Many other cells besides peripheral blood white blood cells play a role in immunity. Table 2 lists some of them, along with a brief description of their function.
Table 2. Immune Cells Seldom or Never Seen in Blood Smear.| Cell | Function |
| Plasma Cell | Fully differentiated form of a B lymphocyte that secretes antibodies |
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| Dendritic Cell | Helps to activate T cells by presenting antigen to them, and thus initiate the adaptive immune response |
| Macrophage | Phagocytosis and killing of microorganisms, secreting cytokines, presenting antigen |
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| Mast Cell | In response to parasites, releases granules containing histamine and other toxic substances |
