Which organ is most commonly affected in sarcoidosis?

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.

Correct Answer: D

Rationale: The correct answer is D: IgG. IgG is the most abundant class of immunoglobulin in serum, constituting about 75% of total immunoglobulins. IgG plays a crucial role in humoral immunity, providing long-term protection against pathogens. IgE (A) is involved in allergic responses, IgA (B) is mainly found in mucosal secretions, and IgD (C) functions as a cell surface receptor on B cells. IgG is the primary immunoglobulin responsible for secondary immune responses and provides the bulk of the adaptive immune response.

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.

Correct Answer: C

Rationale: The correct answer is C because the release of newly formed virus from the infected cell is actually mediated by Neuraminidase (NA), not Hemagglutinin (HA). 1. Influenza virus is indeed an RNA virus (Choice A). 2. In humans, influenza primarily infects lung epithelial cells (Choice B). 3. Hemagglutinin (HA) helps the virus enter host cells, while Neuraminidase (NA) helps release viral particles from infected cells (Choice C is incorrect). 4. Tamiflu is a Neuraminidase (NA) inhibitor, which prevents the release of viral particles, aiding in the treatment of influenza infections (Choice D).

Correct Answer: D

Rationale: Step-by-step rationale: 1. NOD2 is a cytosolic receptor for bacteria, detecting bacterial molecules. 2. Mutations in NOD2 are found in 30% of patients with Crohn's disease. 3. NOD2 activation triggers NFκB signaling pathway. 4. Therefore, all the statements (A, B, C) are correct, making option D the correct answer. Other choices are incorrect as they do not encompass all the correct statements about NOD2.