Questions: Which of the following is the type of cell largely responsible for type I hypersensitivity responses? (A) erythrocyte (B) mast cell (C) T lymphocyte (D) antibody Type I hypersensitivities require which of the following initial priming events to occur?

The answer to the first question is (B): mast cell.

Explanation for each option: (A) Erythrocyte: Incorrect. Erythrocytes, or red blood cells, are primarily responsible for carrying oxygen and do not play a role in hypersensitivity responses. (B) Mast cell: Correct. Mast cells are largely responsible for type I hypersensitivity responses. They release histamine and other mediators that lead to allergic reactions. (C) T lymphocyte: Incorrect. While T lymphocytes are involved in immune responses, they are not the primary cells responsible for type I hypersensitivity. (D) Antibody: Incorrect. Although antibodies, specifically IgE, are involved in type I hypersensitivity, they are not cells. Mast cells bind IgE, which triggers the hypersensitivity response.

For the second question, type I hypersensitivities require the initial priming event of sensitization, where an individual is first exposed to an allergen, leading to the production of IgE antibodies that bind to mast cells.