Which of the following is a clinical feature of Grave's disease?

Correct Answer: B

Rationale: The correct answer is B: Exophthalmos and goiter. In Grave's disease, there is an overproduction of thyroid hormones leading to hyperthyroidism. Exophthalmos (bulging eyes) and goiter (enlarged thyroid gland) are classic clinical features due to autoimmune stimulation of thyroid-stimulating hormone receptors. Pulmonary fibrosis (A) is not typically associated with Grave's disease. Skin vasculitis (C) and eczematous reaction (D) are also not commonly seen in Grave's disease.

Correct Answer: B

Rationale: The correct answer is B because Type II hypersensitivity reactions are mediated by the action of immunoglobulin G (IgG) or immunoglobulin M (IgM), not just IgM alone. IgG or IgM antibodies target specific antigens on the surface of cells or tissues, leading to cell destruction. In contrast, Type I hypersensitivity reactions (choice A) involve immediate IgE-mediated responses to allergens like hay fever and anaphylaxis. Type III reactions (choice C) are characterized by immune complex deposition in tissues, not blood vessel walls. Type IV reactions (choice D) are delayed hypersensitivity reactions involving T cell-mediated responses, such as poison ivy contact dermatitis and transplant rejection.

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).