<unk> s are amoeboid in appearance, and have nongranulated cytoplasm. Thus they are classified as agranulocytes. Containing unilobar nuclei, these cells are one of the types of<unk> nonuclear leukocytes which shelter azurophil granules. The archetypal geometry of the<unk>  nucleus is ellipsoidal; metaphorically bean-shaped or kidney-shaped, although the<unk> st significant distinction is that the nuclear envelope should not be hyperbolically furcated into lobes. Contrast to this classification occurs in polymorphonuclear leukocytes.<unk> s compose 2% to 10% of all leukocytes in the human body and serve multiple roles in immune function. Such roles include: replenishing resident macrophages under normal conditions; migration within approximately 8–12 hours in response to inflammation signals from sites of infection in the tissues; and differentiation into macrophages or dendritic cells to effect an immune response. In an adult human, half of the<unk> s are stored in the spleen. These change into macrophages after entering into appropriate tissue spaces, and can transform into foam cells in the endothelium. Subpopulations In humans There are at least three types of<unk> s in human blood: # The classical<unk>  is characterized by high level expression of the CD14 cell surface receptor (CD14++ CD16−<unk>  # The non-classical<unk>  shows low level expression of CD14 and additional co-expression of the CD16 receptor (CD14+CD16++<unk> . # The intermediate<unk>  with high level expression of CD14 and low level expression of CD16 (CD14++CD16+<unk> s). While in humans the level of CD14 expression can be used to differentiate non-classical and intermediate<unk> s, the slan (6-Sulfo LacNAc) cell surface marker was shown to give an unequivocal separation of the two cell types. Ghattas et al. state that the "intermediate"<unk>  population is likely to be a unique subpopulation of<unk> s, as opposed to a developmental step, due to their comparatively high expression of surface receptors involved in reparative processes (including vascular endothelial growth factor receptors type 1 and 2, CXCR4, and Tie-2) as well as evidence that the "intermediate" subset is specifically enriched in the bone marrow. After stimulation with microbial products the CD14+CD16++<unk> s produce high amounts of pro-inflammatory cytokines like tumor necrosis factor and interleukin-12. Said et al. showed that activated<unk> s express high levels of PD-1 which might explain the higher expression of PD-1 in CD14+CD16++<unk> s as compared to CD14++CD16−<unk> s. Triggering<unk> s-expressed PD-1 by its ligand PD-L1 induces IL-10 production which activates CD4 Th2 cells and inhibits CD4 Th1 cell function. In humans a<unk>  crawling behavior, similar to the patrolling in mice, has been demonstrated both for the classical and the non-classical<unk> s. In mice In mice,<unk> s can be divided in two subpopulations. Inflammatory<unk> s (CX3CR1low, CCR2pos, Ly6Chigh, PD-L1neg), which are equivalent to human classical CD14++ CD16−<unk> s and resident<unk> s (CX3CR1high, CCR2neg, Ly6Clow, PD-L1pos), which are equivalent to human non-classical CD14+ CD16+<unk> s. Resident<unk> s have the ability to patrol along the endothelium wall in the steady state and under inflammatory conditions.
Monocyte
Basophil
Prolymphocyte
Podocyte
Thymocyte
Agranulocyte
Plasma cell
Lymphoblast