Nokea
Colostrum, the yellowish fluid, secreted by mother during the initial days of lactation is very essential to impart immunity to the newborn infants because it contains:
- A. Natural killer cells
- B. Monocytes
- C. Macrophages
- D. Immunoglobulin A
Correct Answer: D
Rationale: The correct answer is D: Immunoglobulin A. Colostrum contains high levels of Immunoglobulin A (IgA), which is crucial for imparting passive immunity to the newborn. IgA helps protect the infant's mucosal surfaces from infections. Natural killer cells, monocytes, and macrophages are not typically found in colostrum and are not responsible for conferring immunity to the newborn.
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Which organ is most commonly affected in sarcoidosis?
- A. Kidney
- B. Lungs
- C. Liver
- D. Thyroid
Correct Answer: B
Rationale: The correct answer is B: Lungs. Sarcoidosis is a systemic inflammatory disease that primarily affects the lungs in about 90% of cases. This is due to the formation of granulomas, inflammatory nodules, in the lung tissue. Kidney (A), Liver (C), and Thyroid (D) are less commonly affected organs in sarcoidosis. Kidney involvement occurs in about 20-30% of cases, liver involvement in about 10-30% of cases, and thyroid involvement is relatively rare. Therefore, based on the prevalence of organ involvement in sarcoidosis, the lungs are the most commonly affected organ.
Which of the following statements is NOT true
- A. Light chains isotypes are functionally different
- B. The antigen binding site of a B cell receptor is identical to the antigen binding site of antibodies secreted by the same B cell
- C. Both heavy and light chain domains assume a compact barrel structure
- D. The hinge region assumes a more open and flexible structure
Correct Answer: A
Rationale: The correct answer is A: Light chains isotypes are functionally different. This statement is NOT true because light chain isotypes (kappa and lambda) have distinct primary structures but serve the same function in antigen binding. The heavy chain determines the effector function of antibodies. The other choices are correct: B) The antigen binding site of a B cell receptor is identical to the antigen binding site of antibodies secreted by the same B cell, as both use the same variable regions for antigen recognition. C) Both heavy and light chain domains assume a compact barrel structure, which is essential for antibody stability and function. D) The hinge region assumes a more open and flexible structure, allowing antibodies to bind antigens at different orientations.
Which of the following is NOT a secondary lymphoid organ?
- A. Bone marrow
- B. Spleen
- C. Lymph nodes
- D. Mucosal immune system
Correct Answer: A
Rationale: The correct answer is A: Bone marrow. Secondary lymphoid organs are where immune responses are initiated. Bone marrow is a primary lymphoid organ where immune cells mature, not where immune responses are initiated like in secondary lymphoid organs. The spleen, lymph nodes, and mucosal immune system are all secondary lymphoid organs where immune responses occur.
Why do opportunistic diseases develop in an individual with AIDS?
- A. They are side effects of drug treatment of AIDS.
- B. They are sexually transmitted to individuals during exposure to HIV.
- C. They are characteristic in individuals with stimulated B and T lymphocytes.
- D. These infections or tumors occur in a person with an incompetent immune system.
Correct Answer: D
Rationale: Opportunistic diseases arise because the immune system is severely compromised in individuals with AIDS, making them susceptible to infections and cancers they would otherwise resist.
The percentage of developing thymocytes undergoing negative selection in the thymus is close to
- A. 90%
- B. 50%
- C. 25%
- D. 10%
Correct Answer: A
Rationale: The correct answer is A (90%). Negative selection in the thymus eliminates self-reactive T cells. The process ensures self-tolerance. The majority of developing thymocytes are removed during negative selection, making it close to 90%. Choices B, C, and D are incorrect because negative selection eliminates a high percentage of thymocytes, not a lower percentage as indicated in those options.