Innate and Adaptive Immunity, Vaccines, and Antimicrobial Drugs: Study Guide

Chapter 11: Innate and Adaptive Immunity

Overview of Innate vs. Adaptive Immunity

The immune system is divided into innate (nonspecific) and adaptive (specific) branches. Each plays a critical role in defending the body against pathogens.

Innate Immunity	Adaptive Immunity
Response time: Immediate Present at birth Non-specific; recognizes a broad range of pathogens No memory; same response each time Major cells: Phagocytes, NK cells, dendritic cells Physical and chemical barriers	Response time: 4-7 days (first exposure) Develops after birth Specific; recognizes unique antigens Memory; faster and stronger response upon re-exposure Major cells: B cells, T cells Antibody production

First Line of Defense: Physical, Chemical, and Mechanical Barriers

• Physical Barriers: Structures that physically block pathogen entry (e.g., skin, mucous membranes).

• Chemical Barriers: Molecules that directly attack microbes or generate an environment hostile to survival (e.g., lysozyme in tears, stomach acid).

• Mechanical Barriers: Actions that remove pathogens (e.g., flushing by tears, urine, saliva).

Example: The skin acts as a physical barrier, while stomach acid destroys ingested pathogens (chemical barrier).

Second Line of Defense: Cellular and Molecular Components

• Phagocytic Cells: Neutrophils, monocytes/macrophages, dendritic cells ingest and destroy pathogens.

• Inflammatory Response: Localized tissue response to injury or infection, involving redness, heat, swelling, and pain.

• Fever: Systemic increase in body temperature that can inhibit pathogen growth and enhance immune function.

• Antimicrobial Proteins: Complement system, interferons, and other proteins that target pathogens.

Relationship with the Lymphatic System

• Lymphatic vessels collect interstitial fluid (lymph) from tissues and return it to the bloodstream.

• Lymph nodes filter lymph and are sites of immune cell activation.

• Primary lymphoid tissues: Bone marrow (site of B cell maturation), thymus (site of T cell maturation).

• Secondary lymphoid tissues: Lymph nodes, spleen, MALT (mucosa-associated lymphoid tissue), tonsils, appendix.

Classification of Immune Defenses

Defense	Classification
Phagocytes	Second-line, cellular
Inflammation	Second-line, chemical
Lysozyme	First-line, chemical
Skin	First-line, physical
Fever	Second-line, chemical
Mucus	First-line, mechanical

Leukocytes and Their Functions

• Monocytes: Highly phagocytic; mature into macrophages.

• Dendritic Cells: Highly phagocytic; activate adaptive immune responses.

• Lymphocytes: NK cells (innate immunity), B and T cells (adaptive immunity).

• Eosinophils, basophils, mast cells: Involved in allergic responses and defense against parasites.

Phagocytosis Process

1. Chemotaxis: Phagocyte moves toward infection site by chemical signals.

2. Adherence: Phagocyte attaches to pathogen surface.

3. Ingestion: Pathogen is engulfed into a phagosome.

4. Digestion: Phagosome fuses with lysosome; enzymes digest pathogen.

5. Exocytosis: Waste materials are expelled from the cell.

Inflammation and Fever

• Stages of Inflammation:

  1. Vascular changes (increased blood flow, vessel permeability)

  2. Recruitment of phagocytes

  3. Resolution (tissue repair)

• Fever: Abnormally high body temperature; can inhibit pathogen growth but may be dangerous if too high.

• Treatment: Antipyretics (e.g., acetaminophen) lower fever; temperatures above 41°C (105.8°F) are life-threatening.

Chapter 12: Adaptive Immunity

Overview of Adaptive Immune Response

The adaptive immune system provides specific, long-lasting defense against pathogens through the actions of B and T lymphocytes.

1. Antigen Presentation: Dendritic cells and macrophages present antigens to T cells.

2. Lymphocyte Activation: T and B cells are activated and proliferate.

3. Lymphocyte Proliferation and Differentiation: Activated cells differentiate into effector and memory cells.

4. Elimination and Memory: Effector cells eliminate pathogens; memory cells provide long-term immunity.

Cellular vs. Humoral Immunity

	T Cells (Cellular)	B Cells (Humoral)
Branch	Cellular	Humoral
Includes	Helper T cells, cytotoxic T cells	B cells, plasma cells
Function	Directly kill infected cells, regulate immune responses	Produce antibodies
MHC Recognition	Yes	No (except for antigen presentation)

Antigens, Epitopes, and Haptens

• Antigen: Any substance that can trigger an immune response.

• Epitope: Specific part of an antigen recognized by immune receptors.

• Hapten: Small molecule that is only immunogenic when attached to a larger carrier.

Antibodies (Immunoglobulins)

• IgG: Most abundant; crosses placenta; long-term immunity.

• IgM: First antibody produced; effective at agglutination.

• IgA: Found in mucosal areas and secretions.

• IgE: Involved in allergic responses and defense against parasites.

• IgD: Functions mainly as a B cell receptor.

Primary vs. Secondary Immune Response

• Primary Response: First exposure to antigen; slower, less robust.

• Secondary Response: Subsequent exposures; faster and stronger due to memory cells.

Types of Adaptive Immunity

• Naturally Acquired Active Immunity: Immunity from infection; long-lasting.

• Naturally Acquired Passive Immunity: Maternal antibodies transferred to fetus or infant; temporary.

• Artificially Acquired Active Immunity: Immunity from vaccination; long-lasting.

• Artificially Acquired Passive Immunity: Injection of antibodies; temporary protection.

Chapter 14: Vaccines and Immunization

History and Principles of Vaccination

• Edward Jenner: Developed the first vaccine (smallpox) using cowpox virus; demonstrated that exposure to a less virulent pathogen could confer immunity.

• Herd Immunity: When a sufficient percentage of a population is immune, the spread of disease is limited, protecting non-immune individuals.

Types of Vaccines

Live Attenuated Vaccines	Inactivated Vaccines
Contain weakened pathogens Strong, long-lasting immunity Risk for immunocompromised patients Examples: MMR, varicella	Contain killed pathogens or subunits Safer, but may require boosters Examples: Polio (Salk), influenza (injected)

• Subunit, toxoid, conjugate, and mRNA vaccines are also used, each with specific properties and applications.

Chapter 15: Antimicrobial Drugs and Resistance

Major Modes of Action of Antimicrobial Drugs

1. Cell Wall Synthesis Inhibition: e.g., penicillins, cephalosporins

2. Protein Synthesis Inhibition: e.g., tetracyclines, macrolides

3. Nucleic Acid Synthesis Inhibition: e.g., quinolones, rifampin

4. Metabolic Pathway Inhibition: e.g., sulfonamides, trimethoprim

5. Cell Membrane Disruption: e.g., polymyxins

Antibiotic Resistance

• Intrinsic Resistance: Naturally resistant due to inherent characteristics (e.g., Gram-negative outer membrane).

• Acquired Resistance: Gained through mutation or gene transfer (e.g., plasmids).

• Mechanisms: Enzyme inactivation, target modification, efflux pumps, reduced permeability.

Human Behaviors and Resistance

• Misuse and overuse of antibiotics in healthcare, agriculture, and clinical settings accelerate resistance.

• Healthcare workers and patients can help by following proper hygiene and prescription guidelines.

Resistant Microbes to Watch

• The CDC tracks top drug-resistant pathogens, including Enterococcus, Staphylococcus, and Clostridioides.

Additional info: These notes cover core concepts from Chapters 11, 12, 14, and 15 of a college-level microbiology course, focusing on immunity, vaccines, and antimicrobial drugs. Tables and diagrams have been recreated in text and HTML table format for clarity.