Immunopathology — MCQs
On this page
Which of the following is true about Graft-versus-Host Disease (GVHD)?
Which of the following statements is not true regarding Ataxia telangiectasia?
A patient with sarcoidosis has non-caseating granulomas. Which type of hypersensitivity reaction is responsible for developing granulomatous inflammation in this patient?
Which cells are responsible for forming circulating antibodies?
A 39-year-old woman presents with acute onset of severe dyspnea. Physical examination reveals she is afebrile with marked laryngeal stridor and severe airway obstruction. Her medical history indicates similar episodes since childhood and episodes of colicky gastrointestinal pain. Her mother and brother are similarly affected. There is no history of severe or recurrent infections, and she does not have urticaria. Laboratory studies show a normal WBC count, hematocrit, and platelet count. A deficiency in which of the following plasma components is most likely to produce these findings?
A 2-year-old boy has had almost continuous infections since he was 6 months old. These infections have included otitis media, pneumonia, and impetigo. Organisms cultured include Haemophilus influenzae, Streptococcus pneumoniae, and Staphylococcus aureus. He also has had diarrhea, with Giardia lamblia cysts identified in stool specimens. The family history indicates that an older brother with a similar condition died because of overwhelming infections. The boy's two sisters and both parents are not affected. Which of the following laboratory findings would most likely be seen in this boy?
A 35-year-old man presents with complaints of seasonal eye itching and a runny nose. Recurrent conjunctivitis in this patient is most likely caused by which of the following mechanisms?
Which interleukin functions as a T-cell growth factor?
Which of the following is false regarding hereditary angioneurotic edema?
Which marker indicates Natural Killer (NK) cell activity?
Immunopathology Indian Medical PG Practice Questions and MCQs
Question 271: Which of the following is true about Graft-versus-Host Disease (GVHD)?
- A. Occurs when the host is immunocompetent.
- B. The most common organ involved is the lung.
- C. It is most common in renal transplants.
- D. Occurs when donor cells are immunocompetent. (Correct Answer)
Explanation: **Explanation:** Graft-versus-Host Disease (GVHD) is a unique immunological phenomenon where the **grafted tissue (donor) attacks the recipient (host)**. For GVHD to occur, three classic criteria (Billingham’s criteria) must be met: the graft must contain immunologically competent cells, the recipient must possess antigens foreign to the donor, and the recipient must be immunologically compromised. * **Why Option D is Correct:** The fundamental requirement for GVHD is that the **donor cells must be immunocompetent** (specifically T-lymphocytes). These donor T-cells recognize the host's HLA antigens as foreign and initiate an immune response against the recipient's tissues. * **Why Option A is Incorrect:** GVHD occurs when the **host is immunocompromised** (not immunocompetent). If the host were immunocompetent, their own immune system would reject the graft (Host-versus-Graft) before the graft could mount an attack. * **Why Option B is Incorrect:** The **skin** is the most common organ involved in GVHD (presenting as a maculopapular rash) [1]. Other primary targets include the **liver** (jaundice/bile duct destruction) and the **gastrointestinal tract** (bloody diarrhea) [1]. * **Why Option C is Incorrect:** GVHD is most common in **Hematopoietic Stem Cell Transplants (HSCT)** or bone marrow transplants [1]. It is rare in solid organ transplants like the kidney because these organs contain fewer lymphoid cells. **High-Yield Clinical Pearls for NEET-PG:** * **Acute GVHD:** Occurs within 100 days; characterized by epithelial cell death in the skin, GI tract, and liver [1]. * **Chronic GVHD:** Occurs after 100 days; mimics autoimmune diseases like Scleroderma or Sjögren’s syndrome. * **Graft-versus-Leukemia (GVL) effect:** In leukemia patients, a mild degree of GVHD is often beneficial as the donor cells also attack residual leukemic cells. **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. 182-183.
Question 272: Which of the following statements is not true regarding Ataxia telangiectasia?
- A. Mutations in the ATM gene on chromosome 11q22-23 are implicated.
- B. It follows an autosomal recessive mode of inheritance. (Correct Answer)
- C. It is associated with humoral and cellular immunodeficiency.
- D. There is an increased risk of certain malignancies, including adenocarcinomas.
Explanation: **Explanation:** Ataxia-telangiectasia (AT) is a complex multisystem disorder characterized by genomic instability [2]. The question asks for the statement that is **not true**. 1. **Why the marked answer is "correct" (The False Statement):** While the question indicates Option B as the answer, there appears to be a technical discrepancy in the prompt's labeling. **Ataxia-telangiectasia DOES follow an autosomal recessive mode of inheritance [1].** If the goal is to identify the *false* statement, **Option D** is the most accurate choice for being "not true." While AT patients have a significantly increased risk of malignancies (up to 40%), these are predominantly **lymphoid malignancies** (Leukemias and Lymphomas) [2]. While some epithelial tumors occur, the association with **adenocarcinomas** is not a classic or defining feature compared to the overwhelming predisposition to hematologic cancers. 2. **Analysis of other options:** * **Option A (True):** The defect lies in the **ATM gene** (Ataxia-Telangiectasia Mutated) located on **chromosome 11q22-23**. This gene encodes a protein kinase that senses DNA double-strand breaks and activates p53. * **Option B (True):** It is a classic **autosomal recessive** genomic instability syndrome [1], [2]. * **Option C (True):** It features a **combined immunodeficiency** [2]. There is a defect in both humoral (low IgA, IgE, and IgG2) and cellular (T-cell lymphopenia and thymic hypoplasia) immunity. **Clinical Pearls for NEET-PG:** * **Clinical Triad:** Progressive cerebellar ataxia, oculocutaneous telangiectasia, and recurrent sinopulmonary infections [2]. * **Key Lab Marker:** Characteristically **elevated Alpha-Fetoprotein (AFP)** levels in children over 8 months old. * **Radiosensitivity:** Patients are hypersensitive to **ionizing radiation** (X-rays/CT scans) because they cannot repair double-strand DNA breaks. * **Morphology:** Look for "Amphicytosis" (enlarged, distorted nuclei in non-neoplastic tissues). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1300-1301. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 250-251.
Question 273: A patient with sarcoidosis has non-caseating granulomas. Which type of hypersensitivity reaction is responsible for developing granulomatous inflammation in this patient?
- A. Type I
- B. Type II
- C. Type III
- D. Type IV (Correct Answer)
Explanation: ### Explanation **Correct Option: D (Type IV Hypersensitivity)** Granulomatous inflammation is a classic manifestation of **Type IV (Delayed-type) Hypersensitivity** [1]. In sarcoidosis, the process is driven by an exaggerated T-cell mediated immune response to an unknown antigen [2]. **The Mechanism:** 1. **Antigen Presentation:** Antigen-presenting cells (APCs) process the trigger and present it to CD4+ T-cells [4]. 2. **Cytokine Cascade:** APCs secrete **IL-12**, which differentiates T-cells into **Th1 cells** [4]. 3. **Macrophage Activation:** Th1 cells secrete **Interferon-gamma (IFN-γ)**, which activates macrophages, transforming them into **epithelioid histiocytes** [3]. 4. **Granuloma Formation:** These epithelioid cells fuse to form **multinucleated giant cells** (Langhans or foreign-body type), surrounded by a rim of lymphocytes and fibroblasts [3]. In sarcoidosis, these granulomas are characteristically **non-caseating** (lacking central necrosis) [2]. --- ### Why Other Options are Incorrect: * **Type I (Immediate):** Mediated by **IgE** and mast cell degranulation (e.g., Anaphylaxis, Asthma). * **Type II (Antibody-mediated):** Involves **IgG/IgM** binding to fixed cell-surface antigens, leading to complement activation or ADCC (e.g., Goodpasture syndrome, Rheumatic fever). * **Type III (Immune-complex):** Caused by deposition of **antigen-antibody complexes** in tissues (e.g., SLE, Post-streptococcal glomerulonephritis). --- ### NEET-PG High-Yield Pearls: * **Sarcoidosis Hallmark:** Non-caseating granulomas with **Schaumann bodies** (laminated calcium-protein inclusions) and **Asteroid bodies** (stellate inclusions within giant cells) [2]. * **Key Cytokines:** IL-2, IL-12, IFN-γ, and TNF-α are elevated in the microenvironment [1], [4]. * **Kveim-Siltzbach Test:** Historically used for diagnosis (Type IV skin reaction), though now largely replaced by biopsy and imaging. * **Other Type IV Examples:** TB (caseating), Leprosy, Contact Dermatitis, and Mantoux test [5]. **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. 173-174. [2] 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. 198-200. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 109. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 216-218. [5] 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. 174-175.
Question 274: Which cells are responsible for forming circulating antibodies?
- A. T-cells
- B. B-cells
- C. Macrophages
- D. Plasma cells (Correct Answer)
Explanation: **Explanation:** The correct answer is **Plasma cells**. These are the terminal differentiation stage of B-lymphocytes and are the actual "antibody factories" of the immune system [1]. **1. Why Plasma cells are correct:** While B-cells are the precursors, they must undergo activation and differentiation into plasma cells to secrete immunoglobulins (antibodies) into the circulation [2]. Plasma cells are characterized by an eccentric nucleus with a "cartwheel" or "clock-face" chromatin pattern and a prominent Golgi apparatus (seen as a perinuclear halo), which is essential for large-scale protein (antibody) synthesis. **2. Why other options are incorrect:** * **T-cells:** These are responsible for **Cell-Mediated Immunity (CMI)** [1]. They do not produce antibodies. CD4+ T-cells (Helper) coordinate the immune response, while CD8+ T-cells (Cytotoxic) directly kill virally infected or tumor cells [2]. * **B-cells:** Although B-cells have surface antibodies (BCRs) to recognize antigens, they do not secrete **circulating** antibodies in significant quantities until they differentiate into plasma cells [1]. * **Macrophages:** These are professional phagocytes and antigen-presenting cells (APCs). They process antigens and present them to T-cells via MHC molecules but do not produce antibodies [1]. **Clinical Pearls for NEET-PG:** * **Russell Bodies:** Eosinophilic cytoplasmic inclusions of condensed immunoglobulins found in plasma cells. * **Mott Cells:** A plasma cell filled with multiple Russell bodies (resembling a bunch of grapes). * **Multiple Myeloma:** A plasma cell dyscrasia characterized by the malignant proliferation of a single clone of plasma cells, leading to a monoclonal (M) spike on electrophoresis. * **Primary Lymphoid Organs:** Bone marrow and Thymus. * **Secondary Lymphoid Organs:** Spleen, Lymph nodes, MALT (where B-cells meet antigens and become plasma cells). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 206-208. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 579-580.
Question 275: A 39-year-old woman presents with acute onset of severe dyspnea. Physical examination reveals she is afebrile with marked laryngeal stridor and severe airway obstruction. Her medical history indicates similar episodes since childhood and episodes of colicky gastrointestinal pain. Her mother and brother are similarly affected. There is no history of severe or recurrent infections, and she does not have urticaria. Laboratory studies show a normal WBC count, hematocrit, and platelet count. A deficiency in which of the following plasma components is most likely to produce these findings?
- A. b2-Microglobulin
- B. C1 inhibitor (Correct Answer)
- C. C3
- D. 5-Hydroxytryptamine
Explanation: The clinical presentation of recurrent laryngeal edema (stridor), colicky abdominal pain, and a positive family history without associated urticaria is classic for **Hereditary Angioedema (HAE)**. **1. Why C1 Inhibitor is Correct:** HAE is an autosomal dominant disorder caused by a deficiency or dysfunction of **C1 inhibitor (C1-INH)**. C1-INH is a serine protease inhibitor that normally regulates the classical complement pathway and the kinin system. In its absence, there is uncontrolled activation of the kallikrein-kinin cascade, leading to excessive production of **bradykinin**. Bradykinin increases vascular permeability, resulting in episodic, non-pitting edema of the skin, larynx (causing life-threatening airway obstruction), and gastrointestinal tract (causing colicky pain) [1]. The absence of urticaria (hives) is a key diagnostic feature that distinguishes HAE from IgE-mediated allergic reactions. **2. Why Other Options are Incorrect:** * **A. $\beta$2-Microglobulin:** This is a component of MHC Class I molecules. Its accumulation is associated with dialysis-related amyloidosis, not acute angioedema. * **C. C3:** C3 deficiency leads to increased susceptibility to pyogenic bacterial infections and Type III hypersensitivity-like symptoms, but does not cause isolated angioedema. * **D. 5-Hydroxytryptamine (Serotonin):** While involved in inflammation and carcinoid syndrome, it is not the mediator responsible for the hereditary episodes described. **Clinical Pearls for NEET-PG:** * **Diagnostic Marker:** The best screening test for HAE is a **low C4 level** (even between attacks), as C1-INH deficiency leads to continuous consumption of C4. * **Trigger:** Attacks can be triggered by trauma, dental procedures, or stress. * **Treatment:** Acute attacks are treated with C1-INH concentrate or **Icatibant** (bradykinin B2 receptor antagonist). Prophylaxis often involves androgens (e.g., Danazol) which increase hepatic synthesis of C1-INH. * **ACE Inhibitors:** These are contraindicated in these patients as they prevent bradykinin breakdown, worsening the edema. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 100-101.
Question 276: A 2-year-old boy has had almost continuous infections since he was 6 months old. These infections have included otitis media, pneumonia, and impetigo. Organisms cultured include Haemophilus influenzae, Streptococcus pneumoniae, and Staphylococcus aureus. He also has had diarrhea, with Giardia lamblia cysts identified in stool specimens. The family history indicates that an older brother with a similar condition died because of overwhelming infections. The boy's two sisters and both parents are not affected. Which of the following laboratory findings would most likely be seen in this boy?
- A. Absence of IgA
- B. Agammaglobulinemia (Correct Answer)
- C. Decreased complement C3
- D. High titer of HIV-1 RNA
Explanation: ### Explanation **Diagnosis: X-linked Agammaglobulinemia (Bruton Disease)** The clinical presentation is classic for **X-linked Agammaglobulinemia (XLA)**. The key features include: 1. **Age of Onset:** Symptoms begin after 6 months of age, coinciding with the waning of maternal IgG [2]. 2. **Infection Profile:** Recurrent sinopulmonary infections (otitis media, pneumonia) caused by **encapsulated pyogenic bacteria** (*H. influenzae, S. pneumoniae, S. aureus*) because antibodies are required for their opsonization and clearance [2]. 3. **Gastrointestinal Involvement:** Recurrent *Giardia lamblia* infections occur due to a lack of secretory IgA. 4. **Inheritance:** The family history (affected brother, unaffected sisters/parents) strongly suggests an **X-linked recessive** pattern [2]. **Pathophysiology:** XLA is caused by a mutation in the **Bruton Tyrosine Kinase (BTK) gene**, which is essential for B-cell maturation. Without BTK, pre-B cells cannot differentiate into mature B cells, leading to a profound deficiency of all immunoglobulin classes (Agammaglobulinemia) and absent B cells in peripheral blood [1]. --- ### Why the other options are incorrect: * **Absence of IgA:** While IgA is absent in XLA, "Isolated IgA deficiency" typically presents with milder respiratory infections or is asymptomatic; it would not explain the severe, life-threatening systemic infections or the death of a sibling. * **Decreased complement C3:** C3 deficiency leads to infections with encapsulated bacteria but does not typically cause *Giardia* infections or show an X-linked inheritance pattern. * **High titer of HIV-1 RNA:** While HIV causes secondary immunodeficiency, the family history and the specific onset at 6 months (post-maternal antibody decay) point toward a primary genetic B-cell defect. --- ### NEET-PG High-Yield Pearls: * **Flow Cytometry:** Will show **absent/markedly decreased CD19+ and CD20+ B cells** [1]. * **Lymphoid Tissue:** Characterized by **underdeveloped/absent germinal centers** in lymph nodes, Peyer's patches, and tiny/absent tonsils [1]. * **T-cell Function:** Remains **normal** (delayed hypersensitivity and viral defense are intact, except for enteroviruses like Polio/Echovirus) [1]. * **Treatment:** Intravenous Immunoglobulin (IVIG) replacement. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 248-249. [2] 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. 165-167.
Question 277: A 35-year-old man presents with complaints of seasonal eye itching and a runny nose. Recurrent conjunctivitis in this patient is most likely caused by which of the following mechanisms?
- A. Autoimmunity
- B. Bacterial infection
- C. Chemical toxicity
- D. Hypersensitivity (Correct Answer)
Explanation: The clinical presentation of seasonal eye itching and a runny nose in a 35-year-old man is classic for **Allergic Rhinoconjunctivitis**. This condition is mediated by a **Type I Hypersensitivity reaction** [1]. **1. Why Hypersensitivity is correct:** Type I (Immediate) Hypersensitivity occurs when an allergen (e.g., pollen) cross-links **IgE antibodies** bound to the surface of **mast cells** in the conjunctiva and nasal mucosa [1], [3]. This triggers degranulation and the release of vasoactive amines like **histamine**. Histamine causes vasodilation, increased vascular permeability, and sensory nerve stimulation, leading to the hallmark symptoms of itching, redness, and watery discharge [1]. **2. Why other options are incorrect:** * **Autoimmunity:** This involves an immune response against "self-antigens" (e.g., SLE or Rheumatoid Arthritis). Seasonal symptoms triggered by external environmental factors are characteristic of allergy, not autoimmunity [3]. * **Bacterial Infection:** While bacteria cause conjunctivitis, it typically presents with purulent (thick, yellow/green) discharge and crusting of eyelids, rather than seasonal itching and clear rhinorrhea. * **Chemical Toxicity:** This results from direct tissue damage by irritants (e.g., smoke, acids). It is usually an acute, non-recurrent event related to specific exposure, not a seasonal pattern. **High-Yield NEET-PG Pearls:** * **Key Cells:** Mast cells and Basophils (early phase); Eosinophils (late phase) [1], [2]. * **Key Cytokines:** IL-4 (stimulates IgE production) and IL-5 (activates eosinophils) [2]. * **Diagnostic Clue:** Presence of **Horner-Trantas dots** (gelatinous clumps of eosinophils) is seen in more severe forms like Vernal Keratoconjunctivitis (VKC). * **Treatment:** Mast cell stabilizers (Cromolyn) and H1-receptor antagonists. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 208-210. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 210. [3] 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.
Question 278: Which interleukin functions as a T-cell growth factor?
- A. IL-3
- B. IL-7 (Correct Answer)
- C. IL-11
- D. IL-5
Explanation: **Explanation:** **Interleukin-7 (IL-7)** is the primary cytokine responsible for the survival, proliferation, and differentiation of lymphoid progenitor cells. It is produced by stromal cells in the bone marrow and thymus. It functions as a critical **T-cell growth factor**, particularly during early thymic development [1]. Without IL-7 signaling, T-cell lymphopoiesis fails, leading to Severe Combined Immunodeficiency (SCID) [1]. **Analysis of Incorrect Options:** * **IL-3 (Multi-CSF):** Acts as a growth factor for hematopoietic stem cells and promotes the proliferation of all myeloid lineages (granulocytes, monocytes, and megakaryocytes). It is not specific to T-cells. * **IL-11:** Primarily functions as a growth factor for **megakaryocytes**. It stimulates platelet production and is used clinically (as Oprelvekin) to treat chemotherapy-induced thrombocytopenia. * **IL-5:** Known as the **Eosinophil differentiation factor**. It promotes the growth, activation, and chemotaxis of eosinophils and stimulates B-cell growth and IgA production. **High-Yield NEET-PG Pearls:** * **IL-2 vs. IL-7:** While IL-7 is the growth factor for *developing* T-cells (lymphopoiesis), **IL-2** is the major growth factor for *mature* T-cells (proliferation after antigen stimulation) [2]. * **Clinical Correlation:** Mutations in the **IL-7 receptor (IL-7R)** are a known cause of autosomal recessive T-cell negative SCID (T-B+NK+) [1]. * **Memory Trick:** IL-**7** is for **S**even (**S**tem cells of lymphoid lineage). IL-**5** is for **E**osinophils (5 looks like an 'S' for EosinophilS). **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. [2] 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. 158-160.
Question 279: Which of the following is false regarding hereditary angioneurotic edema?
- A. It is inherited in an autosomal recessive pattern. (Correct Answer)
- B. It is caused by a deficiency of C1 esterase inhibitor.
- C. The main mediator of edema is C2 kinin.
- D. The treatment of choice is C1 inhibitor concentrate.
Explanation: **Explanation:** Hereditary Angioneurotic Edema (HAE) is a rare but life-threatening genetic disorder characterized by recurrent episodes of non-pitting edema affecting the skin, gastrointestinal tract, and upper airway. **1. Why Option A is the correct (False) statement:** Hereditary angioneurotic edema is inherited in an **Autosomal Dominant** pattern, not recessive [1]. It involves a mutation in the *SERPING1* gene, which encodes the C1 inhibitor protein. A single defective allele is sufficient to cause the clinical syndrome. **2. Analysis of other options:** * **Option B:** It is indeed caused by a **deficiency of C1 esterase inhibitor (C1-INH)**. C1-INH normally inhibits C1 protease, kallikrein, and Factor XIIa. Its absence leads to uncontrolled activation of these pathways. * **Option C:** While **Bradykinin** is the primary mediator of edema in HAE [2], **C2 kinin** (released during the classical complement pathway activation) also plays a significant role in increasing vascular permeability. * **Option D:** The definitive treatment for acute attacks is **C1 inhibitor concentrate**. Other treatments include fresh frozen plasma (FFP) if concentrate is unavailable, and long-term prophylaxis with attenuated androgens (e.g., Danazol). **High-Yield Clinical Pearls for NEET-PG:** * **The "Low C4" Rule:** In HAE, **C4 levels are persistently low** even between attacks, making it the best screening test. C1q levels are typically normal (unlike in acquired angioedema). * **Clinical Presentation:** Patients present with episodic swelling without urticaria (hives) or pruritus (itching). This distinguishes it from allergic angioedema. * **Contraindication:** ACE inhibitors are contraindicated in these patients as they prevent the breakdown of bradykinin, potentially triggering a fatal attack [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 149-150. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 100-101.
Question 280: Which marker indicates Natural Killer (NK) cell activity?
- A. CD3
- B. CD4
- C. CD56 (Correct Answer)
- D. CD19
Explanation: **Explanation:** **Correct Option: C (CD56)** Natural Killer (NK) cells are a subset of innate lymphoid cells that play a crucial role in the rejection of tumors and virally infected cells [3]. The most characteristic surface markers used to identify NK cells in clinical pathology are **CD56** (Neural Cell Adhesion Molecule - NCAM) and **CD16** (FcγRIII). * **CD56** is the primary marker used for identification. * **CD16** mediates antibody-dependent cellular cytotoxicity (ADCC). NK cells are unique because they lack the T-cell receptor (TCR) and do not require prior sensitization [3]. **Incorrect Options:** * **CD3 (Option A):** This is the pan-T-cell marker. It is part of the T-cell receptor (TCR) complex [2]. NK cells are characteristically **CD3-negative**, which helps distinguish them from NKT cells. * **CD4 (Option B):** This is a marker for Helper T-cells (MHC II restricted) [2]. It is also found on monocytes and macrophages. * **CD19 (Option D):** This is a pan-B-cell marker involved in B-cell activation and signal transduction. **High-Yield Clinical Pearls for NEET-PG:** 1. **Morphology:** On a peripheral smear, NK cells appear as **Large Granular Lymphocytes (LGLs)**. 2. **Cytotoxicity:** They kill target cells via **Perforins** (create holes in the membrane) and **Granzymes** (induce apoptosis). 3. **Regulation:** NK cell activity is regulated by **KIR (Killer Cell Immunoglobulin-like Receptors)** which recognize MHC Class I molecules [1]. A "missing self" (downregulation of MHC I by tumors/viruses) triggers NK cell activation [1]. 4. **Cytokine Activation:** Their function is significantly enhanced by **IL-2 and IL-12** [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 200-201. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 198-199. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 207-208.
Practice by Chapter
Cells and Tissues of the Immune System
Practice Questions
Innate Immunity
Practice Questions
Adaptive Immunity
Practice Questions
Hypersensitivity Reactions
Practice Questions
Autoimmune Diseases
Practice Questions
Immunodeficiency Disorders
Practice Questions
Transplantation Immunopathology
Practice Questions
Immune Response to Infections
Practice Questions
Immunologic Laboratory Techniques
Practice Questions
Tumor Immunology
Practice Questions
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free