Antibodies and vaccination

Need to know

What you need to know

• **Hinge region:** gives the antibody flexibility, so its two arms can bind around an antigen.
• **Antigen-binding sites:** the variable regions at the tips of the arms; their amino acid sequence folds into a specific 3D shape, so each antibody binds one type of antigen.
• **Functions of antibodies:** attach to bacterial flagella, making the bacteria less active and easier for phagocytes to engulf; cause agglutination (clumping) of bacteria, reducing the chance of spread; punch holes in bacterial cell walls, so the cells burst as they take in water by osmosis.
• Antibodies also coat bacteria (opsonisation), making phagocytosis easier because phagocytes carry receptor proteins for antibodies; combine with toxins to neutralise them (antitoxins); and bind to viruses and toxins so they cannot enter or damage cells.
• **Hybridoma method:** B cells that divide by mitosis do not secrete antibodies, and plasma cells that secrete antibodies do not divide. Fusing a plasma cell with a myeloma (cancer) cell gives a hybridoma that does both — it divides indefinitely and secretes one specific antibody, a **monoclonal antibody**.
• **Monoclonal antibodies in diagnosis:** locating blood clots; locating cancer cells, which carry different cell-surface proteins; identifying the exact strain of virus or bacterium causing an infection, which speeds up treatment.
• **Monoclonal antibodies in treatment:** in breast cancer the antibody binds to cancerous cells and marks them for destruction by the immune system; in rheumatoid arthritis (an autoimmune disease) it binds to proteins secreted by T cells that damage cartilage in joints, blocking their action.

Explanation

Antibodies & Vaccines Made Simple

1. Understand antibody structure: Y-shape, variable/constant regions, antigen-binding site.
2. Grasp active vs. passive immunity: how they differ in origin and duration.
3. Trace the vaccination process: from antigen exposure to memory cell formation.
4. Connect vaccination to disease control and the concept of herd immunity.