AP BIOLOGY

Detailed explanation-1: -Helper T-cells play the main role in coordinating an immune response once a foreign enemy has been spotted. If a T-cell in the thymus acquires a protein marker known as CD4, it becomes a helper T-cell.

Detailed explanation-2: -Helper T cells are arguably the most important cells in adaptive immunity, as they are required for almost all adaptive immune responses. They not only help activate B cells to secrete antibodies and macrophages to destroy ingested microbes, but they also help activate cytotoxic T cells to kill infected target cells.

Detailed explanation-3: -RB: T cells can play different roles. They can act as “killer cells”, attacking cells which have been infected with a virus or another kind of pathogen, or they can act as “helper cells” by supporting B cells to produce antibodies.

Detailed explanation-4: -6.2. Like CTLs, helper T cells also recognize antigen presented by dendritic cells. In the same way they present antigen to CTLs, dendritic cells acquire antigen in the infected tissue and travel to the regional lymph nodes.