IMMUNOLOGY

Detailed explanation-1: -Helper T cells themselves, however, can only function when activated to become effector cells. They are activated on the surface of antigen-presenting cells, which mature during the innate immune responses triggered by an infection.

Detailed explanation-2: -Human T cells express major histocompatibility complex (MHC) class II antigens and adhesion molecules characteristic of antigen-presenting cells (APCs), and recent in vitro and in vivo evidence supports an antigen-presenting function for T cells.