1. What is the immune system, and why is it essential for survival?
Answer:
The immune system is a complex network of cells, tissues, and organs that work together to defend the body against harmful pathogens, such as bacteria, viruses, fungi, and parasites. It is essential for survival because it identifies and neutralizes foreign invaders while distinguishing them from the body’s own healthy cells. The immune system also plays a role in removing damaged cells and protecting against tumor formation.
2. Explain the key differences between innate immunity and adaptive immunity.
Answer:
| Feature | Innate Immunity | Adaptive Immunity |
|---|---|---|
| Response Time | Immediate | Delayed (requires activation) |
| Specificity | Non-specific | Highly specific |
| Memory Formation | Absent | Present (immunological memory) |
| Key Components | Physical barriers, phagocytes, NK cells | T cells, B cells, antibodies |
Innate immunity provides the first line of defense, while adaptive immunity develops later and offers long-lasting protection.
3. Describe the physical and chemical barriers of innate immunity.
Answer:
- Physical Barriers: These include the skin, which acts as a mechanical barrier, and mucous membranes lining the respiratory, gastrointestinal, and urogenital tracts, trapping pathogens.
- Chemical Barriers: These include enzymes like lysozymes in saliva and tears that break down bacterial cell walls, stomach acid that destroys ingested pathogens, and antimicrobial peptides like defensins.
4. How do phagocytes function in the innate immune response?
Answer:
Phagocytes, such as macrophages and neutrophils, engulf and digest pathogens through a process called phagocytosis. The steps include:
- Recognition: Pathogens are identified via pattern recognition receptors (PRRs) like toll-like receptors (TLRs).
- Engulfment: The phagocyte surrounds and ingests the pathogen into a phagosome.
- Destruction: The phagosome fuses with a lysosome, releasing enzymes that degrade the pathogen.
5. What are natural killer (NK) cells, and what is their role in innate immunity?
Answer:
Natural killer (NK) cells are lymphocytes that recognize and destroy virus-infected cells and tumor cells without prior sensitization. They induce apoptosis (programmed cell death) in abnormal cells by releasing perforins and granzymes. NK cells are crucial for controlling infections during the early stages before adaptive immunity is activated.
6. What is the complement system, and how does it contribute to immunity?
Answer:
The complement system is a group of proteins in the blood that enhance the ability of antibodies and phagocytic cells to clear pathogens. It functions by:
- Opsonization: Marking pathogens for phagocytosis.
- Inflammation: Recruiting immune cells to the infection site.
- Lysis: Forming membrane attack complexes (MACs) that create pores in pathogens, leading to their destruction.
7. How does adaptive immunity achieve specificity?
Answer:
Adaptive immunity achieves specificity through antigen recognition by lymphocytes.
- B cells produce antibodies that specifically bind to antigens.
- T cells recognize antigens presented by major histocompatibility complex (MHC) molecules on infected cells.
The variable regions of antibodies and T cell receptors ensure the immune system can recognize a vast array of pathogens.
8. Explain the role of T lymphocytes in adaptive immunity.
Answer:
- Helper T cells (CD4+): Coordinate the immune response by releasing cytokines that activate B cells, cytotoxic T cells, and macrophages.
- Cytotoxic T cells (CD8+): Destroy infected or cancerous cells by inducing apoptosis.
- Regulatory T cells: Suppress excessive immune responses to maintain homeostasis and prevent autoimmune diseases.
9. Describe the process of antibody production by B cells.
Answer:
- Activation: B cells recognize antigens via their surface receptors and receive help from helper T cells.
- Proliferation: Activated B cells multiply to form plasma cells and memory B cells.
- Antibody Secretion: Plasma cells produce specific antibodies that neutralize antigens, opsonize pathogens, and activate the complement system.
10. What are the primary types of antibodies, and what are their functions?
Answer:
- IgG: Provides long-term immunity and crosses the placenta to protect the fetus.
- IgA: Found in mucosal areas and secretions like saliva, tears, and breast milk.
- IgM: The first antibody produced during an infection.
- IgE: Involved in allergic reactions and defense against parasitic infections.
- IgD: Plays a role in B cell activation.
11. How does immunological memory work in adaptive immunity?
Answer:
Immunological memory is established after an initial exposure to an antigen. Memory B and T cells persist long after the infection, allowing for a faster and more robust response upon subsequent exposures. This principle underlies the effectiveness of vaccines.
12. What are the primary differences between humoral and cell-mediated immunity?
Answer:
| Feature | Humoral Immunity | Cell-Mediated Immunity |
|---|---|---|
| Mediated By | B cells and antibodies | T cells |
| Target | Extracellular pathogens | Intracellular pathogens and abnormal cells |
| Key Component | Antibodies | Cytotoxic T cells |
13. Explain the concept of antigen presentation.
Answer:
Antigen-presenting cells (APCs), such as dendritic cells and macrophages, process and present antigens on MHC molecules to T cells.
- MHC I: Presents antigens to cytotoxic T cells.
- MHC II: Presents antigens to helper T cells.
This process bridges innate and adaptive immunity.
14. What is the role of cytokines in the immune response?
Answer:
Cytokines are signaling proteins released by immune cells to regulate the immune response. They function in:
- Cell recruitment: Attracting immune cells to infection sites.
- Activation: Stimulating immune cell proliferation and differentiation.
- Communication: Coordinating between innate and adaptive immunity.
15. How does the immune system differentiate self from non-self?
Answer:
The immune system uses pattern recognition receptors (PRRs) to identify pathogen-associated molecular patterns (PAMPs) on microbes while recognizing self-antigens through MHC molecules. Regulatory T cells and central tolerance mechanisms in the thymus and bone marrow prevent autoimmunity.
16. What is the inflammatory response, and how is it initiated?
Answer:
The inflammatory response is a protective reaction to infection or injury. It is initiated by the release of histamines, cytokines, and prostaglandins, which increase blood flow, capillary permeability, and immune cell recruitment to the affected area.
17. Describe passive and active immunity with examples.
Answer:
- Passive Immunity: Transfer of antibodies from another source, e.g., maternal antibodies through breast milk or antiserum injections.
- Active Immunity: Body produces its own immune response, e.g., through infection or vaccination.
18. What are autoimmune diseases, and how do they occur?
Answer:
Autoimmune diseases occur when the immune system mistakenly attacks the body’s own tissues due to a failure in self-tolerance. Examples include rheumatoid arthritis and lupus.
19. Explain the significance of vaccines in adaptive immunity.
Answer:
Vaccines stimulate adaptive immunity by introducing a harmless form of a pathogen or its antigens. This triggers memory cell formation, providing long-term protection against the actual pathogen.
20. How do pathogens evade the immune system?
Answer:
Pathogens evade the immune system through various strategies, such as:
- Antigenic variation: Altering surface proteins to avoid detection.
- Hiding in host cells: Preventing recognition by immune cells.
- Suppressing immune responses: Producing molecules that inhibit immune signaling pathways.
These questions and answers provide a comprehensive understanding of innate and adaptive immunity.
