Immunology

ACTIVE AND PASSIVE IMMUNITY

1. Overview of Immunity Types

  • Active Immunity: Immunity developed from the presence of pathogen antigens leading to adaptive immune response.

  • Passive Immunity: Immunity received from external sources, typically antibodies from other organisms.

  • Role of Vaccines: Explaining how vaccines induce immunity without causing disease.

2. Vaccines

2.1 Definition and Function

  • Induction of Immunity: Vaccines artificially induce immunity through immunization.

  • Composition: Contain substances with antigens, prompting the immune response without causing disease.

  • Mechanism: Antigens are introduced and the adaptive immune system responds, leading to the production of memory B cells and T cells.

  • Training the Immune System: The immune system learns to recognize and respond swiftly to the same antigen upon re-exposure.

3. Herd Immunity

  • Concept: Protection of individuals who are not immune when a significant portion of the population is immune.

  • Threshold Percentage: Approximately 80% of people need to be immune to reach herd immunity.

  • Consequences: Non-immune individuals, such as immunocompromised or unvaccinated individuals, are protected because the spread of the disease is reduced.

4. Booster Shots

4.1 Purpose and Function

  • Need for Boosters: Immunity may wane over time as memory cells or antibodies diminish.

  • Definition of Titre: The amount of specific antibodies in the blood.

  • Mechanism: Booster shots are reiterated doses of the original vaccine, raising the antibody titre to protect against disease.

5. Active Immunity Through Immunizations

5.1 Immune Response and Antibody Levels

  • First Exposure: Antibody titre rises slowly as the immune system responds to the pathogen.

  • Second Exposure: Antibody titre rises rapidly and reaches a higher level as memory cells facilitate a faster response.

PASSIVE IMMUNITY

6. Characteristics of Passive Immunity

6.1 Definitions and Examples

  • Source of Antibodies: Received from another person’s immune response.

  • Common Natural Instances:   - Antibodies that cross the placenta during pregnancy last for a few months post-birth.   - Antibodies in breast milk extend immunity in infants.

  • Artificial Sources:   - Antivenom: Derived from injecting large animals with venom to produce antibodies that can be isolated and used.   - Monoclonal Antibody Treatments: Specifically engineered antibodies used for conditions like COVID-19 and cancer.

7. Limitations of Passive Immunity

  • Temporary Nature: Passive immunity does not produce memory cells; hence, it provides limited duration of protection.

  • Specificity: Passive immunity is specific to the antigens from which the antibodies were derived (e.g., no cross-effectiveness of antivenoms between different snake venoms).

IMMUNE THERAPIES

8. Cytokines and Their Role in Immunity

8.1 Definition and Medical Uses

  • Definition: Cytokines are signaling molecules that help regulate immune processes, including white blood cell formation and activity.

  • Applications in Medicine:   - Stimulating blood cell production in cancer patients undergoing treatments that affect bone marrow.   - Treatment regimens designed to enhance the immune system against cancers.   - Interferons: Used to inhibit cancer growth and viral infections.   - Interleukins: Stimulate T cells and natural killer (NK) cells.

9. Monoclonal Antibodies

9.1 Production and Applications

  • Definition: Antibodies produced from a single clone of B cells, rendering them identical.

  • Uses:   - Diagnostic tests (e.g., pregnancy tests).   - Detecting metastatic cancer cells via fluorescent markers.   - Drug delivery systems, binding to specific antigens and delivering therapeutic agents.   - Rapid detection of infections, like in COVID tests.

  • Production Process:   - Hybridomas are created in labs by fusing B cells with myeloma cells (cancerous cells) to produce a continuous supply of monoclonal antibodies.   - Selected cells are clonally expanded to create the needed antibodies.

IMMUNITY GONE WRONG

10. Types of Dysregulation in the Immune System

  1. Allergic Reactions

  2. Tissue Rejection

ALLERGIES

11. Definition and Mechanism of Allergies

  • Hypersensitivity: Allergies occur when the immune system reacts excessively to non-harmful antigens, such as pollen, certain foods, or animal dander.

  • Terminology: The antigens causing allergic reactions are specifically referred to as allergens.

  • Response Timing: Allergic reactions can manifest within seconds of exposure to allergens and can range in severity.

12. Immediate Allergic Response

  • Mediating Molecules: IgE antibodies attach to mast cells, eosinophils, and basophils.

  • Action of Allergens: Upon encountering an allergen, IgE binds and causes histamine release from mast cells.

  • Impact of Histamine:   - Initiates inflammatory responses, often resulting in symptoms like mucus production and respiratory issues (e.g., runny nose).

  • Common Allergies: Hay fever, asthma, food allergies.

13. Anaphylactic Shock

  • Definition: A severe, life-threatening allergic reaction that occurs when an allergen enters the bloodstream.

  • Examples: Reactions can be triggered by bee stings or penicillin injections, causing a dramatic drop in blood pressure and requiring immediate response.

  • Counteraction: Epinephrine is used to treat anaphylactic reactions.

TISSUE REJECTION

14. Challenges in Organ Transplantation

  • MHC I Proteins: Serve as antigens; if a transplant's MHC I type differs from that of the recipient, a rejection process occurs.

  • Compatibility Issues: Difficulty in finding precise matches for MHC I types between donor organs and recipients.

  • Management: Immunosuppressive drugs can help reduce rejection response in transplant patients.  

15. Blood Type Reactions

  • Mechanism: Incorrect blood transfusions lead to antibodies attacking A/B/Rh antigens.

  • Example: An Rh-negative mother may have her antibodies attack an Rh-positive baby’s blood during pregnancy.

IMMUNE SYSTEM DISORDERS

16. Types of Disorders

  1. Autoimmune Diseases

  2. Immunodeficiency

17. Autoimmune Diseases

17.1 Definition and Characteristics

  • Concept: Autoimmune diseases occur when immune cells mistakenly target self-molecules, seeing them as antigens.

  • Formation of Immune Cells: T cells and antibodies may attack the body’s own tissues, leading to dysfunction and degradation of those tissues.

  • Difficulty in Treatment:   - No definitive cure exists due to challenges in eliminating defective immune cells.   - Management entails immunosuppressive medications.

18. Prevalence and Gender Disparities

  • Genetic Links: While hereditary factors may play a role, the connections remain somewhat vague.

  • Familial Patterns: Higher rates of occurrences in families with autoimmune conditions.

  • Gender Disparities: More commonly observed in women compared to men.

19. Specific Autoimmune Conditions

  • Specific Disorders:   - Multiple Sclerosis: Neurodegenerative disorder affecting myelin sheaths of nerve fibers.   - Rheumatoid Arthritis: Autoimmune disease impacting joints.   - Celiac Disease: Condition where ingestion of gluten damages the digestive tract.

20. Immunodeficiency Disorders

20.1 Definition and Examples

  • Concept: Immunodeficiency diseases compromise the body’s ability to defend against pathogens.

  • Acquired Immunodeficiency Syndrome (AIDS):   - Caused by HIV, leading to a gradual breakdown of the immune system.   - Helper T cells are severely affected, which impairs both T cell and B cell responses.