Immunopathology Practice Questions

Q: Which of the following is a secondary mediator of anaphylaxis?

Leukotriene B4. ***Leukotriene B4*** - **Leukotrienes** are synthesized from **arachidonic acid** via the 5-lipoxygenase pathway during an anaphylactic reaction, making them **secondary mediators**. - **Leukotriene B4** is a potent **chemoattractant for neutrophils** and contributes to the inflammatory response in anaphylaxis. - Note: The **cysteinyl leukotrienes (LTC4, LTD4, LTE4)** are the primary leukotrienes responsible for **bronchoconstriction** and increased vascular permeability in anaphylaxis. *Protease* - **Proteases**, such as **tryptase**, are **preformed mediators** stored in mast cell granules and are rapidly released upon activation. - They are considered **primary mediators** due to their immediate release following mast cell degranulation. *Histamine* - **Histamine** is a classic **preformed mediator** stored in mast cell granules and is one of the first substances released during anaphylaxis. - Its rapid release causes immediate effects such as **vasodilation**, **bronchoconstriction**, and increased vascular permeability. *Eosinophilic chemotactic factor* - **Eosinophilic chemotactic factor (ECF-A)** is a **preformed mediator** stored in mast cell granules. - While it attracts eosinophils, it is released immediately from granules upon mast cell activation, classifying it as a **primary mediator**.

Q: Microscopically, epimyoepithelial islands are typically seen in:

Sjögren's syndrome. ***Sjögren's syndrome*** - **Epimyoepithelial islands** are a characteristic histopathological feature of **Sjögren's syndrome**, particularly in affected salivary glands. [1] - These islands represent **benign lymphoepithelial lesions** where ducts are surrounded by lymphocytes, eventually forming true islands. *Epithelial-myoepithelial carcinoma* - This is a **malignant salivary gland tumor** with dual differentiation, but it typically presents as distinct inner epithelial and outer myoepithelial layers around ducts or cords, not as true "islands." - While it involves both epithelial and myoepithelial cells, its arrangement and neoplastic nature differ from the benign epimyoepithelial islands of Sjögren's. *Myoepithelioma* - This is a **benign tumor composed predominantly of myoepithelial cells**, often appearing in various morphological patterns (spindle, plasmacytoid, epithelioid, clear cell). - It does not typically form the well-defined **lymphoepithelial islands** seen in Sjögren's, as its characteristic is the proliferation of myoepithelial cells in a different architectural pattern. *Mucoepidermoid carcinoma* - This is a common **malignant salivary gland tumor** characterized by a mixture of mucin-producing cells, epidermoid cells, and intermediate cells. - Its histological features are distinct and do not include the formation of **epimyoepithelial islands**, which are diagnostically specific to Sjögren's syndrome. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 235-236.

Q: Hyperacute rejection occurs within:-

Minutes to hours. ***Minutes to hours*** - **Hyperacute rejection** is a rapidly occurring complication post-transplant, characterized by its onset within minutes to hours after **organ reperfusion** [1]. - This type of rejection is mediated by pre-formed **recipient antibodies** that recognize donor antigens, leading to immediate graft damage [1]. *12 hours* - While plausible, 12 hours is a bit too broad as **hyperacute rejection** primarily begins much sooner, typically within the first few hours [1]. - This timeframe might overlap with the initial stages of **acute cellular rejection**, which typically occurs days to weeks later [1]. *24 hours* - **Hyperacute rejection** is almost always observed and causes graft failure well before the 24-hour mark, if it is going to happen. - Rejection occurring within this extended period is more indicative of **accelerated acute rejection** rather than true hyperacute rejection. *6 hours* - While hyperacute rejection certainly can occur within 6 hours, "minutes to hours" better captures the immediate onset, often within seconds or minutes [1]. - Some cases of **hyperacute rejection** can be so rapid that the 6-hour mark would be considered a late presentation. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 241-242.

Q: Gene not involved in SCID:

BTK. ***BTK*** - **Bruton's tyrosine kinase (BTK)** is associated with **X-linked agammaglobulinemia (XLA)**, a primary immunodeficiency characterized by the absence of mature B cells and significantly reduced antibody production. While it causes severe immune deficiency, it is not a direct cause of **SCID**. - XLA results in recurrent bacterial infections due to an inability to produce antibodies, rather than the severe combined T and B cell dysfunction seen in SCID. *ZAP70* - **ZAP70** deficiency is a cause of **SCID**. It leads to impaired T-cell receptor signaling, resulting in profound functional T-cell lymphopenia. - Patients with ZAP70 deficiency have normal numbers of CD4 T cells but very low or absent CD8 T cells, and their T cells are functionally impaired, leading to severe immunodeficiency. *IL2RG* - The **IL2RG** gene encodes the common gamma chain (γc), a crucial component of several **interleukin receptors (IL-2, IL-4, IL-7, IL-9, IL-15, IL-21)**. [1] - Mutations in IL2RG cause **X-linked SCID (X-SCID)**, the most common form of SCID, leading to a block in T-cell and NK-cell development due to defective cytokine signaling. [1] *JAK3* - **Janus kinase 3 (JAK3)** is a tyrosine kinase that associates with the **common gamma chain (γc)** and is essential for cytokine signaling downstream of the γc-containing receptors. [1] - **JAK3 deficiency** results in an **autosomal recessive form of SCID**, clinically indistinguishable from X-SCID, with impaired T-cell and NK-cell development due to defective cytokine signaling. [1] **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 247-248.

Q: Choose the correct option regarding graft rejection.

CD4 and CD8 both play a role in graft rejection. ***CD4 and CD8 both play a role in graft rejection*** - **CD4+ T cells** (helper T cells) recognize donor MHC class II molecules and differentiate into effector cells that produce cytokines, promoting inflammation and activating other immune cells involved in rejection - **CD8+ T cells** (cytotoxic T lymphocytes, CTLs) recognize donor MHC class I molecules and directly kill donor cells in the graft, leading to tissue destruction - Both T cell subsets are crucial for initiating and mediating different aspects of the immune response against transplanted organs *CD8 only plays a role in graft rejection* - This is incorrect because while **CD8+ T cells** are vital for direct cytotoxicity, **CD4+ T cells** are also essential for orchestrating the overall immune response - **CD4+ T cells** provide help to B cells and CD8+ T cells, and their cytokines can also directly injure graft tissue *CD4 only plays a role in graft rejection* - This is incorrect because although **CD4+ T cells** are critical for initiating and amplifying the immune response through cytokine production and activation of other cells, **CD8+ T cells** are directly responsible for killing graft cells - Both cell types contribute significantly to the complex pathophysiology of graft rejection

Q: Which of the following disorders presents with repeated catalase positive infections?

CGD. ***CGD*** - Chronic Granulomatous Disease (CGD) is characterized by a defect in **NADPH oxidase**, preventing phagocytes from producing a **respiratory burst** to kill certain bacteria and fungi. - Patients with CGD are particularly susceptible to infections by **catalase-positive organisms** because these organisms degrade hydrogen peroxide, which CGD phagocytes rely on for killing. *Chediak higashi syndrome* - This syndrome involves defective lysosomal trafficking, leading to impaired neutrophil chemotaxis and degranulation, resulting in recurrent infections, but not specifically to **catalase-positive organisms**. - Other features include **partial albinism**, peripheral neuropathy, and normal respiratory burst. *SCID* - Severe Combined Immunodeficiency (SCID) involves a profound defect in both **T-cell and B-cell immunity**, leading to severe and recurrent infections by a wide range of pathogens, not limited to catalase-positive ones [1]. - Patients typically present in infancy with **failure to thrive**, opportunistic infections, and lack of lymphoid tissue [1]. *X linked hypogammaglobulinemia* - Also known as **Bruton's agammaglobulinemia**, this disorder involves a defect in B-cell maturation, leading to the absence of antibodies and recurrent bacterial infections [1]. - The infections are typically with **encapsulated bacteria** and are not specifically linked to catalase-positive organisms [1].

Q: A patient with recurrent infections has a defect in the NADPH oxidase complex. Which condition is most likely?

Chronic granulomatous disease. ***Chronic granulomatous disease*** - This condition is characterized by a defect in the **NADPH oxidase complex**, impairing the generation of **reactive oxygen species** and leading to recurrent, severe infections [1]. - Patients are highly susceptible to infections with **catalase-positive organisms** like *Staphylococcus aureus* and fungi [1]. *Chediak-Higashi syndrome* - This is an **autosomal recessive disorder** characterized by a defect in lysosomal trafficking, leading to impaired phagosome-lysosome fusion and giant lysosomes. - It presents with **oculocutaneous albinism**, recurrent pyogenic infections, and peripheral neuropathy. *Leukocyte adhesion deficiency* - This immune deficiency is caused by defects in **integrins**, preventing leukocytes from adhering to endothelial cells and migrating to sites of infection. - It typically manifests as recurrent bacterial infections, impaired wound healing, and **delayed umbilical cord separation**. *Wiskott-Aldrich syndrome* - This is an **X-linked recessive disorder** characterized by a classic triad of **thrombocytopenia**, **eczema**, and recurrent infections. - It involves defects in the **WASP protein**, affecting cytoskeleton rearrangement in hematopoietic cells.

Question 1

Which of the following is a secondary mediator of anaphylaxis?

Accepted Answer

Leukotriene B4

Answer

Protease

Answer

Histamine

Answer

Eosinophilic chemotactic factor

Question 2

Microscopically, epimyoepithelial islands are typically seen in:

Accepted Answer

Sjögren's syndrome

Answer

Epithelial-myoepithelial carcinoma

Answer

Myoepithelioma

Answer

Mucoepidermoid carcinoma

Question 3

All are true about autoimmune disease except:

Accepted Answer

Higher incidence among males

Answer

T cells recognize self-antigen

Answer

Polyclonal B cell activation

Answer

Hashimoto's thyroiditis is an example

Question 4

Hyperacute rejection occurs within:-

Accepted Answer

Minutes to hours

Answer

12 hours

Answer

24 hours

Answer

6 hours

Question 5

Gene not involved in SCID:

Accepted Answer

BTK

Answer

ZAP70

Answer

IL2RG

Answer

JAK3

Question 6

Serum sickness is mediated by which type of hypersensitivity?

Accepted Answer

Type III

Answer

Type II

Answer

Type IV

Answer

Type I

Question 7

Choose the correct option regarding graft rejection.

Accepted Answer

CD4 and CD8 both play a role in graft rejection

Answer

None of the options

Answer

CD8 only plays a role in graft rejection

Answer

CD4 only plays a role in graft rejection

Question 8

Which of the following disorders presents with repeated catalase positive infections?

Accepted Answer

CGD

Answer

Chediak higashi syndrome

Answer

SCID

Answer

X linked hypogammaglobulinemia

Question 9

A patient with recurrent infections has a defect in the NADPH oxidase complex. Which condition is most likely?

Accepted Answer

Chronic granulomatous disease

Answer

Chediak-Higashi syndrome

Answer

Leukocyte adhesion deficiency

Answer

Wiskott-Aldrich syndrome

Question 10

Which type of hypersensitivity reaction is involved in allergic contact dermatitis?

Accepted Answer

Type IV

Answer

Type I

Answer

Type II

Answer

Type III

Immunopathology — MCQs

Immunopathology — MCQs

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