Overview
The transcript explains acquired immunity, covering humoral and cell-mediated responses, and contrasts active vs passive and natural vs artificial immunity.
Humoral Immunity (Antibody-Mediated)
- Antigen binds to a B cell antibody; B cell engulfs antigen.
- Antigen is presented on B cell surface via MHC II proteins.
- Helper T cell binds the MHC II–antigen complex and releases cytokines.
- Cytokines induce B cell proliferation into plasma cells and memory cells.
- Plasma cells produce and release antibodies specific to the antigen.
- Memory B cells become sensitized; act quickly upon re-exposure.
- Antibodies bind antigens, triggering reactions leading to neutralization and destruction.
Cellular Immunity (Cell-Mediated)
- Naive T cell contacts an MHC–antigen complex and becomes activated.
- Activated T cell releases cytokines, driving proliferation and activation of T cells.
- Helper/Inducer T cells (CD4+): recognize self vs non-self; release cytokines to recruit WBCs.
- Regulatory T cells: release cytokines that suppress immune responses; prevent hypersensitivity.
- Cytotoxic T cells (CD8+): destroy infected, cancerous, or damaged cells.
Types of Immunity: Active vs Passive; Natural vs Artificial
- Active immunity: body actively produces antibodies after exposure.
- Passive immunity: antibodies are provided to the body; no endogenous production.
| Type | Active vs Passive | Natural vs Artificial | Source of Antibodies | Memory Cells Formed | Example Detail |
|---|
| Active Natural | Active | Natural | Self (after live pathogen exposure) | Yes | Antibodies made after infection |
| Active Artificial | Active | Artificial | Self (after vaccine exposure) | Yes | Antibodies made after vaccination |
| Passive Natural | Passive | Natural | Mother to baby (placenta or breast milk) | No | Antibodies gifted from mom |
| Passive Artificial | Passive | Artificial | Administered immunoglobulins | No | Helps current infection; no future memory |
Key Terms & Definitions
- Antigen: foreign substance that triggers an immune response.
- Antibody: protein produced by plasma cells that binds specific antigens.
- B cell: lymphocyte that produces antibodies and memory cells.
- MHC II: molecules presenting processed antigen on B cells to helper T cells.
- Helper T cell (CD4+): T cell aiding immune activation via cytokines.
- Regulatory T cell: T cell that suppresses immune responses to prevent overreaction.
- Cytotoxic T cell (CD8+): T cell that kills infected, cancerous, or damaged cells.
- Cytokines: chemical messengers coordinating immune cell actions.
- Memory cells: long-lived cells enabling rapid response upon re-exposure.
- Immunoglobulins: externally provided antibodies for passive artificial immunity.
Action Items / Next Steps
- Review roles of CD4+ and CD8+ T cells for future HIV/AIDS discussion.
- Prepare for next lesson on immune system malfunction and infection.