LymphocytesLymphocytes are a type of white blood cell generated by the immune system to defend the body against cancerous cells, pathogens, and foreign matter. Lymphocytes circulate in blood and lymph fluid and are found in body tissues including the spleen, thymus, bone marrow, lymph nodes, tonsils, and liver. Lymphocytes provide a means for immunity against antigens. This is accomplished through two types of immune responses: humoral immunity and cell mediated immunity. Humoral immunity focuses on identifying antigens prior to cell infection, while cell mediated immunity focuses on the active destruction of infected or cancerous cells.
Types of LymphocytesThere are three main types of lymphocytes: T cells, B cells, and natural killer cells. Two of these types of lymphocytes are critical for specific immune responses. They are B lymphocytes (B cells) and T lymphocytes (T cells).
B cells develop from bone marrow stem cells in adults. When B cells become activated due to the presence of a particular antigen, they create antibodies that are specific to that specific antigen. Antibodies are specialized proteins that travel thorough the bloodstream and are found in bodily fluids. Antibodies are critical to humoral immunity as this type of immunity relies on the circulation of antibodies in bodily fluids and blood serum to identify and counteract antigens.
T cells develop from liver or bone marrow stem cells that mature in the thymus. These cells are responsible for cell mediated immunity. T cells contain proteins called T-cell receptors that populate the cell membrane. These receptors are capable of recognizing various types of antigens. There are three major classes of T cells that play specific roles in the destruction of antigens. They are cytotoxic T cells, helper T cells, and regulatory T cells.
- Cytotoxic T cells directly terminate cells containing antigens by binding to them and lysing or causing them to burst open.
- Helper T cells precipitate the production of antibodies by B cells and also produce substances that activate other T cells.
- Regulatory T cells (also called suppressor T cells) suppress the response of B cells and other T cells to antigens.