What is the function of MHC molecules on antigen-presenting cells?

Correct Answer: C

Rationale: The correct answer is C, displaying antigen fragments for T cell recognition. MHC molecules bind to antigen fragments and present them on the cell surface for T cells to recognize. This process is crucial for activating the immune response. Choice A is incorrect as MHC molecules do not secrete cytokines. Choice B is incorrect as MHC molecules do not directly destroy pathogens. Choice D is incorrect as MHC molecules do not produce antibodies; that is the function of B cells.

Correct Answer: B

Rationale: The correct answer is B (IgG and IgM) because in Type II hypersensitivity, antibodies target antigens on cell surfaces or tissues. IgG and IgM antibodies are involved in this type of immune response by binding to antigens and triggering cell destruction through complement activation or phagocytosis. IgE and IgA (choice A) are typically associated with Type I and Type III hypersensitivity, respectively. IgD (choice C) is primarily involved in B cell activation, while IgA (choice D) is more commonly associated with mucosal immunity.

Correct Answer: A

Rationale: The correct answer is A: Crohn's disease. Granulomas are a characteristic feature of Crohn's disease, forming in response to chronic inflammation in the gastrointestinal tract. Granulomas consist of immune cells and are seen in the affected tissues of Crohn's patients. Choice B: Grave's disease is an autoimmune condition affecting the thyroid gland, not typically associated with granulomas. Choice C: Anaphylaxis is a severe allergic reaction involving the immune system's response, but it does not lead to granuloma formation. Choice D: Eczema is a skin condition characterized by inflammation and itching, but it does not typically involve granulomas.

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: 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.