T-cell immunity is a type of immune response that uses white blood cells called T cells to destroy foreign invaders. There are different types of T cells, including helper, killer, suppressor, and memory T cells. Antigen presentation is required for T-cell immunity to work, and killer T cells attack and kill infected cells. T-cell immunity can be disrupted by viruses such as HIV.
T-cell immunity is a reaction in the body’s immune system by which the immune system recognizes a foreign invader, called an antigen, and responds by destroying it. There are two types of white blood cells: B cells and T cells. T-cell immunity uses white blood cells or lymphocytes, called T cells or T lymphocytes, to destroy antigens. This particular immune response is distinct from other immune responses, such as the complement system protein response or the body’s use of phagocytes to eat foreign bodies, although these elements take part in the act of T-cell immunity.
There are several types of T cells at work in the body: helper T cells, killer T cells, suppressor T cells, and memory T cells. Although T cells, like other lymphocytes, form in the body’s bone marrow, T cells move to the thymus after development. This feature also gives it its name, “T-cell”.
T-cell immunity requires the summoning of other components of the immune system, starting with a process called antigen presentation. First, a phagocyte, such as a macrophage, captures and devours the invader. It then travels to a lymph node to relay information about the invader to a helper T cell by presenting pieces of the antigen on its surface. The receptors on each helper T cell recognize only one type of antigen, so the phagocyte must find the right helper T cell to recognize it and elicit a response. When a T cell finally recognizes the antigen, it begins to divide and create proteins called cytokines to inform the rest of the immune system — killer T cells and B cells — to continue the immune response.
Killer T cells are also known as cytotoxic T lymphocytes. As the name suggests, they react by attacking and killing infected cells that would go unnoticed by other components of the immune system. Its receptors inspect each nearby cell and then attack any cell showing signs of infection using an enzyme that ultimately kills the cell in question. The types of infections that can strike a cell — and thus a killer T cell reaction — include viruses, bacteria, and even cancer.
Once the antigen has been processed, other T cells spring into action. Suppressor T cells, for example, work to curb the formation of more unnecessarily killer T cells. Additionally, memory T cells remember that specific antigen to elicit a faster response if the invader returns to the body.
T-cell immunity is also known as cell-mediated immunity and can itself be disrupted by viruses such as human immunodeficiency virus (HIV). These types of viruses specifically target and kill helper T cells to severely weaken even the basic immune response. This action of HIV, for example, is what causes the body to eventually succumb to acquired immune deficiency syndrome (AIDS).
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