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

All of the following organisms can cause serious infection in chronic granulomatous disease except?

Accepted Answer

Streptococcus pneumoniae

Answer

Staphylococcus aureus

Answer

Pseudomonas

Answer

Haemophilus influenzae

Question 2

Biopsy of the parotid gland in Sjogren's syndrome typically shows infiltration by which type of inflammatory cell?

Accepted Answer

Lymphocytes

Answer

Neutrophils

Answer

Eosinophils

Answer

Basophils

Question 3

Hemolytic disease of the newborn is an example of which type of hypersensitivity reaction?

Accepted Answer

Type II hypersensitivity

Answer

Type III hypersensitivity

Answer

Arthus reaction

Answer

Type IV hypersensitivity

Question 4

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 5

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 6

HLA-DR4 is a marker of which disease?

Accepted Answer

Rheumatoid arthritis

Answer

Sarcoidosis

Answer

Sero-negative gouty arthritis

Answer

Psoriasis

Question 7

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 8

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 9

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 10

What type of HLA molecules are primarily involved in graft rejection?

Accepted Answer

MHC Class I

Answer

MHC Class II

Answer

MHC Class III

Answer

MHC Class IV

Immunopathology — MCQs

Immunopathology — MCQs

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