Delayed hypersensitivity involves:

Ans. is 'd' i.e., Lymphocytes (Ref: Ananthanarayan, 9th/e, p. 167 and 8th/e, p. 168)* Reaction is mediated by sensitized T-lymphocytes which, on contact with specific antigen, release lymphokines that cause biological effects on macrophages, leucocytes and tissue cells.* Delayed type by CD4 Th1 cell.