Langerhans cells in the skinalso bring antigens to theparacortical zone of the lymph node where they are calledinterdigitating dendritic cells.Dendritic cells areconsidered as the true link between innate and adaptiveimmunity.Other white blood cells that are part of the innate arm ofthe immune system include eosinophils, basophils, andplatelets. Eosinophils possess eosinophilic granules thatplay a in type I hypersensitivity reaction or allergy. Inaddition, eosinophils also secrete a that is called majorbasic protein that is toxic to parasites, especially helminthsor worms. during Like eosinophils, basophils also play arole in allergies. The granules of both eosinophils andbasophils contain histamine which when released isresponsible for the changes seen the initial phase of anallergic reaction. Finally, platelets are membrane-boundcell fragments that are derived from large cells calledmegakaryocytes. Platelets are mainly involved in bloodcoagulation, however, they secrete substances that play arole in inflammation.Natural killer cells are large granular lymphocytes that arealso called NK cells or Null cells. They were originallyclassified as cytotoxic T cells because they had the samemanner of killing target antigens. However, studiesconducted on their structures showed that all T cells had aT-Cell Receptor (TCR) on their surface that was not presentin NK cells, hence NK cells are not classified anymore as Tcells. NK cells are classified as large granular lymphocytesand are part of the body's innate immune system.Neutrophil•Multilobed nucleus, pale red and bluecytoplasmicgranulesEosinophil•Bilobed nucleus, red cytoplasmic granulesBasophil•Bilobed nucleus, purplish-black cytoplasmicgranulesLymphocyte (small)•Large spherical vilk nucleus, thin rim of pale bluecytoplasmMonocyte•Kidney-shaped nucleus, abundant pale bluecytoplasmThemost important cells of the immune system that playpivotal roles in adaptive immunity are the T lymphocytesand the B lymphocytes. As mentioned, both cells originatefrom the bone marrow. B cells mature in the fetal liver andin the adult bone marrow, which is the equivalent of thebursa of Fabricius in birds. In the peripheral lymphoidorgans, they are located mostly in the germinal centers ofthe lymph nodes and in the spleen. In the presence of theappropriate antigen, the B cells differentiate into antibody-producing plasma cells as well as memory B cells. They areinvolved in the body's humoral immunity. At the sametime, the B cells also function as a professional antigenpresenting cell.T cells- are located mainly in the paracortical andinterfollicular areas of the lymph nodes and spleen. Theyare involved in the body's cell-mediated immunity.
