Which molecule is essential for antigen presentation to T cells?

Correct Answer: B

Rationale: The correct answer is B: Major Histocompatibility Complex (MHC). MHC molecules present antigens to T cells for immune response activation. They bind to antigenic peptides and present them on the cell surface for recognition by T cells. This is crucial for the immune system to distinguish between self and non-self antigens. Antibodies (A) are produced by B cells and do not directly present antigens to T cells. Complement protein C3 (C) is involved in the complement system for immune defense, not antigen presentation. Cytokines (D) are signaling molecules that regulate immune responses but do not directly present antigens to T cells.

Correct Answer: B

Rationale: The correct answer is B: Immediate phase and late phase. In Type I hypersensitivity, the immediate phase occurs rapidly after exposure to an allergen, leading to the release of mediators like histamine. The late phase occurs several hours later, involving sustained inflammatory response. A: Early phase and latent phase - Incorrect because the terms do not accurately describe the phases of Type I hypersensitivity. C: Acute phase and chronic phase - Incorrect because Type I hypersensitivity does not typically progress to a chronic phase. D: Primary phase and secondary phase - Incorrect as these terms are not commonly used to describe the phases of Type I hypersensitivity.

Correct Answer: B

Rationale: The correct answer is B: A collection of macrophages filled with antigens. Granulomas are tissue responses to chronic inflammation, where macrophages form a cluster to engulf and contain foreign substances like antigens. This leads to the formation of a granuloma, which can be seen in conditions like tuberculosis. Other choices are incorrect because: A) Antibodies are proteins produced by the immune system, not structures like granulomas; C) Mast cells are involved in allergic reactions and not typically associated with granulomas; D) An antibody-antigen complex is a different concept related to immune response but not specific to granulomas.

Correct Answer: B

Rationale: The correct answer is B: Thyroid-stimulating hormone (TSH) receptor. In Grave's disease, autoantibodies bind to and activate the TSH receptor on thyroid cells, leading to hyperthyroidism. This is a Type II hypersensitivity reaction. Insulin receptor (A) is not involved in Grave's disease. Complement receptor (C) is not the target in this condition. CD4 receptor (D) is primarily involved in T cell activation, not in Grave's disease.

Correct Answer: B

Rationale: The correct answer is B because macrophages play a crucial role in granuloma formation by engulfing antigens but failing to destroy them, leading to the formation of a cluster of immune cells to contain the persistent antigen. Macrophages present antigens to T cells, triggering an immune response. Other choices are incorrect as macrophages do not neutralize histamine, stimulate IgE production, or produce antibodies against antigens in the context of granuloma formation.