IMMUNOLOGY

Detailed explanation-1: -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-2: -T lymphocytes originate from bone marrow progenitors that migrate to the thymus for maturation, selection, and subsequent export to the periphery.

Detailed explanation-3: -There are several types of T cells; the most common and well-known are the CD4+ T cells (helper T cells) and CD8+ T Cells (cytotoxic T cells, or killer T cells). T cells cannot recognize soluble, free antigens. T cells can only recognize protein-based, receptor-bound antigens.

Detailed explanation-4: -Liver dendritic cells (DCs) facilitate the priming of T cells, and virus infections of the liver can generate T-cell immunity that allows the infection to be cleared, as is generally the case for hepatitis A virus in healthy humans and mouse hepatitis virus in immunocompetent mice1, 2, 3.

Detailed explanation-5: -Helper T cells do all of the following except: enhance nonspecific defenses.

Detailed explanation-6: -T Cell Activation There are three types of signals: TCR, BCR, and cytokine signals. If a cell receives all three signals, it will mature into an effector cell. If a cell only receives one of the signals (TCR or BCR), the cell will become useless.