What is T cell immunity?

T-cell immunity is a reaction in the body's immune system whereby 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 participate in the act of T-cell immunity.

There are several types of T cells that function in the body: helper T cells, killer T cells, suppressor T cells, and memory T cells. Although T cells, like other lymphocytes, are formed in the body's bone marrow, T cells move to the thymus after development. This function also gives it its name, "T cell."

T-cell immunity requires other components of the immune system to be evoked, beginning 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 only recognize one type of antigen, so the phagocyte must find the right helper T cell to recognize it and generate a response. When a T cell finally recognizes the antigen, it begins to divide and create proteins called cytokines to notify 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 their name implies, they react by attacking and killing infected cells that would go unnoticed by other components of the immune system. Its receptors inspect all nearby cells and thus attack any cell showing signs of infection by using an enzyme that ultimately kills the cell in question. The types of infections that can occur in a cell, and thus a killer T-cell reaction, include viruses, bacteria, and even cancer.

Once the antigen is treated, other T cells spring into action. Suppressor T cells, for example, work to curb the unnecessary formation of additional killer T cells. Additionally, memory T cells remember that specific antigen to elicit a faster response if the invader ever returns to the body.

T-cell immunity is also known as cell-mediated immunity, and it can be disrupted by viruses such as the 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 immunodeficiency syndrome (AIDS).

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