White Blood Cells

White blood cells are much less numerous than red (the ratio between the two is around 1:700); have nuclei; participate in protecting the body from infection; consist of lymphocytes and monocytes with relatively clear cytoplasm, and three types of granulocytes, whose cytoplasm is filled with granules. Lymphocytes There are several kinds of lymphocytes (although they all look alike under the microscope), each with different functions to perform .

The most common types of lymphocytes are B lymphocytes ("B cells"). These are responsible for making antibodies. T lymphocytes ("T cells"). There are several subsets of these: inflammatory T cells that recruit macrophages and neutrophils to the site of infection or other tissue damage cytotoxic T lymphocytes (CTLs) that kill virus-infected and, perhaps, tumor cells helper T cells that enhance the production of antibodies by B cells. Although bone marrow is the ultimate source of lymphocytes, the lymphocytes that will become T cells migrate from the bone marrow to the thymus where they mature.

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; mature into fully functional cells.