White blood cells, also called leukocytes, are found throughout the body and are essential for protecting against infectious agents and foreign material.
Neutrophils and monocytes are phagocytes.
Lymphocytes are comprised of B cells, T cells, and NK cells. (Monocytes have a longer life span than other leukocytes.) Dendritic cells, macrophages and B lymphocytes are called antigen-presenting cells, which basically have the same function.