Immunology Quiz on Defense Mechanisms

Innate Immunity

• First line of defense: skin and mucous membranes
• Second line of defense: phagocytes, natural killer (NK) cells, inflammation, antimicrobial cells.
• Mechanical barrier: waterproof skin resistant to weak acids and bacteria due to keratin.
• Mucous membranes protect body cavities from the external environment.
• Mucus traps microorganisms; cilia move mucus and debris out of the lower respiratory tract.
• Tears and saliva contain lysozyme to clean cavities.
• Urine, due to its acidity, inhibits bacterial growth.
• Phagocytes engulf and destroy germs and debris.
• Phagosomes merge with lysosomes to form phagolysosomes, breaking down germs.
• Skin acidity (pH 3-5) inhibits bacterial growth.
• Skin oils and stomach acid kill bacteria.
• Saliva and tears contain enzymes that kill bacteria.
• Mucus traps germs in the digestive and respiratory systems.
• Cilia in the nose and lungs help remove germs.

Inflammation

• Part of the body's second line of defense.
• Response to injury, infections, allergies, or lack of blood flow.
• Always the same process, regardless of the cause.
• Vasodilation: Widens blood vessels, causing redness and heat in inflamed areas.
• Increased capillary permeability: Allows helpful substances (clotting factors, antibodies) to leave the blood and enter tissues, causing swelling (edema).
• Systemic effects: tiredness, feeling unwell, headaches, loss of appetite, fever.
• Fever (pyrexia): higher than normal body temperature, fights infections, and speeds up cell activity.

Fever

• Occurs when white blood cells (WBCs) detect harmful substances and release pyrogens.
• Pyrogens (interleukin 1, interleukin 6, and tumor necrosis factor) travel to the hypothalamus and increase body temperature, making it temporarily higher.

Local Inflammation

• Causes less swelling and fluid than acute inflammation.
• Involves more fibroblasts and collagen for tissue repair.
• Systemic or chronic inflammation (SCI): Long-term, low-level inflammation that can weaken the immune system and increase the risk of other diseases.

NK Cells

• Patrol blood and lymph to kill cancer or virus-infected cells.
• Identify cells lacking "self" markers.
• Kill these cells using perforins, chemicals.

Antimicrobial Proteins

• Proteins that directly fight germs or stop their reproduction.
• Includes interferons and complement proteins.
• Interferons protect from viruses by stopping their spread and activating macrophages and NK cells.
• Complement is a group of over 20 proteins that circulate in the blood in an inactive form. When activated, complement helps destroy pathogens and boost inflammation.

Adaptive Immunity

• Targets specific foreign invaders, often taking longer to activate but being more effective.
• Involves immune and lymphoid tissues.
• Key cells include T and B lymphocytes, antibodies, macrophages, and dendritic cells.

Immunity

• Protects the whole body, not just the site of infection.
• The immune system can recognize different pathogens and distinguish them from normal cells.
• Can remember previous infections and respond faster and stronger to subsequent exposure, adapting to infections.
• Can cause allergies and autoimmune diseases.
• Normally defends against infections, cancer cells, and organ transplants.

Antigens

• Foreign substances that trigger an immune response (immunogens).
• The immune system recognizes antigens using receptors on immune cells and antibodies (proteins designed to fight the antigen).
• Examples include bacteria, viruses, fungi, pollen, poison ivy.

Antigenic Determinants

• Small parts of an antigen called epitopes or antigenic determinants that immune cells and antibodies recognize.
• Each antigen can have several epitopes, each triggering an immune response.

Immune Cells

• Main immune system cells are T and B lymphocytes, which are types of white blood cells (WBCs).
• Macrophages and dendritic cells process antigens and activate lymphocytes.
• Immune cells can be regulatory or effector cells.
• Regulatory cells (T helper cells) help control and coordinate the immune response.
• Effector cells (T cytotoxic cells) destroy and remove antigens.

Lymphocytes

• After training, T and B lymphocytes stay in lymph nodes, spleen, and mucosa.

• They must learn to recognize harmful invaders—avoiding self-attack—becoming "educated."

• Lymphocytes are made in bone marrow from stem cells called hemocytoblasts.

• Lymphocyte activation occurs when receptors on their surface recognize specific antigens.

• B cells have antibody receptors; T cells recognize antigens shown with "self" markers (MHC).

• MHC markers are on special cells called antigen-presenting cells (APCs), helping T cells identify the antigen.

• When an antigen is recognized, cytokines (signaling proteins) release and activate T and B cells, creating effector or memory cells.

Memory Lymphocytes

• Lymphocytes created during an immune response that stay in the body for long periods.
• Help the body respond faster and more strongly if the same antigen appears again.
• Often occur without the individual noticing the response.

Major Histocompatibility Complex (MHC)

• Cell surface proteins that allow the body to recognize its own cells and identify foreign invaders.
• Each person has a unique set of MHC proteins (also called human leukocyte antigens (HLA)).
• Two types: Class 1 and Class 2.

Humoral vs. Cell-Mediated Immunity

• B cells control humoral immunity by producing antibodies—fighting bacteria, neutralizing toxins, stopping viruses.
• T cells control cell-mediated immunity by attacking infected cells—stronger and faster with memory cells.
• Both types work together for effective immune defence.

Humoral Immunity p2

• Primary response: occurs during the first encounter with an antigen; B cells mature into plasma cells and produce antibodies, with a delay of about a week.
• Secondary response: a faster and stronger response to subsequent encounters due to memory cells.

Active and Passive Immunity

• Active: happens when the body is exposed to a pathogen naturally or through vaccination.
• Passive: occurs when antibodies are transferred naturally (mother to baby) or artificially.

T Lymphocytes

• Different types of T cells with various roles in the immune response.
• T cells mature in the thymus, travel to other parts of the body, and look for antigens.
• T cell receptors (TCRs) interact with antigens presented by MHC complexes.

T Helper Cells

• Have CD4 markers on their surface.
• Activated when they bind to an antigen presented by MHC Class II molecules.
• Release cytokines to activate other immune cells.

Cytotoxic T Cells

• Have CD8 markers on their surface.
• Activated when they bond to an antigen on MHC Class I molecules (infected or cancerous cells).
• Kill infected or cancerous cells, sparing healthy cells.

T Regulatory Cells

• Help turn off the immune response after the threat is gone by releasing cytokines.
• Suppress other immune cell activities and prevent excessive responses.

T Memory Cells

• Responsible for a faster secondary response when the same antigen is encountered again.

Cytokines

• Proteins that regulate the immune response, made mostly by T helper cells and macrophages.
• Cause inflammation, attract immune cells, and control the activity of other immune cells.

Cell-Mediated Immunity

• T cells, with help from antigen-presenting cells (APCs), provide this type of immunity.
• T helper cells or T cytotoxic cells are activated, leading to their growth and release of cytokines.

Antibodies

• Also known as immunoglobulins (Ig).
• 5 types (IgG, IgA, IgM, IgD, IgE) with different structures and functions.
• Y-shaped, with 2 identical sites to bind antigens.
• Binding to antigens help with neutralization, agglutination, precipitation, and complement fixation.

Inflammation

• Histamine: stored in platelets, basophils, and mast cells; triggers blood vessel widening, making capillaries more permeable.
• Prostaglandins: lipids from arachidonic acid; cause blood vessel widening, pain, and fever.
• Plasma proteins: kinins, complement proteins, and clotting factors.
• Clotting system: creates a mesh, helping prevent spread of infection and for tissue repair.
• Leukotrienes: from arachidonic acid in WBCs; help white blood cells move to infection sites.
• Platelet-activating factor: helps platelets stick together and activate eosinophils.
• Cytokines: produced by cells for communication in the immune response, including interleukins and interferons.
• Acute inflammation: rapid, minimal damage, and quick resolution.

Chronic Inflammation

• Can last weeks or years, often following repeated acute inflammation or a low-grade response.
• Involves macrophages and lymphocytes, resulting in scar tissue formation.
• Often caused by substances like talc, asbestos, silica, or pathogens.
• Granulomatous lesions (e.g., tuberculosis) are areas where macrophages are surrounded by lymphocytes.

Cell Death: Apoptosis & Necrosis

• Apoptosis: controlled, natural cell death; useful for removing old, damaged, or unneeded cells.
• Necrosis: uncontrolled cell death, often caused by injury or lack of oxygen (hypoxia); involves cell swelling, membrane rupture, and inflammation.

Test your knowledge on the immune system's roles and mechanisms. This quiz covers topics including pyrogens, inflammation, NK cells, and the body's defense strategies against infections. Perfect for students studying immunology or related fields.