Lesson Notes By Weeks and Term v4 - SHS 3

Lesson Video

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Performance objectives

• Define antigens and their role in the immune response.
• Categorize antigens as exogenous, endogenous, and autoantigens.
• Describe the steps of the immune response to antigens.
• Analyze the importance of understanding antigens for managing diseases.

Lesson summary

This lesson explores how our bodies defend themselves against disease-causing agents. In Ghana, we are constantly exposed to various microorganisms that can cause illnesses like malaria, typhoid, cholera, and the common cold. Understanding how our body's internal army, the immune system, identifies and fights these invaders is fundamental to biomedical science. We will learn about the "uniform" that these invaders wear, called an antigen, and the detailed battle plan our body uses to defeat them, known as the immune response. This knowledge is crucial for understanding vaccinations, allergies, and why we sometimes get sick while other times we don't.

Lesson notes

This section breaks down the core content you need to understand the immune response to antigens. A. The Immune System: Our Body's Defence Force

Think of the immune system as the Ghana Armed Forces for your body. Its job is to protect you from invaders (pathogens like bacteria, viruses, fungi, parasites) and internal threats (like cancer cells). It has two main branches: Innate Immunity: This is the rapid, non-specific defence. It's like the first line of security guards. It includes physical barriers (skin, mucous), chemical barriers (stomach acid), and cells (like phagocytes) that attack any foreign object they encounter. It's fast but doesn't have a long-term memory. Adaptive (or Acquired) Immunity: This is the highly specialized, specific defence. It's like the special forces unit. It targets specific invaders and, most importantly, *remembers* them. This memory is what gives us long-term immunity after an infection or vaccination. This is the system we will focus on today. B. What is an Antigen?

An antigen (short for antibody generator) is any substance or molecule that the adaptive immune system recognises as foreign or "non-self" and triggers an immune response. Analogy: Imagine our body's cells all wear a specific uniform (a "self-antigen"). An invading bacterium or virus wears a different, foreign uniform. The immune system's job is to patrol the body, check uniforms, and attack any cell wearing a foreign one. Chemical Nature: Most antigens are proteins or large polysaccharides found on the surface of pathogens (like bacteria, viruses, fungi, and parasites), pollen grains, or even the cells of a transplanted organ. C. Types of Antigens

Based on their origin, antigens are classified into three main groups: Exogenous Antigens ("Exo" = Outside) These are antigens that enter the body from the outside environment. They are the most common type we encounter. How they work: They are taken up by special immune cells called Antigen-Presenting Cells (APCs), such as macrophages. The APC "eats" the invader, breaks it down, and displays the antigen pieces on its surface to alert other immune cells. Ghanaian Examples: Bacteria: The proteins on the surface of *Salmonella typhi* bacteria, which cause typhoid fever from contaminated food or water. Parasites: Proteins from the *Plasmodium* parasite, which is transmitted by mosquitoes and causes malaria. Viruses: The spike protein on the surface of the Influenza virus (causes flu) or SARS-CoV-2 (causes COVID-19). Allergens: Proteins in pollen from grasses or trees, or in dust mites, that can cause allergic reactions in some people. Endogenous Antigens ("Endo" = Inside) These are antigens that are produced *inside* our own body's cells. This happens when our cells become infected or cancerous. How they work: When a virus infects a cell, it forces the cell's machinery to make viral proteins. The infected cell then displays pieces of these foreign viral proteins on its own surface. This acts as a signal, essentially saying, "I am infected, please destroy me before I release more viruses." Ghanaian Examples: Virus-infected cells: A liver cell infected with the Hepatitis B virus will display viral antigens on its surface. Cancer cells: Tumour cells often have mutated proteins on their surface that the immune system can recognise as foreign. Autoantigens ("Auto" = Self) These are normal self-proteins or molecules from our own body that the immune system mistakenly recognises as foreign and attacks. How they work: This is a failure of the immune system's ability to distinguish "self" from "non-self." This leads to autoimmune diseases. Ghanaian Examples: Type 1 Diabetes: The immune system attacks and destroys the insulin-producing cells in the pancreas. The proteins of these cells are the autoantigens. Rheumatoid Arthritis: The immune system attacks the tissues of the joints, causing chronic inflammation and pain. Lupus: A systemic autoimmune disease where the immune system can attack various body tissues, including the skin, joints, and kidneys. D. The Adaptive Immune Response: A Step-by-Step Battle Plan

Evaluation guide

• Explore the immune response in relation to the introduction of antigens.
• Managing Talk for Learning : Teacher leads a discussion with the class on ways they think the
• body responds to the invasion of foreign and harmful materials. Engage in a discussion on immune
• response and the meaning of the term “antigens”