Agranulocyte

Agranular cells are noted by the absence of granules in their cytoplasm, which distinguishes them from granulocytes.

Second, monocytes and the granulocytes are closely related cell types developmentally, physiologically and functionally.

[citation needed] Lymphocytes are much more common in the lymphatic system and include natural killer T-cells.

CD4+ (helper) T cells co-ordinate the immune response (they are what becomes defective in an HIV infection).

Monocytes share the phagocytosis function of neutrophils, but are much longer lived as they have an additional role: they present pieces of pathogens to T cells so that the pathogens may be recognized again and killed, or so that an antibody response may be mounted.