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Immunology Study Notes Part 1, Study notes of Biology

Biology

Immunology notes for high school, pre-med, nursing, medical students.

Typology: Study notes

2025/2026

Uploaded on 04/24/2026

stgn25
stgn25 🇬🇾

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IMMUNOLOGY NOTES – Part 1
Contents
1. Basic Concepts of Immunology ....................................................................................................... 1
2. Types of Immune Responses .......................................................................................................... 1
3. Types of Antigens ............................................................................................................................ 2
4. Types of Immunity ........................................................................................................................... 2
5. Types of Adaptive Immunity ............................................................................................................ 3
6. Inflammation.................................................................................................................................... 3
6.1. Types of Inflammation ............................................................................................................... 4
7. Molecular Patterns in Inflammation ................................................................................................. 4
8. Initiation of Inflammation ................................................................................................................. 5
9. Mast Cell Activation and Mediators ................................................................................................. 5
10. Physiological Effects of Inflammatory Mediators ........................................................................... 6
11. Neutrophil Recruitment and Migration ........................................................................................... 6
11.1. Intracellular Killing ................................................................................................................... 7
11.2. Exocytosis After Phagocytosis ................................................................................................ 8
1. Basic Concepts of Immunology
• Immunology: Study of the immune system.
• Immunity: Body’s capability to resist pathogens.
• Immune System: Network of cells, tissues, and organs responsible for immunity.
• Immune Response: Series of coordinated reactions to identify, neutralize, eliminate pathogens.
2. Types of Immune Responses
There are two major types of immune responses:
Primary immune response occurs when the immune system encounters a pathogen for the first
time, and primarily involves the production of IgM class antibodies. E.g., the first dose of a vaccine
serves as the initial exposure to the antigen (foreign body, typically a protein). In certain cases,
additional doses (booster doses) are required when immunological memory is insufficient.
secondary immune response occurs upon subsequent exposure to the same pathogen, involves
immunological memory, and involves IgG class antibodies which provide long-lasting protection.
Feature
Primary Immune Response
Secondary Immune Response
Exposure
First encounter
Subsequent encounter
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IMMUNOLOGY NOTES – Part 1

Contents

  1. Basic Concepts of Immunology ....................................................................................................... 1
  2. Types of Immune Responses .......................................................................................................... 1
  3. Types of Antigens ............................................................................................................................ 2
  4. Types of Immunity ........................................................................................................................... 2
  5. Types of Adaptive Immunity ............................................................................................................ 3
  6. Inflammation.................................................................................................................................... 3 6.1. Types of Inflammation............................................................................................................... 4
  7. Molecular Patterns in Inflammation ................................................................................................. 4
  8. Initiation of Inflammation ................................................................................................................. 5
  9. Mast Cell Activation and Mediators ................................................................................................. 5
  10. Physiological Effects of Inflammatory Mediators ........................................................................... 6
  11. Neutrophil Recruitment and Migration ........................................................................................... 6 11.1. Intracellular Killing ................................................................................................................... 7 11.2. Exocytosis After Phagocytosis ................................................................................................ 8

1. Basic Concepts of Immunology

  • Immunology : Study of the immune system.
  • Immunity : Body’s capability to resist pathogens.
  • Immune System : Network of cells, tissues, and organs responsible for immunity.
  • Immune Response : Series of coordinated reactions to identify, neutralize, eliminate pathogens.

2. Types of Immune Responses

There are two major types of immune responses: Primary immune response occurs when the immune system encounters a pathogen for the first time, and primarily involves the production of IgM class antibodies. E.g., the first dose of a vaccine serves as the initial exposure to the antigen (foreign body, typically a protein). In certain cases, additional doses (booster doses) are required when immunological memory is insufficient. secondary immune response occurs upon subsequent exposure to the same pathogen, involves immunological memory, and involves IgG class antibodies which provide long-lasting protection. Feature Primary Immune Response Secondary Immune Response Exposure First encounter Subsequent encounter

Antibody IgM IgG Speed Slow, weak Rapid, strong Example First vaccine dose Booster dose

3. Types of Antigens

An antigen is any foreign substance, typically a protein, capable of eliciting an immune response. Antigens are classified into exogenous and endogenous types.

  • Exogenous antigens originate from outside the body and are targeted by humoral immunity.
  • Endogenous antigens originate from within the cells and are targeted by cell-mediated immunity.

4. Types of Immunity

Immunity is broadly classified into innate immunity and adaptive immunity. Innate Immunity (first line of defense) Acquired / Adaptive Immunity Present from birth Acquired during life Non-specific, can’t distinguish b/w bacteria, viruses, fungi. Specific, can also distinguish between self and non-self-antigens. No immunological memory (same short-lived response for repeated exposure) Memory-based Components:

  • Neutrophils (primary cells in acute inflammation)
  • Macrophages (phagocytosis, antigen presentation)
  • Mast cells (initiates inflammation via histamine)
  • Basophils and eosinophils (HSR, parasitic defense)
  • Monocytes (in blood)
  • Macrophages (in tissues) Occur in
  • Skin, mucosal membranes and secretions (enzymes, acidic pH).
  • Recognizes PAMPs/DAMPs via PRRs Components: Lymphocytes (recirculating immune cells)
  • B lymphocytes (mature in Bone Marrow)
  • T lymphocytes (mature in Thymus) Occur in
  • Blood (~2–5%), Lymph nodes, Spleen, Mucosa-associated lymphoid tissue (MALT), peripheral tissues.
  • Needed for Antigen surveillance, Immune activation, Memory formation
  • B lymphocytes, upon activation, differentiate into plasma cells that secrete antibodies (immunoglobulins).

Inflammation is broadly classified into acute and chronic types based on duration and cellular involvement. Acute inflammation occurs within 24 hours and is predominantly mediated by neutrophils. Chronic inflammation persists beyond 24 hours and involves macrophages, lymphocytes, and fibroblasts. Fibroblasts are essentially transformed or elongated macrophages and are responsible for collagen formation and tissue repair.

6.1. Types of Inflammation

Type Duration Cells Involved Acute < 24 hours Neutrophils Chronic > 24 hours Macrophages, lymphocytes, fibroblasts (elongated or transformed macrophages associated with Collagen synthesis, Fibrosis, Tissue repair). Chronic inflammation is common in granulomatous diseases

  • Tuberculosis (necrotizing granulomas)
  • Sarcoidosis (non-necrotizing granulomas) Causes of Inflammation
  • Infection
  • Tissue injury
  • Immune reactions-- formation of immune complexes or antigen-antibody complexes that can trigger inflammatory responses, particularly in autoimmune diseases

7. Molecular Patterns in Inflammation

Innate immunity recognizes pathogens through pattern recognition receptors (PRRs). During infection, pathogens release specific molecules known as Pathogen Associated Molecular Patterns (PAMPs). These molecules enable the immune system to recognize the presence of infection. Examples of PAMPs: lipopolysaccharides (LPS), pathogen-derived DNA and RNA, cell wall or membrane proteins. Tissue injury leads to the release of Damage Associated Molecular Patterns (DAMPs). These include host DNA and heat shock proteins (HSPs), which are released in response to cellular stress or damage. These molecular patterns are recognized by specific receptors present on immune cells, primarily Toll-like receptors (TLRs) and C-type lectin receptors. Receptors detect:

  • PAMPs (Pathogen Associated Molecular Patterns). E.g., LPS, microbial DNA/RNA
  • DAMPs (Damage Associated Molecular Patterns). E.g., host DNA, heat shock proteins Major receptors include:
  • Toll-like receptors (TLRs)
  • C-type lectin receptors (lectins are proteins that bind to carbs)

8. Initiation of Inflammation

The initiation of inflammation is primarily mediated by mast cells ( first responders ) and dendritic cells. Upon activation, mast cells undergo degranulation, which involves the release of cytoplasmic granules into the extracellular environment. These granules contain various mediators of inflammation. Mediators are classified into primary and secondary mediators.

  • Primary mediator is histamine, derived from amino acid histidine through decarboxylation.
  • Secondary mediators include leukotrienes and prostaglandins, both derived from arachidonic acid. Arachidonic acid originates from membrane phospholipids and is metabolized via two pathways: the lipoxygenase pathway and the cyclooxygenase pathway. The lipoxygenase pathway produces leukotrienes, whereas the cyclooxygenase pathway produces prostaglandins and thromboxanes. Non-steroidal anti-inflammatory drugs (NSAIDs) exert their effects by inhibiting the cyclooxygenase pathway, thereby reducing the production of prostaglandins and thromboxanes. Aspirin inhibits thromboxane synthesis, particularly thromboxane A2.

9. Mast Cell Activation and Mediators

Mast cells initiate inflammation. Mast cells are highly granulated immune cells. Upon activation, they undergo degranulation , defined as the rupture of intracellular granules (lysis of the cell) leading to the release of cytoplasmic granules. These granules contain biologically active substances called mediators. Mediators are classified into two categories: primary and secondary mediators.

  • Primary mediators are preformed and stored within mast cell granules. The primary mediator is histamine , which is synthesized from the amino acid histidine via decarboxylation.
  • Secondary mediators are synthesized de novo following mast cell activation and are derived from arachidonic acid metabolism. They are leukotrienes and prostaglandins , both derived from arachidonic acid. o Leukotrienes are produced via the lipoxygenase pathway, o Prostaglandins are produced via the cyclooxygenase pathway.
  • Stages of Phagocytosis o Recognition and attachment : extension of plasma membrane to internalize pathogen o Engulfment : formation of phagosome with engulfed matter o Fusion with lysosome/peroxisome to form phagolysosome/phagoperioxisome complexes that facilitate intracellular killing. Lysosomes contain lysozymes, lactoferrin, defensins, and hydrolases. Peroxisomes contain NADPH oxidase, superoxide dismutase, myeloperoxidase, and nitric oxide synthase. o Intracellular killing

11.1. Intracellular Killing

Intracellular killing occurs through two major mechanisms: Oxygen-Dependent Killing (Respiratory Burst) Oxygen-Independent Killing mediated by enzymes present within peroxisomes mediated by enzymes present within lysosomes NADPH oxidase catalyzes the conversion of molecular oxygen into reactive oxygen species, (ROS aka superoxide ions or reactive oxygen intermediates) Lysozymes degrade peptidoglycan of bacterial cell wall. Disruption of peptidoglycan compromises cell wall integrity, leading to bacterial lysis. Superoxide dismutase converts these reactive oxygen species into hydrogen peroxide Lactoferrin chelates (steals) iron and by sequestering (stealing) inhibits pathogens (no Fe means no metabolism / replication / growth) Myeloperoxidase utilizes hydrogen peroxide and chloride ions to generate hypochlorous acid (HOCl), a highly corrosive substance highly effective in destroying pathogens. Defensins form tiny pores onto the surface of the bacterial cell membrane, increases cell permeability, leading to osmotic imbalance and osmotic lysis of the cell Nitric oxide synthase catalyzes the conversion of L-arginine into nitric oxide and L-citrulline. Nitric oxide is a highly reactive molecule with potent antimicrobial properties Hydrolases are a group of enzymes that degrade various biomolecules, including proteins, lipids, and nucleic acids, contributing to the destruction of pathogens. Clinical Correlation: Deficiencies in enzymes involved in oxygen-dependent killing, particularly NADPH oxidase, result in chronic granulomatous disease , characterized by impaired microbial killing and recurrent infections.

  • Defects in innate immunity → recurrent infections
  • Chronic granulomatous disease → impaired respiratory burst

11.2. Exocytosis After Phagocytosis

Following intracellular killing, the degraded material must be expelled from the cell. Exocytosis occurs in two stages.

  • Dissociation : phagosome separates from lysosome / peroxisome, to prevent leakage of destructive enzymes into surrounding tissues, which could lead to cellular damage or autoimmune reactions.
  • Packaging of the phagosome into exocytic vesicles by Golgi apparatus, that migrate to cell membrane, fuse with cell membrane, and release their contents into extracellular environment. This process is tightly regulated by genes such as the AIRE (autoimmune regulator) gene , which ensures proper dissociation, prevents damage to host tissues and autoimmunity.