Which type of Hypersensitivity reaction is considered to be cell mediated?

The correct choice is Type 4 hypersensitivity reaction, which is also known as delayed-type hypersensitivity. This type of reaction is primarily mediated by T lymphocytes (T cells), specifically helper T cells and cytotoxic T cells. Unlike other types of hypersensitivity that involve antibodies, Type 4 hypersensitivity involves the direct involvement of immune cells.

In Type 4 hypersensitivity, when an individual is exposed to a particular antigen, sensitized T cells recognize the antigen and release cytokines, leading to the recruitment and activation of macrophages and other inflammatory cells. This process can take several hours to days to manifest, which is why it is termed "delayed." Common examples of Type 4 hypersensitivity include contact dermatitis (such as from poison ivy) and the tuberculin skin test.

Understanding the mechanisms underlying Type 4 hypersensitivity is crucial in recognizing its distinct features and implications in immune responses, differentiating it from other hypersensitivity types that are predominantly antibody-mediated.