immune system & cell recognition

• What is an antigen?

  Cell-surface molecule
• Antigens are always proteins.

  False
• The immune system recognises antigens as either self or non-self.
• Steps in phagocytosis

  1️⃣ Phagocyte moves towards pathogen via chemotaxis

  2️⃣ Phagocyte engulfs pathogen via endocytosis to form a phagosome

  3️⃣ Phagosome fuses with a lysosome

  4️⃣ Lysozymes digest the pathogen

  5️⃣ Phagocyte absorbs the products of hydrolysis
• What is the role of antigen-presenting cells (APCs)?

  Display antigens on surface
• T helper cells can directly interface with pathogens in body fluid.

  False
• A nonspecific immune response is the same for all pathogens.
• Which immune cells are involved in specific immune responses?

  B and T lymphocytes
• Match the type of specific immune response with its description:

  Cell-mediated ↔️ Involves cytotoxic T cells

  Humoral ↔️ Involves antibodies secreted by plasma cells
• Outline the process of the cell-mediated response.

  1️⃣ Complementary TH lymphocytes bind to foreign antigen on APC

  2️⃣ TH cells release cytokines to stimulate clonal expansion of complementary TH cells

  3️⃣ Cytotoxic T cells secrete perforin to destroy infected cells
• In the humoral response, complementary TH lymphocytes bind to foreign antigens on antigen-presenting T cells.
• Plasma cells secrete antibodies with variable regions complementary to antigens.
• What are antibodies secreted by?

  Plasma cells
• The variable region of an antibody has a specific tertiary structure complementary to an antigen.
• The formation of an antigen-antibody complex enhances phagocytosis.
• What are monoclonal antibodies produced from?

  Single clone of B cells
• Memory cells remain in low levels in the blood after a primary immune response.
• In a secondary immune response, the rate of antibody production is faster than in a primary response.
• What is the primary cause of antigen variability?

  Random genetic mutation
• Antigen variability makes it easier to develop universal vaccines.

  False
• A vaccine contains a dead or inactive form of a pathogen or antigen.
• What is herd immunity achieved by?

  Vaccinating a large population
• Vaccine production may involve the use of animals, raising ethical concerns.
• What type of genetic material does HIV contain?

  2 x RNA
• Outline the process by which HIV results in AIDS.

  1️⃣ Attachment proteins bind to CD4 receptors on TH cells

  2️⃣ HIV replicates inside TH cells, damaging or killing them

  3️⃣ AIDS develops when there are too few TH cells for the immune system
• Antibiotics are ineffective against viruses because viruses have no cell wall.
• What hormone do pregnancy tests using monoclonal antibodies detect?

  HCG
• Outline the principle of a direct ELISA test.

  1️⃣ Monoclonal antibodies bind to the bottom of a test plate

  2️⃣ Antigen molecules in the sample bind to the antibodies

  3️⃣ Mobile antibodies with reporter enzymes bind to the fixed antigens

  4️⃣ Substrate is added, and a positive result is indicated by a colour change
• Match the type of ELISA test with what it detects:

  Direct ELISA ↔️ Detects specific antigens

  Indirect ELISA ↔️ Detects antibodies against specific antigens
• Ethical issues surrounding monoclonal antibodies often arise because their production involves animals.