Lymphocytes- Types and Functions


Lymphocytes are a type of white blood cell that play a vital role in the immune system. They are responsible for recognizing and responding to foreign substances (antigens) that may cause infection or disease. Lymphocytes can also remember previous encounters with antigens and mount a faster and stronger response upon re-exposure.

Lymphocytes originate from stem cells in the bone marrow and differentiate into various subsets that have different functions and locations in the body. The three main types of lymphocytes are B cells, T cells, and natural killer (NK) cells. Each type of lymphocyte has a unique way of recognizing and eliminating antigens.

B cells produce antibodies, which are proteins that bind to specific antigens and mark them for destruction by other immune cells. B cells also act as antigen-presenting cells (APCs), which means they display fragments of antigens on their surface and activate T cells.

T cells are involved in cellular immunity, which means they directly attack and kill infected or abnormal cells. T cells have receptors on their surface that recognize antigens presented by APCs. There are two major subsets of T cells: helper T cells and cytotoxic T cells. Helper T cells secrete cytokines, which are chemical messengers that regulate the activity of other immune cells. Cytotoxic T cells release substances that induce apoptosis, or programmed cell death, in target cells.

NK cells are part of the innate immune system, which means they do not require prior exposure to antigens to become activated. NK cells can recognize and kill cells that are infected by viruses or transformed by cancer. NK cells have receptors on their surface that sense changes in the expression of molecules on the target cell`s surface.

Lymphocytes circulate in the blood and lymphatic system and migrate into various tissues and organs where they encounter antigens. Lymphocytes also congregate in specialized structures called lymphoid organs, such as the spleen, lymph nodes, tonsils, and thymus. These organs provide an environment where lymphocytes can interact with each other and with other immune cells.

Lymphocytes are essential for the protection of the body against pathogens and tumors. However, lymphocytes can also cause problems when they malfunction or become overactive. For example, autoimmune diseases occur when lymphocytes attack the body`s own tissues, while allergies occur when lymphocytes react to harmless substances. Therefore, the regulation of lymphocyte activation and function is crucial for maintaining a balanced immune system.