Immunopathology — MCQs

Immunopathology Indian Medical PG Practice Questions and MCQs

Question 241: A skin biopsy study of a Systemic Lupus Erythematosus (SLE) patient, using C-labeled human IgG antiserum, shows deposition of irregular particles at the dermoepidermal junction. What does this finding indicate?

A. Anti-nuclear antibody
B. Anti-collagen antibody
C. Anti-epithelial antibody
D. Immune complex deposits (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Immune complex deposits** The finding described is the **Lupus Band Test (LBT)**. In Systemic Lupus Erythematosus (SLE), the fundamental pathogenesis involves a **Type III Hypersensitivity reaction** [1]. This involves the formation of antigen-antibody (immune) complexes in the circulation, which subsequently deposit in various tissues, including the dermoepidermal junction (DEJ) of the skin [2]. When a skin biopsy is studied using direct immunofluorescence (DIF) with labeled antiserum (like anti-IgG or anti-C3), these complexes appear as **granular, irregular deposits** of immunoglobulin and complement along the basement membrane zone [1]. In SLE, this "band" is typically seen in both sun-exposed and non-exposed skin, whereas in Discoid Lupus (DLE), it is restricted to the skin lesions. **Why other options are incorrect:** * **A. Anti-nuclear antibody (ANA):** While ANA is the hallmark screening test for SLE, it is detected in the **serum** via indirect immunofluorescence or ELISA, not as irregular particles at the DEJ on a skin biopsy [1]. * **B. Anti-collagen antibody:** These are not characteristic of SLE. SLE involves antibodies against nuclear components (DNA, histones, etc.), not structural collagen. * **C. Anti-epithelial antibody:** These are typically seen in blistering diseases like **Pemphigus Vulgaris** (targeting desmogleins), where the staining pattern is "fishnet-like" or "lace-like" around individual keratinocytes, rather than a band at the DEJ. **High-Yield Clinical Pearls for NEET-PG:** * **Lupus Band Test:** Positive in ~90% of SLE patients (involved and uninvolved skin). * **Hypersensitivity:** SLE is primarily Type III, but the associated hemolytic anemia/thrombocytopenia is Type II. * **Most Specific Antibody:** Anti-dsDNA and Anti-Smith (Sm) antibodies. * **Most Sensitive Antibody:** ANA (best screening test). * **Complement Levels:** C3 and C4 levels are typically **decreased** during active flares due to consumption by immune complex deposition [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 226-230. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 214-215.

Question 242: Acute cellular rejection following solid organ transplantation typically occurs within which timeframe?

A. Within minutes to hours of transplantation
B. Within 48 hours of transplantation
C. Between 5 to 30 days of transplantation (Correct Answer)
D. Beyond 30 days after transplantation

Explanation: ### Explanation **Correct Answer: C. Between 5 to 30 days of transplantation** **Mechanism:** Acute cellular rejection (ACR) is a **Type IV hypersensitivity reaction** (cell-mediated immunity). It is primarily driven by host T-lymphocytes (CD8+ cytotoxic and CD4+ helper T-cells) that recognize the donor’s HLA antigens as foreign [2]. This process requires time for the activation and proliferation of T-cells and their subsequent infiltration into the graft. While it can occur anytime, it typically manifests within the first few weeks (5–30 days) post-transplant, especially if immunosuppression is inadequate [1]. **Analysis of Incorrect Options:** * **Option A & B (Minutes to 48 hours):** This timeframe characterizes **Hyperacute Rejection**. It is a Type II hypersensitivity reaction caused by pre-formed anti-donor antibodies (e.g., ABO incompatibility). It leads to immediate thrombosis and graft necrosis [1]. * **Option D (Beyond 30 days):** While acute rejection can occur late if immunosuppression is tapered, the period beyond 3 months to years is typically associated with **Chronic Rejection**. This involves Type II and IV reactions leading to intimal fibrosis (arteriosclerosis) and organ atrophy. **High-Yield NEET-PG Pearls:** * **Hallmark Histology:** Look for **interstitial mononuclear cell infiltrates** (lymphocytes) and **endothelitis** (inflammation of graft vessels) [2]. * **Treatment:** Unlike hyperacute rejection (which requires immediate removal), acute cellular rejection is often **reversible** with high-dose corticosteroids or anti-thymocyte globulin (ATG). * **Acute Antibody-Mediated Rejection (AMR):** Distinguished from cellular rejection by the presence of **C4d deposition** in graft capillaries. **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. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 242.

Question 243: Which antibody is commonly seen in antiphospholipid syndrome?

A. Anticardiolipin (Correct Answer)
B. Anti-b2GPI
C. ANA
D. Anti-Sm

Explanation: **Explanation:** **Antiphospholipid Syndrome (APS)** is an autoimmune prothrombotic state characterized by recurrent arterial or venous thrombosis and pregnancy complications (recurrent miscarriages) [1]. 1. **Why Option A is Correct:** **Anticardiolipin (aCL) antibody** is one of the three major laboratory criteria for diagnosing APS. It is an autoantibody directed against cardiolipin, a phospholipid found in mitochondrial membranes [1]. In clinical practice, it is the most commonly detected antibody in these patients. It can also cause a **false-positive VDRL/RPR test** for syphilis because the reagent used in syphilis testing contains cardiolipin [2]. 2. **Analysis of Incorrect Options:** * **Option B (Anti-β2GPI):** While Anti-β2 glycoprotein I is a highly specific diagnostic marker for APS and is included in the revised Sapporo criteria, **Anticardiolipin** is historically and clinically the most "commonly" cited and tested antibody in the context of general medical examinations. * **Option C (ANA):** Anti-Nuclear Antibody is a screening marker for Systemic Lupus Erythematosus (SLE). While APS can occur secondary to SLE, ANA is not specific to APS [2]. * **Option D (Anti-Sm):** Anti-Smith antibodies are the most specific marker for SLE but have no direct role in the pathogenesis or diagnosis of APS. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Triad (Laboratory):** 1. Lupus Anticoagulant (LA), 2. Anti-cardiolipin (IgG/IgM), 3. Anti-̢2-Glycoprotein I. * **Paradox:** Lupus Anticoagulant causes a **prolonged aPTT** *in vitro* (acting as an anticoagulant) but causes **thrombosis** *in vivo* (acting as a procoagulant) [2]. * **Clinical Hallmark:** Recurrent fetal loss (usually after 10 weeks) and DVT/Stroke [1]. * **Treatment:** Long-term anticoagulation (Warfarin); however, in pregnancy, **Low Molecular Weight Heparin (LMWH)** and Aspirin are used as Warfarin is teratogenic. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 626-627. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Hemodynamic Disorders, Thromboembolic Disease, and Shock, pp. 134-135.

Question 244: Which of the following is not an example of immune complex disease?

A. Systemic lupus erythematosus
B. Arthus reaction
C. Contact dermatitis (Correct Answer)
D. Post-streptococcal glomerulonephritis

Explanation: **Explanation:** The question tests your ability to distinguish between different types of hypersensitivity reactions. The correct answer is **Contact Dermatitis** because it is a **Type IV (Delayed-type) Hypersensitivity** reaction [1], whereas the other options are examples of **Type III (Immune Complex-mediated) Hypersensitivity** [3]. **1. Why Contact Dermatitis is the correct answer:** Contact dermatitis (e.g., reaction to poison ivy or nickel) is mediated by **T-lymphocytes** (CD4+ and CD8+ cells), not antibodies or immune complexes [1]. Upon re-exposure to an antigen, sensitized T-cells release cytokines that recruit macrophages, leading to tissue injury. This process typically takes 48–72 hours to manifest [2]. **2. Why the other options are incorrect (Type III Hypersensitivity):** Type III reactions involve the formation of **antigen-antibody (IgG/IgM) complexes** that deposit in tissues, activate the complement system, and cause neutrophil-mediated inflammation [4]. * **Systemic Lupus Erythematosus (SLE):** A classic systemic Type III reaction where DNA-anti-DNA complexes deposit in various organs (kidneys, joints, skin) [3]. * **Arthus Reaction:** A localized Type III reaction [5]. It occurs when an antigen is injected into the skin of an individual with pre-existing antibodies, leading to localized tissue necrosis and vasculitis [3]. * **Post-streptococcal Glomerulonephritis (PSGN):** Occurs when streptococcal antigen-antibody complexes deposit in the glomerular basement membrane, leading to "lumpy-bumpy" deposits on immunofluorescence [3]. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Hypersensitivity:** **ACID** (Type **A**naphlyactic, **C**ytotoxic, **I**mmune-complex, **D**elayed). * **Serum Sickness** is the systemic prototype of Type III, while **Arthus Reaction** is the localized prototype [5]. * **Granuloma formation** (e.g., in TB or Sarcoidosis) is also a form of Type IV hypersensitivity. * **Key mediator in Type III:** Complement fragment **C5a** (chemotactic for neutrophils). **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. 174-175. [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. 173-174. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 215-216. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 214-215. [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. 172-173.

Question 245: A 40-year-old female presented with hemoptysis and hematuria. Lab studies show the presence of anti-basement membrane antibodies, and the patient's symptoms improved with plasmapheresis. Which of the following diseases is of the same hypersensitivity category as this disease?

A. Systemic lupus erythematosus
B. Seasonal allergies
C. Myasthenia gravis (Correct Answer)
D. Poison ivy rash

Explanation: ### Explanation **Diagnosis and Hypersensitivity Type:** The clinical presentation of hemoptysis (pulmonary hemorrhage) and hematuria (glomerulonephritis) associated with anti-basement membrane antibodies describes **Goodpasture Syndrome** [5]. This is a classic example of **Type II Hypersensitivity (Antibody-mediated)**, where IgG or IgM antibodies bind to fixed antigens on cell surfaces or extracellular matrix (Type IV Collagen in this case), leading to complement activation and tissue damage [3]. **Why Myasthenia Gravis (MG) is Correct:** MG is also a **Type II Hypersensitivity** reaction [1]. In MG, antibodies are directed against the acetylcholine receptors at the neuromuscular junction [2]. Like Goodpasture syndrome, the pathology is mediated by specific antibodies targeting fixed self-antigens. Plasmapheresis is an effective treatment for both conditions because it physically removes these pathogenic circulating antibodies [5]. **Analysis of Incorrect Options:** * **A. Systemic Lupus Erythematosus (SLE):** Primarily a **Type III Hypersensitivity** (Immune-complex mediated). Damage is caused by the deposition of circulating antigen-antibody complexes in various tissues. * **B. Seasonal Allergies:** A **Type I Hypersensitivity** (Immediate/IgE-mediated). It involves IgE binding to mast cells and the subsequent release of histamine. * **D. Poison Ivy Rash:** A **Type IV Hypersensitivity** (Delayed-type/Cell-mediated). It is mediated by T-lymphocytes rather than antibodies. **Clinical Pearls for NEET-PG:** * **Goodpasture Syndrome:** Characterized by "Linear" immunofluorescence on renal biopsy (due to uniform antibody binding along the GBM) [4]. * **Type II Subtypes:** Remember that Type II can be **cytotoxic** (e.g., Rheumatic fever, Goodpasture) or **non-cytotoxic/cell-dysfunction** (e.g., Myasthenia Gravis, Graves' disease) [3]. * **Plasmapheresis:** High-yield "clue" in questions; it indicates the disease is primarily driven by circulating factors (antibodies or immune complexes) [5]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 213-214. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1237-1238. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 214. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Kidney, p. 909. [5] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 537-538.

Question 246: MHC Class I molecules are primarily involved in the presentation of which type of antigens?

A. Endogenous antigens (Correct Answer)
B. Exogenous antigens
C. Self antigens not presented to T cells
D. Bacterial antigens presented to B cells

Explanation: ### Explanation **MHC Class I molecules** are specialized surface proteins found on almost all nucleated cells. Their primary role is to present **endogenous antigens** (intracellularly derived proteins) to **CD8+ Cytotoxic T cells** [1]. #### Why Option A is Correct: Endogenous antigens include viral proteins synthesized within an infected cell, proteins from intracellular bacteria, or mutated proteins in tumor cells [1]. These proteins are degraded by the **proteasome** into peptides, transported into the Endoplasmic Reticulum (ER) via **TAP (Transporter associated with Antigen Processing)**, and loaded onto MHC Class I molecules for surface expression [1]. This signals the immune system to destroy the compromised cell. #### Why Other Options are Incorrect: * **Option B:** **Exogenous antigens** (extracellular pathogens) are presented by **MHC Class II** molecules. These are found only on professional Antigen-Presenting Cells (APCs) like dendritic cells, macrophages, and B cells, which present to **CD4+ Helper T cells** [1]. * **Option C:** Self-antigens *are* presented to T cells, but primarily during T-cell maturation in the thymus to ensure **central tolerance**. If self-antigens are presented in the periphery, it usually leads to anergy or autoimmunity, not a lack of presentation. * **Option D:** B cells recognize native, unprocessed antigens directly via their B-cell receptors (BCR), not via MHC presentation. MHC molecules specifically interact with T-cell receptors (TCR). --- ### High-Yield Clinical Pearls for NEET-PG: * **Rule of 8:** MHC I × CD8 = 8; MHC II × CD4 = 8. * **Structure:** MHC I consists of a **heavy chain (α1, α2, α3)** and a **β2-microglobulin** (encoded on Chromosome 15). * **Loci:** MHC I is encoded by **HLA-A, HLA-B, and HLA-C** genes on Chromosome 6. * **Cross-presentation:** A unique process where dendritic cells can present exogenous antigens on MHC I to activate CD8+ T cells (essential for anti-tumor immunity). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 318-319.

Question 247: Nude mice are used in genetics research due to which of the following properties?

A. Absence of thymus
B. Xenografts can be sustained for weeks (Correct Answer)
C. Severe combined immunodeficiency mice are the same as nude mice
D. They can generate mature T lymphocytes

Explanation: **Explanation:** **Nude mice** (athymic mice) are a laboratory strain characterized by a genetic mutation in the **FOXN1 gene**. This mutation results in two primary phenotypes: the absence of hair (hence "nude") and the **congenital absence of the thymus**. 1. **Why Option B is Correct:** Because these mice lack a functional thymus, they cannot produce mature T-lymphocytes [1]. This profound cell-mediated immunodeficiency prevents them from rejecting foreign tissues. Consequently, **xenografts** (transplants from different species, such as human tumor cells) can be sustained for weeks or months. This makes them invaluable in oncology research for studying tumor growth and drug responses *in vivo*. 2. **Why Other Options are Incorrect:** * **Option A:** While the absence of the thymus is a *feature* of nude mice, it is the **functional consequence** (the ability to sustain xenografts) that makes them specifically useful for the "genetics and oncology research" context implied in the question. (Note: In many exams, if both are present, the functional utility is often the preferred answer). * **Option C:** Nude mice are **not** the same as SCID (Severe Combined Immunodeficiency) mice. Nude mice lack T-cells but have functional B-cells and NK cells [2]. SCID mice lack both T and B-cell function due to a defect in V(D)J recombination. * **Option D:** They cannot generate mature T-lymphocytes because T-cell maturation is dependent on the thymic epithelium, which is absent [1]. **High-Yield Facts for NEET-PG:** * **Mutation:** FOXN1 gene (Forkhead box N1) on Chromosome 11. * **Immunology:** Lack Cell-Mediated Immunity (CMI) but have normal/elevated NK cell activity. * **Clinical Correlation:** The human equivalent of the nude mouse condition is **DiGeorge Syndrome** (22q11.2 deletion), characterized by thymic hypoplasia and T-cell deficiency [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, p. 634. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 246-247.

Question 248: Which of the following conditions is characterized by the presence of LE cells?

A. Systemic lupus erythematosus (Correct Answer)
B. Lupus vulgaris
C. Hereditary nonpolyposis colorectal cancer
D. Medullary carcinoma of the thyroid

Explanation: **Explanation:** **Systemic Lupus Erythematosus (SLE)** is the correct answer. The **LE cell (Lupus Erythematosus cell)** is a classic hematological finding in SLE [4]. It is a neutrophil or macrophage that has ingested the denatured nucleus of another injured cell [4]. This occurs when Antinuclear Antibodies (ANA) coat the nucleus of a damaged cell, transforming it into a homogeneous, amorphous mass called an **LE body** (or hematoxylin body) [4]. Phagocytes then engulf this mass, creating the characteristic LE cell. While highly specific for SLE in the past, it is now largely of historical interest and has been replaced by more sensitive tests like ANA and anti-dsDNA [2][3]. **Analysis of Incorrect Options:** * **Lupus Vulgaris:** This is a chronic, progressive form of **cutaneous tuberculosis** caused by *Mycobacterium tuberculosis*. It is characterized by "apple-jelly" nodules on diascopy, not LE cells. * **Hereditary Nonpolyposis Colorectal Cancer (HNPCC/Lynch Syndrome):** This is an autosomal dominant condition caused by mutations in **mismatch repair (MMR) genes** (e.g., MSH2, MLH1), leading to microsatellite instability. * **Medullary Carcinoma of the Thyroid:** This is a neuroendocrine tumor derived from parafollicular C-cells. It is characterized by **amyloid stroma** (calcitonin-derived) and is associated with MEN 2A and 2B syndromes. **High-Yield Pearls for NEET-PG:** * **Hematoxylin Bodies:** These are the *in vivo* equivalent of LE bodies, seen in tissues (e.g., heart valves in Libman-Sacks endocarditis) [4]. * **Most Sensitive Test for SLE:** ANA (Indirect Immunofluorescence) [1]. * **Most Specific Tests for SLE:** Anti-dsDNA and Anti-Smith (Anti-Sm) antibodies [3]. * **Drug-Induced Lupus:** Associated with **Anti-Histone antibodies**; LE cells may also be present here, but the clinical context differs [3]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 226-227. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 226. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 228. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 230.

Question 249: Which of the following statements accurately describes cytokines?

A. Includes interleukins (Correct Answer)
B. Produced only in sepsis
C. Are simple proteins
D. Have highly specific action

Explanation: ### Explanation **Cytokines** are low-molecular-weight soluble proteins that act as chemical messengers, mediating and regulating immunity, inflammation, and hematopoiesis. **Why Option A is Correct:** Cytokines are a broad category of signaling molecules. They include **interleukins (IL)**, interferons (IFN), tumor necrosis factors (TNF), chemokines, and colony-stimulating factors (CSF) [1]. Interleukins are the largest group, primarily responsible for communication between leukocytes [1]. **Why Incorrect Options are Wrong:** * **Option B:** Cytokines are produced during **normal physiological states** (e.g., wound healing, cell growth) and various pathological conditions (e.g., chronic inflammation, malignancy, autoimmune diseases), not just in sepsis [3]. * **Option C:** They are **glycoproteins**, not simple proteins. Their carbohydrate moieties often influence their stability and half-life. * **Option D:** Cytokines exhibit **pleiotropy** (one cytokine acts on multiple cell types) and **redundancy** (multiple cytokines exert the same effect) [4]. Their actions are often non-specific and overlapping rather than highly specific. **High-Yield NEET-PG Pearls:** 1. **Autocrine, Paracrine, and Endocrine:** Cytokines can act on the cell that secreted them, nearby cells, or distant cells (though systemic/endocrine action is usually seen only in severe inflammation). 2. **Cytokine Storm:** An overproduction of pro-inflammatory cytokines (IL-1, IL-6, TNF-α) seen in conditions like COVID-19 and Septic Shock [2]. 3. **Key Pro-inflammatory Triad:** IL-1, IL-6, and TNF-α are the primary mediators of the acute phase response (fever and CRP elevation) [2]. 4. **IL-8:** The major chemotactic factor for neutrophils ("Neutrophils arrive at 8"). **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. 153-154. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 111. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 97-99. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 93-94.

Question 250: Which of the following statements regarding cytokines is FALSE?

A. Mediators of inflammation
B. Produced by macrophages
C. Are soluble proteins
D. Do not mediate specific reactions (Correct Answer)

Explanation: ### Explanation **Cytokines** are low-molecular-weight, soluble proteins that act as chemical messengers in the immune system. The statement **"Do not mediate specific reactions" is FALSE** because cytokines are characterized by their high degree of specificity and potency. They exert their effects by binding to specific high-affinity receptors on target cells, triggering precise intracellular signaling pathways. #### Why the other options are TRUE: * **Mediators of inflammation (Option A):** Cytokines like TNF, IL-1, and IL-6 are the primary drivers of the acute inflammatory response, systemic effects (fever), and the recruitment of leukocytes to injury sites [1]. * **Produced by macrophages (Option B):** While many cells produce cytokines, activated macrophages are a major source (along with T-lymphocytes, dendritic cells, and endothelial cells) [1]. Macrophages specifically secrete "monokines" like IL-12 and TNF-α. * **Are soluble proteins (Option C):** Cytokines are secreted, soluble polypeptides that act in an autocrine, paracrine, or endocrine fashion to regulate immune responses [1]. #### High-Yield NEET-PG Clinical Pearls: 1. **Pleiotropy:** One cytokine can act on multiple cell types (e.g., IL-4 acts on B-cells, T-cells, and mast cells). 2. **Redundancy:** Multiple cytokines can carry out the same function (e.g., IL-1 and TNF both induce fever) [1]. 3. **Cytokine Storm:** An uncontrolled release of pro-inflammatory cytokines (IL-1, IL-6, TNF-α), classically seen in severe COVID-19 or Sepsis. 4. **Key Association:** **IL-8** is the major chemotactic factor for **neutrophils**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 93-99.

Practice by Chapter

Cells and Tissues of the Immune System

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Innate Immunity

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Adaptive Immunity

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Hypersensitivity Reactions

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Autoimmune Diseases

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Immunodeficiency Disorders

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Transplantation Immunopathology

Practice Questions

Immune Response to Infections

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Immunologic Laboratory Techniques

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Tumor Immunology

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