Natural killer (NK) cells are large mononuclear lymphocytes that target abnormal cells, including virus-infected and cancerous cells, and lack either T cell receptors (TCRs) or surface immunoglobulin (Ig). Abnormal cells do not express the normal major histocompatibility complex (MHC). Normal MHC markers prevent NK cell activation, so abnormal MHC expression by abnormal cells recruits NK cells (signals cell distress). Binding of NK cells on target cells (and detect abnormal MHC levels) also leads to activation. After activation, NK cells can employ several mechanisms for target cell destruction.

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Natural Killer Cells

Monocytes are granulocytes that clear microbes via phagocytosis as well as other antigens that have been labeled by immunoglobulin (Ig).  These cells are activated after neutrophils are, and they have been found to present in places with chronic inflammation and infection.  Additionally, monocytes are involved in acute inflammation and causing inflammation in granulomatous conditions, which are chronic infections.  They are able to kill microbes by producing nitric oxide and regulate adaptive immunity by producing cytokines such as IL-12 and interferon (IFN)-γ.  Monocytes can differentiate into macrophages and dendritic cells.

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Monocytes

Some types of agranulocytes include:

- Lymphocytes (Specifically natural killer cells)
- Monocytes

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Leukocytes lacking granules in their cytoplasm

Agranulocytes

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