The majority of white blood cells are either neutrophils (band cells and polymorphonuclear granulocytes, 35–70%) or lymphocytes (20–45%). Leucocytopenia is almost always caused by a reduced number of neutrophils.
Lymphocytopenia is only seldom associated with a specific disease. It may be seen in acute or chronic infections caused by a variety of microbes as well as both in congenital and acquired immune deficiency states.