monoblast

Monoblasts are the committed progenitor cells that differentiated from a committed macrophage or dendritic cell precursor (MDP) in the process of hematopoiesis. They are the first developmental stage in the monocyte series leading to a macrophage. Their myeloid cell fate is induced by the concentration of cytokines they are surrounded by during development. These cytokines induce the activation of transcription factors which push completion of the monoblast's myeloid cell fate. Monoblasts are normally found in bone marrow and do not appear in the normal peripheral blood. They mature into monocytes which, in turn, develop into macrophages. They then are seen as macrophages in the normal peripheral blood and many different tissues of the body. Macrophages can produce a variety of effector molecules that initiate local, systemic inflammatory responses. These monoblast differentiated cells are equipped to fight off foreign invaders using pattern recognition receptors to detect antigen as part of the innate immune response.

== Structure == thumb|400px|Comparison of monoblast, promonocyte and monocyte. A typical monoblast is about 12 to 20 μm in diameter, has a nuclear to cytoplasm ratio of 4:1 to 3:1, and, like most myeloid blasts, has a round to oval nucleus with fine chromatin structure. Compared to other myeloid blasts, monoblasts have more cytoplasm. The nucleoli it contains is usually distinct. One to four nucleoli are usually visible. The nucleus can be central or eccentric and it can show evidence of indentation or folding. The cytoplasm stains moderately to lightly basophilic and may contain small azurophilic granules. These granules contain enzymes that can damage or digest pathogens and also release inflammatory signals in the periphery. Auer rods are there, but rarely seen. Easily observed in the round monoblast nucleus is lacy, clear chromatin and distinct nucleoli.