Complement System Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Complement System. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Complement System Indian Medical PG Question 1: Which component is considered the central part of the complement pathway?
- A. C1 (complement component 1)
- B. C3 (complement component 3) (Correct Answer)
- C. C2 (complement component 2)
- D. C5 (complement component 5)
Complement System Explanation: ***C3***
- **C3** is considered the central component because all three major pathways of complement activation (classical, alternative, and lectin) converge at the point of **C3 activation**.
- Its cleavage product, **C3b**, is crucial for opsonization, formation of the C5 convertase, and initiating the assembly of the **membrane attack complex (MAC)**.
*C1 (complement component 1)*
- **C1** is the initial component of the **classical complement pathway** but does not play a direct role in the alternative or lectin pathways.
- Its primary function is to bind to **antibody-antigen complexes** or directly to pathogens to activate C4 and C2.
*C2 (complement component 2)*
- **C2** is a component of the **classical** and **lectin pathways**, acting as a substrate for C1s and MASP to form the C3 convertase.
- It is not involved in the initial activation of the **alternative pathway**.
*C5 (complement component 5)*
- **C5** is activated downstream of C3 and is a key component in the formation of the **membrane attack complex (MAC)**.
- While critical for pathogen lysis, its activation is dependent on the prior cleavage of **C3** into C3b.
Complement System Indian Medical PG Question 2: What is the classification of intelligence corresponding to an IQ score of 90-109?
- A. Below average
- B. Average (Correct Answer)
- C. Slightly below average
- D. Above average
Complement System Explanation: ***Average***
- An **IQ score** range of **90-109** is traditionally classified as **Average** intelligence.
- This range represents the **mean** and surrounding **standard deviation** of IQ scores in the general population.
*Below average*
- This classification usually corresponds to IQ scores in the range of **70-79** or **80-89**, depending on the specific scale.
- It does not represent the central tendency of the population's intelligence.
*Slightly below average*
- This category typically corresponds to IQ scores in the range of **80-89**.
- It falls just below the average range but is not as low as the "below average" classification.
*Above average*
- This classification is typically assigned to IQ scores that are in the range of **110-119** or higher.
- It signifies cognitive abilities that are greater than the majority of the population.
Complement System Indian Medical PG Question 3: Increased susceptibility to N. meningitidis infections is associated with deficiency of which complement component:
- A. C1-C4 deficiency
- B. C3 deficiency
- C. C5-C9 deficiency (Correct Answer)
- D. C2 deficiency
Complement System Explanation: ***C5-C9 deficiency***
- Deficiencies in **C5-C9 components** impair the formation of the **Membrane Attack Complex (MAC)**, which is crucial for lysing Gram-negative bacteria like **N. meningitidis**.
- Patients with MAC deficiencies are at significantly higher risk for recurrent invasive **N. meningitidis** infections.
*C1-C4 deficiency*
- Deficiencies in **C1-C4 components** primarily affect the **classical complement pathway** and are associated with increased susceptibility to **bacterial infections** and **immune complex diseases** (e.g., SLE).
- While these deficiencies compromise opsonization and inflammation, they are not specifically linked to recurrent **N. meningitidis** infections.
*C3 deficiency*
- **C3 deficiency** is a severe primary immunodeficiency leading to profound defects in complement activation via all pathways, affecting **opsonization** and the formation of the MAC.
- This deficiency causes severe recurrent **pyogenic infections** due to encapsulated bacteria but is not as specifically or commonly linked to **N. meningitidis** as deficiencies in the terminal pathway.
*C2 deficiency*
- **C2 deficiency** is the most common complement deficiency and primarily impacts the **classical pathway**, leading to impaired opsonization and immune complex clearance.
- It is often associated with recurrent infections (especially with encapsulated bacteria) and **lupus-like syndromes**, but not specifically increased susceptibility to **N. meningitidis** infections.
Complement System Indian Medical PG Question 4: Match the following drugs in Column A with their contraindications in Column B.
| Column A | Column B |
| :-- | :-- |
| 1. Morphine | 1. QT prolongation |
| 2. Amiodarone | 2. Thromboembolism |
| 3. Vigabatrin | 3. Pregnancy |
| 4. Estrogen preparations | 4. Head injury |
- A. A-1, B-3, C-2, D-4
- B. A-4, B-1, C-3, D-2 (Correct Answer)
- C. A-3, B-2, C-4, D-1
- D. A-2, B-4, C-1, D-3
Complement System Explanation: ***A-4, B-1, C-3, D-2***
- **Morphine** is contraindicated in **head injury** as it can increase intracranial pressure and mask neurological symptoms.
- **Amiodarone** is contraindicated in patients with **QT prolongation** due to its risk of inducing more severe arrhythmias like Torsades de Pointes.
- **Vigabatrin** is contraindicated during **pregnancy** due to its potential for teratogenicity and adverse effects on fetal development.
- **Estrogen preparations** are contraindicated in patients with a history of **thromboembolism** due to their increased risk of blood clot formation.
*A-1, B-3, C-2, D-4*
- This option incorrectly matches **Morphine** with QT prolongation and **Estrogen preparations** with head injury, which are not their primary contraindications.
- It also incorrectly links **Vigabatrin** with thromboembolism and **Amiodarone** with pregnancy.
*A-3, B-2, C-4, D-1*
- This choice incorrectly associates **Morphine** with pregnancy and **Vigabatrin** with head injury, which are not the most critical or direct contraindications.
- It also misaligns **Amiodarone** with thromboembolism and **Estrogen preparations** with QT prolongation.
*A-2, B-4, C-1, D-3*
- This option incorrectly matches **Morphine** with thromboembolism and **Amiodarone** with head injury, which are not their most significant contraindications.
- It also incorrectly links **Vigabatrin** with QT prolongation and **Estrogen preparations** with pregnancy.
Complement System Indian Medical PG Question 5: Hereditary angioneurotic edema is due to?
- A. Deficiency of C1 inhibitor (Correct Answer)
- B. Deficiency of NADPH oxidase
- C. Deficiency of MPO
- D. Deficiency of properdin
Complement System Explanation: ***Deficiency of C1 inhibitor***
- **Hereditary angioedema (HAE)** is caused by a genetic deficiency or dysfunction of the **C1 esterase inhibitor (C1-INH)** protein.
- C1-INH normally regulates the **complement system**, kinin system (mediating **bradykinin** release), and coagulation pathways, and its deficiency leads to uncontrolled activation and excessive bradykinin production, causing angioedema.
*Deficiency of NADPH oxidase*
- A deficiency in **NADPH oxidase** is associated with **Chronic Granulomatous Disease (CGD)**, a primary immunodeficiency characterized by recurrent bacterial and fungal infections due to impaired phagocytic oxidative burst.
- It does not cause angioedema, which involves fluid extravasation rather than impaired microbial killing.
*Deficiency of MPO*
- **Myeloperoxidase (MPO) deficiency** typically leads to mild to moderate impairment in the killing of certain microorganisms by phagocytes but is often asymptomatic or causes only recurrent candidal infections.
- It is not linked to the pathogenesis of angioedema, which involves dysregulation of vasoactive peptides.
*Deficiency of properdin*
- A deficiency in **properdin** affects the **alternative pathway of the complement system**, increasing susceptibility to **Neisseria infections**.
- While properdin is part of the complement system, its deficiency does not directly lead to the uncontrolled production of bradykinin, which is the primary mediator in angioedema due to C1-INH deficiency.
Complement System Indian Medical PG Question 6: Which of the following components are involved in non-IgE mediated anaphylactic reactions?
- A. Complement
- B. Ig G
- C. Ig M
- D. All of the options (Correct Answer)
Complement System Explanation: ***All of the options***
- **Non-IgE mediated anaphylactic reactions** can involve various immune components beyond IgE, including **IgG**, **IgM**, and the **complement system**.
- For instance, **IgG antibodies** can bind to mast cells or basophils and trigger degranulation, while **complement activation** can directly release anaphylatoxins, both leading to anaphylactoid symptoms.
*Ig G*
- While many anaphylactic reactions are **IgE-mediated**, **IgG antibodies** can also contribute to anaphylaxis, particularly in drug reactions or reactions to biologics.
- **IgG-mediated anaphylaxis** often involves immune complexes that activate mast cells or basophils through Fcγ receptors.
*Ig M*
- **IgM antibodies** are less commonly implicated in direct anaphylactic reactions compared to IgE or IgG.
- However, **IgM** can play a role in complex formation that activates the complement system, indirectly contributing to **anaphylactoid responses**.
*Complement*
- The **complement system** can be directly activated by certain drugs, physical stimuli, or immune complexes without the involvement of immunoglobulins.
- This activation releases **anaphylatoxins (C3a, C4a, C5a)**, which can directly degranulate mast cells and basophils, leading to symptoms mimicking true anaphylaxis.
Complement System Indian Medical PG Question 7: What is the primary effect of superantigens on T-cells?
- A. Polyclonal activation of T-cells leading to cytokine release (Correct Answer)
- B. Stimulation of B cells and antibody production
- C. Enhancement of phagocytosis by macrophages
- D. Activation of the complement system
Complement System Explanation: ***Polyclonal activation of T-cells leading to cytokine release***
- **Superantigens** bypass the normal antigen presentation pathway by binding directly to the **MHC class II molecule** and the **T-cell receptor (TCR) beta chain**, activating a large proportion of T-cells.
- This widespread T-cell activation results in a massive release of various **cytokines**, leading to systemic inflammation and conditions like **toxic shock syndrome**.
*Stimulation of B cells and antibody production*
- While B cells can be activated, the primary and most significant effect of superantigens is on T-cells, leading to **non-specific T-cell activation**.
- Superantigen-mediated T-cell activation does not directly lead to **antigen-specific B cell activation** and **antibody production** in the same manner as conventional antigens.
*Enhancement of phagocytosis by macrophages*
- Superantigens do not primarily enhance **macrophage phagocytosis**. Their main mechanism involves direct interaction with **APC MHC class II** and **TCRs**.
- Macrophages themselves can act as **antigen-presenting cells** in the superantigen pathway, but their phagocytic function is not the main target.
*Activation of the complement system*
- The complement system is primarily activated by **antibody-antigen complexes** or directly by pathogen surfaces, not directly by **superantigens**.
- While the inflammatory response from superantigens can indirectly affect other immune components, direct activation of the complement cascade is not their primary mechanism of action.
Complement System Indian Medical PG Question 8: Both antibody dependent and independent complement pathways converge on which complement component
- A. C8
- B. C1q
- C. C3 (Correct Answer)
- D. C5
Complement System Explanation: ***Correct: C3***
- Both the **classical** (antibody-dependent) and **alternative** (antibody-independent) complement pathways lead to the activation and cleavage of **C3** into C3a and C3b.
- This convergence on C3 is critical as **C3b** acts as a central opsonin and initiator of the downstream common pathway (terminal pathway).
- The **lectin pathway** also converges at C3, making it the central hub of complement activation.
*Incorrect: C8*
- **C8** is a component of the **membrane attack complex (MAC)**, which forms much later in the complement cascade and is downstream from C3 activation.
- While essential for cell lysis, C8 does not represent the initial point of convergence between the antibody-dependent and independent pathways.
*Incorrect: C1q*
- **C1q** is specifically involved only in the **classical pathway**, where it binds to antibody-antigen complexes or directly to pathogen surfaces.
- It plays no direct role in the **alternative pathway**, thus not a point of convergence for both pathways.
*Incorrect: C5*
- **C5** is activated downstream of C3 and initiates the formation of the **membrane attack complex (MAC)**, similar to C8.
- While central to the lytic phase, its activation occurs after the convergence at C3 and is not the initial point where the classical and alternative pathways meet.
Complement System Indian Medical PG Question 9: Which one of the following is a major component in activation of the complement alternative pathway?
- A. C2
- B. C3 (Correct Answer)
- C. C4
- D. C1
Complement System Explanation: ***C3***
- **C3** is a central component in all complement pathways. In the alternative pathway, spontaneous hydrolysis of **C3** leads to C3(H2O), initiating the formation of the **C3 convertase**.
- This **C3 convertase** (C3bBb) further cleaves more **C3** into C3a and C3b, amplifying the pathway and leading to downstream complement activation.
*C2*
- **C2** is a crucial component of the **classical** and **lectin pathways**, where it is cleaved by C1s or MASP-2, respectively, to form C2b and C2a.
- **C2a** then combines with C4b to form the **C3 convertase** (C4b2a) of these pathways; it does not play a direct role in initiating the alternative pathway.
*C4*
- **C4** is primarily involved in the **classical** and **lectin pathways**, where it is cleaved by C1s or MASP-2 to form C4a and C4b.
- **C4b** binds to pathogens or immune complexes and then associates with C2a to form the **C3 convertase** (C4b2a), which is not part of the alternative pathway initiation.
*C1*
- **C1** is the initiating complex of the **classical complement pathway** and is composed of C1q, C1r, and C1s.
- It recognizes and binds to antibody-antigen complexes or pathogen surfaces, but it has no direct role in the **alternative pathway activation**.
Complement System Indian Medical PG Question 10: Classical complement is activated by:
- A. C3 Convertase
- B. C1
- C. Ag-Ab complex (Correct Answer)
- D. IgA
Complement System Explanation: ***Ag-Ab complex***
- The **classical complement pathway** is initiated by the binding of **C1q** to an antigen-antibody complex, specifically involving **IgM** or certain subclasses of **IgG**.
- This binding triggers a cascade of events leading to the activation of the complement system, ultimately resulting in the **lysis of target cells**, **opsonization**, and **inflammation**.
*C3 Convertase*
- **C3 convertase** is an enzyme complex formed later in the complement cascade, responsible for cleaving C3 into C3a and C3b.
- While essential for all complement pathways, it is a **downstream effector** and not the initial activator of the classical pathway.
*C1*
- **C1** is a complex protein that includes C1q, C1r, and C1s. While C1 plays a crucial role in the classical pathway, it is **activated by** the antigen-antibody complex, not an independent activator.
- The activation sequence is: **Ag-Ab complex → C1q binding → C1 activation → cascade initiation**. Thus, the Ag-Ab complex is the primary trigger, and C1 is the responder.
*IgA*
- **IgA** primarily functions in mucosal immunity and is generally **not an activator** of the classical complement pathway.
- Instead, IgA can activate the **alternative complement pathway** under specific circumstances, but not the classical pathway through direct binding to C1q.
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