1. Define antigens and explain their role in the immune system.
Answer:
Introduction:
Antigens are foreign molecules or substances that elicit an immune response when introduced into the body.
Role in the Immune System:
- Recognition: Antigens are recognized by immune cells like B cells and T cells through receptors.
- Immune Response: They activate the production of antibodies or stimulate cellular responses to eliminate pathogens.
- Types: Antigens can be proteins, polysaccharides, lipids, or nucleic acids found on the surfaces of bacteria, viruses, and other pathogens.
2. What are antibodies, and how are they structured?
Answer:
Introduction:
Antibodies, also known as immunoglobulins, are Y-shaped proteins produced by B cells in response to antigens.
Structure:
- Variable Region: Binds specifically to antigens at the epitope.
- Constant Region: Determines the antibody class and interacts with other immune components.
- Heavy and Light Chains: Two heavy chains and two light chains connected by disulfide bonds form the structure.
- Fab and Fc Fragments: The Fab fragment binds to antigens, while the Fc fragment interacts with effector systems.
3. Explain the different classes of antibodies and their functions.
Answer:
Classes and Functions:
- IgG: Provides long-term immunity, crosses the placenta to protect the fetus.
- IgA: Found in mucosal areas like the respiratory and gastrointestinal tracts; protects against pathogens.
- IgM: First antibody produced in an infection; effective in forming antigen-antibody complexes.
- IgE: Involved in allergic responses and parasitic infections.
- IgD: Functions primarily as a receptor on immature B cells.
4. Describe the process of antigen-antibody binding.
Answer:
Mechanism:
- Specificity: The variable region of the antibody binds to the specific epitope of the antigen.
- Forces: Binding is facilitated by non-covalent forces like hydrogen bonds, ionic interactions, and van der Waals forces.
- Outcome: This binding neutralizes the antigen or marks it for destruction by immune cells.
5. What are the mechanisms of antibody-mediated immunity?
Answer:
Mechanisms:
- Neutralization: Antibodies block the activity of toxins or viruses.
- Opsonization: Antibodies coat pathogens, making them easier to phagocytose.
- Complement Activation: Antibodies trigger the complement system, leading to cell lysis.
- Antibody-Dependent Cellular Cytotoxicity (ADCC): Antibodies recruit natural killer cells to destroy infected cells.
6. How do antigens trigger an immune response?
Answer:
Process:
- Recognition: Antigen-presenting cells (APCs) process and present antigens to T cells.
- Activation: Helper T cells activate B cells and cytotoxic T cells.
- Response: B cells produce antibodies, and T cells target infected cells.
- Memory: The immune system retains memory cells for faster future responses.
7. Differentiate between T-dependent and T-independent antigens.
Answer:
- T-Dependent Antigens: Require T-helper cells to activate B cells. Example: Protein antigens.
- T-Independent Antigens: Directly activate B cells without T-helper cells. Example: Polysaccharide antigens.
8. What is an epitope, and why is it important?
Answer:
An epitope is the specific region of an antigen that binds to an antibody. It is crucial because it determines the specificity of the immune response and the interaction with receptors.
9. Describe the process of antibody production.
Answer:
- Antigen Recognition: B cells recognize antigens using their receptors.
- Activation: Helper T cells provide signals for B cell activation.
- Differentiation: Activated B cells differentiate into plasma cells and memory cells.
- Secretion: Plasma cells secrete large amounts of antibodies specific to the antigen.
10. Explain the significance of monoclonal antibodies.
Answer:
Monoclonal antibodies are identical antibodies produced by a single clone of B cells. They are used in diagnostics, cancer therapy, and autoimmune disease treatment.
11. What are autoantigens, and how do they lead to autoimmune diseases?
Answer:
Autoantigens are self-molecules mistakenly targeted by the immune system. This leads to autoimmune diseases such as lupus and rheumatoid arthritis.
12. How do vaccines utilize antigens for immunity?
Answer:
Vaccines introduce antigens (weakened or inactivated) to stimulate an immune response and develop memory cells without causing disease.
13. Explain the concept of cross-reactivity in antigen-antibody interactions.
Answer:
Cross-reactivity occurs when an antibody binds to a similar epitope on a different antigen. It can lead to misdirected immune responses or complications in diagnostics.
14. What is the role of antibodies in passive immunity?
Answer:
In passive immunity, pre-formed antibodies are transferred to an individual, providing immediate protection. Examples include maternal antibodies and antibody-based therapies.
15. Discuss the role of complement activation in antigen-antibody complexes.
Answer:
Antigen-antibody complexes activate the complement system, leading to:
- Lysis of pathogens.
- Enhanced phagocytosis (opsonization).
- Inflammation to recruit immune cells.
16. How do allergens act as antigens in hypersensitivity reactions?
Answer:
Allergens are antigens that trigger IgE-mediated hypersensitivity, causing allergic reactions like asthma, hay fever, and anaphylaxis.
17. Describe how antibodies are used in diagnostic tests.
Answer:
Antibodies are used in ELISA, Western blotting, and immunohistochemistry to detect specific antigens in samples, aiding disease diagnosis.
18. What is the difference between primary and secondary immune responses?
Answer:
- Primary Response: Occurs upon first exposure to an antigen; slower and less robust.
- Secondary Response: Faster and stronger due to memory cells.
19. Explain the mechanism of antigen-antibody precipitation reactions.
Answer:
When soluble antigens and antibodies mix, they form insoluble complexes (precipitates), which are useful in immunological assays.
20. How do antibodies neutralize toxins and pathogens?
Answer:
Antibodies bind to toxins or surface proteins of pathogens, blocking their interaction with host cells and preventing infection or damage.
