What triggers the activation of lymphocytes in adaptive immunity?

Correct Answer: B

Rationale: The correct answer is B because lymphocytes are activated in adaptive immunity by recognizing their specific antigen. This recognition is crucial for initiating an immune response tailored to combat a specific pathogen. Phagocytosis (A) is the process of engulfing and destroying pathogens, but it does not directly activate lymphocytes. Cytokine release by macrophages (C) can help in activating other immune cells, but lymphocytes specifically require antigen recognition for activation. Opsonization of pathogens (D) enhances phagocytosis but is not the direct trigger for lymphocyte activation.

Correct Answer: B

Rationale: The correct answer is B: Mast cells. Mast cells play a central role in Type I hypersensitivity reactions by releasing histamine, cytokines, and other inflammatory mediators in response to allergens. This triggers the allergic response. Neutrophils (A), Macrophages (C), and Dendritic cells (D) are not central to Type I hypersensitivity reactions. Neutrophils are involved in acute inflammation, macrophages play a role in phagocytosis and antigen presentation, and dendritic cells are important in initiating adaptive immune responses.

Correct Answer: A

Rationale: The correct answer is A: Multiple sclerosis. Type IV hypersensitivity involves T cell-mediated immune reactions, leading to tissue damage. In multiple sclerosis, myelin sheath destruction is caused by activated T cells attacking self-antigens. Incorrect choices: B: Grave's disease is an example of Type II hypersensitivity involving autoantibodies targeting specific cells. C: Anaphylaxis is a Type I hypersensitivity reaction mediated by IgE antibodies causing rapid and severe allergic reactions. D: Eczema is a chronic inflammatory skin condition involving complex immune mechanisms not specific to Type IV hypersensitivity.

Correct Answer: B

Rationale: The correct answer is B: Antibody binding to cell surface antigens, triggering complement activation or phagocytosis. In Type II hypersensitivity, antibodies bind to antigens on host cells, leading to complement activation or phagocytosis by immune cells. This results in cell damage or destruction. Immune complex deposition (A) is more characteristic of Type III hypersensitivity. Mast cell degranulation (C) is seen in Type I hypersensitivity. T cell-mediated cytotoxicity (D) is associated with Type IV hypersensitivity, not Type II. Therefore, choice B is the most accurate mechanism of tissue damage in Type II hypersensitivity.

Correct Answer: B

Rationale: Granuloma formation is characterized by the persistent recruitment of macrophages around undigested antigens. Initially, macrophages attempt to phagocytose the antigen but fail to digest it completely, leading to the formation of a granuloma. This process is a protective mechanism to isolate the antigen and prevent its spread. IgE-mediated mast cell activation (choice A) is associated with allergic reactions, not granuloma formation. Deposition of immune complexes in tissues (choice C) is linked to immune complex-mediated diseases, not granuloma formation. Complement-mediated cell lysis (choice D) involves the destruction of target cells by the complement system, which is not directly related to granuloma formation.