Module 1_ intro to immune system

Learning Outcomes

• Describe the components of the immune system, including the organs involved, to explain their relevance in inflammation.

• Discriminate between the two principal types of immunity based on their hallmark characteristics.

• Compare the humoral and cellular components of innate and adaptive immunity.

• Describe the non-specific killing of pathogens by phagocytosis.

Section 1: Introduction to Immunology

What is Immunology?

• Study of the immune system and its response to invading pathogens and foreign substances.

• Immune response: coordinated reaction of cells, tissues, and molecules to infectious microbes and foreign substances.

Historical Context

• Edward Jenner's Experiment (1795): Observed that milkmaids who recovered from cowpox never contracted smallpox.

• Conducted an experiment on an 8-year-old boy by vaccinating him with cowpox and later exposing him to smallpox, resulting in no illness.

• 1967: WHO initiated a vaccination program for smallpox.

• 1979: Smallpox was declared eradicated.

Components of the Immune System

Lymphatic Organs

• Primary Lymphatic Organs:

  • Thymus

  • Bone marrow

• Secondary Lymphatic Organs:

  • Adenoids

  • Tonsils

  • Bronchus-associated lymphoid tissue (BALT)

  • Lymph nodes

  • Spleen

  • Intestinal lymphoid tissue

  • Peyer's patches

  • Appendix

• Lymphatic Vessels: Transport lymph fluid and immune cells throughout the body.

Functions of the Immune System

1. Innate Immunity

• Key Features:

  • Physical barriers (e.g., skin)

  • Chemical elements (e.g., enzymes)

  • Innate immune cells (e.g., neutrophils, phagocytic cells)

  • Provides a non-specific cellular response to pathogens.

2. Adaptive Immunity

• Also known as acquired immunity.

• Involves B and T lymphocytes.

  • First Encounter: Development of a primary immune response.

  • Memory Cells: Some lymphocytes develop into memory cells that mount a secondary immune response.

3. Surveillance

• Detects foreign or defective cells in the body, preventing proliferation of dangerous cells.

Targets of the Immune System

1. Microbes

• Microorganisms causing disease:

  • Bacteria

  • Viruses

  • Parasites

  • Fungi

• Discovery: Bruce Beutler received the Nobel Prize for discovering the connection between the Toll gene, fruit flies, and Toll-like receptors (TLRs) that sense microbial components in humans.

2. Macromolecules

• Large, non-living molecules in foods, drugs, and chemicals.

  • Example: Allergic reactions to strawberry proteins.

• Some immune responses to macromolecules can be beneficial, such as against bacterial toxins.

3. Cells

• Distinguishes self from non-self cells:

  • Tumor cells

  • Virally infected cells

  • Cells in mismatched blood transfusions or organ transplants.

Importance of Health and Disease

Allergic Reactions

• Immune system overreactions to usually non-harmful allergens, leading to symptoms like:

  • Hives

  • Itching

  • Swelling

  • Sneezing

• Common allergens: ragweed pollen, dust mites, bee stings, dermatitis.

Autoimmune Diseases

• Immune system misidentifies 'self' cells as foreign:

  • Examples: Rheumatoid arthritis, Grave's disease, systemic lupus erythematosus.

• Symptoms include inflammation, redness, heat, pain, and swelling.

Laboratory Tests

• Immunological tests can check for defects in immune responses and confirm diagnoses (e.g., TB tests).

• Vaccinations: Boost immune defenses.

Adverse Effects of the Immune System

• Discomfort associated with inflammation.

• Diseases:

  • Immunodeficiencies (e.g., AIDS)

  • Conditions affected by the immune system (e.g., TB)

  • Allergic responses.

Section 2: The Innate Immune System

Characteristics

• Present at birth, unchanging, immediate (within minutes), and non-specific.

• Reacts to common components of multiple pathogens without memory or improvement through repeated exposure.

Barriers

• Physical: Skin

• Chemical: Enzymes, pH levels.

Leukocytes in the Innate Immune System

• Relies on white blood cells (WBCs):

  • Protects the body by identifying and eliminating foreign invaders.

  • Derived from hematopoietic stem cells in the bone marrow and found in blood and lymph.

Cells of the Immune System

Phagocytes

• Neutrophils: First responders, ingesting microbes; account for 50-70% of immune cells.

• Macrophages: Professional phagocytes, secrete cytokines, account for 1-6%.

• Dendritic Cells: Found in tissues, link innate and adaptive immunity.

Granulocytes

• Eosinophils: Secrete histamines and free radicals; participate in allergic responses; make up 1-3%.

• Basophils: Secrete heparin and histamine in response to allergies; less than 1% of immune cells.

• Mast Cells: Role in allergy and tissue repair; less than 1%.

• Natural Killer Cells (NK): Cytotoxic lymphocytes involved in tumor and virally infected cell surveillance; do not require activation for killing.

Section 3: Adaptive Immune System

Features

1. Discrimination: Distinguishes self from non-self to prevent injury.

2. Diversity: Wide variety of targets.

3. Specificity: Recognizes subtle differences among antigens.

4. Specialization: Antigen-dependent response; lag time of 4-5 days for activation.

5. Memory: Enhanced response upon re-exposure.

6. Self-limitation: Returns immune response to a basal state after activation.

Cells of Adaptive Immune System

• B and T Lymphocytes: Key players in adaptive immunity.

  • T cells require activation by professional antigen-presenting cells (APCs).

  • APCs present antigens via MHC molecules.

T-cells

• Possess T-cell receptors that aid in infection protection; differentiated into:

  • Helper T-cells (CD4+): Activate macrophages and B-cells for antibody production.

  • Cytotoxic T-cells (CD8+): Kill infected or cancerous cells.

B-cells

• Responsible for antibody production; derived from hematopoietic stem cells and mature in the bone marrow.

  • Plasma B-cells: Secrete antibodies after antigen stimulation.

  • Memory B-cells: Respond rapidly during subsequent exposures.

Antibodies in the Adaptive Immune System

• IgA: Found in mucosal surfaces; neutralizes pathogens.

• IgD: Present in small amounts; role mostly unknown, associated with B-cells.

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

• IgG: Most common, can cross the placenta; fights viral and bacterial infections.

• IgM: First to respond in infections; largest antibody.