All are true regarding the development of T-cells, except?
Rosette formation with sheep RBCs (SRBCs) indicates functioning of -
Cytolytic activity of membrane attack complex is modulated by ?
Which of the following statements about interleukin-1 is false?
Which of the following is a superantigen ?
What is the primary use of the Hybridoma technique?
An adolescent male developed vomiting and diarrhea 1 hour after having food from a restaurant. The most likely pathogen is?
Which of the following bacteria is known to exhibit antigenic variation?
Most common organism causing ventilator associated pneumonia -
Which fungus is commonly known as golden yellow jelly fungus?
NEET-PG 2013 - Microbiology NEET-PG Practice Questions and MCQs
Question 71: All are true regarding the development of T-cells, except?
- A. T-cells are formed in bone marrow
- B. In lymph nodes, T-cells are found in paracortical area
- C. Maturation of T-cells take place in thymus
- D. T-cells are located in mantle layer of spleen (Correct Answer)
Explanation: ***T-cells are located in mantle layer of spleen*** - The **mantle layer** (or marginal zone) of the spleen is primarily associated with **B-lymphocytes**, which are involved in antibody production. - While T-cells are present in the spleen, they are predominantly found in the **periarteriolar lymphoid sheath (PALS)**, which is part of the white pulp, rather than the mantle layer. *T-cells are formed in bone marrow* - **Hematopoietic stem cells** in the **bone marrow** are the progenitors of all blood cells, including lymphocytes. - These stem cells differentiate into **lymphoid stem cells**, which then travel to the thymus to become T-cells. *Maturation of T-cells take place in thymus* - **T-cell precursors** migrate from the bone marrow to the **thymus**, where they undergo a complex process of differentiation and selection. - In the thymus, T-cells acquire their **T-cell receptors (TCRs)** and undergo positive and negative selection to ensure they are self-MHC restricted and tolerant to self-antigens. *In lymph nodes, T-cells are found in paracortical area* - The **paracortical area** (or paracortex) of the lymph node is the **T-cell zone**, rich in T-lymphocytes and dendritic cells. - This region is crucial for the interaction between T-cells and antigen-presenting cells, initiating adaptive immune responses.
Question 72: Rosette formation with sheep RBCs (SRBCs) indicates functioning of -
- A. T-cells (Correct Answer)
- B. B-cells
- C. Neutrophils
- D. Monocytes
Explanation: ***T-cells*** - **T-cells** possess specific receptors, like **CD2** on their surface, that can bind to ligands on sheep red blood cells (SRBCs). - This binding leads to the formation of characteristic **rosettes**, where SRBCs cluster around the T-lymphocytes, indicating functional T-cells. *B-cells* - **B-cells** primarily function in **humoral immunity** by producing antibodies and do not typically form rosettes with sheep RBCs. - While B-cells have surface receptors, they are not CD2 and thus do not facilitate this specific type of rosette formation. *Neutrophils* - **Neutrophils** are **phagocytic cells** involved in innate immunity, primarily combating bacterial and fungal infections. - They lack the specific surface receptors (like CD2) required to form rosettes with sheep RBCs. *Monocytes* - **Monocytes** are precursors to macrophages and dendritic cells, involved in phagocytosis and antigen presentation. - They do not possess the necessary surface markers to form rosettes with sheep RBCs.
Question 73: Cytolytic activity of membrane attack complex is modulated by ?
- A. Factor I
- B. Factor B
- C. Factor S (vitronectin) (Correct Answer)
- D. Factor H
Explanation: ***Correct Option: Factor S (vitronectin)*** - Vitronectin (S-protein) is a **plasma protein** that directly modulates the **cytolytic activity of the membrane attack complex (MAC)**. - It binds to the **C5b-7 complex** in the fluid phase, preventing its insertion into target cell membranes and thereby blocking the formation of the complete, functional MAC. - By inhibiting membrane insertion of C5b-7, vitronectin prevents the subsequent binding of **C8 and C9**, which are essential for the cytolytic pore formation. - This is a **direct modulation** of MAC's cytolytic activity at the MAC assembly stage. *Incorrect Option: Factor H* - Factor H is a regulatory protein that controls the **alternative pathway** of complement activation by promoting degradation of **C3b**. - By degrading C3b, Factor H prevents formation of **C5 convertase**, thereby reducing downstream MAC formation. - However, Factor H acts **early in the complement cascade** and does not directly modulate the cytolytic activity of already-formed MAC components. - Its effect is on **preventing MAC formation**, not on modulating MAC's cytolytic function itself. *Incorrect Option: Factor I* - Factor I is a **serine protease** that cleaves and inactivates C3b and C4b, requiring cofactors like Factor H or C4bp. - Like Factor H, it regulates complement activation **upstream** of MAC formation. - It does not directly interact with or modulate the cytolytic activity of the MAC. *Incorrect Option: Factor B* - Factor B is a component of the **alternative pathway C3 convertase** (C3bBb). - It **promotes complement activation** rather than modulating MAC's cytolytic activity. - Factor B functions early in the cascade and has no direct role in regulating MAC function.
Question 74: Which of the following statements about interleukin-1 is false?
- A. IL-1 is an endogenous pyrogen.
- B. The primary source of IL-1 is the monocyte-macrophage system.
- C. IL-1 inhibits IL-2 production by T-cells. (Correct Answer)
- D. IL-1 promotes acute phase protein synthesis in the liver.
Explanation: ***IL-1 inhibits IL-2 production by T-cells*** - This statement is false because **IL-1** actually **enhances the production of IL-2** by T-cells, which is crucial for T-cell proliferation and immune response. - **IL-1 acts synergistically with IL-6 and TNF-α** to promote inflammation and immune cell activation, where IL-2 plays a key role. *The primary source of IL-1 is the monocyte-macrophage system* - This statement is true; **monocytes and macrophages** are the main producers of **IL-1α and IL-1β** upon activation by various stimuli. - Other cells, such as neutrophils, dendritic cells, and endothelial cells, can also produce IL-1, but monocytes and macrophages are the predominant source. *IL-1 is an endogenous pyrogen* - This statement is true; **IL-1** is a potent **endogenous pyrogen** that acts on the hypothalamus to induce fever, a hallmark of the acute phase response. - It triggers prostaglandin synthesis in the hypothalamus, leading to an elevation in the body's thermoregulatory set point. *IL-1 promotes acute phase protein synthesis in the liver* - This statement is true; **IL-1** is a key mediator that stimulates **hepatocytes** to produce **acute phase proteins**, such as C-reactive protein and serum amyloid A. - This hepatic response is part of the innate immune system's effort to control infection and inflammation.
Question 75: Which of the following is a superantigen ?
- A. Cholera toxin
- B. Diphtheria toxin
- C. TSST (Correct Answer)
- D. Vero-cytoxin
Explanation: ***TSST*** - **Toxic Shock Syndrome Toxin-1 (TSST-1)** is a classic example of a superantigen produced by *Staphylococcus aureus*. - Superantigens **bind directly to MHC class II molecules and T-cell receptors (TCRs)** outside of the antigen-binding groove, leading to non-specific activation of a large percentage of T cells and a massive release of cytokines. *Cholera toxin* - **Cholera toxin** is an exotoxin produced by *Vibrio cholerae* that causes massive fluid secretion in the intestine by **activating adenylate cyclase** in enterocytes. - It functions by **ADP-ribosylating the Gs alpha subunit**, leading to constitutive activation of cyclic AMP production, but it is not a superantigen. *Diphtheria toxin* - **Diphtheria toxin**, produced by *Corynebacterium diphtheriae*, inhibits protein synthesis in eukaryotic cells by **ADP-ribosylating elongation factor-2 (EF-2)**. - This action leads to cell death and the characteristic pseudomembrane formation in diphtheria, but it does not act as a superantigen. *Vero-cytoxin* - **Vero-cytoxin** (also known as Shiga toxin or Shiga-like toxin) is produced by *E. coli* O157:H7 and other Shiga toxin-producing *E. coli* (STEC). - It inhibits protein synthesis by **cleaving ribosomal RNA**, primarily causing damage to intestinal cells and renal endothelial cells, but it is not a superantigen.
Question 76: What is the primary use of the Hybridoma technique?
- A. Monoclonal antibodies (Correct Answer)
- B. Antigen
- C. Specific antibodies
- D. Cytokines
Explanation: ***Monoclonal antibodies*** - The **hybridoma technique** is primarily used to produce **monoclonal antibodies (MAbs)**, which are highly specific antibodies derived from a single B-cell clone. - These antibodies recognize a **single epitope** on an antigen, providing exceptional specificity and uniformity. - The technique involves **fusing a B-lymphocyte** (antibody-producing cell) with a **myeloma cell** (immortal cancer cell) to create a hybridoma that continuously produces identical antibodies. - This is the **gold standard** for producing large quantities of identical, highly specific antibodies for diagnostic and therapeutic use. *Specific antibodies* - While monoclonal antibodies are indeed specific, this term is **too vague** and could refer to any antibody with specificity, including polyclonal antibodies. - **Polyclonal antibodies** are also specific but are produced through conventional immunization, not the hybridoma technique. - The defining characteristic of the hybridoma technique is that it produces **monoclonal** (single clone) antibodies, not just "specific" ones. *Antigen* - An **antigen** is a molecule that elicits an immune response and is used to immunize animals during antibody production. - However, antigens are the **input** for antibody production, not the **product** of the hybridoma technique. *Cytokines* - **Cytokines** are signaling molecules involved in immune cell communication and regulation. - They are not produced by the hybridoma technique, which is specifically designed for **antibody production**.
Question 77: An adolescent male developed vomiting and diarrhea 1 hour after having food from a restaurant. The most likely pathogen is?
- A. Clostridium perfringens
- B. Vibrio parahaemolyticus
- C. Staphylococcus aureus (Correct Answer)
- D. Salmonella
Explanation: ***Staphylococcus aureus*** - The rapid onset of symptoms (within 1 hour) strongly suggests **pre-formed toxin ingestion**, which is characteristic of *Staphylococcus aureus* food poisoning. - While the typical incubation period is **1-6 hours** (average 2-4 hours), onset within 1 hour can occur with **high toxin loads** in contaminated food. - **Vomiting** is often the predominant symptom, occurring shortly after consuming contaminated food, which distinguishes it from other bacterial causes. *Clostridium perfringens* - Onset of symptoms caused by *Clostridium perfringens* is typically **8-16 hours** after ingestion, which is much longer than observed here. - It primarily causes **diarrhea and abdominal cramps** due to toxin production in the intestine, with minimal vomiting. *Vibrio parahaemolyticus* - Symptoms usually appear **4-96 hours** (average 12-24 hours) after consuming contaminated seafood, which is a longer incubation period than described. - It typically causes **watery diarrhea**, abdominal cramps, nausea, and occasional vomiting, but not within 1 hour. *Salmonella* - The incubation period for *Salmonella* infection is typically **6-72 hours** (average 12-36 hours), making it highly unlikely for symptoms to appear within 1 hour. - **Diarrhea, fever, and abdominal cramps** are common with *Salmonella*, but rapid-onset vomiting from pre-formed toxin is not its mechanism.
Question 78: Which of the following bacteria is known to exhibit antigenic variation?
- A. Yersinia
- B. Bordetella
- C. Brucella
- D. Borrelia (Correct Answer)
Explanation: ***Borrelia*** - *Borrelia* species, particularly *Borrelia burgdorferi* (causing **Lyme disease**), are known for extensive **antigenic variation** of their outer surface proteins (Osps), especially OspC. - This variation helps the bacteria evade the host's immune response, contributing to persistent infection. *Yersinia* - While *Yersinia* species produce various virulence factors, including proteins that interfere with immune cell function, they are not primarily known for the type of rapid and extensive **antigenic variation**seen in *Borrelia*. - Their immune evasion strategies often involve modifying host cell signaling pathways and resisting phagocytosis. *Bordetella* - *Bordetella pertussis*, causative agent of **whooping cough**, varies its expression of adhesins and toxins through **phase variation**, which is a form of phenotypic switching. - However, this is distinct from the frequent and sequential changes in surface antigens (antigenic variation) observed in *Borrelia*. *Brucella* - *Brucella* species are **intracellular pathogens** that primarily evade the immune system by surviving and replicating within host cells. - They do not typically engage in significant **antigenic variation** of their surface components as a primary immune evasion mechanism.
Question 79: Most common organism causing ventilator associated pneumonia -
- A. Legionella
- B. Pneumococcus
- C. Pseudomonas (Correct Answer)
- D. Coagulase negative staphylococcus
Explanation: ***Pseudomonas*** - **Pseudomonas aeruginosa** is one of the most common causes of **ventilator-associated pneumonia (VAP)**, particularly in **late-onset VAP** (≥5 days) and in patients with prolonged mechanical ventilation, prior antibiotic exposure, or underlying lung disease. - Its ability to form **biofilms** and its intrinsic antibiotic resistance contribute to its prevalence in hospital-acquired infections. - Along with **Staphylococcus aureus** (especially MRSA), Pseudomonas is consistently among the leading causes of VAP in ICU settings. *Legionella* - **Legionella** is a less common cause of VAP and is typically associated with contaminated water sources, manifesting as **Legionnaires' disease**. - It usually causes severe, rapidly progressive pneumonia and is often harder to culture than other bacteria. *Pneumococcus* - **Streptococcus pneumoniae (Pneumococcus)** is the most common cause of **community-acquired pneumonia (CAP)**, but it is less frequently implicated in VAP. - While it can cause severe pneumonia and may be seen in **early-onset VAP**, its incidence in late-onset VAP is lower compared to Gram-negative rods like Pseudomonas. *Coagulase negative staphylococcus* - **Coagulase-negative Staphylococci** (e.g., *Staphylococcus epidermidis*) are common **contaminants** in cultures and primarily cause device-related infections, such as those associated with central venous catheters. - They are rarely a primary cause of VAP, as they typically have low virulence in the respiratory tract.
Question 80: Which fungus is commonly known as golden yellow jelly fungus?
- A. T. tonsurans
- B. Tremella mesenterica (Correct Answer)
- C. Epidermophyton floccosum
- D. T. mentagrophytes
Explanation: ***Tremella mesenterica*** - This fungus is commonly referred to as **golden yellow jelly fungus** or **witch's butter** due to its distinctive golden-yellow, gelatinous, and brain-like appearance. - It is a **jelly fungus** that typically grows on dead hardwood branches, especially after rain, and is known for its pliable, quivering texture. *T. tonsurans* - This refers to **Trichophyton tonsurans**, a dermatophytic fungus primarily known for causing **tinea capitis** (ringworm of the scalp). - Its common name relates to its effect on hair, causing breakage and a "black dot" appearance, rather than a golden yellow, jelly-like form. *Epidermophyton floccosum* - This is a dermatophytic fungus that specifically causes infections of the **skin and nails**, particularly **tinea pedis** (athlete's foot) and **tinea cruris** (jock itch). - It does not produce a fruiting body and is not described as a jelly-like fungus. *T. mentagrophytes* - This refers to **Trichophyton mentagrophytes**, another common dermatophyte responsible for various superficial fungal infections, including **tinea pedis**, **tinea corporis**, and **tinea unguium**. - Its clinical presentation is not that of a golden yellow jelly fungus.