AP BIOLOGY

Detailed explanation-1: -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-2: -Helper T-cells stimulate B-cells to make antibodies and help killer cells develop. Killer T-cells directly kill cells that have already been infected by a foreign invader.

Detailed explanation-3: -A type of immune cell that can kill certain cells, including foreign cells, cancer cells, and cells infected with a virus. Cytotoxic T cells can be separated from other blood cells, grown in the laboratory, and then given to a patient to kill cancer cells.

Detailed explanation-4: -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-5: -Armed helper T cells activate B cells when they recognize the appropriate peptide:MHC class II complex on the B-cell surface (Fig. 9.5).