NEET-PG 2015 Practice Questions

Q: Which human IgG subclass has the highest serum concentration?

IgG1. ***IgG1*** - **IgG1** constitutes approximately **60-70%** of the total IgG in human serum, making it the most abundant subclass. - Its high concentration reflects its crucial role in **neutralizing toxins**, agglutinating viruses, and opsonizing bacteria for phagocytosis. *IgG2* - **IgG2** makes up about **20-30%** of total IgG and is primarily important in protecting against **polysaccharide-encapsulated bacteria**. - While significant, its serum concentration is notably lower than that of IgG1. *IgG3* - **IgG3** is the least abundant IgG subclass, accounting for only **5-8%** of total IgG, and is characterized by a shorter half-life. - Despite its low concentration, it is highly efficient in activating the **complement system** due to its flexible hinge region. *IgG4* - **IgG4** comprises approximately **3-6%** of total IgG and is unique for its ability to undergo **Fab arm exchange**, leading to bispecific antibodies. - It does not activate complement and is often associated with allergy and protection against parasitic infections, but its concentration is significantly less than IgG1.

Q: Which of the following does not stimulate active immunity?

Transplacental antibody transfer in newborn. ***Transplacental antibody transfer in newborn*** - This is a form of **passive immunity**, where pre-formed **antibodies from the mother** are transferred to the newborn, providing immediate but temporary protection. - It does not involve the newborn's own immune system generating an immune response or creating **memory cells**. *Subclinical infection* - Even without overt symptoms, a **natural infection** exposes the immune system to pathogens, triggering an active immune response and generating **memory cells**. - This leads to **long-term immunity** against future exposures to the same pathogen. *Clinical infection* - A **symptomatic natural infection** involves the immune system actively responding to the pathogen, producing antibodies and **memory cells**. - This process is the basis of **naturally acquired active immunity** and provides durable protection. *Vaccination* - Vaccines contain weakened or inactive forms of pathogens, or their components, which stimulate the immune system to produce **antibodies** and **memory cells** without causing disease. - This is an example of **artificially acquired active immunity**, providing long-lasting protection.

Q: Which of the following is a specific feature of acquired immunity?

Immunological memory. ***Immunological memory*** - A key characteristic of **acquired immunity** is the ability to "remember" previous encounters with specific pathogens. - This memory leads to a more rapid and robust immune response upon subsequent exposure to the same pathogen. - This is the **defining feature** that distinguishes acquired immunity from innate immunity. *Affected by genetic makeup* - While genetic makeup can influence the *efficiency* of the acquired immune system, it is not a **specific feature** that distinguishes it from innate immunity. - **Both innate and acquired immunity** are affected by genetic factors, determining baseline resistance and immune response capability. *No antigen exposure* - **Acquired immunity** is specifically characterized by its *dependence* on antigen exposure to develop specific responses. - The phrase "no antigen exposure" describes how the **innate immune system** functions, providing immediate, non-specific protection without prior contact with a pathogen. *Immediate response* - **Innate immunity** provides an immediate, non-specific response to pathogens. - **Acquired immunity** takes time to develop (days to weeks) after initial antigen exposure, but provides a faster response upon re-exposure due to immunological memory.

Q: Lattice phenomenon is seen in which of the following?

Precipitation test. ***Precipitation test*** - The **lattice phenomenon** describes the formation of an interconnected network of antigen-antibody complexes, which is essential for visible precipitation to occur. - This phenomenon dictates that optimal precipitation requires a specific **antigen-to-antibody ratio**; an excess of either can lead to false-negative results due to soluble immune complexes (prozone or postzone effects). *Complement fixation test* - This test relies on the **binding of complement** to antigen-antibody complexes, leading to the lysis of indicator red blood cells if complement is not fixed. - It is a **two-stage test** that measures the consumption of complement, not the direct observation of a lattice. *None of the options* - This option is incorrect because the **precipitation test** clearly demonstrates the lattice phenomenon. - The formation of a visible precipitate is a direct result of antigen-antibody lattice formation. *Neutralization reaction* - Neutralization involves antibodies binding to toxins or viruses, **blocking their biological activity** rather than forming a visible precipitate. - It is a **functional assay** that measures the ability of antibodies to inhibit harmful effects, not the formation of large immune complexes.

Q: To which part of an antigen do monoclonal antibodies specifically bind?

Specific epitope on the antigen. ***Specific epitope on the antigen*** - Monoclonal antibodies are designed to recognize and bind to a **unique, specific region** on an antigen, known as an **epitope**. - This high specificity is crucial for their clinical applications, such as targeted therapies and diagnostic tests. *Both the epitope and the paratope* - The **epitope** is the part of the antigen, while the **paratope** is the part of the antibody that binds to the epitope. - An antibody binds to an epitope, not to both itself and its own binding site. *None of the options* - This option is incorrect because there is a correct answer among the choices provided, which accurately describes the binding site of monoclonal antibodies. *Part of the antibody that binds to the epitope* - This describes the **paratope**, which is the antigen-binding site on the antibody, not the part of the antigen to which the antibody binds. - The question specifically asks about the part of the antigen.

Q: What type of immunity is primarily associated with the administration of transfer factor?

Adoptive immunity. ***Adoptive immunity (Correct)*** - **Transfer factor** consists of small, dialyzable molecules extracted from immune T lymphocytes of an immune donor - Its administration transfers **cell-mediated immunity** from donor to recipient, which defines adoptive immunity - This represents transfer of **immune cells or their products** (not antibodies), providing antigen-specific cellular immunity - Also called **adoptive immunotherapy** or adoptive transfer *Artificial passive immunity (Incorrect)* - Involves the **transfer of pre-formed antibodies** (e.g., antitoxins, immunoglobulins, antiserum) from an immune individual or animal - Provides **immediate but temporary humoral protection** - Does NOT transfer cellular immunity - this is the key distinction from adoptive immunity - Examples: Anti-rabies immunoglobulin, anti-tetanus serum *Natural active immunity (Incorrect)* - Occurs when an individual is **naturally exposed to an antigen** (infection) and produces their own antibodies and immune cells - The host's own immune system **actively responds** to develop long-lasting immunity - Example: Immunity after recovering from measles or chickenpox *Artificial active immunity (Incorrect)* - Achieved through **vaccination** with attenuated, inactivated, or subunit antigens - The recipient's body is **actively stimulated** to produce protective immunity - Provides long-lasting protection through immunological memory

Q: Which of the following tests is not classified as an in vivo test?

Elek's gel precipitation test. ***Elek's gel precipitation test*** - This test is an **in vitro** method used to detect the production of **diphtheria toxin** by *Corynebacterium diphtheriae* strains in a lab setting, not within a living organism. - It involves the precipitation of toxin and antitoxin in an agar gel, forming visible lines. *Schick test* - The Schick test is an **in vivo** test used to determine susceptibility to **diphtheria** by injecting diphtheria toxin subcutaneously and observing for a localized inflammatory reaction. - A positive reaction (inflammation) indicates a lack of protective antitoxin antibodies. *Lepromin test* - The Lepromin test is an **in vivo** test used to assess the type of **leprosy** a patient has and to evaluate their cell-mediated immune response to *Mycobacterium leprae*. - It involves the intradermal injection of lepromin antigen and observing for a delayed hypersensitivity reaction. *Tuberculin test* - Also known as the **Mantoux test**, this is an **in vivo** test used to screen for exposure to **tuberculosis** by injecting purified protein derivative (PPD) intradermally. - A positive reaction indicates a **cell-mediated immune response** to *Mycobacterium tuberculosis*.

Q: In a patient presenting with fever and suspected systemic infection, which of the following specimens is the most appropriate for the isolation of microorganisms in laboratory diagnosis?

Blood culture for isolation of bacteria. ***Blood culture for isolation of bacteria*** - For **systemic infection** and **fever**, **blood culture** is the most direct method to isolate and identify the causative microorganism disseminated throughout the body. - It helps guide **appropriate antibiotic therapy** by determining the pathogen's **susceptibility profile**. *Stool sample in cases of gastroenteritis* - This specimen is appropriate for diagnosing **gastrointestinal infections** where the pathogen primarily affects the digestive tract. - It is not the primary choice for suspected **systemic infection** unless GI symptoms are prominent and dissemination is suspected. *Throat swab for suspected pharyngitis* - A throat swab is specific for diagnosing **pharyngitis** or upper **respiratory tract infections**, localizing the infection to the pharynx. - It would not sufficiently identify a **systemic infection**, as the pathogen may not be present in the throat in such cases. *Urine sample for urinary tract infection* - A urine sample is indicated for diagnosing **urinary tract infections (UTIs)**, where the pathogen is concentrated in the urinary system. - While a UTI can lead to systemic symptoms, a urine sample alone is insufficient to confirm a generalized systemic infection unless the infection has specifically localized there.

Q: Which condition is not associated with complement deficiency?

Membranous nephritis. Membranous nephritis - Membranous nephritis is associated with immune complex deposition rather than complement deficiencies. [1] - The disease is characterized by thickening of the glomerular basement membrane without significant complement involvement. [1] PNH - Paroxysmal nocturnal hemoglobinuria (PNH) is due to a defect in the GPI-anchor leading to complement-mediated hemolysis. - Complement activation plays a critical role in the destruction of red blood cells in this condition. Hereditary angioedema - Hereditary angioedema is caused by deficiencies in C1 inhibitor, leading to uncontrolled activation of complement. - This results in edema episodes, directly linked to complement pathway dysregulation. SLE - Systemic lupus erythematosus (SLE) involves complement consumption due to autoantibody formation against nuclear antigens. - The disease often presents with hypocomplementemia, indicating complement system involvement.

Q: Indirect Coombs test detects:

Antibodies in the serum. ***Antibodies in the serum*** - The **indirect Coomb's test** is designed to detect the presence of **antibodies** against red blood cells (RBCs in the serum) before transfusion or during pregnancy [1]. - It is crucial in identifying **hemolytic disease of the newborn** (HDN) and ensuring safe blood transfusions [1]. *Antibodies attached to RBC Surface* - This scenario describes the **direct Coomb's test**, which identifies antibodies that are already bound to **RBCs**. - Direct testing assesses conditions like **autoimmune hemolytic anemia**, not the serum. *Antigens attached to RBC Surface* - This option suggests evaluating **antigens** present on the surface of RBCs, which is not the purpose of the indirect Coomb's test. - Antigens are important in blood typing and compatibility assessments, but this test focuses on antibodies. *Antigens in the serum* - Indirect Coomb's does not detect **antigens** but rather the **antibodies** related to those antigens. - Additionally, serum testing for antigens is not a standard procedure for assessing transfusion compatibility. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 627-628.

Question 1

Which human IgG subclass has the highest serum concentration?

Accepted Answer

IgG1

Answer

IgG2

Answer

IgG3

Answer

IgG4

Question 2

Which of the following does not stimulate active immunity?

Accepted Answer

Transplacental antibody transfer in newborn

Answer

Clinical infection

Answer

Vaccination

Answer

Subclinical infection

Question 3

Which of the following is a specific feature of acquired immunity?

Accepted Answer

Immunological memory

Answer

Affected by genetic makeup

Answer

No antigen exposure

Answer

Immediate response

Question 4

Lattice phenomenon is seen in which of the following?

Accepted Answer

Precipitation test

Answer

Complement fixation test

Answer

None of the options

Answer

Neutralization reaction

Question 5

To which part of an antigen do monoclonal antibodies specifically bind?

Accepted Answer

Specific epitope on the antigen

Answer

None of the options

Answer

Both the epitope and the paratope

Answer

Part of the antibody that binds to the epitope

Question 6

What type of immunity is primarily associated with the administration of transfer factor?

Accepted Answer

Adoptive immunity

Answer

Natural active immunity

Answer

Artificial active immunity

Answer

Artificial passive immunity

Question 7

Which of the following tests is not classified as an in vivo test?

Accepted Answer

Elek's gel precipitation test

Answer

Schick test

Answer

Tuberculin test

Answer

Lepromin test

Question 8

In a patient presenting with fever and suspected systemic infection, which of the following specimens is the most appropriate for the isolation of microorganisms in laboratory diagnosis?

Accepted Answer

Blood culture for isolation of bacteria

Answer

Stool sample in cases of gastroenteritis

Answer

Throat swab for suspected pharyngitis

Answer

Urine sample for urinary tract infection

Question 9

Which condition is not associated with complement deficiency?

Accepted Answer

Membranous nephritis

Answer

SLE

Answer

PNH

Answer

Hereditary angioedema

Question 10

Indirect Coombs test detects:

Accepted Answer

Antibodies in the serum

Answer

Antibodies bound to RBC Surface

Answer

Antigens bound to RBC Surface

Answer

Antigens in the plasma

NEET-PG 2015

Microbiology

Pathology