noun, plural: lymphocytes
Lymphocytes are a type of white blood cells. There are two main groups and a null group of lymphocytes. The two main groups are B lymphocytes and T lymphocytes. The B lymphocytes are involved in the production of antibodies in the humoral immune response. The T lymphocytes participate in the cell-mediated immune response. The null group of lymphocytes include the natural killer cells, cytotoxic cells involved in the innate immune response of vertebrates. Lymphocytes are derived from the stem cells of the lymphoid series, thus the name. Lymphocyte count is typically part of the complete blood cell count. It is expressed as the percentage of lymphocytes to the total number of white blood cells. An increase in the normal range of lymphocytes is known as lymphocytosis whereas a decrease is called lymphocytopenia.