Microbiology
4 questionsSmallpox belongs to which genus of poxviruses?
When is the prozone phenomenon seen?
A patient with sore throat has a positive Paul Bunnell test, indicating infectious mononucleosis. The causative organism is?
Which of the following statements is true regarding T cell independent antigens?
NEET-PG 2012 - Microbiology NEET-PG Practice Questions and MCQs
Question 481: Smallpox belongs to which genus of poxviruses?
- A. Leporipoxvirus
- B. Orthopoxvirus (Correct Answer)
- C. Capripoxvirus
- D. Parapoxvirus
Explanation: ***Orthopoxvirus*** - **Smallpox** (caused by the **variola virus**) is a classic member of the Orthopoxvirus genus. - This genus includes other human pathogens like **monkeypox** and vaccinia virus (used in the smallpox vaccine). *Parapoxvirus* - This genus includes viruses like **Orf virus** (causing contagious pustular dermatitis in sheep and goats) and pseudocowpox virus. - These viruses typically cause milder, localized lesions and are morphologically distinct from orthopoxviruses. *Capripoxvirus* - This genus includes viruses primarily affecting livestock, such as **lumpy skin disease virus**, sheep pox virus, and goat pox virus. - They cause systemic infections and skin lesions in their respective animal hosts and are not associated with human disease like smallpox. *Leporipox virus* - This genus includes viruses that primarily infect rabbits and hares, such as **myxoma virus** and fibroma virus. - These viruses typically cause tumors or severe systemic disease in their rabbit hosts and are not known to infect humans.
Question 482: When is the prozone phenomenon seen?
- A. Same concentration of antibody and antigen
- B. Hyperimmune reaction
- C. In antigen excess to antibody
- D. Antibody excess to antigen (Correct Answer)
Explanation: ***Antibody excess to antigen*** - The **prozone phenomenon** occurs when there is a significant **excess of antibodies** relative to the antigen, leading to inhibition of lattice formation. - In this state, too many antibodies bind to individual antigen sites, preventing cross-linking and thus inhibiting visible **agglutination** or **precipitation**. *Same concentration of antibody and antigen* - This scenario typically represents the **zone of equivalence**, where optimal lattice formation and visible reaction (agglutination or precipitation) occur. - It is where the concentrations of antibody and antigen are balanced, leading to maximum complex formation. *In antigen excess to antibody* - This situation is known as the **postzone phenomenon**, where an excess of antigen prevents the formation of stable antibody-antigen complexes. - The antigen saturates the limited antibody sites, resulting in no or minimal visible reaction. *Hyperimmune reaction* - A hyperimmune reaction refers to an **exaggerated immune response**, often resulting from repeated exposure to an antigen. - While it involves high antibody levels, it is a clinical state rather than a specific phenomenon describing antibody-antigen ratios in *in vitro* tests.
Question 483: A patient with sore throat has a positive Paul Bunnell test, indicating infectious mononucleosis. The causative organism is?
- A. EBV (Correct Answer)
- B. Adenovirus
- C. CMV
- D. HSV (Herpes Simplex Virus)
Explanation: ***Correct: EBV*** - The **Paul-Bunnell test** (monospot test) detects **heterophile antibodies**, which are characteristic of acute **Epstein-Barr virus (EBV)** infection. - **EBV** is the primary causative agent of **infectious mononucleosis**, commonly known as "mono." *Incorrect: Adenovirus* - **Adenoviruses** can cause various infections, including **pharyngitis** and **conjunctivitis**, but are not associated with a positive **Paul-Bunnell test** or heterophile antibodies. - While it can cause sore throat, the presence of a **positive Paul-Bunnell test** differentiates it from EBV. *Incorrect: CMV* - **Cytomegalovirus (CMV)** can cause a mononucleosis-like syndrome, but it typically results in a **negative Paul-Bunnell test** (i.e., it is heterophile antibody-negative). - CMV mononucleosis is often seen in individuals who are **immunocompromised** or in infants as a congenital infection. *Incorrect: HSV (Herpes Simplex Virus)* - **Herpes simplex virus (HSV)** causes infections such as **oral herpes (cold sores)** and **genital herpes**, and in some cases, **pharyngitis**. - HSV infection is not associated with a positive **Paul-Bunnell test** or the production of heterophile antibodies.
Question 484: Which of the following statements is true regarding T cell independent antigens?
- A. They primarily activate T-cells.
- B. They primarily activate B-cells. (Correct Answer)
- C. They primarily activate macrophages.
- D. They primarily activate CD8+ T cells.
Explanation: ***Correct: They primarily activate B-cells*** - T-cell independent antigens are typically **polysaccharides** (TI-2) or **lipopolysaccharides** (TI-1) with repeating epitopes that can directly cross-link B cell receptors (BCRs) - This direct binding and cross-linking provide a strong enough signal to activate B cells and induce **antibody production** (mainly IgM) without the need for T cell help - They induce a rapid but limited immune response with minimal memory formation *Incorrect: They primarily activate T-cells* - T-cell independent antigens do not require processing and presentation by **MHC molecules**, which is essential for T cell activation - T cells recognize processed peptides presented by MHC, a mechanism not utilized by T-cell independent antigens - By definition, these antigens activate B cells **without** T cell involvement *Incorrect: They primarily activate macrophages* - While macrophages are antigen-presenting cells, their primary role in adaptive immunity is to process and present antigens to T cells - Macrophages are involved in **phagocytosis** and antigen processing, but are not the primary target cells for T-independent antigens - The key feature of TI antigens is direct B cell activation, not macrophage activation *Incorrect: They primarily activate CD8+ T cells* - **CD8+ T cells** are activated by processed antigens presented on **MHC class I molecules**, typically derived from intracellular pathogens - T-cell independent antigens do not utilize this pathway and are primarily involved in **humoral immunity** through direct B cell activation - TI antigens cannot activate CD8+ T cells as they bypass the T cell-dependent pathway entirely
Pediatrics
1 questionsCongenital varicella infection causes all except:
NEET-PG 2012 - Pediatrics NEET-PG Practice Questions and MCQs
Question 481: Congenital varicella infection causes all except:
- A. Macrocephaly (Correct Answer)
- B. Cortical atrophy
- C. Cicatrix
- D. Limb hypoplasia
Explanation: ***Macrocephaly*** - **Macrocephaly** is generally not a direct consequence of congenital varicella infection; rather, **microcephaly** due to brain damage is more commonly observed. - Congenital varicella typically causes destructive lesions leading to tissue loss, not increased head circumference. *Cortical atrophy* - **Cortical atrophy** results from the destructive effects of the virus on the developing brain, leading to **neuronal loss** and reduced brain volume. - This can manifest as **microcephaly**, an indirect but common finding associated with congenital varicella. *Cicatrix* - **Cicatrix** (zig-zag scarring) is a classic dermatological manifestation of congenital varicella, resulting from the virus's impact on developing skin. - These characteristic **skin lesions** are one of the most identifiable features of the syndrome. *Limb hypoplasia* - **Limb hypoplasia**, involving underdeveloped limbs, is a hallmark feature of congenital varicella, often due to **viral damage** to limb buds and associated neural structures. - This can lead to **bone shortening** and muscle atrophy in affected limbs.
Pharmacology
5 questionsWhat is Dinoprost?
Which diuretic exhibits paradoxical antidiuretic activity in diabetes insipidus?
Which of the following is the most common side effect of Cimetidine?
Romiplostim mimics which of the following receptors?
What is the mechanism of action of quinolones?
NEET-PG 2012 - Pharmacology NEET-PG Practice Questions and MCQs
Question 481: What is Dinoprost?
- A. Prostaglandin E2 (PGE2)
- B. Prostaglandin F2α (PGF2α) (Correct Answer)
- C. Prostaglandin I2 (PGI2)
- D. Prostaglandin E1 (PGE1)
Explanation: ***Prostaglandin F2α (PGF2α)*** - **Dinoprost** is the generic name for **Prostaglandin F2α**. - It works by stimulating **myometrial contractions** and promoting cervical ripening, making it useful in obstetrics. *Prostaglandin E2 (PGE2)* - **PGE2** is known as **Dinoprostone** and is also used for cervical ripening and labor induction. - While similar in function, **Dinoprostone** (PGE2) is distinct from **Dinoprost** (PGF2α). *Prostaglandin I2 (PGI2)* - **PGI2** is also known as **Prostacyclin** and acts as a potent **vasodilator** and **inhibitor of platelet aggregation**. - Its primary therapeutic uses are in conditions like **pulmonary hypertension**, which differs from Dinoprost's obstetric uses. *Prostaglandin E1 (PGE1)* - **PGE1** is also known as **Alprostadil** and is used to maintain the **patency of the ductus arteriosus** in neonates with certain congenital heart defects. - It is distinct from Dinoprost and has different clinical applications.
Question 482: Which diuretic exhibits paradoxical antidiuretic activity in diabetes insipidus?
- A. Thiazide diuretics (Correct Answer)
- B. Aldosterone antagonists (Spironolactone)
- C. Loop diuretics (Furosemide)
- D. Potassium-sparing diuretics (Triamterene)
Explanation: ***Thiazide diuretics*** - Thiazides cause a modest **volume depletion**, leading to increased proximal tubular reabsorption of water and solutes [1]. - They also lower the **glomerular filtration rate**, further reducing the amount of fluid delivered to the collecting ducts, thus paradoxically reducing urine output in diabetes insipidus [2]. - This effect is particularly useful in **nephrogenic diabetes insipidus**, where the kidneys cannot respond to ADH [2]. *Potassium-sparing diuretics (Triamterene)* - Triamterene is a **potassium-sparing diuretic** that blocks epithelial sodium channels in the late distal tubule and collecting duct. - It increases sodium and water excretion, which would worsen, not improve, the polyuria of diabetes insipidus. *Aldosterone antagonists (Spironolactone)* - Spironolactone is a **mineralocorticoid receptor antagonist** that increases sodium and water excretion while conserving potassium in the collecting duct. - Its primary action is to counteract aldosterone, and it does not exhibit the paradoxical antidiuretic effect seen with thiazides in diabetes insipidus. *Loop diuretics (Furosemide)* - Loop diuretics like furosemide act on the **thick ascending limb of the loop of Henle** to inhibit sodium, potassium, and chloride reabsorption. - They cause significant diuresis and would **exacerbate the polyuria** in patients with diabetes insipidus, rather than improving it.
Question 483: Which of the following is the most common side effect of Cimetidine?
- A. Diarrhea
- B. Impotence
- C. CNS effects (confusion, dizziness) (Correct Answer)
- D. Gynaecomastia
Explanation: ***CNS effects (confusion, dizziness)*** - **Cimetidine** is a **H2-receptor antagonist** that can cross the **blood-brain barrier**, leading to **central nervous system (CNS) side effects**. - These effects, including **confusion, dizziness**, and **headache**, are more common in elderly patients or those with renal impairment due to reduced drug clearance. *Impotence* - While **cimetidine** can cause **endocrine effects** due to its anti-androgenic activity, **impotence** is a less common side effect compared to CNS disturbances. - It results from the drug's interference with **testosterone metabolism** and binding to **androgen receptors**. *Gynaecomastia* - **Gynaecomastia** is a known **endocrine side effect** of **cimetidine** due to its **anti-androgenic activity** and promotion of **prolactin release**. - However, CNS side effects are generally encountered more frequently in clinical practice. *Diarrhea* - **Gastrointestinal side effects** like **diarrhea** are possible with various medications, but they are not the most common or characteristic side effect of **cimetidine**. - Nausea and constipation are also reported, but generally less frequently than CNS effects.
Question 484: Romiplostim mimics which of the following receptors?
- A. IL 6
- B. IL 8
- C. PGE 1
- D. Thrombopoietin (Correct Answer)
Explanation: ***Thrombopoietin*** - **Romiplostim** is a **thrombopoietin receptor agonist**, meaning it binds to and activates the **thrombopoietin receptor** [1]. - This activation mimics the effect of endogenous thrombopoietin, stimulating the production of **platelets** in the bone marrow [2].*IL 6* - **Interleukin-6 (IL-6)** is a cytokine involved in inflammation, immune response, and hematopoiesis, but it is not the primary target of romiplostim. - While IL-6 can influence platelet production indirectly, romiplostim directly targets the thrombopoietin pathway.*IL 8* - **Interleukin-8 (IL-8)** is a chemokine primarily involved in neutrophil chemotaxis and inflammation. - It plays no direct role in the mechanism of action of romiplostim.*PGE 1* - **Prostaglandin E1 (PGE1)** is a lipid compound with various effects, including vasodilation and inhibition of platelet aggregation. - Romiplostim's mechanism of action is distinct from that of prostaglandins, as it specifically targets platelet production rather than platelet function or vascular tone.
Question 485: What is the mechanism of action of quinolones?
- A. Inhibit tetrahydrofolate reductase
- B. Inhibit DNA gyrase (Correct Answer)
- C. Bind to 30S ribosomal subunit
- D. Bind to bacterial cell membrane
Explanation: ***Inhibit DNA gyrase*** - Quinolones, particularly **fluoroquinolones**, exert their bactericidal effect by targeting **bacterial DNA gyrase (topoisomerase II)** and **topoisomerase IV**. - This inhibition prevents the uncoiling and replication of bacterial DNA, leading to cell death. *Bind to 30S ribosomal subunit* - This mechanism is characteristic of **aminoglycosides** and **tetracyclines**, which disrupt bacterial protein synthesis. - Quinolones do not interfere with ribosomal function but rather with **DNA replication**. *Bind to bacterial cell membrane* - This is the mechanism of action for **polymyxins** and **daptomycin**, which disrupt the integrity of the bacterial cell membrane. - Quinolones specifically target **intracellular enzymes** involved in DNA handling. *Inhibit tetrahydrofolate reductase* - This enzyme name in the option is technically imprecise; **trimethoprim** actually inhibits **dihydrofolate reductase**, which is part of the **sulfonamide-trimethoprim (Bactrim)** combination. - This pathway is involved in **folic acid synthesis**, crucial for bacterial DNA and RNA production, a mechanism distinct from quinolones.