Immunology Practice Questions

Q: What are the changes in the variable region of immunoglobulins?

Idiotype. ***Idiotype*** - **Idiotype** refers to the unique set of antigenic determinants in the **variable region** of an antibody molecule, specifically within the **hypervariable regions (complementarity-determining regions, CDRs)**. - These unique determinants allow antibodies to recognize specific antigens and are generated by the specific **V(D)J gene rearrangements** in B cells. *Isotype* - **Isotype** refers to the constant region of an antibody, determining its class (e.g., **IgG, IgM, IgA, IgD, IgE**). - This region defines the antibody's effector functions and has nothing to do with the antigen-binding variability. *Allotype* - **Allotype** refers to minor genetic variations within the **constant region** of an antibody molecule within a species. - These variations are due to different alleles inherited from parents and are not associated with the variable region that binds to antigens. *Epitope* - An **epitope** is the specific part of an **antigen** that an antibody or T-cell receptor recognizes and binds to. - It is a feature of the antigen, not a change within the variable region of the immunoglobulin itself.

Q: What is the most common genetic factor associated with increased susceptibility to Neisseria infections?

Complement deficiency. ***Complement deficiency*** - Deficiencies in the **terminal complement pathway (C5-C9)**, particularly C5b-C9 (membrane attack complex, MAC), significantly increase susceptibility to disseminated *Neisseria* infections. - The MAC is crucial for lysing Gram-negative bacteria like *Neisseria meningitidis* and *Neisseria gonorrhoeae*, and its absence allows for uncontrolled bacterial proliferation. *Factor H deficiency* - **Factor H** is a regulatory protein of the alternative complement pathway, preventing its overactivation on host cells. - Its deficiency typically leads to conditions like **atypical hemolytic uremic syndrome (aHUS)** and **dense deposit disease**, not primarily increased susceptibility to *Neisseria* infections. *HLA B27* - **HLA-B27** is a human leukocyte antigen strongly associated with a group of autoimmune inflammatory diseases called **spondyloarthropathies**, such as ankylosing spondylitis. - It does not directly impact the immune response to *Neisseria* infections or increase susceptibility to them. *IgA deficiency* - **Selective IgA deficiency** is the most common primary immunodeficiency, characterized by low or absent IgA levels. - Individuals with IgA deficiency are more prone to **recurrent respiratory and gastrointestinal infections**, but not specifically disseminated *Neisseria* infections.

Q: Which of the following statements about interleukin-1 is false?

IL-1 inhibits IL-2 production by T-cells.. ***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.

Q: Rosette formation with sheep RBCs (SRBCs) indicates functioning of -

T-cells. ***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.

Q: Which of the following is considered the most professional antigen presenting cell (APC) in the immune system?

Dendritic cells. ***Dendritic cells*** - **Dendritic cells** are specialized for capture, processing, and presentation of antigens to T lymphocytes. - They are often referred to as the "**professional APCs**" due to their superior ability to initiate primary T cell responses. *B cells* - While B cells can present antigens, they are generally less efficient than **dendritic cells** and primarily serve to present antigens to **helper T cells** during secondary immune responses. - Their main role is **antibody production** after activation, not initiating primary T cell responses. *T cells* - **T cells** are effector cells of the adaptive immune system and recognize antigen presented by APCs; they do not typically function as antigen-presenting cells themselves. - Some T cells, like **gamma-delta T cells**, can present antigens, but this is not their primary role. *NK cells* - **Natural Killer (NK) cells** are part of the innate immune system and primarily target and kill infected or cancerous cells without prior sensitization. - They do not present antigens in the classical sense and are not considered professional APCs.

Q: Which cytokine activates macrophages?

IFN-γ. ***IFN-γ (Interferon-gamma)*** - **IFN-γ is the classic macrophage-activating cytokine**, enhancing phagocytic and antimicrobial functions - Promotes expression of **MHC class I and II molecules**, increasing antigen presentation capacity - Produced mainly by **Th1 cells and NK cells** during cell-mediated immunity - Key cytokine in defense against **intracellular pathogens** (mycobacteria, viruses) *IL-8* - **IL-8 is a chemokine** (cytokine subfamily) primarily involved in **neutrophil chemotaxis** - Recruits neutrophils to sites of infection or inflammation - Does not directly activate macrophages like IFN-γ - Important in acute inflammatory responses *PAF (Platelet-Activating Factor)* - **Not a cytokine** - it is a **phospholipid mediator** - Involved in allergic and inflammatory responses - Functions include **platelet aggregation**, **vasodilation**, and **bronchoconstriction** - While it affects immune responses, it doesn't function as a macrophage-activating cytokine *Leukotriene B4* - **Not a cytokine** - it is a **lipid mediator** (eicosanoid) derived from arachidonic acid - Primarily acts as a **chemoattractant for neutrophils** - Promotes neutrophil and monocyte adhesion and migration to inflammatory sites - Does not directly activate macrophages

Q: Which complement proteins are formed in the liver?

C2, C4. ***C2, C4*** - While **all complement proteins (C1-C9) are primarily synthesized in the liver**, this question (NEET PG 2012) expects this as the answer based on the context of **classical pathway activation**. - **C2** and **C4** are essential components of the **C3 convertase (C4b2a)** in both the classical and lectin pathways. - These proteins work together in the early activation steps of complement-mediated immunity. - **Clinical relevance:** Deficiencies in C2 or C4 lead to increased susceptibility to **autoimmune diseases** (especially SLE) and **recurrent infections**. *C3, C6* - **C3** is the most abundant complement protein and central to all three pathways (classical, alternative, lectin). - **C6** is part of the membrane attack complex (MAC: C5b-C6-C7-C8-C9). - Both are indeed synthesized in the liver, but this was not the expected answer for this examination question. *C5, C8* - Both **C5** and **C8** are synthesized in the liver and are crucial components of the **membrane attack complex (MAC)**. - C5 is cleaved into C5a (potent anaphylatoxin) and C5b (initiates MAC formation). - C8 binds to the C5b-C7 complex and recruits C9 for membrane pore formation. *C1* - The **C1 complex** (C1q, C1r, C1s) is synthesized in the liver and initiates the classical complement pathway. - C1q recognizes antibody-antigen complexes (IgG or IgM bound to antigen). - **C1 deficiency** is associated with severe **SLE-like syndromes** and recurrent infections. **Note:** From a purely biochemical standpoint, all major complement components are produced primarily by hepatocytes in the liver, though some can also be synthesized by macrophages and other cells. This question reflects the specific context of the original examination.

Q: Which immunoglobulin is the most efficient at activating the classical complement pathway?

IgM. ***IgM*** - **IgM** is a **pentamer** with **ten antigen-binding sites**, allowing it to bind multiple antigens on a surface - This **multivalency** enables formation of stable antigen-antibody complexes, creating an efficient platform for **C1q binding** - A **single IgM molecule** bound to antigen provides sufficient binding sites for activating C1q, making it the **most efficient** activator of the classical complement pathway - Its pentameric structure means it requires only **one molecule** to initiate complement activation *IgG* - IgG is a **monomer** and the **most abundant** serum immunoglobulin - Requires **at least two IgG molecules in close proximity** on an antigen surface to effectively activate the classical complement pathway - While it **can activate** the classical pathway, it is **less efficient per molecule** than pentameric IgM due to lower avidity for C1q *IgA* - Primarily functions in **mucosal immunity** (secretory IgA in saliva, tears, respiratory and GI tract) - **Poor activator** of the classical complement pathway - Can activate the **alternative pathway** of complement, but minimal role in classical pathway compared to IgM and IgG *IgD* - Primarily found on the **surface of naïve B lymphocytes** as a B cell receptor - Limited role as a **secreted antibody** in serum - **Does not activate** the complement pathway (neither classical nor alternative)

Q: Which cells are known to cause rosette formation with sheep red blood cells?

T cells. ***T cells*** - **T cells** are the classic cells known to form rosettes with sheep red blood cells, a phenomenon called **E-rosette formation** - This interaction is mediated by the **CD2 receptor** on human T cells binding to **CD58 (LFA-3)** on sheep red blood cells - E-rosette formation was historically used as a diagnostic test to identify and enumerate T cells before the advent of flow cytometry - This is a characteristic feature of **mature T cells** and was widely used in immunology laboratories *NK cells* - **NK cells** do NOT typically form rosettes with sheep red blood cells - NK cells lack the specific CD2-mediated interaction required for classical E-rosette formation - NK cells are identified by other markers such as CD16 and CD56, and by their ability to kill target cells without prior sensitization *Monocytes* - **Monocytes** do not form rosettes with sheep red blood cells - Their primary functions include phagocytosis, antigen presentation, and cytokine production - They are identified by surface markers like **CD14** and their characteristic morphology (large size, kidney-shaped nucleus) *All types of T cells* - While this option is technically correct since all mature T cells express CD2 and can form E-rosettes, the more conventional answer is simply **"T cells"** - Both CD4+ helper T cells and CD8+ cytotoxic T cells possess the CD2 receptor and can participate in rosette formation - The distinction between "T cells" and "All types of T cells" is subtle, but "T cells" is the standard textbook answer

Q: Which immunoglobulin is known as the pentameric immunoglobulin?

IgM. ***IgM*** - **IgM** is found as a **pentamer** in its secreted form, meaning it is composed of five immunoglobulin monomer units joined together. - This pentameric structure gives IgM a high valency, making it very effective at **binding multiple antigens** simultaneously and activating the **complement system**. *IgA* - **IgA** primarily exists as a **monomer** in serum and as a **dimer** in secretions like mucus, tears, and saliva. - Its main function is to provide **mucosal immunity**, protecting epithelial surfaces from pathogens. *IgG* - **IgG** is the most abundant immunoglobulin in serum and exists as a **monomer**. - It crosses the **placenta** to provide passive immunity to the fetus and is crucial for **opsonization** and neutralizing toxins and viruses. *IgE* - **IgE** is present in very low concentrations in serum and exists as a **monomer**. - It plays a critical role in **allergic reactions** and defense against **parasites** by binding to mast cells and basophils.

Question 1

What are the changes in the variable region of immunoglobulins?

Accepted Answer

Idiotype

Answer

Isotype

Answer

Epitope

Answer

Allotype

Question 2

What is the most common genetic factor associated with increased susceptibility to Neisseria infections?

Accepted Answer

Complement deficiency

Answer

HLA-B27

Answer

IgA deficiency

Answer

Factor H deficiency

Question 3

Which of the following statements about interleukin-1 is false?

Accepted Answer

IL-1 inhibits IL-2 production by T-cells.

Answer

IL-1 is an endogenous pyrogen.

Answer

The primary source of IL-1 is the monocyte-macrophage system.

Answer

IL-1 promotes acute phase protein synthesis in the liver.

Question 4

Rosette formation with sheep RBCs (SRBCs) indicates functioning of -

Accepted Answer

T-cells

Answer

B-cells

Answer

Neutrophils

Answer

Monocytes

Question 5

Which of the following is considered the most professional antigen presenting cell (APC) in the immune system?

Accepted Answer

Dendritic cells

Answer

B cells

Answer

T cells

Answer

NK cells

Question 6

Which cytokine activates macrophages?

Accepted Answer

IFN-γ

Answer

Leukotriene B4

Answer

IL-8

Answer

PAF

Question 7

Which complement proteins are formed in the liver?

Accepted Answer

C2, C4

Answer

C3, C6

Answer

C5, C8

Answer

C1

Question 8

Which immunoglobulin is the most efficient at activating the classical complement pathway?

Accepted Answer

IgM

Answer

IgA

Answer

IgG

Answer

IgD

Question 9

Which cells are known to cause rosette formation with sheep red blood cells?

Accepted Answer

T cells

Answer

Monocytes

Answer

NK cells

Answer

All types of T cells

Question 10

Which immunoglobulin is known as the pentameric immunoglobulin?

Accepted Answer

IgM

Answer

IgA

Answer

IgG

Answer

IgE

Immunology — MCQs

Immunology — MCQs

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