PATHOLOGY

Detailed explanation-1: -Answer (b) is correct. Memory cells do respond more quickly than naive T cells to an antigen that they have previously encountered.

Detailed explanation-2: -Memory T cells are necessary for protective immunity against invading pathogens, especially under conditions of immunosuppression. However, their presence also threatens transplant survival, making transplantation a great challenge.

Detailed explanation-3: -Memory T cells are antigen-specific T cells that remain long-term after an infection has been eliminated. The memory T cells are quickly converted into large numbers of effector T cells upon reexposure to the specific invading antigen, thus providing a rapid response to past infection.

Detailed explanation-4: -The lifespan of a human memory T cell is of the order of 30–160 days [12, 13, 15, 16], in contrast to the typical half-life of human T cell memory of 8–15 years [1, 4, 5]. Longevity thus does not seem to be an intrinsic characteristic of circulating memory T cells.