Immunopathology Practice Questions

Q: What laboratory findings are associated with common variable hypogammaglobulinemia?

Low serum immunoglobulin levels. ***Low serum immunoglobulin levels*** - **Common variable hypogammaglobulinemia (CVID)** is characterized by significantly **low levels of IgG, IgA, and/or IgM** due to impaired B cell differentiation into plasma cells. - This deficiency in antibodies is the hallmark of the disorder, explaining the increased susceptibility to infections. *Decreased B cell count* - While CVID involves impaired B cell function, the **B cell counts** in the peripheral blood are typically **normal** or sometimes even elevated [1]. - The problem lies in their inability to differentiate and produce adequate antibodies, not in their numerical presence [1]. *Increased B cell count* - An increased B cell count is not a characteristic finding in CVID; peripheral B cell numbers are usually normal [1]. - If B cell counts are significantly increased, other conditions such as certain **lymphoproliferative disorders** should be considered. *Neutropenia* - **Neutropenia** (low neutrophil count) is not a primary diagnostic feature of CVID, although it can occur in some patients with autoimmune complications. - The defining laboratory finding is the **deficiency of immunoglobulins**, leading to recurrent infections. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 249-250.

Q: Which of the following best explains the development of intravascular hemolysis in a 54-year-old woman who was given type A Rh+ blood by mistake, despite being a type B Rh+ patient, after a blood transfusion following an automobile accident?

Antibody-mediated complement fixation. ***Antibody-mediated complement fixation*** - Intravascular hemolysis occurs when type B blood is transfused with type A blood, triggering **IgM antibodies** to activate **complement**, leading to the destruction of transfused red blood cells [1][2]. - This mechanism is rapid and results in **hemolytic transfusion reactions**, which are life-threatening and present shortly after the transfusion [1]. *Antibody-dependent cellular cytotoxicity* - This process primarily involves **IgG antibodies** targeting cells for destruction by **NK cells** or macrophages, rather than complement activation. - It usually leads to **extravascular hemolysis** rather than intravascular hemolysis caused by complement. *Delayed-type hypersensitivity* - This immune response is mediated by **T cells** and typically occurs days to weeks after exposure, not immediately as seen in transfusion reactions. - It does not directly lead to **hemolysis** but rather to tissue damage due to cellular immunity. *Immune complex disease* - Characterized by **formation of immune complexes** leading to inflammation and sometimes tissue damage, but not specifically linked to immediate hemolytic reactions. - This mechanism is more relevant in conditions like **serum sickness**, rather than the direct hemolysis observed in this transfusion scenario. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Red Blood Cell and Bleeding Disorders, pp. 673-674. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 627-628.

Q: Defective phagolysosome formation is a feature of which condition?

Chediak-Higashi syndrome. ***Chediak-Higashi syndrome*** - This condition is characterized by **defective phagolysosome formation** due to mutations in the LYST gene, leading to impaired killing of pathogens [1]. - Clinical features include **partial oculocutaneous albinism** and **neurological deficits**, along with recurrent infections [1]. *Chronic granulomatous disease* - It primarily involves a defect in the **NADPH oxidase enzyme**, leading to ineffective respiratory burst and inability to kill certain bacteria. - Patients experience recurrent infections from **catalase-positive organisms**, not primarily due to phagolysosome defects. *Ataxia telangiectasia* - This is an inherited disorder affecting DNA repair mechanisms and results in **neurological issues** and **immunodeficiency** but not specifically phagolysosome dysfunction. - Common features include **ataxia**, **telangiectasias**, and an increased risk of malignancies, rather than recurrent infections from phagocyte defects. *Fanconi Anemia* - This condition is associated with **bone marrow failure** and increased susceptibility to cancer, particularly **acute myeloid leukemia**, rather than phagolysosomal dysfunction. - Clinically, it presents with **hypoplastic anemia**, **short stature**, and **skeletal anomalies**, not recurrent infections due to impaired phagolysosome function. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 245-246.

Q: Which of the following tests would be most beneficial in the diagnosis of a patient suspected of having chronic granulomatous disease of childhood?

Nitroblue tetrazolium (NBT) test. ***Nitroblue tetrazolium (NBT) test*** - The **NBT test** is the **specific diagnostic test** for **chronic granulomatous disease (CGD)** as it directly assesses the defective pathophysiology. - CGD results from defective **NADPH oxidase**, preventing phagocytes from producing a **respiratory burst** needed to kill intracellular pathogens. - In the NBT test, normal phagocytes reduce the yellow NBT dye to blue **formazan** via superoxide production. In CGD, this reaction **fails**, confirming the diagnosis. - This functional assay directly demonstrates the **oxidative burst defect** characteristic of CGD. *E rosette - forming assay* - This assay identifies **T lymphocytes** by their ability to bind sheep red blood cells. - It evaluates **cellular immunity** and T cell numbers, not phagocyte function. - CGD is a **phagocytic disorder**, not a T cell deficiency, making this test irrelevant for diagnosis. *Cell-mediated cytolysis* - This test measures the killing ability of **cytotoxic T lymphocytes (CTLs)** and **NK cells** against target cells. - It assesses **adaptive and innate cellular immunity** but does not evaluate the **phagocytic oxidative burst** that is defective in CGD. *Determination of CD4: CD8 ratio* - This ratio evaluates the balance between **helper (CD4+)** and **cytotoxic (CD8+)** T cell subsets. - It is useful for diagnosing **HIV infection, autoimmune diseases**, and monitoring immunosuppression. - It does not assess **phagocyte function** and is not relevant to the diagnosis of CGD.

Q: What is the consequence of preformed antibodies in organ transplantation?

Immediate graft failure due to preformed antibodies. ***Hyperacute rejection*** - This occurs immediately after transplant due to **preformed antibodies** reacting against donor antigens, leading to rapid allograft failure [1]. - It is typically associated with **complement activation** and often results in thrombosis of the graft vessels [1]. *Acute rejection* - Primarily mediated by **T cells** rather than preformed antibodies, occurring days to months after transplantation [2]. - Involves a **cellular immune response**, unlike hyperacute rejection which is antibody-mediated [2]. *Acute humoral rejection* - Also involves antibodies but develops **days to weeks** post-transplant rather than immediately like hyperacute rejection. - This type is characterized by a **specific antibody response** and complement activation, but is not due to preformed antibodies. *Chronic rejection* - A long-term process that develops over months to years due to **persistent immune-mediated injury** to the graft, leading to gradual loss of function. - Involves mechanisms such as **tissue fibrosis and vascular changes**, differing from the immediate action of preformed antibodies in hyperacute rejection. **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.

Q: Which one is found in Henoch-Schönlein purpura?

IgA. ***IgA*** - **Henoch-Schönlein purpura (HSP)** is an **IgA-mediated vasculitis**, meaning that **IgA immune complex deposition** is central to its pathology. - These IgA deposits are found in the walls of small blood vessels in affected organs, including the skin, gut, joints, and kidneys, leading to the characteristic symptoms. *IgM* - While IgM antibodies are involved in the **initial immune response** and can be found in some autoimmune conditions, they are **not the primary immunoglobulin** associated with HSP pathogenesis. - Conditions like **Waldenström macroglobulinemia** or some autoimmune hemolytic anemias are more typically linked to IgM involvement. *IgG* - IgG antibodies are the **most abundant immunoglobulins** in the body and are involved in many immune responses and autoimmune diseases, such as **systemic lupus erythematosus** or **rheumatoid arthritis**. - However, IgG is **not the defining immunoglobulin** for HSP. *IgE* - IgE antibodies are primarily associated with **allergic reactions** and **parasitic infections**. - Conditions like **asthma**, **anaphylaxis**, or **atopic dermatitis** involve IgE, not vasculitis like HSP.

Question 1

What laboratory findings are associated with common variable hypogammaglobulinemia?

Accepted Answer

Low serum immunoglobulin levels

Answer

Decreased B cell count

Answer

Increased B cell count

Answer

Neutropenia

Question 2

Which of the following best explains the development of intravascular hemolysis in a 54-year-old woman who was given type A Rh+ blood by mistake, despite being a type B Rh+ patient, after a blood transfusion following an automobile accident?

Accepted Answer

Antibody-mediated complement fixation

Answer

Direct cytotoxic T-cell mediated lysis

Answer

Immune complex mediated hemolysis

Answer

Antibody-dependent cellular cytotoxicity

Question 3

Which among the following is an example of type I hypersensitivity reaction?

Accepted Answer

Casoni's test

Answer

Graves' disease

Answer

Pernicious anemia

Answer

Arthus reaction

Question 4

Defective phagolysosome formation is a feature of which condition?

Accepted Answer

Chediak-Higashi syndrome

Answer

Fanconi Anemia

Answer

Ataxia telangiectasia

Answer

Chronic granulomatous disease

Question 5

Which of the following statements about transplant rejection reactions is false:

Accepted Answer

Liver is extremely sensitive to hyperacute rejection

Answer

Acute rejection is readily reversible with appropriate treatment

Answer

Hyperacute rejection is uncommon

Answer

Chronic rejection is a major cause of late graft loss

Question 6

Type I hypersensitivity includes all of the following except:

Accepted Answer

Autoimmune hemolytic anemia

Answer

Extrinsic asthma

Answer

Hay fever

Answer

Anaphylaxis

Question 7

Which of the following histologic alterations is most characteristic of Sjögren's syndrome?

Accepted Answer

Intense lymphocytic infiltration of the gland replacing the acinar structures.

Answer

Proliferation of the ductal epithelium.

Answer

Atrophy of the glands due to lymphocytic infiltration.

Answer

All of the options.

Question 8

Which of the following tests would be most beneficial in the diagnosis of a patient suspected of having chronic granulomatous disease of childhood?

Accepted Answer

Nitroblue tetrazolium (NBT) test

Answer

E rosette - forming assay

Answer

Cell-mediated cytolysis

Answer

Determination of CD4: CD8 ratio

Question 9

What is the consequence of preformed antibodies in organ transplantation?

Accepted Answer

Immediate graft failure due to preformed antibodies

Answer

Delayed T-cell mediated rejection

Answer

Long-term graft dysfunction due to chronic inflammation

Answer

Post-transplant antibody-mediated rejection

Question 10

Which one is found in Henoch-Schönlein purpura?

Accepted Answer

IgA

Answer

IgM

Answer

IgE

Answer

IgG

Immunopathology — MCQs

Immunopathology — MCQs

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