Immunology Quiz on Blood and Allergies

Immunology Overview

• This is a subject matter overview covering different immunological concepts and components

Instructional Objectives

• Inventory of antigens and antibodies (including IgA, IgD, IgE, IgG, and IgM) are detailed
• Illustrations of the processes of the immune response are outlined
• The different hypersensitivity types are examined
• Comparison of autoimmune and immunodeficiency diseases is provided
• HIV definition, transmission, and testing are discussed
• Major blood group systems are compared, with a brief overview of other systems
• Contrast of Rh antibody formation and hemolytic disease of the newborn (HDN) is presented
• Different laboratory tests (Type and Cross Match, Type and Screen, Direct and Indirect Coombs) are explained
• The role and indications of blood transfusions (red cell, cryoprecipitate, platelet, and fresh frozen plasma) and reactions are reviewed

Refresh on Immunity

• Innate immunity is nonspecific, with physical/physiological barriers such as skin, GI lining, gastric acid, and phagocytes (neutrophils and macrophages)
• Adaptive immunity is specific, focused on acquired responses with specific targets.
  • Cell-mediated immunity: T-lymphocytes
  • Antibody-mediated (humoral) immunity: B-lymphocytes

Immune Response (Simplified)

• Local neutrophils encounter pathogens and begin phagocytosis, triggering cytokines
• Cytokines cause vasodilation, attracting more neutrophils and monocytes
• Monocytes differentiate into macrophages
• Macrophages and neutrophils continue phagocytosis
• Macrophages act as antigen-presenting cells (APCs), presenting to T-cells (cytotoxic, helper, and regulatory) and B-cells
• Memory B-cells are dormant, enabling faster response to future pathogens
• Plasma B-cells secrete antibodies (immunoglobulins)

Immunoglobulins (Antibodies)

• Immunoglobulins are synonymously used with antibodies
• Measured in blood, values vary by age
• Used to monitor the progress of hypersensitivities, immune deficiencies, autoimmune diseases, and chronic infections
• Serum Ig testing is not a sole diagnostic but can indicate disease
• Electrophoresis separates them based on mass and charge
• Five isotypes: IgG, IgA, IgM, IgE, IgD

Monoclonal vs Polyclonal Antibodies

• Polyclonal antibodies bind to different epitopes of the same antigen
• Monoclonal antibodies bind to one epitope of the same antigen
• Differences are used in drug development, research and lab evaluations

Immunoglobulin G (IgG)

• Constitutes approximately 75% of serum immunoglobulins
• Key component of the immune response, including neutralization, opsonization, complement activation.
• Plays an important role in antibody-dependent cytotoxicity against infected cells.
• Involved in fighting infections and in many other disorders
• Exists in four subclasses with varying actions in fighting infections

Immunoglobulin A (IgA)

• IgA is approximately 15% of the body's immunoglobulin
• Found in tears, blood, respiratory and gastrointestinal secretions
• Supports mucosal tissue protection (maintains homeostasis) from pathogens
• Increased levels are linked with various inflammatory conditions
• Decreased levels are associated with conditions like leukemia and immunodeficiencies

Immunoglobulin M (IgM)

• Primarily involved in ABO blood grouping and immediate responses to infections
• Involved importantly in immune responses to many infections
• Forms a pentamer, possessing 10 antigen-binding sites
• Effective in antigen-antibody complex formation
• Does not cross the placenta

Immunoglobulin E (IgE)

• Mediates allergic response and parasitic diseases
• Helps in detecting allergic and hypersensitivity diseases
• Not a standalone test as it is frequently involved in other non-allergic conditions
• Does not activate complement system for opsonization
• Elevated levels can be indicative of various diseases

Immunoglobulin D (IgD)

• Little is understood about IgD, with limited clinical evaluation
• Potentially involved in B-cell function, but not in direct immune responses

Hypersensitivity

• An exaggerated immune response, ranging from mild to fatal.
• Classified into four types (Type I, Type II, Type III, and Type IV)
• Type I: IgE-mediated, immediate hypersensitivity
• Type II: Antibody-mediated, involves the killing of self-cells by the immune system
• Type III: Immune complex-mediated, involves antigens and antibodies forming complexes and causing damage
• Type IV: Cell-mediated, delayed hypersensitivity

Human Immunodeficiency Virus (HIV)

• A virus that leads to a progressive immune system failure
• Associated with an increased infection and cancer risk
• CD4 is a protein on immune cells (especially helper T cells), playing a role in signaling
• HIV leads to the progressive reduction of CD4+ T cells
• CD4 test helps in tracking HIV and treatment efficacy
• Lower CD4 counts correlate with increased risks of opportunistic infections
• Increased CD4 count suggests successful treatment
• CD4 counts below 200 indicate AIDS.

HIV Diagnosis and Treatment

• HIV differentiation immunoassay (serology) confirms HIV type
• HIV RNA quantification (viral load) quantifies HIV RNA after confirmation
• Results from CD4 and viral load direct treatment

HIV Diagnosis Tests

• ELISA (Enzyme-Linked ImmunoSorbent Assay) detects HIV antibodies
• CBC (Complete Blood Count) can reveal leukopenia, lymphopenia, and thrombocytopenia, potentially caused by infections

Blood Types

• ABO typing and Rh typing depend on inherited antigens on erythrocytes
• Blood type compatibility is crucial to avoid adverse effects in transfusions
• Antigens trigger immune responses; antibodies attack antigens

Rh Factor

• An erythrocyte antigen first discovered in rhesus monkeys
• Antibodies to the Rh factor typically develop after exposure to Rh-positive blood
• There are many human erythrocyte antigen systems; in emergencies these are cross-matched before transfusion

Transfusion Reactions

• Exposure to incompatible blood can lead to severe reactions in recipients
• Two major types of antigen-antibody reactions occur
• Often involves recipient's plasma antibodies and donor's erythrocyte antigens
• Can cause severe complications like acute kidney failure

Hemolytic Disease of the Newborn (HDN)

• Transfusion reactions
• An important aspect to consider in pregnancy and blood transfusions

Coombs Tests

• Used to detect antibodies against red blood cells (RBCs).
• Two types: direct and indirect.
  • Direct Coombs test detects antibodies directly on RBCs
  • Indirect Coombs test detects antibodies in the serum

Type and Screen/Crossmatch

• ABO grouping and Rh typing are checked
• Other antibodies are also often screened.
• Recipient plasma is added to donor blood to determine compatibility
• Often performed before transfusions to reduce risk of reactions

Blood Product Indications

• Whole blood: Not suitable for most patients, ideal for specific conditions
• Packed red blood cells: Used for treating low hemoglobin, decreased oxygen saturation
• Platelet-rich plasma (PRP): Used for patients with a risk of spontaneous bleeding and before high-risk procedures (e.g. surgeries)
• Fresh frozen plasma (FFP): Contains clotting factors and used for those with bleeding and clotting deficiency
• Cryoprecipitate: Contains high concentrations of clotting factors, including Factors VIII and XIII, fibrinogen, and von Willebrand factor, typically used when those specific clotting factors are low.

Midterm Topics

• A listing of tested components of immunity, blood types, and diseases.