Summary of "منهج الفيروسات الوزاري| المحاضرة 5 | الجزء الأول P1"
Summary of “منهج الفيروسات الوزاري | المحاضرة 5 | الجزء الأول P1”
This lecture is part of a Ministry of Health virology curriculum series and focuses on immunity, specifically the immune response to viral infections. It serves as the concluding part of an introductory series on viruses, covering the immune system’s role in defending the body against viral pathogens.
Main Ideas and Concepts
1. Introduction to Immunity
The immune system is a complex defense mechanism consisting of cells, molecules, and tissues that protect the body from viruses, bacteria, cancer cells, and other harmful agents. Immunity is essential for survival despite the presence of numerous pathogens and harmful substances in the environment.
2. Types of Immunity
Innate Immunity (Non-specific)
- Present from birth.
- Non-specific: reacts similarly to all pathogens (viruses, bacteria, cancer cells).
- Acts immediately or shortly after exposure.
- Does not rely on immune memory.
- Includes physical barriers (e.g., skin), phagocytic cells (neutrophils, monocytes, macrophages), natural killer (NK) cells, interferons, and complement proteins.
- Key mechanisms:
- Phagocytosis: engulfing and destroying pathogens.
- Interferon production: proteins that inhibit viral replication and activate NK cells.
- Complement system: proteins that attack viral envelopes and mark infected cells for destruction.
- Natural killer cells: kill infected cells by releasing perforin and granzyme, inducing apoptosis (programmed cell death).
Adaptive Immunity (Specific or Acquired)
- Develops after exposure to specific pathogens.
- Highly specific: different responses for different viruses or pathogens.
- Relies on immune memory, enabling stronger and faster responses upon re-exposure.
- Divided into:
- Humoral Immunity (mediated by B cells producing antibodies)
- Cell-mediated Immunity (mediated by cytotoxic T lymphocytes, CTLs or CD8+ T cells)
3. Innate Immunity Components and Mechanisms
- Physical Barriers: Skin and membranes prevent pathogen entry.
- Phagocytic Cells: Neutrophils, monocytes (circulate in blood), and macrophages (in tissues) engulf pathogens.
- Interferons (IFNs):
- Three types: alpha, beta (produced by monocytes, macrophages, fibroblasts), and gamma (produced by T-helper cells, cytotoxic T cells, and NK cells).
- Functions:
- Inhibit viral replication by blocking viral protein synthesis.
- Increase expression of MHC Class I molecules on infected cells to enhance immune recognition.
- Activate NK cells.
- Natural Killer (NK) Cells:
- Recognize infected cells via MHC Class I molecules or antibodies coating the infected cells.
- Kill infected cells by releasing perforin and granzyme, inducing apoptosis.
- Use Fc receptors (FCRs) to bind antibodies attached to infected cells, enabling antibody-dependent cellular cytotoxicity (ADCC).
4. Adaptive Immunity Components and Mechanisms
Humoral Immunity
- Mediated by B cells producing antibodies (immunoglobulins: IgG, IgM, IgE).
- Antibodies specifically recognize viral antigens and:
- Neutralize viruses.
- Prevent virus entry into cells.
- Cause virus particles to clump together (agglutination), making them easier targets.
- Activate phagocytic cells via Fc receptors to engulf and destroy viruses.
- Activate the complement system to mark viruses and infected cells.
- Different antibodies protect different entry routes:
- IgE protects mucosal surfaces (respiratory and digestive tracts).
- IgG and IgM protect against viruses spreading through the bloodstream.
Cell-mediated Immunity
- Mediated by cytotoxic T lymphocytes (CTLs, CD8+ T cells).
- CTLs recognize viral peptides presented on MHC Class I molecules on infected cells.
- Upon recognition, CTLs release perforin and granzyme to induce apoptosis in infected cells.
- T cell receptors (TCRs) on CTLs specifically bind viral antigen peptides presented by MHC Class I.
Detailed Methodologies and Mechanisms
Interferon Mechanism of Action
- Produced by infected cells to inhibit viral replication.
- Two main mechanisms:
- Activation of RNAse enzymes that degrade viral mRNA, blocking viral protein synthesis.
- Phosphorylation of eukaryotic initiation factor 2 (eIF2), halting protein synthesis in infected cells.
- Increases MHC Class I expression to enhance CTL recognition.
- Prevents killing of uninfected cells by cytotoxic T cells by signaling “self” status.
Natural Killer Cell Killing Mechanisms
- Recognition of infected cells with reduced or altered MHC Class I expression.
- Recognition of antibody-coated infected cells via Fc receptors (ADCC).
- Release of perforin and granzyme induces apoptosis in target cells.
Antibody Functions in Humoral Immunity
- Neutralization: Antibodies bind viral particles to prevent cell entry.
- Agglutination: Antibodies cause viruses to clump for easier clearance.
- Opsonization: Antibody-coated viruses are recognized and engulfed by phagocytes.
- Complement activation: Leads to lysis or enhanced phagocytosis of viruses.
Cytotoxic T Lymphocyte Function
- TCRs recognize viral peptides presented by MHC Class I on infected cells.
- CTLs release cytotoxic proteins (perforin and granzyme) to induce apoptosis.
- Eliminates virus-infected cells to control infection.
Key Terms and Abbreviations
- Innate immunity: Non-specific, immediate defense.
- Adaptive immunity: Specific, acquired immunity with memory.
- Phagocytosis: Engulfing and destroying pathogens.
- Interferon (IFN): Antiviral proteins (alpha, beta, gamma).
- Natural Killer (NK) cells: Innate immune cells killing infected cells.
- MHC Class I: Molecules presenting viral peptides on infected cells.
- CTLs (Cytotoxic T Lymphocytes): CD8+ T cells killing infected cells.
- Antibodies (IgG, IgM, IgE): Proteins that neutralize and mark viruses.
- Fc receptor (FCR): Receptors on NK and phagocytic cells binding antibodies.
- Apoptosis: Programmed cell death of infected cells.
- ADCC (Antibody-dependent cellular cytotoxicity): Killing of antibody-coated cells by NK cells.
Speakers/Sources Featured
- Primary Speaker: Lecturer explaining the Ministry of Health virology curriculum.
- The lecture is presented in Arabic, aimed at students preparing for ministry exams.
- No other distinct speakers or sources are explicitly mentioned.
Conclusion
This lecture provides a comprehensive overview of the immune system’s response to viral infections, emphasizing the distinction between innate and adaptive immunity, their components, and mechanisms. It highlights critical concepts such as immune memory, interferon action, natural killer cell function, antibody roles, and cytotoxic T cell-mediated killing, all essential for understanding viral immunity and relevant for ministerial health exams.
Category
Educational
