for the next lecture on cellular immunity.