IMMUNOLOGY

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: -Your lymphocytes include T-cells and B-cells. Both types are part of your body’s defense. B-cells make proteins called antibodies to fight pathogens. T-cells protect you by destroying harmful pathogens and by sending signals that help control your immune system’s response to threats.

Detailed explanation-3: -There are two major types of T cells: the helper T cell and the cytotoxic T cell. As the names suggest helper T cells ‘help’ other cells of the immune system, whilst cytotoxic T cells kill virally infected cells and tumours. Unlike antibody, the TCR cannot bind antigen directly.

Detailed explanation-4: -Helper T cells express a protein called CD4 on their surface. This protein plays a critical role in helper T cell activation by binding class II major histocompatibility complex (MHC) molecules, which specialize in helping the immune system recognize foreign substances.

Detailed explanation-5: -Answer and Explanation: The correct option is a. They recognize antigen-MHC complexes. The T-cells contain T-cell receptors that recognize the peptides produced by processing the antigens in the antigen-presenting cell.

Detailed explanation-6: -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.