White Blood Cell Function Lymphocyte Lymphocytes have an important role in producing antibodies and in cellular immunity.  Lymphocytes are produced within bone marrow. If they achieve immune-competence within the bone marrow, they are known as B cells, or if in the thymus (also a primary lymphoid organ), they are known as T cells. Neutrophil Neutrophils are attracted by various chemical signals (chemotaxis). They can leave the blood and enter infected tissue by amoeboid motion. Neutrophils are phagocytes ingest and destroy bacteria. They tend to self destruct as they destroy foreign invaders. Monocyte Monocytes create a very effective defense. Once at the site of infection, they develop into macrophages, the largest phagocyte, and readily engulf microbes by extending pseudopods around them.  Monocytes ingest nonbacterial foreign substances, usually during chronic infection.  Monocytes circulate in the peripheral blood prior to emigration into the tissues. Within certain organs they have special names, e.g. in liver they are known as Kupfer cells, in brain as microglia, in kidney as mesangial cells, and in bone as osteoclasts. Elsewhere they are referred to as tissue macrophages. Eosinophil Eosinophils increase and become active in the presence of certain infections and allergies.  Although they have limited phagocytic activity they can destroy larger parasites such as worm larvae. This is accomplished by latching onto the surface of the parasite then releasing destructive enzymes stored within the cytoplasmic granules of the eosinophil. Basophil Basophils are non-phagocytic cells which, when activated, release numerous compounds from the basophilic granules within their cytoplasm. They secrete the anticoagulant heparin and the substance histamine, which stimulates inflammation. B-cells B-cells are responsible for humoral immunity.  B-cells can recognise very specific features of foreign invaders called antigens (Ag's). Every B cell recognises a different shaped Ag and secrete specific proteins called antibodies. T-cells T-cells are responsible for cell-mediated immunity and help to control the overall specific response. Memory T cells Remain after the pathogens have been killed to stop re-infection Memory B-cells Memory B-cells act as "reserve army" fully prepared to respond quickly to reoccurrence of infection by the same pathogen. Killer T-cells combine with the antigens on the surface of any invading cell and release a powerful group of chemicals called lymphokines.  Some lymphokines kill the pathogens directly, others stimulate other lymphocytes to become active, and still others increase the inflammation so that there are more macrophages Supressor T-cells Supressor t-cells damp down the immune response when the infection is over. Helper T-cells co-operate with B cells in antibody production. They also activate macrophages and promote inflammation Natural Killer (NK) cells Natural Killer (NK) cells attack the body's own cells; either cells infected by a virus or cancerous cells. .The NKs mode of destruction is not phagocytosis but an attack on the membrane of the target cell, which causes that cell to lyse (break open). This is similar to the cytotoxic T-cell but non-specific.