Which type of hypersensitivity reaction involves cytotoxic T cells and can take several days to develop?

The correct choice is indicative of a reaction characterized by the involvement of cytotoxic T cells, which are a type of white blood cell essential for immune responses. This hypersensitivity reaction is known as delayed-type hypersensitivity and typically takes 24 to 48 hours, or even longer, to manifest fully after exposure to the antigen.

In this type of hypersensitivity, T cells recognize and respond to a specific antigen that has been presented to them, leading to the destruction of target cells. This can be seen in reactions such as contact dermatitis, where a skin reaction occurs due to exposure to substances like poison ivy or certain metals.

The other types of hypersensitivity reactions do not primarily involve cytotoxic T cells or take a significantly shorter time to develop. For instance, Type 1 hypersensitivity involves immediate reactions facilitated by immunoglobulin E (IgE) and mast cells, while Type 2 and Type 3 hypersensitivities involve humoral immunity and antibodies targeting cells or complexes rather than T cell-mediated responses. This specificity to T cell involvement and the delayed onset of symptoms are what set this particular reaction apart as the correct answer.