Immunopathology Practice Questions

Q: HLA-mismatched transplant is not a problem in which of the following diseases?

Bare lymphocyte syndrome. **Bare lymphocyte syndrome (Correct)** - **Bare Lymphocyte Syndrome** (BLS) is characterized by a failure to express **MHC Class I (Type I)** or **MHC Class II (Type II)** molecules on the cell surface, crucial for antigen presentation. - The absence of functional MHC in the recipient means their cells cannot effectively present the donor's HLA antigens, minimizing host immune rejection (host-versus-graft rejection) and allowing for the successful use of **HLA-mismatched transplants**. *Wiskott-Aldrich syndrome (Incorrect)* - This X-linked immunodeficiency involves the **WASp gene** and affects the cytoskeleton of hematopoietic cells, leading to defects in **T-cell function** and a high risk of autoimmune disease. - Since the patient's capacity for MHC presentation is generally intact, standard severe **Graft-versus-Host Disease (GvHD)** is a major risk following mismatched transplant, necessitating stringent HLA matching. *Job's syndrome (Incorrect)* - Job's syndrome (Hyper-IgE syndrome) is typically caused by mutations in **STAT3**, impairing signal transduction necessary for Th17 cell differentiation and resulting in defective neutrophil chemotaxis. - This syndrome does not eliminate the ability of the recipient's cells to express and utilize MHC molecules; therefore, an **HLA-matched donor** is required to prevent transplant rejection and GvHD. *Chediak-Higashi syndrome (Incorrect)* - Caused by a mutation in the **LYST gene**, leading to defective lysosomal trafficking, which primarily affects phagocytes and pigment cells. - Although it is an immunodeficiency, the fundamental mechanisms for T-cell recognition of foreign alloantigens (such as mismatched HLA) are functional, making a severe **HLA mismatch** highly problematic and usually fatal.

Q: A person was brought to the emergency department with facial swelling, itching, and hypotension following a bee sting. The mentioned clinical features are due to the increase in which immunoglobulin?

IgE. IgE - The symptoms of **facial swelling, itching, and hypotension** following a bee sting are characteristic of an immediate hypersensitivity reaction, specifically **anaphylaxis**, which is predominantly mediated by **IgE antibodies** [1]. - **IgE** binds to mast cells and basophils, and upon re-exposure to the allergen (bee venom), triggers the release of potent inflammatory mediators like **histamine**, causing vasodilation, increased vascular permeability, and smooth muscle contraction [1], . *IgG* - **IgG** antibodies are primarily involved in secondary immune responses, conferring long-term immunity, and neutralizing toxins and viruses [1]. - While IgG can be involved in some hypersensitivity reactions (Type II and Type III), it is not the primary immunoglobulin responsible for the acute, systemic symptoms of **anaphylaxis** from a bee sting [1]. *IgA* - **IgA** is the main immunoglobulin found in mucosal secretions, such as those in the gastrointestinal, respiratory, and genitourinary tracts, providing mucosal immunity. - It does not play a significant role in immediate hypersensitivity reactions or the systemic symptoms described in this scenario. *IgM* - **IgM** is the first antibody produced during a primary immune response and is important for activating the complement system and agglutinating antigens [1]. - It is not directly implicated in the pathogenesis of **Type I hypersensitivity reactions** like the anaphylactic response to a bee sting. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 208-213.

Q: A 34-year-old female medical professional who works for a non-governmental organization visits her primary care provider for a routine health check-up. She made a recent trip to Sub-Saharan Africa where she participated in a humanitarian medical project. Her medical history and physical examination are unremarkable. A chest radiograph and a tuberculin skin test (PPD) are ordered. The chest radiograph is performed at the side and the PPD reaction measures 12 mm after 72 hours. Which of the following mechanisms is involved in the skin test reaction?

Th1-mediated delayed-type hypersensitivity. ***Th1-mediated delayed-type hypersensitivity*** - The **tuberculin skin test (PPD)** is a classic example of a **Type IV hypersensitivity reaction**, which is mediated by **T-helper 1 (Th1) cells** [3]. - Upon re-exposure to mycobacterial antigens (tuberculin), previously sensitized Th1 cells release **cytokines** that recruit and activate **macrophages**, leading to the characteristic induration and erythema [3]. *Complement activation* - This mechanism is primarily involved in host defense against microbial infections and in **Type II** and **Type III hypersensitivity reactions**, not Delayed-Type Hypersensitivity [2]. - Activation of the complement system leads to cell lysis, opsonization, and inflammation, but it does not directly drive the PPD skin test response [2]. *Formation of immune complexes* - This describes a **Type III hypersensitivity reaction**, where **antigen-antibody complexes** deposit in tissues, leading to inflammation and tissue damage [1]. - Examples include serum sickness and Arthus reaction, which are distinct from the cell-mediated PPD response [1]. *IgE cross-linking* - This mechanism is characteristic of **Type I (immediate) hypersensitivity reactions**, commonly known as allergies [4]. - **IgE antibodies** bind to mast cells and basophils; subsequent cross-linking by antigens triggers the release of mediators like histamine, leading to rapid allergic symptoms [4].

Q: Acute graft rejection occurs within?

< 6 months. ***< 6 months*** - **Acute graft rejection** typically occurs within the first few **weeks to months** after transplantation due to a T-cell mediated immune response against the donor organ [1]. - While it can manifest at any time, the majority of cases occur within the **first 6 months** post-transplant, making this the most appropriate time frame [1]. *Few minutes* - Rejection presenting within minutes of transplantation is characteristic of **hyperacute rejection**, which is caused by pre-existing **donor-specific antibodies** [1]. - This rapid form of rejection is mediated by **complement activation** and leads to immediate graft failure [1]. *6-12 months* - Rejection occurring in this timeframe might still be acute, but the peak incidence is generally earlier. - Rejection presenting after 6 months is often categorized as **late acute rejection** or may start to transition towards signs of chronic rejection, which occurs over a longer period. *Few hours* - Rejection within a few hours could be a very early form of **acute rejection** or a delayed presentation of **hyperacute rejection** [1]. - However, the classic presentation of acute rejection is more prolonged than a few hours, usually developing over days to weeks. **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: Meningococcal meningitis is seen with which of the following complement deficiency?

C5. ***C5*** - Deficiencies in terminal complement components (C5-C9) lead to impaired formation of the **membrane attack complex (MAC)**, which is crucial for lysing Neisseria species [1]. - This significantly increases susceptibility to recurrent infections, particularly by **encapsulated bacteria** like *Neisseria meningitidis*, causing diseases such as meningococcal meningitis [2]. *C4* - C4 deficiency is primarily associated with **lupus-like syndromes** and **vasculitis**, due to impaired clearance of immune complexes. - While it can lead to some increased risk of infection, it is not specifically linked to a marked predisposition to meningococcal disease. *C1q* - C1q deficiency also leads to impaired **immune complex clearance** and is strongly associated with **systemic lupus erythematosus (SLE)**. - Like C4 deficiency, it does not typically present with recurrent meningococcal infections as the primary manifestation. *C2* - C2 deficiency is the **most common complement deficiency** and is associated with **lupus-like syndromes** and increased susceptibility to **pyogenic bacterial infections**. - Though it can lead to some increased infection risk, C2 deficiency is not as strongly or specifically linked to recurrent meningococcal meningitis as deficiencies in the terminal complement pathway [2].

Q: Rheumatoid factor is an antibody of which class -

IgM. ***IgM*** - **Rheumatoid factor (RF)** is typically an **IgM autoantibody** directed against the Fc region of IgG. - While other isotypes of RF (IgG, IgA) exist, **IgM RF** is the most common form detected in serological tests for **rheumatoid arthritis**. *IgD* - **IgD** antibodies are found in small amounts in the serum and are primarily located on the surface of **B lymphocytes**, where they function as antigen receptors. - They are not associated with autoantibodies like **rheumatoid factor**. *IgE* - **IgE** antibodies are primarily involved in **allergic reactions** and defense against parasites [1]. - High levels of IgE are characteristic of **atopic diseases** such as asthma and allergic rhinitis, not autoimmune conditions like rheumatoid arthritis [1]. *IgG* - While IgG is the most abundant immunoglobulin in serum and plays a crucial role in immune defense, **rheumatoid factor** itself is usually an **IgM or IgA antibody** that targets the Fc portion of IgG. - Therefore, IgG is the *target* of RF often, but **not the isotype of RF itself** in the most common clinical assay. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 171-172.

Q: Agammaglobulinemia can present with?

All of the options. ***All of the options*** - **Agammaglobulinemia**, characterized by the absence of **B cells** and very low levels of antibodies, leads to significant **immunodeficiency** [1]. - This deficiency results in a broad range of infections and inflammatory conditions affecting various body systems, encompassing all the listed options. *Rhinitis* - Patients with agammaglobulinemia are prone to **recurrent bacterial infections** of the upper respiratory tract [1]. - This susceptibility often manifests as **chronic or recurrent rhinitis** and sinusitis due to impaired antibody-mediated host defense [1]. *Bronchiectasis* - Due to frequent and inadequately controlled **bacterial infections of the lower respiratory tract**, such as pneumonia and bronchitis. - These chronic infections can cause irreversible damage and dilation of the **bronchial airways**, leading to bronchiectasis. *Giardia infections* - **Agammaglobulinemia** severely impairs the body's ability to produce **IgA antibodies**, which are crucial for mucosal immunity in the gastrointestinal tract. - This deficiency makes patients highly susceptible to **chronic and severe infections** with enteric pathogens, such as *Giardia lamblia* [1].

Q: An isograft indicates transfer of tissues between:

Monozygotic twins. ***Monozygotic twins*** - An **isograft**, also known as an **isogeneic graft**, refers to the transplantation of tissues or organs between two genetically identical individuals. - **Monozygotic (identical) twins** are genetically identical, making them ideal donors and recipients for isografts as there is minimal risk of immune rejection. *Related donors* - This describes **allografts** or **homografts**, where tissue is transferred between genetically non-identical individuals of the same species. - While related donors may have better histocompatibility than unrelated donors, they are typically not genetically identical, leading to a risk of immune rejection. *Unrelated donors* - This also describes **allografts**, where tissue is transferred between genetically non-identical individuals of the same species. - The greater genetic disparity between unrelated individuals increases the risk of **graft rejection** compared to related donors or identical twins. *Parts of same individual* - This describes an **autograft**, where tissue is transplanted from one part of an individual's body to another part of the *same* individual. - Autografts are immunologically ideal as there is no risk of rejection, but this is distinct from an isograft which involves two separate individuals.

Question 1

HLA-mismatched transplant is not a problem in which of the following diseases?

Accepted Answer

Bare lymphocyte syndrome

Answer

Job's syndrome

Answer

Wiskott-Aldrich syndrome

Answer

Chediak-Higashi syndrome

Question 2

A middle-aged woman presents with dry eyes and dry mouth. Laboratory tests reveal positive anti-Ro (SSA) and anti-La (SSB) antibodies. What is the most likely underlying pathological mechanism?

Accepted Answer

Lymphocytic infiltration and destruction of salivary and lacrimal glands

Answer

IgE-mediated hypersensitivity reaction

Answer

Destruction of exocrine glands by neutrophils

Answer

Deposition of amyloid in salivary glands

Question 3

A person was brought to the emergency department with facial swelling, itching, and hypotension following a bee sting. The mentioned clinical features are due to the increase in which immunoglobulin?

Accepted Answer

IgE

Answer

IgG

Answer

IgA

Answer

IgM

Question 4

Which cell acts as the primary effector cell in type IV (delayed-type) hypersensitivity reactions?

Accepted Answer

Macrophage

Answer

Neutrophil

Answer

Dendritic cell

Answer

Cytotoxic T cell

Question 5

A 34-year-old female medical professional who works for a non-governmental organization visits her primary care provider for a routine health check-up. She made a recent trip to Sub-Saharan Africa where she participated in a humanitarian medical project. Her medical history and physical examination are unremarkable. A chest radiograph and a tuberculin skin test (PPD) are ordered. The chest radiograph is performed at the side and the PPD reaction measures 12 mm after 72 hours. Which of the following mechanisms is involved in the skin test reaction?

Accepted Answer

Th1-mediated delayed-type hypersensitivity

Answer

Complement activation

Answer

Formation of immune complexes

Answer

IgE cross-linking

Question 6

Acute graft rejection occurs within?

Accepted Answer

< 6 months

Answer

Few minutes

Answer

6-12 months

Answer

Few hours

Question 7

Meningococcal meningitis is seen with which of the following complement deficiency?

Accepted Answer

C5

Answer

C4

Answer

C1q

Answer

C2

Question 8

Rheumatoid factor is an antibody of which class -

Accepted Answer

IgM

Answer

IgD

Answer

IgE

Answer

IgG

Question 9

Agammaglobulinemia can present with?

Accepted Answer

All of the options

Answer

Rhinitis

Answer

Bronchiectasis

Answer

Giardia infections

Question 10

An isograft indicates transfer of tissues between:

Accepted Answer

Monozygotic twins

Answer

Related donors

Answer

Unrelated donors

Answer

Parts of same individual

Immunopathology — MCQs

Immunopathology — MCQs

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