exam review

Key Definitions

• Antigen / Immunogen
    - Definition: “A substance that reacts with an antibody… may or may NOT be able to trigger an immune response.”
    - Note: All immunogens are antigens, but not all antigens are immunogens.

• Immunogenicity
    - Definition: Ability of an antigen to trigger an immune response → leads to antibody formation.

• Immunoglobulin (Antibody)
    - Definition: Protein produced by plasma cells (from B-lymphocytes).
    - Classes:
      - IgG
      - IgA
      - IgM
      - IgD
      - IgE
    - Note: IgM & IgG are the most important in transfusion.

• Isotype/Class Switching
    - Definition: Activated B-cells change antibody class (e.g., from IgM to IgG) without changing antigen specificity.

• Isoagglutinins
    - Definition: Naturally occurring ABO antibodies (usually IgM).

• Naturally Occurring Antibodies
    - Definition: Antibodies present without known exposure.
    - Production: Produced due to cross-reactive bacterial or food antigens.

• Immune Antibodies (Alloantibodies)
    - Definition: Formed after exposure to antigens (e.g., via transfusion or pregnancy).
    - Characteristics: Usually IgG, react at 37°C, clinically significant (can lead to Hemolytic Transfusion Reactions (HTR) or Hemolytic Disease of the Fetus and Newborn (HDFN)).

• Autoantibodies
    - Definition: Antibodies directed against self RBC antigens.
    - Characteristics: Often cause panagglutination.
    - Commonly target high-frequency Rh antigens (e.g., “e”).

• Panagglutination
    - Definition: “Patient serum agglutinates all reagent RBCs.”

Chimerism

• Definition: Presence of two RBC populations in one individual.

• Types:
    - True Chimerism: e.g., twins.
    - Artificial Chimerism: e.g., from transfusion or transplant.

ABO Blood Group System

Discovery

• Noted by Landsteiner through observation of RBC agglutination upon mixing blood from different individuals.

ABO Antigens

• Description: Carbohydrate structures located on RBC membrane.

ABO Antibodies

• Characteristics: Mostly IgM, naturally occurring.

Forward Typing

• Method: Patient RBCs are mixed with anti-A/anti-B antisera to detect antigens present.

Reverse Typing

• Method: Patient plasma is mixed with A1/B reagent cells to detect antibodies present.

Why ABO IgM is Clinically Significant

• Reason: Efficient complement activation leading to rapid intravascular hemolysis.

Landsteiner’s Rule

• Stipulations:
    - If antigen is present → antibody is absent.
    - If antigen is absent → antibody is present.

Transfusion Reactions

Mechanism

• Explanation: Recipient antibodies bind to donor RBC antigens, leading to agglutination and hemolysis.

Acute Hemolytic Transfusion Reaction (AHTR)

• Symptoms:
    - Fever
    - Chills
    - Hypotension
    - Hemoglobinuria
    - Renal failure
    - Shock

Universal Donor/Recipient

• Blood Types:
    - RBC donor: O-negative
    - RBC recipient: AB-positive
    - Plasma donor: AB
    - Plasma recipient: O

Antibody Screen (Indirect Antibody Test - IAT)

Purpose

• Explanation: To detect unexpected clinically significant antibodies (IgG).

Method

1. Patient plasma is combined with group O screening cells.

2. Incubate the mixture at 37°C.

3. Wash to remove unbound antibodies.

4. Add AHG (anti-IgG).

5. Agglutination indicates a positive result.

Limitations

• Note: Does NOT detect cold IgM antibodies.

ABO Discrepancies

General Rules

• Guidelines:
    - Always suspect the weakest reaction.
    - Repeat testing with fresh suspension.
    - Check patient age, diagnosis, and transfusion history.

Category I — Unexpected Reverse Reactions

Characteristics

• Caused by weak or missing antibodies, often seen in:
    - Newborns
    - Elderly
    - Immunodeficiency
    - Leukemia/Lymphoma
    - Immunosuppressive therapy
    - Plasma dilution
    - Chimerism

Resolution

• Recommended Steps:
    - Incubate reverse typing at room temperature (RT) → then at 4°C with controls.

Category II — Weak/Missing RBC Antigens

Causes

• Factors include:
    - A/B subgroups
    - Leukemia
    - Hodgkin’s disease
    - Acquired B phenomenon
    - Blood group-specific soluble substances (BGSS)

Resolution

• Recommended Steps:
    - Extend incubation time
    - Test at 4°C
    - Enzyme treatment of RBCs

Category III — Plasma/Protein Abnormalities

Causes

• Factors include:
    - Rouleaux (Multiple Myeloma, Waldenström’s macroglobulinemia)
    - High fibrinogen
    - Dextran
    - Wharton’s jelly (from cord blood)

Resolution

• Recommended Steps:
    - Saline replacement
    - Wash cells thoroughly

Category IV — Miscellaneous Causes

Causes

• Factors that can lead to discrepancies:
    - Cold autoantibodies
    - Unexpected alloantibodies
    - Mixed cell populations (from transfusion or transplant)

Resolution

• Recommended Steps:
    - Utilize pre-warm techniques
    - Conduct antibody identification
    - Test A1/A2/B/O cells + autocontrol

Immunology Part 1

Basic Concepts

• Immunity: Resistance to infection.

• Infection vs Disease:
    - Infection = invasion of pathogens.
    - Disease = altered health status due to infection.

• Normal Flora: Protective microorganisms; disruption can lead to opportunistic infections.

• Opsonization: The process of tagging pathogens to facilitate phagocytosis.

Innate Immunity (Non-specific)

Characteristics

• Immediate response, lacks memory, and exhibits the same response each time.

First Line of Defense (External)

• Components:
    - Skin
    - Mucous membranes
    - Cilia
    - Flushing mechanisms such as tears, saliva, urine
    - Enzymes like lysozyme
    - Stomach acid
    - Normal flora

Second Line of Defense (Internal)

• Components:
    - Phagocytes (such as neutrophils and monocytes/macrophages)
    - Natural Killer (NK) cells
    - Complement system
    - Inflammation

Phagocytic Cells

• Neutrophils:
    - Characteristics: First responders to infection, contain primary (myeloperoxidase, defensins) & secondary granules (lactoferrin).
    - Main function: Phagocytosis.

• Monocytes/Macrophages:
    - Monocytes circulate in the blood and become macrophages in tissues.
    - Functions: Antigen-presenting cells (APCs) that activate T-cells, produce cytokines that activate inflammation.

• Eosinophils:
    - Role: Combat parasites, involved in allergic reactions mediated by IgE, contain major basic protein that is toxic to parasites.

• Basophils/Mast Cells:
    - Function: Release histamine leading to vasodilation and increased vascular permeability.
    - Involved in Type I hypersensitivity (anaphylaxis); mast cells reside in tissues, while basophils circulate.

• Dendritic Cells:
    - Description: Most potent APC, capturing antigens in tissues and migrating to lymph nodes to activate naïve T-cells.
    - Role: Bridge the innate and adaptive immune systems.

• Natural Killer (NK) Cells:
    - Function: Kill virus-infected and tumor cells without prior sensitization.
    - Recognition: Detect cells lacking MHC class I.
    - Killing mechanism: Utilize perforin and granzyme to induce apoptosis in target cells.

Inflammation

• Characteristics: Redness, heat, swelling, and pain.

• Mechanism:
    - Histamine release causes vasodilation and increased vascular permeability.
    - Diapedesis of neutrophils into the affected area.

Adaptive Immunity

Characteristics

• Features: Specific, involves memory and is slower in the first response compared to innate immunity.

Two Branches of Adaptive Immunity

1. Humoral Immunity: Involves B-cells and the production of antibodies.

2. Cell-mediated Immunity: Involves T-cells that mediate immune responses.

B-Cells

• Production site: Bone marrow.

• Features: Each B-cell has a unique membrane immunoglobulin (Ig).

• Activation leads to:
    - Formation of plasma cells
    - Formation of memory B-cells for rapid secondary responses

T-Cells

• Maturation site: Thymus.

• Types:
    - Helper T (CD4+): Activate B-cells and cytotoxic T-cells.
    - Cytotoxic T (CD8+): Kill infected cells.
    - Regulatory T-cells: Prevent autoimmunity.

Major Histocompatibility Complex (MHC)

• MHC Class I: Present on all nucleated cells; present endogenous antigens to CD8+ T-cells.

• MHC Class II: Present on antigen-presenting cells (APCs) such as macrophages and dendritic cells; present exogenous antigens to CD4+ T-cells.

Primary vs Secondary Immune Response

• Primary Response: Characterized by a slow and weaker response.

• Secondary Response: Faster, stronger, and more effective due to memory cells.

Complement System

Purpose

• Functions:
    - Opsonization
    - Cell lysis
    - Inflammation
    - Chemotaxis
    - Clearance of immune complexes

Pathways

• Classical Pathway: Triggered by IgM or IgG antibodies bound to an antigen (IgM is the most efficient).

• Alternative Pathway: Antibody-independent, initiated by pathogen surfaces and involves factors B, D, H, I, and properdin.

• Lectin Pathway: Triggered by mannose-binding lectin that binds to specific microbial structures.

Key Components

• C3: The most abundant complement protein, central to all pathways.

• C5b-9: Form the Membrane Attack Complex (MAC) leading to cell lysis.

Complement in Transfusion

• Mechanism: ABO incompatibility activates the classical pathway, resulting in intravascular hemolysis.

Blood Donation & Products

Canadian Blood Services Responsibilities

• Duties:
    - Collect, test, process, and distribute blood.
    - Manage stem cell registry.
    - Oversee organ/tissue donation.

Donor Eligibility

• Criteria:
    - Minimum age 17 years old.
    - Minimum weight of 110 lbs.
    - Good health status.
    - Hemoglobin requirements:
      - Women: ≥125 g/L.
      - Men: ≥130 g/L.

Deferrals

Temporary Deferrals

• Circumstances:
    - Tattoos/piercing: 3 months.
    - Transfusion: 6 months.
    - Pregnancy: 6 months postpartum.
    - Dental surgery: 72 hours.
    - Zika travel: 21 days.
    - Malaria risk: 3 months to 3 years depending on exposure.

Indefinite Deferrals

• Conditions:
    - IV drug use.
    - Risk of Creutzfeldt-Jakob disease (CJD).

Permanent Deferrals

• Conditions:
    - HIV.
    - Hepatitis.
    - Ebola.

Types of Donation

• Allogenic: General supply.

• Autologous: Self-donated blood.

• Directed: Donor to specific recipient (e.g., parent to child).

• Designated: Specific matching to recipients.

Blood Components

Packed RBCs

• Storage: 1–6°C.

• Shelf life: 42 days.

• Function: Raises hemoglobin by approximately 10 g/L.

Platelets

• Storage: 20–24°C with agitation.

• Shelf life: 7 days.

• Types: Can be pooled or apheresis; ABO-identical preferred but not required.

Plasma (FP/AFFP)

• Storage: Frozen at ≤ −18°C.

• Shelf life: 1 year.

• Compatibility: Must be ABO compatible.

Cryoprecipitate

• Function: Provides fibrinogen.

• Shelf life: 1 year frozen; not ABO-specific.

Whole Blood Processing

• Techniques:
    - Buffy coat method (combines RBC, plasma, platelets).
    - Filtration method (combines RBC and plasma).

Irradiation

• Purpose: Prevents Transfusion-Associated Graft Versus Host Disease (TA-GVHD).

• Use: Applied to immunocompromised patients.

Transport & Storage

• RBC: 1–6°C.

• Platelets: 20–24°C, agitated.

• Plasma/Cryoprecipitate: ≤ −18°C.

Neutrophils

Overview

• Definition: Most abundant white blood cell (WBC) in circulation (50–70%).

Characteristics

• Role: First responders to infection, particularly bacterial infections.

• Lifespan: Short-lived (hours to days).

• Granules:
    - Primary granules (myeloperoxidase, defensins) and secondary granules (lactoferrin).

• Killing mechanisms:
    - Phagocytosis: Engulfment and destruction of pathogens.
    - Degranulation: Release of antimicrobial substances.
    - NETs: Formation of neutrophil extracellular traps to ensnare and kill pathogens.
  
  

Monocytes / Macrophages

Overview

• Monocytes: Circulate in the blood and migrate into tissues to become macrophages.

• Lifespan: Long-lived, highly phagocytic.

Functions

• Act as antigen-presenting cells (APCs) to T-cells.

• Produce cytokines that activate and modulate inflammation.

Eosinophils

Overview

• Main functions: Combat parasitic infections and participate in allergic reactions mediated by IgE.

• Contains major basic protein, which is toxic to parasites.

Basophils & Mast Cells

Functions

• Release histamine, contributing to vasodilation and increased vascular permeability.

• Key players in Type I hypersensitivity reactions (such as anaphylaxis).

• Mast Cells: Reside in tissues, while basophils circulate in the bloodstream.

Dendritic Cells

Characteristics

• Most potent antigen-presenting cells (APCs).

• Capture antigens in tissues and migrate to lymph nodes to activate naïve T-cells.

• Act as a bridge between innate and adaptive immunity.

Natural Killer (NK) Cells

Overview

• Function: Kill virus-infected and tumor cells without prior sensitization.

• Recognition mechanism: Detect cells missing MHC class I.

• Killing mechanism: Utilize perforin and granzyme to mediate apoptosis.

Inflammation — Expanded Notes

Steps of the Inflammatory Response

1. Tissue injury leads to release of histamine, prostaglandins, and cytokines.

2. Vasodilation occurs, leading to redness and heat.

3. Increased vascular permeability causes swelling (edema).

4. Diapedesis occurs, allowing neutrophils to squeeze through vessel walls.

5. Chemotaxis: White blood cells (WBCs) follow chemical signals to the infection site.

6. Phagocytosis leads to destruction of pathogens.

Complement System — Expanded Notes

Major Functions

• Opsonization facilitated by C3b.

• Chemotaxis mediated by C5a.

• Anaphylatoxins (C3a and C5a) contribute to inflammation.

• Formation of the Membrane Attack Complex (MAC), leading to cell lysis (C5b-9).

Pathway Types

• Classical Pathway: Activated by IgM or IgG antibodies bound to an antigen.

• Alternative Pathway: Direct activation triggered by pathogen surfaces.

• Lectin Pathway: Triggered by binding of mannose-binding lectin to microbial structures.

Innate vs Adaptive Immunity — Clear Comparison

Adaptive Immunity — Additional Clarifications

Humoral Immunity (B-cells)

• Role: Produces antibodies effective against extracellular pathogens.

Cell-Mediated Immunity (T-cells)

• Helper T-cells (CD4+) coordinate immune responses.

• Cytotoxic T-cells (CD8+) are responsible for killing infected cells.

MHC — Expanded Notes

MHC Class I

• Distribution: Present on all nucleated cells.

• Function: Presents endogenous antigens (e.g., from viruses) and activates CD8+ T-cells.

MHC Class II

• Distribution: Present on antigen-presenting cells (APCs) such as macrophages, dendritic cells, and B-cells.

• Function: Presents exogenous antigens and activates CD4+ T-cells.

Primary vs Secondary Immune Response — Expanded

Primary Response

• Characteristics: First exposure to antigen.

• Speed: Slow response (5–10 days).

• Antibody Type: IgM produced first, followed by IgG.

Secondary Response

• Characteristics: Memory cells respond rapidly to re-exposure.

• Features: Stronger, faster, and longer lasting.

• Antibody Type: IgG dominates.

Canadian Blood Services Responsibilities

• Duties:
   - Collect, test, process, and distribute blood.
   - Manage stem cell registry.
   - Oversee organ/tissue donation.

Donor Eligibility

• Criteria:
   - Minimum age 17 years old.
   - Minimum weight of 110 lbs.
   - Good health status.
   - Hemoglobin requirements:
   - Women: ≥125 g/L.
   - Men: ≥130 g/L.

Deferrals

Temporary Deferrals

• Circumstances:
   - Tattoos/piercing: 3 months.
   - Transfusion: 6 months.
   - Pregnancy: 6 months postpartum.
   - Dental surgery: 72 hours.
   - Zika travel: 21 days.
   - Malaria risk: 3 months to 3 years depending on exposure.

Indefinite Deferrals

• Conditions:
   - IV drug use.
   - Risk of Creutzfeldt-Jakob disease (CJD).

Permanent Deferrals

• Conditions:
   - HIV.
   - Hepatitis.
   - Ebola.

Types of Donation

• Allogenic: General supply.

• Autologous: Self-donated blood.

• Directed: Donor to specific recipient (e.g., parent to child).

• Designated: Specific matching to recipients.

Blood Components

Packed RBCs

• Storage: 1–6°C.

• Shelf life: 42 days.

• Function: Raises hemoglobin by approximately 10 g/L.

Platelets

• Storage: 20–24°C with agitation.

• Shelf life: 7 days.

• Types: Can be pooled or apheresis; ABO-identical preferred but not required.

Plasma (FP/AFFP)

• Storage: Frozen at ≤ −18°C.

• Shelf life: 1 year.

• Compatibility: Must be ABO compatible.

Cryoprecipitate

• Function: Provides fibrinogen.

• Shelf life: 1 year frozen; not ABO-specific.

Purpose

• Functions:      - Opsonization      - Cell lysis      - Inflammation      - Chemotaxis      - Clearance of immune complexes

Pathways

• Classical Pathway: Triggered by IgM or IgG antibodies bound to an antigen (IgM is the most efficient).

• Alternative Pathway: Antibody-independent, initiated by pathogen surfaces and involves factors B, D, H, I, and properdin.

• Lectin Pathway: Triggered by mannose-binding lectin that binds to specific microbial structures.

Key Components

• C3: The most abundant complement protein, central to all pathways.

• C5b-9: Form the Membrane Attack Complex (MAC) leading to cell lysis.

Complement in Transfusion

• Mechanism: ABO incompatibility activates the classical pathway, resulting in intravascular hemolysis.

Basic Concepts

• Immunity: Resistance to infection.

• Infection vs Disease:   - Infection = invasion of pathogens.   - Disease = altered health status due to infection.

• Normal Flora: Protective microorganisms; disruption can lead to opportunistic infections.

• Opsonization: The process of tagging pathogens to facilitate phagocytosis.

Innate Immunity (Non-specific)

Characteristics

• Immediate response, lacks memory, and exhibits the same response each time.

First Line of Defense (External)

• Components:   - Skin   - Mucous membranes   - Cilia   - Flushing mechanisms such as tears, saliva, urine   - Enzymes like lysozyme   - Stomach acid   - Normal flora

Second Line of Defense (Internal)

• Components:   - Phagocytes (such as neutrophils and monocytes/macrophages)   - Natural Killer (NK) cells   - Complement system   - Inflammation

Phagocytic Cells

• Neutrophils:   - Characteristics: First responders to infection, contain primary (myeloperoxidase, defensins) & secondary granules (lactoferrin).   - Main function: Phagocytosis.

• Monocytes/Macrophages:   - Monocytes circulate in the blood and become macrophages in tissues.   - Functions: Antigen-presenting cells (APCs) that activate T-cells, produce cytokines that activate inflammation.

• Eosinophils:   - Role: Combat parasites, involved in allergic reactions mediated by IgE, contain major basic protein that is toxic to parasites.

• Basophils/Mast Cells:   - Function: Release histamine leading to vasodilation and increased vascular permeability.   - Involved in Type I hypersensitivity (anaphylaxis); mast cells reside in tissues, while basophils circulate.

• Dendritic Cells:   - Description: Most potent APC, capturing antigens in tissues and migrating to lymph nodes to activate naïve T-cells.   - Role: Bridge the innate and adaptive immune systems.

• Natural Killer (NK) Cells:   - Function: Kill virus-infected and tumor cells without prior sensitization.   - Recognition: Detect cells lacking MHC class I.   - Killing mechanism: Utilize perforin and granzyme to induce apoptosis in target cells.

Inflammation

• Characteristics: Redness, heat, swelling, and pain.

• Mechanism:   - Histamine release causes vasodilation and increased vascular permeability.   - Diapedesis of neutrophils into the affected area.

Adaptive Immunity

Characteristics

• Features: Specific, involves memory and is slower in the first response compared to innate immunity.

Two Branches of Adaptive Immunity

1. Humoral Immunity: Involves B-cells and the production of antibodies.

2. Cell-mediated Immunity: Involves T-cells that mediate immune responses.

B-Cells

• Production site: Bone marrow.

• Features: Each B-cell has a unique membrane immunoglobulin (Ig).

• Activation leads to:   - Formation of plasma cells   - Formation of memory B-cells for rapid secondary responses

T-Cells

• Maturation site: Thymus.

• Types:   - Helper T (CD4+): Activate B-cells and cytotoxic T-cells.   - Cytotoxic T (CD8+): Kill infected cells.   - Regulatory T-cells: Prevent autoimmunity.

Major Histocompatibility Complex (MHC)

• MHC Class I: Present on all nucleated cells; present endogenous antigens to CD8+ T-cells.

• MHC Class II: Present on antigen-presenting cells (APCs) such as macrophages and dendritic cells; present exogenous antigens to CD4+ T-cells.

Primary vs Secondary Immune Response

• Primary Response: Characterized by a slow and weaker response.

• Secondary Response: Faster, stronger, and more effective due to memory cells.

ABO Blood Group System

Discovery

• Noted by Landsteiner through observation of RBC agglutination upon mixing blood from different individuals.

ABO Antigens

• Description: Carbohydrate structures located on RBC membrane.

ABO Antibodies

• Characteristics: Mostly IgM, naturally occurring.

Forward Typing

• Method: Patient RBCs are mixed with anti-A/anti-B antisera to detect antigens present.

Reverse Typing

• Method: Patient plasma is mixed with A1/B reagent cells to detect antibodies present.

Why ABO IgM is Clinically Significant

• Reason: Efficient complement activation leading to rapid intravascular hemolysis.

Landsteiner’s Rule

• Stipulations:   - If antigen is present → antibody is absent.   - If antigen is absent → antibody is present.

Rh Testing

• Purpose: To determine the presence or absence of the Rh antigen (D antigen) on RBCs.

• Testing Method:   - Blood sample is mixed with anti-D serum.   - Agglutination indicates the presence of Rh positive (Rh+); no agglutination indicates Rh negative (Rh-).

• Importance:   - Determines Rh compatibility for transfusions.   - Critical for prenatal care to prevent Rh incompatibility in pregnancies.   

• Rh Antibodies:   - If an Rh- person is exposed to Rh+ blood, they may form anti-Rh antibodies which can lead to hemolytic disease in future pregnancies.

Blood Components

Packed RBCs

• Storage: 1–6°C.

• Shelf life: 42 days.

• Function: Raises hemoglobin by approximately 10 g/L.

Platelets

• Storage: 20–24°C with agitation.

• Shelf life: 7 days.

• Types: Can be pooled or apheresis; ABO-identical preferred but not required.

Plasma (FP/AFFP)

• Storage: Frozen at ≤ −18°C.

• Shelf life: 1 year.

• Compatibility: Must be ABO compatible.

Cryoprecipitate

• Function: Provides fibrinogen.

• Shelf life: 1 year frozen; not ABO-specific.