Immune Cells | Introduction to Mast Cells and Selection of Identification Indicators

In the previous installment, I provided a detailed introduction to granulocytes and their indicator selection. In this issue, let's delve into mast cells and explore the selection of indicators related to them.

What is Mast Cell?

Mast cells are widely distributed in the microvasculature surrounding the skin and mucous membranes of internal organs. They secrete various cytokines involved in immune regulation, such as activation of T cells, B cells, and antigen-presenting cells (APCs). Mast cells express MHC molecules and B7 molecules, exhibiting APC functions. They also express a large number of IgE Fc receptors and release allergic mediators. Mast cells possess weak phagocytic activity and, like blood eosinophils, are tissue cells with strongly basophilic granules. Based on their tissue distribution, mast cells can be classified into connective tissue mast cells (CTMCs) and mucosal mast cells (MMCs).

Figure 1. Electron Micrograph of Mast Cells

Mast cells typically exhibit a round, oval, triangular, or irregular quadrilateral shape, with a cell diameter ranging from 5 to 25 μm. Their nuclei are generally round, occasionally showing binucleation. The cytoplasm is densely packed with round basophilic granules, each measuring 0.2-0.5 μm in diameter. These granules are water-soluble and may display metachromasia. Under electron microscopy, mast cells reveal pseudopodia-like processes on their surface, grid-like or fingerprint-like structures within their cytoplasmic granules, abundant mitochondria and Golgi apparatus in the cytoplasm, and rough endoplasmic reticulum between granules.

The Role of Mast Cells

Mast cells play diverse roles in the immune system. Primarily known for their involvement in allergic and autoimmune reactions, they also contribute significantly to wound healing, pathogen resistance, and immunity against parasites and environmental toxins such as venoms.

Similar to eosinophils, mast cells express FcεRI, a receptor that binds to the Fc region of immunoglobulin E (IgE) antibodies secreted in response to parasitic infections and allergens. Cross-linking of IgE bound to FcεRI triggers degranulation and release of inflammatory mediators such as histamine, proteases, cytokines, and leukotrienes. This process initiates immune responses, including inflammation, vasodilation, and recruitment of other immune cells, to combat infections or neutralize harmful substances.

Figure 2. Mast Cells and Secreted Cytokines

The Development and Identification of Mast Cells

The development of mast cells is still poorly understood, as they are unique among hematopoietic cells in that they mature in peripheral tissues rather than in lymphoid organs or circulation. Initially thought to derive from circulating eosinophils that migrate into tissues, they were later identified as a distinct lineage. Immature mast cell progenitors arise from the granulocyte/monocyte progenitor pool in the bone marrow and are released into circulation before completing their development as tissue-resident cells. Throughout their development, they express CD117 or c-Kit, a receptor for stem cell factor (SCF), and the presence of this marker, along with high-affinity IgE receptor (FcεRI), is commonly used to identify mast cells from heterogeneous cell populations.

Currently, key indicators used to identify mast cells include CD117 (c-kit) and FcεRIα, with mast cells typically identified by their expression of CD117⁺ and FcεRIα⁺.

Figure 3. Detection of Mast Cells in C57BL/6 Mouse Bone Marrow Sample (Double Staining with PE-CD117 and FITC-FcεRIα)

Commonly used indicators for identifying mast cells include:

Alright, that concludes our introduction to mast cells for this issue. If you have any further experimental-related questions, feel free to leave them in the comments or contact us directly.