Immunopathology Practice Questions

Q: Which type of transplantation requires all cellular components to be irradiated prior to transfusion?

Bone marrow. **Explanation:** The correct answer is **Bone marrow (C)**. The underlying medical concept is the prevention of **Transfusion-Associated Graft-Versus-Host Disease (TA-GVHD)**. In bone marrow transplantation, the recipient is severely immunocompromised due to conditioning regimens (chemotherapy/radiation). If non-irradiated blood products are transfused, viable donor T-lymphocytes can recognize the recipient's HLA antigens as foreign and mount an immune attack against the host's tissues (skin, liver, and bone marrow). Since the recipient’s immune system is suppressed, it cannot reject these donor cells. **Irradiation** (usually 25-30 Gy) inactivates donor T-lymphocytes by causing DNA cross-linking, preventing them from proliferating without affecting the function of red cells or platelets. **Why other options are incorrect:** * **Heart, Liver, and Lung (A, B, D):** While these are solid organ transplants requiring immunosuppression, the risk of TA-GVHD is significantly lower compared to hematopoietic stem cell transplants. Standard protocols for solid organ transplants do not routinely mandate irradiation of all cellular components unless the patient is undergoing specific high-intensity T-cell depleting therapy (like ATG). **High-Yield Clinical Pearls for NEET-PG:** * **Indications for Irradiated Blood:** Bone marrow/Stem cell transplant recipients, patients with Hodgkin lymphoma, intrauterine transfusions, and directed donations from first-degree relatives. * **TA-GVHD Mortality:** Unlike chronic GVHD, TA-GVHD is nearly always fatal (mortality >90%) due to profound bone marrow aplasia. * **Shelf Life:** Irradiation shortens the shelf life of RBCs to 28 days due to increased potassium leakage from the cells.

Q: Which cell type lacks HLA antigen?

Red blood cell. The Human Leukocyte Antigen (HLA) system is the human version of the Major Histocompatibility Complex (MHC). **MHC Class I** antigens (HLA-A, B, and C) are expressed on the surface of almost all **nucleated cells** in the body, as well as on platelets. **Why Red Blood Cells (RBCs) are the correct answer:** Mature erythrocytes (RBCs) lack a nucleus and most organelles [1]. Consequently, they **do not express HLA antigens** on their surface. Instead, RBCs express their own specific blood group antigens (ABO and Rh systems). This lack of HLA expression is clinically significant as it prevents HLA-mediated graft-versus-host reactions during simple packed red cell transfusions. **Analysis of Incorrect Options:** * **Monocytes (A) and Neutrophils (C):** As nucleated white blood cells, both are rich in MHC Class I antigens. Monocytes, being professional antigen-presenting cells (APCs), also express **MHC Class II** (HLA-DR, DP, DQ). * **Thrombocytes (B):** Although platelets (thrombocytes) are anucleated fragments of megakaryocytes, they **do express MHC Class I** antigens. This is a high-yield distinction; HLA antibodies can lead to "platelet refractoriness" in multi-transfused patients. **High-Yield Clinical Pearls for NEET-PG:** * **MHC Class I:** Found on all nucleated cells + Platelets (except RBCs). * **MHC Class II:** Found only on Antigen Presenting Cells (Macrophages, B-cells, Dendritic cells) and activated T-cells. * **Exceptions:** Neurons, corneal endothelium, and placental trophoblasts also show very low or absent HLA expression, contributing to their "immune-privileged" status. * **Gene Locus:** HLA genes are located on the **Short arm of Chromosome 6**. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 577-586.

Question 1

A 31-year-old man with AIDS complains of difficulty in swallowing. Examination of his oral cavity demonstrates whitish membranes covering much of his tongue and palate. Endoscopy also reveals several whitish, ulcerated lesions in the esophagus. These pathologic findings are fundamentally caused by loss of which of the following immune cells?

Accepted Answer

Helper T lymphocytes

Answer

B lymphocytes

Answer

Killer T lymphocytes

Answer

Monocytes/macrophages

Question 2

The HLA class II region genes are an important element in which of the following?

Accepted Answer

Governing susceptibility to autoimmune disease

Answer

Graft rejection phenomenon

Answer

Immune surveillance

Answer

Antigen presentation and elimination

Question 3

Which type of transplantation requires all cellular components to be irradiated prior to transfusion?

Accepted Answer

Bone marrow

Answer

Heart

Answer

Liver

Answer

Lung

Question 4

A 12-year-old boy presents with a history of recurrent infections over 10 years, including Pneumocystis jiroveci pneumonia, Streptococcus pneumoniae otitis media, and Pseudomonas aeruginosa urinary tract infection. His current examination reveals a temperature of 38.5°C and pharyngeal erythema with exudate. Laboratory findings include hemoglobin of 9.1 g/dL, hematocrit of 27.6%, platelet count of 130,900/mm³, and a WBC count of 3440/mm³ with 47% segmented neutrophils, 3% bands, 40% lymphocytes, and 10% monocytes. Serum immunoglobulin levels show very low IgG, very high IgM, and undetectable IgA. A peripheral blood smear reveals nucleated RBCs. Which of the following immunologic defects is most likely to produce this clinical presentation?

Accepted Answer

Abnormal CD40-CD40L interaction

Answer

Absence of adenosine deaminase

Answer

Deletion of chromosome 22q11

Answer

HIV infection

Question 5

Which of the following represents a delayed type of hypersensitive reaction?

Accepted Answer

All of the above

Answer

Arthus reaction

Answer

Bronchial asthma

Answer

Hemolytic anemia

Question 6

Band test is done in which of the following conditions?

Accepted Answer

Systemic Lupus Erythematosus

Answer

Rheumatoid Arthritis

Answer

Scleroderma

Answer

Polyarteritis Nodosa

Question 7

Which of the following can be seen in Severe Combined Immunodeficiency (SCID)?

Accepted Answer

Graft-versus-host disease (GVHD)

Answer

Autoimmune diseases

Answer

Granuloma formation

Answer

Graft rejection

Question 8

Which of the following statements regarding bone marrow transplantation is true?

Accepted Answer

Marrow is highly immunogenic and easily rejected by the non-immunosuppressed host.

Answer

Marrow transplantation has not been successful in the treatment of aplastic anemias.

Answer

Marrow transplantation has not been successful in the treatment of congenital immunodeficiency diseases.

Answer

Marrow transplantation can be used as a successful therapy for stage IV breast cancer following high-dose chemotherapy.

Question 9

Hyperacute rejection is due to which of the following mechanisms?

Accepted Answer

Preformed antibodies

Answer

Cytotoxic T-lymphocyte mediated injury

Answer

Circulating macrophage mediated injury

Answer

Endothelitis caused by donor antibodies

Question 10

Which cell type lacks HLA antigen?

Accepted Answer

Red blood cell

Answer

Monocyte

Answer

Thrombocyte

Answer

Neutrophil

Immunopathology — MCQs

Immunopathology — MCQs

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