Mast cells are a type of white blood cell that are integral to the body’s immune system, particularly recognized for their involvement in allergic reactions. They function as immediate responders to various stimuli, releasing potent chemicals that influence inflammation and immune responses. These cells are found throughout the body, playing a role in defense against pathogens and in conditions like asthma and anaphylaxis.
The Origin of Mast Cells
Mast cells originate from hematopoietic stem cells (HSCs), which are specialized cells found in the bone marrow. These HSCs are the foundational “parent” cells capable of producing all types of blood cells, including various immune cells. From these multipotent progenitors, mast cell precursors develop.
Human mast cells specifically derive from pluripotent CD34+, Kit+, CD13+, and CD117+ stem cells. While the bone marrow is the primary source of these progenitors in adults, some research indicates that primitive mast cells can also be generated during embryonic development in the yolk sac. The c-Kit protein (CD117) is expressed on HSCs and is retained on mast cells throughout their development, playing a role in their maturation when exposed to stem cell factor.
Their Journey and Maturation
Immature mast cell progenitors leave the bone marrow and enter the bloodstream, circulating throughout the body. These cells are not fully mature upon exiting the bone marrow; they undergo their final differentiation and maturation once they reach specific peripheral tissues. This process allows mast cells to adapt to the unique microenvironment of their destination.
The migration of these progenitors from the bloodstream into tissues is a controlled process, influenced by various factors. Within the tissues, local environmental cues, such as stem cell factor (SCF) and other cytokines, play a significant role in guiding their complete maturation and differentiation.
Mast Cells in Body Tissues and Their Functions
Once matured, mast cells are strategically located in various connective tissues throughout the body, particularly at interfaces with the external environment. They are abundantly found in the skin, lungs, gastrointestinal tract, and around blood vessels and nerves. This positioning allows them to act as immediate sentinels, poised to respond rapidly to invading pathogens or allergens.
Their functions in these tissues are diverse and contribute to both immune surveillance and immediate responses. Upon activation, often by allergens binding to IgE on their surface, mast cells release various mediators. These mediators include histamine, proteases, and various cytokines, which collectively orchestrate inflammatory responses. Histamine, for example, contributes to common allergic symptoms like itching, swelling, and increased mucus production, while other mediators play roles in tissue repair and the formation of new blood vessels.