Overview
This lecture covers Chapter 15 on the immune system’s first and second lines of defense, focusing on innate (nonspecific) immunity, physical and chemical barriers, the roles of white blood cells, lymphatic organs, inflammation, fever, interferons, complement proteins, and natural killer cells.
Lines of Defense in Immunity
- The immune system is divided into three lines of defense: first (physical/chemical barriers), second (innate cellular responses), and third (adaptive immunity).
- The first and second lines are innate (nonspecific), functioning the same way every time and lacking memory.
- The third line, covered in Chapter 16, is specific/acquired immunity with memory, involving B cells and T cells.
First Line of Defense: Physical and Chemical Barriers
- Skin acts as a physical barrier to pathogen entry.
- Mucous membranes, tears, saliva, ear wax, and stomach acid are chemical barriers.
- Microbiota in the gut also assist as part of the first line.
Second Line of Defense: Innate Cellular Responses
- Includes phagocytic cells (neutrophils, monocytes, macrophages, dendritic cells) and processes like inflammation and fever.
- Innate immunity does not target specific pathogens but recognizes general patterns found on microbes.
Phagocytosis and Pattern Recognition
- Phagocytes detect pathogens via pattern recognition receptors (PRRs) binding to pathogen-associated molecular patterns (PAMPs), e.g., peptidoglycan, flagellin, LPS.
- Steps of phagocytosis: chemotaxis, ingestion, phagosome formation, fusion with lysosome, destruction, and exocytosis.
Inflammation and Fever
- Signs of inflammation: redness (rubor), warmth (calor), swelling (tumor), pain (dolor), and sometimes loss of function.
- Inflammation mobilizes immune cells, aids in tissue repair, and limits further infection.
- Fever (triggered by pyrogens/cytokines) slows pathogen growth, reduces available iron, and boosts immune responses.
Lymphatic System and Organs
- Lymphatic system transports lymph (fluid with white blood cells and antigens) through lymph nodes and vessels.
- Primary organs: bone marrow (produces all blood cells; B cells mature here), thymus (T cells mature here).
- Secondary organs: lymph nodes, spleen, and lymphoid tissues (SALT, GALT, MALT).
Antigens, Self vs. Non-Self, and Autoimmunity
- Antigens are molecules recognized by the immune system; can be self (should not be attacked) or foreign (should be attacked).
- Autoimmune disease results when the immune system cannot distinguish self from non-self.
Interferons and Antiviral Response
- Infected cells release interferons to alert neighboring cells, which then produce antiviral proteins to resist viral takeover.
- Interferon response is nonspecific and part of the innate system.
Complement Proteins
- Over 50 complement proteins in blood can be activated to assist in inflammation, promote phagocytosis, and form membrane attack complexes to lyse pathogens.
Natural Killer (NK) Cells
- NK cells, lymphocytes of the innate system, scan for cells lacking MHC1 and kill them if detected, helping eliminate infected or cancerous cells.
Key Terms & Definitions
- Innate Immunity — Non-specific, general immune defenses present from birth.
- Phagocytosis — Ingestion and destruction of pathogens by specialized cells.
- PRR (Pattern Recognition Receptor) — Receptors on phagocytes that detect PAMPs.
- PAMP (Pathogen-Associated Molecular Pattern) — Molecules common to groups of pathogens recognized by PRRs.
- Antigen — Any molecule recognized by the immune system; can be self or foreign.
- Pyrogen — Substance that causes fever by affecting the hypothalamus.
- Interferon — Innate antiviral cytokine signaling molecule.
- Complement Proteins — Serum proteins that assist in lysis of pathogens and enhance immune responses.
- Natural Killer Cell — Innate lymphocyte that kills cells lacking MHC1.
Action Items / Next Steps
- Watch and summarize (draw and label) the five recommended YouTube videos on innate immunity for bonus points.
- Review the chapter’s key cell types, inflammation steps, and the functions of different innate defenses.