Immunology Basics Quiz

Immunopathology I: Immune System & Hypersensitivity

• The immune system is a functional system, not an organ system, encompassing various components.
• Key components include: skin, mucus membranes, secretions (tears, mucus), blood cells, vasculature, bone marrow (WBC production), liver (complement proteins), lymphatic system, and lymphoid organs.
• Most tissues contain immune cells.

Objectives

• Understanding the basics of immune response.
• Identifying common types of immune response.
• Exploring cellular involvement in immune responses.
• Outlining immune defense mechanisms.
• Defining and clarifying auto-immune processes.
• Describing major hypersensitivity reactions.

Immunity

• Immunity is the body's ability to resist or eliminate potentially harmful foreign materials or abnormal cells.
• Immune activities include defense against pathogens, removal of worn-out cells and debris from injuries/disease, identification and destruction of abnormal/mutant cells, rejection of foreign cells (like organ transplant), and appropriate responses to allergens or autoimmune diseases.

Overview of the Immune System

• The immune system is divided into innate (non-specific) and adaptive (specific) components.
• Innate immunity is the first line of defense, with a rapid response that's not antigen-specific and lacks memory.
• Adaptive immunity is the second line of defense, with a slower response, antigen-specific components, and memory. Interaction between both is critical.

A Typical Immune Response

• Innate immunity rapidly responds to a wide range of microbes, including external (skin, mucus membranes, secretions) and internal (phagocytic cells, antimicrobial proteins) defenses.
• Acquired immunity has a slower response targeting particular microbes such as B lymphocytes (humoral and antibodies) and T lymphocytes (cell-mediated cytotoxic response).

Innate vs. Adaptive Immunity

• Innate immunity has no time lag, is not antigen-specific, and does not have memory.
• Adaptive immunity has a delay (at least 2-3 weeks) in response, is antigen-specific, and has memory (important for vaccinations).

Cells of the Immune System

• Hematopoiesis is the process of blood cell production in bone marrow, originating from hematopoietic stem cells (pluripotent).
• Key cells include lymphocytes (B cells, T cells, NK cells), myeloid progenitor cells (polymorphonuclear leukocytes, monocytes, and dendritic cells), and erythroid progenitor cells (platelets and erythrocytes).

Lymphoid Cells

• Lymphoid progenitors give rise to cells critical in immune function.
• B cells produce antibodies.
• T cells are involved in cellular immune responses (activated T cells, helper T cells, cytotoxic T cells).
• NK cells directly kill non-self or infected cells.
• These cell types use CD markers (CD3, CD4, CD8, CD53) as surface markers for differentiation and function.

T & B Lymphocytes

• T lymphocytes (T cells) have a long lifespan (70% of blood lymphocytes), form rosettes with sheep RBCs, and are characterized by a smooth surface and CD3 markers.
• B lymphocytes (B cells) have a short lifespan (25% of blood lymphocytes), contain surface immunoglobulins (Ig's) and surface markers like CD19 and CD20.

Organs of the Immune System

• Primary (central): bone marrow (B-cell generation), thymus (T-cell maturation).
• Secondary (peripheral): lymph nodes (lymphocyte activation), spleen, mucosa-associated lymphoid tissue (MALT), tonsils, adenoids, and Peyer's patches (antigen encounters).

General Scheme of Immune Response to Tissue Antigen

• Antigens are trapped in lymph nodes via afferent lymphatics.
• Naive lymphocytes continuously circulate from blood to lymph nodes.
• Activation of immune cells occurs upon encountering the antigen to target antigen source, resulting in eradication.

Antigen—Ag (Immunogen)

• An antigen (immunogen) is any substance stimulating the immune system to produce antibodies.
• Antigens, typically proteins, exhibit high molecular weight.
• Complete antigens are usually foreign proteins with distinctive points (epitopes) inducing an immune response.
• Incomplete antigens (haptens) lack inherent antigenic properties and gain this property on interaction with a carrier molecule.
• Heterophilic or cross-reacting antigens share similar epitopes, initiating a response.

Antigen Stimulation of T-cells

• Antigen-presenting cells (APCs, like macrophages) internalize and process antigens in association with MHC molecules.
• Processed antigens are presented to T cells (differentiated T and B cells) with specific receptors, initiating immune responses.
• MHC class I presents intracellular antigens to CD8+ T cells mediating cellular cytotoxicity.
• MHC class II presents extracellular antigens to CD4+ T cells enabling cytokine-mediated responses.

Lymphokines

• Lymphokines are proteins secreted by lymphocytes affecting cellular activities.
  • Chemotactic factor, migration inhibitor factor, mitogenic factor, transfer factor, cytotoxic factor, interferons, and skin-reactive factor are examples involved in a cascade of immune responses.

Antigens Stimulation of B-cells

• B cells recognize antigens through antigen receptors on their surface.
• When triggered by T cells (and cytokines released by T cells), B cells proliferate and differentiate into antibody-producing plasma cells.
• Memory B cells also play a crucial role by providing rapid and strong response upon re-exposure to the same antigen.

Antibody (Immunoglobulins—Ig)

• Antibodies, produced by plasma cells, are proteins specifically targeting and reacting with antigens that triggered their production.
• Antibody types (functional classification) include agglutinins (clumping of soluble antigens), precipitins (precipitating soluble antigens), neutralizing antibodies (neutralizing toxins/enzymes), and opsonins (coating antigens for enhanced phagocytosis) and complement-fixing antibodies.

Antibody Classification (Structural)

• Immunoglobulins (Igs) are classified based on their structure. Specific Igs like IgM, IgG, IgA, IgE, and IgD play distinct roles in immune responses.

Pathogens

• Extracellular pathogens (bacteria, bacterial products, parasites) stimulate B cells and Th2 cells, triggering antibody production.
• Intracellular pathogens (intracellular bacteria, viruses) stimulate Th1-cells and CD8+ CTLs initiating cytokine-mediated phagocytosis or cellular cytotoxicity respectively.

Regulation of Immune Response

• Immune responses need to be turned off (when the antigen is removed).
• Improper regulation contributes to autoimmune diseases, hypersensitivity reactions, and tissue damage/necrosis.

Disorders of Immunity

• Disorders affecting immune responses can include hypersensitivity reactions, autoimmune diseases, or immunodeficiency diseases.

Hypersensitivity

• Hypersensitivity involves undesirable reactions from the normal immune system with potential causes being misdirected or amplified immune reactions.
• These reactions are categorized into four types based on immune mechanisms leading to tissue damage: Type I (immediate), Type II (cytotoxic), Type III (immune complex), and Type IV (delayed).

Hypersensitivity Type I

• Known as immediate or anaphylactic hypersensitivity, often called allergy.
• Mediated by IgE antibodies.
• Allergens (house dust, pollen, cosmetics, or food) trigger IgE production on mast cells.
• Recurrent exposure leads to mast cell degranulation causing vasodilation, bronchoconstriction, and other reactions.
• Two phases: primary rapid response and secondary delayed.
• Can be systemic (anaphylaxis) or localized (allergic rhinitis, asthma).

Hypersensitivity Type II

• Cytotoxic hypersensitivity, involving IgG or IgM antibodies targeting cell-surface antigens.
• Complement system activation results in cell lysis or damage.
• Mediated by complement-dependent reactions or antibody-dependent cell-mediated cytotoxicity (ADCC) causing target cell death.
• Examples include transfusion reactions, hemolytic anemias, and Grave's disease.

Hypersensitivity Type III

• Immune complex hypersensitivity, involving the formation of antigen-antibody complexes that deposit in tissues.
• Activation of the complement system leads to inflammation, tissue damage, and possible organ damage.
• Examples include acute serum sickness and certain types of glomerulonephritis.

Hypersensitivity Type IV

• Delayed-type hypersensitivity or cell-mediated hypersensitivity triggered by T lymphocytes.
• Response occurs hours or days after exposure to the antigen.
• Involves T cells and macrophages.
• Delayed hypersensitivity plays a role in defense against intracellular pathogens (like tuberculosis) as well as graft rejection and tumor immunity

Granuloma Formation

• Granulomas are a form of chronic inflammation with macrophages and T cells forming a protective barrier.

Test your knowledge of immunology with this quiz covering key concepts such as immune system functions, hypersensitivity reactions, and the role of various cells in immunity. Challenge yourself to correctly answer questions about immediate and delayed immune responses, as well as specific mediators involved in hypersensitivity.