Granule maturation in mast cells: histamine in control

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Mast cells are crucial immune cells originating from bone marrow (BM) progenitors.
• Mast cell maturation involves the development of cytoplasmic secretory granules, regulated by factors like proteoglycans.
• The precise mechanisms governing mast cell granule maturation are not fully understood.

Purpose of the Study:

• To investigate the role of mast cell-derived histamine in mast cell granule maturation.
• To determine the involvement of histamine receptor type 4 (H4) in this process.

Main Methods:

• Utilized histidine decarboxylase (HDC)-deficient mice, which are incapable of producing histamine.
• Examined peritoneal mast cells and bone marrow (BM)-derived mast cells co-cultured with fibroblasts.
• Assessed granule formation, secretory granule protease expression (tryptase, chymase), and histamine receptor H4 function.

Main Results:

• HDC-deficient mast cells exhibited poorly formed secretory granules and reduced protease expression.
• Co-culture with fibroblasts failed to induce normal granule maturation in HDC-deficient mast cells.
• Exogenous histamine partially restored granule differentiation in an H4-dependent manner, though H4-deficient mice showed intact granule formation.

Conclusions:

• Mast cell-derived histamine is a critical factor for proper mast cell granule maturation.
• Intrinsic histamine production by HDC is sufficient for most granule maturation, rendering H4 dispensable when HDC is functional.
• The intracellular target of histamine in mast cell maturation remains to be identified.