Related Experiment Video
Updated: Aug 8, 2026
Analyzing the Functions of Mast Cells In Vivo Using 'Mast Cell Knock-in' Mice
Published on: May 27, 2015
Human synovial mast cells. I. Ultrastructural in situ and in vitro immunologic characterization
A de Paulis1, I Marinò, A Ciccarelli
1University of Naples Federico II, Italy.
Insights
Human synovial mast cells exhibit unique ultrastructure and mediator release profiles compared to other tissues. Their distinct characteristics suggest the local microenvironment influences mast cell phenotype, impacting arthritis research.
Area of Science:
- Immunology
- Cell Biology
- Histopathology
Background:
- Mast cells are key immune cells found in various tissues, including synovium.
- Their role in inflammatory conditions like arthritis is significant but not fully understood.
- Previous research has focused on mast cells from other human tissues, leaving synovial mast cell characteristics less defined.
Purpose of the Study:
- To investigate the ultrastructure of human synovial mast cells in their native tissue.
- To identify stimuli that activate these cells and analyze their mediator release.
- To compare synovial mast cells with those from other human tissues.
Main Methods:
- Ultrastructural analysis of synovial mast cells in situ using immunoelectron microscopy.
- Biochemical, immunological, and functional analysis of isolated synovial mast cells in vitro.
- Comparison of synovial mast cells with mast cells from lung, heart, and skin.
Main Results:
- Synovial mast cells possess distinct granular structures and lipid bodies, with a subset showing degranulation.
- Tryptase and chymase are localized to granules in over 90% of mast cells, identifying them as the MCTC subtype.
- These cells release histamine in response to immunologic (anti-IgE, anti-FcεRI) and non-immunologic (substance P, SCF, 48/80) stimuli, and synthesize prostaglandin D2 and leukotriene C4 upon IgE cross-linking.
Conclusions:
- Human synovial mast cells exhibit unique ultrastructural and biochemical features compared to mast cells from other tissues.
- The local microenvironment of the synovium likely influences mast cell phenotype.
- Studying isolated synovial mast cells offers valuable insights into their function and mediators in arthritis.
Objective:
To examine the ultrastructure of human synovial mast cells in situ, to identify immunologic and nonimmunologic stimuli that activate these cells in vitro, and to quantify a number of preformed and de novo-synthesized mediators.
Methods:
We conducted an ultrastructural study of synovial mast cells in situ and performed immunoelectron microscopy localization of tryptase and chymase. Isolated synovial mast cells were analyzed biochemically, immunologically, and functionally in vitro and compared with cells from human lung, heart, and skin.
Results:
Ultrastructural study of synovial tissue revealed mast cells with homogeneously dense, scrolled, crystal, and mixed granules, and lipid bodies in the cytoplasm. A small percentage of mast cells showed evidence of degranulation. Immunoelectron microscopy demonstrated the subcellular localization of tryptase and chymase over granules of > 90% of the mast cells, which were of the MCTC subtype. Isolated synovial mast cells released histamine in response to immunologic (anti-IgE and anti-Fc epsilon receptor I [anti-Fc epsilon RI]) and nonimmunologic (substance P, recombinant human stem cell factor, and 48/80) stimuli, but did not respond to recombinant human C5a in vitro. Synovial mast cells differed from those isolated from other human tissues, in a variety of immunologic and biochemical features. There was a linear correlation between the percentage of histamine secretion and tryptase release (r = 0.79, P < 0.001) induced by cross-linking of Fc epsilon RI. Cross-linking of IgE with anti-IgE on synovial mast cells induced de novo synthesis of prostaglandin D2 (mean +/- SEM 87.5 +/- 4.9 ng/10(6) cells) and of leukotriene C4 (57.6 +/- 17.8 ng/10(6) cells).
Conclusion:
Mast cells ultrastructurally characterized in situ in synovial tissue were seen to differ from mast cells previously isolated from other human tissues. This raises the possibility that the local microenviroment influences their phenotype. Isolation of mast cells from human synovia can be useful for studying their role and their mediators in patients with arthritis.
