Immunology Practice Questions

Q: Which of the following best describes the nature of complement components in the immune system?

Proteins. ***Proteins*** - The complement system is a complex network of over 30 **proteins** that play a crucial role in innate immunity. - These proteins are synthesized mainly by the **liver** and circulate in the blood in an inactive form until activated by pathogens or immune complexes. - Major components include **C1-C9**, factors **B, D, H, I**, and properdin. *Lipids* - Lipids are primarily involved in cell membrane structure, energy storage, and signaling, not as direct components of the complement system. - While they can be targets or modulators of complement activity, they are not the components themselves. *Lipoproteins* - Lipoproteins are complexes of lipids and proteins involved in transporting fats in the blood. - They are not the molecular components of the complement cascade. *Polysaccharide* - Polysaccharides are complex carbohydrates, often found on the surface of bacteria and fungi. - They are **recognized by** the complement system for activation (e.g., LPS on gram-negative bacteria activates the alternative pathway), but they are not the complement components themselves.

Q: Which of the following best describes complement components in the immune system?

Glycoproteins. ***Glycoproteins*** - Complement components are primarily **proteins** that have **carbohydrate chains** attached to them. - This glycosylation is crucial for their structure, stability, and proper function within the immune cascade. - **All complement proteins are glycoproteins**, making this the most comprehensive and accurate classification. *Lipoproteins* - **Lipoproteins** are complexes of proteins and lipids, primarily involved in transporting fats in the blood. - While some immune cells might interact with lipoproteins, complement proteins themselves are not classified as such. *Nucleoproteins* - **Nucleoproteins** are proteins associated with nucleic acids (DNA or RNA), such as histones or ribosomal proteins. - Complement components are not directly involved in binding or interactions with nucleic acids as their primary function. *Metalloproteins* - **Metalloproteins** are proteins that contain a metal ion co-factor, essential for their biological activity. - While some complement components (like C3 convertases) do require metal ions such as **Mg²⁺** or **Ca²⁺** for catalytic activity, this is not a defining characteristic of all complement proteins. - Since not all complement proteins are metalloproteins, but all are glycoproteins, **glycoproteins** is the better answer.

Q: Activation of naïve B lymphocytes by protein antigens is?

T cell dependent. ***T cell dependent*** - Activation of naive B lymphocytes by **protein antigens** requires help from **helper T cells (CD4+ T cells)**. - B cells act as **antigen-presenting cells (APCs)**, processing and presenting protein antigens via MHC class II to T cells. - This interaction leads to **T cell help** through cytokines and CD40-CD40L signaling, resulting in **class switching, somatic hypermutation, and memory B cell formation**. *T Cell independent* - **T-cell-independent activation** of B lymphocytes typically occurs in response to **non-protein antigens**, such as polysaccharides, lipopolysaccharides (LPS), or lipids. - These antigens have **repetitive epitopes** that can cross-link multiple B cell receptors simultaneously. - This activation does not require T cell help and often leads to a **weaker, shorter-lived immune response** with limited class switching and no memory B cells. *NK cell dependent* - **NK cells** (Natural Killer cells) are part of the innate immune system and primarily involved in **killing infected or cancerous cells**. - They do not directly participate in the activation of naive B lymphocytes in response to protein antigens. - NK cells function independently of antigen-specific recognition. *NK cell independent* - This term is **not relevant** to the classification of B cell activation mechanisms. - The key distinction in B cell activation is whether it is **T cell dependent or T cell independent**, not whether it involves NK cells. - NK cells are not part of the adaptive immune response pathway for B cell activation by protein antigens.

Q: Which of the following is considered a non-professional antigen presenting cell?

Fibroblast cells. ***Fibroblast cells*** - **Fibroblast cells** are considered **non-professional antigen-presenting cells** as they do not constitutively express **MHC class II molecules** or **co-stimulatory molecules (B7, CD80/CD86)**. - Under **chronic inflammatory conditions**, fibroblasts can be induced to express MHC class II and present antigens, but they lack the specialized machinery for efficient **T-cell activation** that professional APCs possess. - They represent a classic example of non-professional APCs alongside endothelial cells, keratinocytes, and other tissue cells. *Endothelial cells* - **Endothelial cells** can express **MHC class II molecules** and co-stimulatory molecules during **inflammation or infection**. - They function as **non-professional APCs** (or semi-professional APCs) and can activate T cells in specific contexts, particularly in vascular immunity. - Also considered a valid example of non-professional APCs. *Epidermal cells* - **Epidermal cells** (specifically **keratinocytes**) can express **MHC class II molecules** under inflammatory conditions and present antigens to T cells. - They act as **non-professional APCs** in the context of skin immunity. - Like fibroblasts and endothelial cells, they can present antigens but are less efficient than professional APCs (dendritic cells, macrophages, B cells). *Red blood cells* - **Red blood cells** are **anucleate cells** that completely **lack MHC molecules** (both class I and class II). - RBCs **cannot present antigens** and are not classified as antigen-presenting cells of any type. - They are structurally incapable of antigen presentation due to absence of nuclei and cellular machinery.

Q: All of the following statements are true regarding neutrophil extracellular trapping (NET) except for which of the following?

Mitochondrial DNA is seen. ***Mitochondrial DNA is seen*** - NETs (Neutrophil Extracellular Traps) are made primarily of **nuclear chromatin**, not mitochondrial DNA [2]. - The main purpose of NETs is to trap and kill pathogens, focusing on **nuclear genetic material** rather than mitochondrial components. *It is detected in blood during sepsis* - NETs can indeed be found in the **circulation during sepsis**, serving as a defense mechanism against infections. - Their presence in blood indicates an **active immune response**, particularly in severe systemic infections. *It is produced in response to bacterial infection* - NET formation is a known response to **bacterial infections**, as neutrophils deploy them to capture and neutralize pathogens. - This process helps in controlling infections, showcasing the importance of NETs in **innate immunity**. *It is chromatin with antibacterial enzymes* - NETs consist primarily of **decondensed chromatin**, embedded with **antimicrobial proteins** and enzymes to combat pathogens [1][2]. - This characteristic underscores their role in targeting and eliminating invading microorganisms effectively. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 91-92. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 92-93.

Q: The image of an immunoglobulin is shown below. Which type of immunoglobulin is it?

Immunoglobulin A (IgA). ***Immunoglobulin A (IgA)*** - The image depicts two Y-shaped immunoglobulin monomers linked by a central purple component, which represents the **J-chain**, and enveloped by a yellow structure, which represents the **secretory component**. This **dimeric** structure with a secretory component is characteristic of secretory IgA. - **Secretory IgA** is primarily found in mucosal secretions such as saliva, tears, breast milk, and gastrointestinal fluids, where it plays a crucial role in **mucosal immunity** by preventing pathogen adhesion. *Immunoglobulin G (IgG)* - IgG exists as a **monomer** (single Y-shaped unit) in its functional form. - It is the most abundant immunoglobulin in serum and plays a major role in **secondary immune responses** and can cross the placenta. *Immunoglobulin M (IgM)* - In serum, IgM typically exists as a **pentamer**, meaning five Y-shaped units are joined together by a J-chain, forming a star-like structure. - It is the first antibody produced in a **primary immune response** and is effective in complement activation. *Immunoglobulin E (IgE)* - IgE exists as a **monomer** and is primarily associated with **allergic reactions** and defense against parasites. - It binds to receptors on mast cells and basophils, triggering immune responses upon allergen exposure.

Q: Which interleukin is primarily responsible for inducing IgE production from B cells?

IL-4. ***IL-4*** - **IL-4** is the primary cytokine responsible for promoting B cell differentiation into **plasma cells** that produce **IgE antibodies**. - It plays a crucial role in the development of **allergic reactions** by stimulating IgE class switching. *IL-1* - **IL-1** is a pro-inflammatory cytokine primarily involved in the **innate immune response**, fever, and acute phase reactions. - It does not directly induce IgE production but can modulate immune responses in a broader context. *IL-3* - **IL-3** is a cytokine that primarily supports the growth and differentiation of **hematopoietic stem cells** in the bone marrow. - It is crucial for the development of various blood cell lineages but is not directly involved in IgE class switching. *IL-1 and IL-3* - While both **IL-1** and **IL-3** have important roles in immunity and hematopoiesis, neither directly induces **IgE production** from B cells. - **IL-4** is the specific and most significant interleukin for this function.

Q: Which protein is produced by B lymphocytes and not synthesized in the liver?

Immunoglobulins. ***Immunoglobulins*** - **B lymphocytes** differentiate into **plasma cells**, which are the primary producers of **immunoglobulins (antibodies)**. - The liver is not involved in the synthesis of immunoglobulins; their production is a key function of the **immune system**. *Acute phase proteins* - **Acute phase proteins** are primarily synthesized in the **liver** in response to inflammation. - While they are part of the immune response, they are not produced by **B lymphocytes**. *Serum albumin* - **Serum albumin** is the most abundant protein in plasma and is exclusively synthesized by the **liver**. - It plays a crucial role in maintaining **oncotic pressure** and transporting various substances, but is not produced by B lymphocytes. *Hormones in plasma* - **Hormones in plasma** are diverse chemical messengers produced by various **endocrine glands** throughout the body. - While the liver can metabolize some hormones, it is not their primary site of synthesis, nor are B lymphocytes.

Q: What is one of the primary functions of Interleukin-1 (IL-1)?

Acts as an endogenous pyrogen. ***Acts as an endogenous pyrogen*** - **Interleukin-1 (IL-1)** is a key **pro-inflammatory cytokine** that plays a central role in the body's response to infection and injury. - One of its primary functions is to act as an **endogenous pyrogen**, meaning it can induce **fever** by promoting prostaglandin synthesis in the hypothalamus, thereby raising the body's set point temperature. *Inhibits T cell proliferation* - IL-1 generally **enhances T cell activation and proliferation**, particularly in conjunction with other signals, rather than inhibiting it. - **Immunosuppressive cytokines** like **TGF-β** or **IL-10** are known to inhibit T cell proliferation. *Suppresses antibody production* - IL-1 is generally involved in **promoting B cell activation** and **antibody production**, either directly or indirectly through its effects on T helper cells. - Cytokines like **IL-10** can sometimes suppress certain aspects of antibody production but IL-1 is not known for this role. *Reduces inflammatory cell recruitment* - IL-1 is a potent **pro-inflammatory cytokine** that actively **promotes the recruitment** of immune cells, such as neutrophils and monocytes, to sites of inflammation. - It does this by inducing the expression of **adhesion molecules** and **chemokines** on endothelial cells.

Q: What is required for precipitation in comparison to agglutination?

Soluble antigen. ***Soluble antigen*** - **Precipitation reactions** involve the interaction of antibodies with **soluble antigens** to form a detectable precipitate. - Unlike **agglutination**, which involves particulate antigens (e.g., cells), precipitation requires the antigen to be dissolved in a solution. *Increased temperature* - Most immunologic reactions, including precipitation and agglutination, are typically performed at **physiological temperatures** (e.g., 37°C) or room temperature. - An **increased temperature** is not a specific requirement that differentiates precipitation from agglutination. *Specific cofactor* - While some complex immunologic reactions might require **cofactors**, neither precipitation nor agglutination inherently requires a specific cofactor to occur. - The primary components are **antigen** and **antibody**. *Lower pH* - Both precipitation and agglutination reactions are sensitive to pH and typically occur within a **narrow pH range** close to neutral (e.g., pH 7.0-7.4). - A **lower pH** (acidic environment) could lead to antibody denaturation or non-specific aggregation, ultimately hindering the reaction rather than being a requirement.

Question 1

Which of the following best describes the nature of complement components in the immune system?

Accepted Answer

Proteins

Answer

Lipids

Answer

Lipoproteins

Answer

Polysaccharide

Question 2

Which of the following best describes complement components in the immune system?

Accepted Answer

Glycoproteins

Answer

Lipoproteins

Answer

Nucleoproteins

Answer

Metalloproteins

Question 3

Activation of naïve B lymphocytes by protein antigens is?

Accepted Answer

T cell dependent

Answer

T Cell independent

Answer

NK cell dependent

Answer

NK cell independent

Question 4

Which of the following is considered a non-professional antigen presenting cell?

Accepted Answer

Fibroblast cells

Answer

Endothelial cells

Answer

Epidermal cells

Answer

Red blood cells

Question 5

All of the following statements are true regarding neutrophil extracellular trapping (NET) except for which of the following?

Accepted Answer

Mitochondrial DNA is seen

Answer

It is detected in blood during sepsis

Answer

It is chromatin with antibacterial enzymes

Answer

It is produced in response to bacterial infection

Question 6

The image of an immunoglobulin is shown below. Which type of immunoglobulin is it?

Accepted Answer

Immunoglobulin A (IgA)

Answer

Immunoglobulin G (IgG)

Answer

Immunoglobulin M (IgM)

Answer

Immunoglobulin E (IgE)

Question 7

Which interleukin is primarily responsible for inducing IgE production from B cells?

Accepted Answer

IL-4

Answer

IL-1 and IL-3

Answer

IL-3

Answer

IL-1

Question 8

Which protein is produced by B lymphocytes and not synthesized in the liver?

Accepted Answer

Immunoglobulins

Answer

Acute phase proteins

Answer

Serum albumin

Answer

Hormones in plasma

Question 9

What is one of the primary functions of Interleukin-1 (IL-1)?

Accepted Answer

Acts as an endogenous pyrogen

Answer

Reduces inflammatory cell recruitment

Answer

Inhibits T cell proliferation

Answer

Suppresses antibody production

Question 10

What is required for precipitation in comparison to agglutination?

Accepted Answer

Soluble antigen

Answer

Increased temperature

Answer

Specific cofactor

Answer

Lower pH

Immunology — MCQs

Immunology — MCQs

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