1. Enlist the steps of immune response.
Answer: The immune response is a highly coordinated sequence of events that the body uses to defend against pathogens. It can be broken down into five key steps:
Step 1: Recognition (Detection of Antigen) When a pathogen enters the body, it carries unique molecular markers called antigens. Specialized immune cells, primarily macrophages and dendritic cells, recognize these antigens as "foreign" or "non-self." These cells engulf the pathogen and break it down.
Step 2: Presentation (Antigen Presentation) After breaking down the pathogen, the macrophage or dendritic cell displays fragments of the antigen on its surface using a molecule called MHC (Major Histocompatibility Complex). This acts like a "wanted poster" to alert other immune cells.
Step 3: Activation (Clonal Selection) The antigen-presenting cell travels to a lymph node and presents the antigen to helper T cells. Helper T cells that recognize the
specific antigen become activated. These helper T cells then activate:
B cells: Which will produce antibodies. Cytotoxic T cells: Which will kill infected cells.
Step 4: Effector Phase (Attack and Elimination) This is the phase where the pathogen is actively destroyed.
Humoral Response: Activated B cells differentiate into plasma cells, which secrete millions of antibodies. These antibodies bind to the pathogen, neutralizing it and marking it for destruction by phagocytes (opsonization). Cell-Mediated Response: Cytotoxic T cells travel to the site of infection and directly kill infected cells by releasing perforin and granzymes.
Step 5: Memory Phase (Formation of Memory Cells) After the infection is cleared, most of the effector cells die. However, a small population of memory B cells and memory T cells remain in the body. These cells "remember" the specific antigen. If the same pathogen enters the body again, these memory cells can mount a rapid and powerful response (secondary immune response), often preventing illness.
In summary, the immune response involves recognition, presentation, activation, elimination of the pathogen, and the formation of memory for future protection.
2. Explain the first line of defence.
Answer: The first line of defense is the body's initial, non-specific barrier against pathogens. It is designed to prevent pathogens from entering the body in the first place. It is part of the innate immune system, meaning it is present from birth and does not distinguish between different types of pathogens.
The first line of defense consists of:
1. Physical Barriers:
Skin: The skin is a tough, waterproof, and slightly acidic barrier. The outer layer (epidermis) consists of dead, keratinized cells that are difficult for pathogens to penetrate. The skin also constantly sheds, removing any microbes that might have attached. Mucous Membranes: These line the internal cavities of the body that are exposed to the external environment, such as the respiratory, digestive, and reproductive tracts. They secrete a sticky fluid called mucus, which traps pathogens, dust, and other particles. Cilia: Microscopic, hair-like structures on the surface of cells in the respiratory tract. They beat in coordinated waves, sweeping mucus and trapped pathogens toward the throat to be swallowed or coughed out.
2. Chemical Barriers:
Lysozyme: An enzyme found in tears, saliva, and sweat. It destroys the cell walls of bacteria, causing them to burst. Stomach Acid: The stomach secretes hydrochloric acid (HCl), which is extremely acidic (pH 1.5-2.0). This acid kills most pathogens that are swallowed with food. Antimicrobial Peptides: Cells in the skin and mucous membranes secrete peptides (like defensins) that disrupt the cell membranes of bacteria and fungi. Sebum: Oil secreted by sebaceous glands in the skin, which contains fatty acids that lower the pH of the skin, inhibiting bacterial growth.
In summary, the first line of defense is a combination of physical and chemical barriers that prevent pathogens from entering the body. It is the body's first and most important defense against infection.
3. What is a flow chart of different types of white blood cells?
Answer: White blood cells (leukocytes) are the cells of the immune system. They are nucleated and are produced in the bone marrow. They
can be classified into two main groups based on the presence or absence of granules in their cytoplasm.
(Flow Chart Description)
White Blood Cells (Leukocytes) [source symbol unavailable][source symbol unavailable][source symbol unavailable] Granulocytes (contain visible granules) [source symbol unavailable] [source symbol unavailable][source symbol unavailable][source symbol unavailable] Neutrophils: The most abundant WBCs. They are phagocytic and are the first responders to bacterial infections. [source symbol unavailable] [source symbol unavailable][source symbol unavailable][source symbol unavailable] Eosinophils: Fight parasitic infections and are involved in allergic reactions. [source symbol unavailable] [source symbol unavailable][source symbol unavailable][source symbol unavailable] Basophils: Release histamine (inflammation) and heparin (anticoagulant). [source symbol unavailable][source symbol unavailable][source symbol unavailable] Agranulocytes (lack visible granules) [source symbol unavailable][source symbol unavailable][source symbol unavailable] Lymphocytes: [source symbol unavailable] [source symbol unavailable][source symbol unavailable][source symbol unavailable] T cells: Mature in the thymus. Involved in cell-mediated immunity. [source symbol unavailable] [source symbol unavailable][source symbol unavailable][source symbol unavailable] B cells: Mature in the bone marrow. Involved in humoral immunity (antibody production). [source symbol unavailable] [source symbol unavailable][source symbol unavailable][source symbol unavailable] Natural Killer (NK) cells: Kill virus-infected and cancer cells. [source symbol unavailable][source symbol unavailable][source symbol unavailable] Monocytes: Differentiate into macrophages and dendritic cells in tissues.
In summary, WBCs are divided into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes and monocytes), each with specific roles in immunity.
4. How lymph nodes prevent the spread of pathogens in human body?
Answer: Lymph nodes are small, bean-shaped organs located along lymphatic vessels. They act as biological filters and are strategically placed throughout the body (e.g., neck, armpits, groin) to intercept pathogens before they can spread.
How they work:
1. Filtration: Lymph fluid, which contains interstitial fluid, waste products, and potentially pathogens, flows through the
lymphatic vessels. As it enters a lymph node, it passes through a network of reticular fibers.
2. Trapping: Macrophages and dendritic cells within the lymph node trap pathogens, debris, and cancer cells.
3. Destruction: The lymph node contains high concentrations of lymphocytes (B and T cells). When antigens are detected, B cells produce antibodies, and T cells activate other immune cells, destroying the trapped pathogens.
4. Prevention of Spread: By filtering and destroying pathogens locally, lymph nodes prevent them from entering the bloodstream and spreading to other parts of the body.
Clinical Significance: When an infection is present, lymph nodes may become swollen and tender (lymphadenopathy) as they actively fight the infection. This is a sign the immune system is working.
In summary, lymph nodes are crucial for trapping and destroying pathogens, preventing their spread through the body.
5. Name few vaccines and the diseases they control.
Answer: Vaccines are biological preparations that provide active acquired immunity against a specific infectious disease. They typically contain an agent that resembles a disease-causing microorganism and are often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins.
| Vaccine | Disease Controlled |
| BCG | Tuberculosis |
| OPV/IPV | Poliomyelitis (Polio) |
| MMR | Measles, Mumps, Rubella |
| |
| Hepatitis B | Hepatitis B |
| DTP | Diphtheria, Tetanus, Pertussis |
| COVID-19 | Coronavirus Disease 2019 |
| HPV | Human Papillomavirus (cervical cancer) |
In summary, vaccines are essential tools for preventing and controlling infectious diseases.
6. What are the types of memory cells? Why they are important?
Answer: Memory cells are a crucial component of the adaptive immune system. They are long-lived lymphocytes that remain in the body after an infection or vaccination.
Types:
1. Memory B Cells: These cells are produced during an initial infection. They remain in the lymph nodes and spleen. Upon re-exposure to the same antigen, they rapidly differentiate into antibody-secreting plasma cells.
2. Memory T Cells: These cells remain in the body after an infection. Upon re-exposure, they rapidly proliferate and mount a strong cell-mediated response, killing infected cells.
Importance:
Rapid Response: Memory cells provide a faster and more powerful secondary immune response compared to the
primary response. Long-lasting Immunity: They provide long-term protection against specific pathogens, often for decades or even a lifetime. Vaccination: Vaccines work by inducing the formation of memory cells without causing the disease.
In summary, memory cells are essential for long-term immunity and the effectiveness of vaccines.
7. Why booster doses of vaccine are important?
Answer: A booster dose is an additional dose of a vaccine given after the initial vaccination series. It is important for several reasons:
1. Waning Immunity: Over time, the number of antibodies and memory cells produced by the initial vaccination can decrease. A booster dose helps to maintain a high level of immunity.
2. Stimulation of Memory Cells: Booster doses "remind" the immune system of the pathogen. They stimulate memory B and T cells to proliferate and produce more antibodies, strengthening the immune response.
3. Protection Against New Variants: For viruses that mutate rapidly (like COVID-19 or influenza), booster doses may be updated to target new variants and provide broader protection.
4. Ensuring Herd Immunity: Widespread booster vaccination helps to maintain herd immunity, protecting vulnerable populations who cannot be vaccinated.
In summary, booster doses are essential to maintain and enhance immunity over time and to protect against evolving pathogens.
8. What are the symptoms of allergy?
Answer: Allergy symptoms occur when the immune system overreacts to a harmless substance (allergen). Symptoms can range from mild to
severe and can affect various parts of the body.
Common Symptoms:
Respiratory: Sneezing, runny or stuffy nose, wheezing, coughing, shortness of breath. Skin: Hives (urticaria), itching, redness, eczema. Eyes: Itchy, red, watery eyes (allergic conjunctivitis). Gastrointestinal: Nausea, vomiting, diarrhea, abdominal pain (food allergies).
Severe Symptoms (Anaphylaxis):
Difficulty breathing, swelling of the throat, drop in blood pressure, loss of consciousness. This is a medical emergency.
In summary, allergy symptoms vary from mild discomfort to life-threatening anaphylaxis.
9. Name different causes of allergy?
Answer: Allergies are caused by allergens, which are typically harmless substances that the immune system mistakenly identifies as threats.
Common Causes:
Airborne Allergens: Pollen (trees, grasses, weeds), dust mites, pet dander (cats, dogs), mold spores. Food Allergens: Peanuts, tree nuts, milk, eggs, shellfish, wheat, soy. Insect Stings: Bee stings, wasp stings, fire ant bites. Medications: Penicillin, aspirin, ibuprofen. Contact Allergens: Latex, nickel, certain cosmetics, poison ivy.
In summary, allergens are diverse and can trigger allergic reactions through inhalation, ingestion, injection, or contact.
10. What substances cause allergy? Enlist them. (This is a repeat of Question 9. The answer is the same.)
11. Write the differences between:
a. Granulocytes and lymphocytes
Answer:
| Feature | Granulocytes | Lymphocytes |
| Cytoplasm | Contain visible granules. | Lack visible granules. |
| Types | Neutrophils, Eosinophils, Basophils. | T cells, B cells, NK cells. |
| Origin | Bone marrow. | Bone marrow (B cells), Thymus (T cells). |
| Function | Innate immunity; phagocytosis, allergic response. | Adaptive immunity; specific immune response. |
| Nucleus | Multi-lobed. | Large, round. |
In summary, granulocytes are involved in non-specific defense, while lymphocytes are involved in specific, adaptive immunity.
b. Macrophages and dendritic cells
Answer:
| Feature | Macrophages | Dendritic Cells |
| Function | Phagocytose pathogens; present antigens. | Capture antigens; present antigens. |
| Location | Tissues throughout the body. | Tissues in contact with external environment (skin, mucosa). |
| Role | Key role in innate immunity and cleanup. | Key role in initiating adaptive immunity. |
| Shape | Irregular, amoeboid. | Star-shaped with dendrites. |
In summary, both are antigen-presenting cells, but dendritic cells are more specialized for initiating adaptive immunity.
c. Allergy and autoimmunity
Answer:
| Feature | Allergy | Autoimmunity |
| Target | Harmless foreign substances (allergens). | Body's own tissues (self-antigens). |
| | |
| Response | Overreaction of immune system. | Misdirected immune attack. |
| Examples | Hay fever, food allergies. | Rheumatoid arthritis, type 1 diabetes. |
| Cause | Immune system mistakes harmless substances as threats. | Immune system fails to recognize self. |
In summary, allergy is an overreaction to foreign substances, while autoimmunity is an attack on self.
d. Cytotoxic T cells and helper T cells
Answer:
| Feature | Cytotoxic T Cells (CD8+) | Helper T Cells (CD4+) |
| Function | Directly kill infected/cancerous cells. | Coordinate immune response. |
| Mechanism | Release perforin and granzymes. | Secrete cytokines to activate B cells and cytotoxic T cells. |
| Recognition | Recognize antigens on MHC class I. | Recognize antigens on MHC class II. |
| Role | Cell-mediated immunity. | Master regulator of immunity. |
In summary, cytotoxic T cells kill, while helper T cells coordinate.
e. Plasma cells and memory B cells
Answer:
| Feature | Plasma Cells | Memory B Cells |
| Function | Produce and secrete antibodies. | Provide long-term immunity. |
| Lifespan | Short-lived (days to weeks). | Long-lived (years to decades). |
| Response | Immediate effector response. | Rapid secondary response upon re-exposure. |
| Origin | Differentiated from activated B cells. | Differentiated from activated B cells. |
In summary, plasma cells are antibody factories, while memory B cells provide lasting protection.
f. Primary and secondary immune response
Answer:
| Feature | Primary Response | Secondary Response |
| Onset | Slow (days to weeks). | Rapid (hours to days). |
| Magnitude | Lower antibody levels. | Higher antibody levels. |
| Antibody Class | Mainly IgM. | Mainly IgG. |
| Memory Cells | Formed. | Already present; rapidly activated. |
| Trigger | First exposure to antigen. | Re-exposure to same antigen. |
In summary, the secondary response is faster and stronger due to memory cells.
g. Innate immunity and acquired immunity
Answer:
| Feature | Innate Immunity | Acquired Immunity |
| Specificity | Non-specific. | Specific to pathogen. |
| | |
| Onset | Immediate. | Delayed (days). |
| Memory | None. | Yes. |
| Components | Barriers, phagocytes, inflammation. | B cells, T cells, antibodies. |
| Inheritance | Present at birth. | Develops after exposure. |
In summary, innate immunity is the first line of defense, while acquired immunity provides specific, long-lasting protection.
