IMMUNOLOGY

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 helper cells recognize viral peptides in association with class II MHC protein, usually on the surface of an antigen-presenting cell (APC). These interactions result in T helper cell activation, proliferation and differentiation, providing the affinity of binding is sufficiently high.

Detailed explanation-4: -Armed effector cytotoxic CD8 T cells are essential in host defense against pathogens that live in the cytosol, the commonest of which are viruses. These cytotoxic T cells can kill any cell harboring such pathogens by recognizing foreign peptides that are transported to the cell surface bound to MHC class I molecules.