PATHOLOGY

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: -T cells (also called T lymphocytes) are major components of the adaptive immune system. Their roles include directly killing infected host cells, activating other immune cells, producing cytokines and regulating the immune response.

Detailed explanation-4: -Cytotoxic CD8 T cells carry out their killing function by releasing two types of preformed cytotoxic protein: the granzymes, which seem able to induce apoptosis in any type of target cell, and the pore-forming protein perforin, which punches holes in the target-cell membrane through which the granzymes can enter.