A lymphocyte is a type of white blood cell present in the blood. White blood cells help protect the body against diseases and fight infections. When the general defense systems of the body have been penetrated by dangerous invading microorganisms, lymphocytes help provide a specific response to attack the invading organisms.
There are several kinds of lymphocytes (although they all look alike under the microscope), each with different functions to perform. Lymphocytes, like other blood cells, develop in the bone marrow and arise from immature cells called stem cells. In early childhood, some lymphocytes then migrate to the thymus, an organ in the top of the chest, where they mature to become ‘T’ cells. Others remain in the bone marrow and mature there to become ‘B’ cells. Both B cells and T cells also take up residence in lymph nodes, the spleen and other tissues where they encounter antigens; continue to divide by mitosis and mature into fully functional cells. These lymphocytes play an important role in recognising and destroying infecting organisms such as bacteria and viruses.
In normal conditions, most of the lymphocytes circulating in the body are T cells. Their role is to recognise and destroy abnormal body cells (for example, cells that have been infected by a virus). There are several subsets of T-lymphocytes– inflammatory T cells that recruit macrophages and neutrophils to the site of infection or other tissue damage; T-suppressor/cytotoxic cells (CTLs) possess that kill virus-infected and, perhaps, tumor cells and also inhibit B-cell development; helper T cells that help immature B cells develop into mature B cells and enhance the production of antibodies by B cells. B-lymphocytes are responsible for making antibodies as they recognise foreign cells and material (for example, bacteria that have invaded the body). When these cells come into contact with a foreign protein (for example, on the surface of bacteria), they produce antibodies, which then stick to the surface of the foreign cell and cause its destruction.
If the number of T-lymphocytes is reduced, that is referred to as low T-cell count. There is no term in medicine like ‘low liver cell count.’