Which antibody isotype is involved in allergic reactions?

Correct Answer: D

Rationale: The correct answer is D: IgE. IgE is the antibody isotype involved in allergic reactions. It binds to allergens and triggers the release of histamine and other chemicals, leading to allergic symptoms. IgG (choice A) is involved in long-term immunity, IgM (choice B) is the first antibody produced in response to an infection, and IgA (choice C) is mainly found in mucosal areas and helps prevent pathogens from entering the body. IgE is specifically associated with allergic responses due to its role in triggering the release of inflammatory mediators in response to allergens.

Correct Answer: C

Rationale: The correct answer is C: IgG. In the secondary immune response, IgG antibodies predominate due to memory B cells rapidly producing them upon re-exposure to the same antigen. IgG provides long-lasting immunity and is more efficient in neutralizing pathogens. IgM (A) is the primary antibody in the initial immune response. IgE (B) is involved in allergic reactions. IgD (D) functions as a receptor on B cells.

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.