Saturday, October 3, 2009

A lymphocyte is a type of leukocyte (white blood cell) which is responsible for immune responses. Lymphocytes make up 25% of the white blood cells and they regulate and take part in acquired immunity. According to their physical appearence under the microscope, there are categories of lymphocytes: the large granular lymphocytes and the small lymphocytes. According to their functions, there are three types of lymphocytes: 1) natural killer cells, which are large granular lymphocytes; 2) T cells, which are small lymphocytes; 3) B cells, also small.

Natural killer cells are toxin-containing lymphocytes which kill virus-infected cells and tumor cells. T cells are lymphocytes which are involved in cell-mediated immunity; they have the ability to recognize specific peptide antigens through the receptors on their cell surface. B cells recognize specific “non-self” antigens, during a process known as antigen presentation; once they have identified the foreign microorganism, the cells generate specific responses to eliminate specific pathogens or pathogen infected cells; when B cells are activated by antigens, or pathogens, they bind them by their protein-receptor and begin to produce large quantities of antibodies which then neutralize foreign objects like bacteria and viruses.

Lymphocytes are produced in the bone marrow, but some them mature in the thymus and the spleen.