Immunopathology Practice Questions

Q: MHC class III genes encode which of the following?

Tumor necrosis factor. The Major Histocompatibility Complex (MHC) is a large genetic locus on **chromosome 6p** in humans. While MHC Class I and II are primarily involved in antigen presentation, the **MHC Class III** region is unique because its gene products do not present antigens but instead play critical roles in the innate immune response and inflammation. ### Explanation of the Correct Answer **B. Tumor necrosis factor (TNF):** The MHC Class III region encodes several non-HLA proteins, most notably cytokines like **TNF-α** and **Lymphotoxin (TNF-β)**. These proteins are potent mediators of inflammation and immune regulation [1]. ### Explanation of Incorrect Options * **A. Complement component C3:** While MHC Class III encodes several complement components (**C2, C4A, C4B, and Factor B**), it does **not** encode C3. C3 is encoded by a gene on chromosome 19. The functions of the complement system are mediated by breakdown products of C3 [1]. * **C. Interleukin 2:** IL-2 is a cytokine primarily produced by T-cells and is encoded by a gene on chromosome 4. * **D. Beta 2 microglobulin:** This is the invariant light chain of the MHC Class I molecule. Crucially, while the heavy chain of MHC Class I is encoded on chromosome 6, $\beta_2$-microglobulin is encoded on **chromosome 15**. ### High-Yield Clinical Pearls for NEET-PG * **MHC Class III Products:** Remember the mnemonic **"C2, C4, Factor B, and TNF."** It also includes Heat Shock Proteins (HSP). * **MHC Class I vs. II:** Class I (HLA-A, B, C) is found on all nucleated cells; Class II (HLA-DP, DQ, DR) is found only on Antigen Presenting Cells (APCs). * **Linkage Disequilibrium:** MHC Class III genes are often inherited together with specific Class I and II alleles, which is significant in autoimmune disease associations (e.g., SLE and C4 deficiency). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 97-99.

Question 1

MHC class III genes encode which of the following?

Accepted Answer

Tumor necrosis factor

Answer

Complement component C3

Answer

Interleukin 2

Answer

Beta 2 microglobulin

Question 2

Which of the following features distinguishes a Type 1 hypersensitivity reaction from a Type 2 hypersensitivity reaction?

Accepted Answer

Type 1 reaction is IgE mediated.

Answer

Type 1 reaction is complement mediated.

Answer

Type 1 reaction involves opsonization.

Answer

Type 2 reaction is IgE mediated.

Question 3

HLA-DR4 is a marker of which disease?

Accepted Answer

Rheumatoid arthritis

Answer

Sarcoidosis

Answer

Sero-negative gouty arthritis

Answer

Psoriasis

Question 4

Which of the following is an example of a Type II hypersensitivity reaction?

Accepted Answer

Blood transfusion reaction

Answer

Autoimmune hemolytic anemia

Answer

Allergic rhinitis (Hay Fever)

Answer

Post-streptococcal glomerulonephritis

Question 5

ABO incompatibility leads to which type of transplant rejection?

Accepted Answer

Hyperacute rejection

Answer

Acute rejection

Answer

Chronic rejection

Answer

None of the above

Question 6

p-ANCA positivity is specific for which of the following conditions?

Accepted Answer

Wegener's granulomatosis

Answer

Polyarteritis nodosa

Answer

Henoch-Schonlein purpura

Answer

Churg-Strauss syndrome

Question 7

A patient presents with generalized edema, sweating, flushing, tachycardia, and fever after a bee sting. What type of hypersensitivity reaction is this?

Accepted Answer

IgE mediated reaction

Answer

T cell mediated cytotoxicity

Answer

IgG mediated reaction

Answer

IgA mediated hypersensitivity reaction

Question 8

Common variable hypogammaglobulinemia shows which of the following?

Accepted Answer

Defective complement opsonization

Answer

Decreased B cell count

Answer

Increased B cell count

Answer

Neutropenia

Question 9

What is the role of macrophages in antibody production?

Accepted Answer

Antigen presentation

Answer

B cell production

Answer

Class switching

Answer

B cell activation

Question 10

Bruton's agammaglobulinemia is due to which defect?

Accepted Answer

B-cell defect

Answer

IgA deficiency

Answer

IgM deficiency

Answer

IgG deficiency

Immunopathology — MCQs

Immunopathology — MCQs

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