Mastocytosis.

OBJECTIVES: The 2019 Workshop of the Society for Hematopathology/European Association for Haematopathology received and reviewed cases covering the spectrum of mastocytosis and related diseases, including morphologic mimics, focusing on recent updates and relevant findings for pathologists. METHODS: The workshop panel reviewed 99 cases of cutaneous and systemic mastocytosis (SM) and SM and associated hematologic neoplasms (SM-AHN). RESULTS: Despite a common theme of KIT mutation (particularly D816V), mastocytosis is a heterogeneous neoplasm with a wide variety of presentations. This spectrum, including rare subtypes and extramedullary organ involvement, is discussed and illustrated by representative cases. CONCLUSIONS: In the age of targeted treatment aimed at KIT, the accurate diagnosis and classification of mastocytosis has major implications for therapy and further interventions. Understanding the clinical, pathologic, and genetic findings of mastocytosis is crucial for selecting the proper tests to perform and subsequent arrival at a correct diagnosis in this rare disease.

Role of mast cells in skin tag development: an immunohistochemical study.

OBJECTIVE: To detect mast cell density by toluidine blue and immunohistochemical staining for mast cell tryptase in skin tags as compared to normal skin to determine whether they have a role in skin tag development. STUDY DESIGN: This study was carried out on 30 patients with skin tags and 10 age- and sex-matched healthy controls without skin tags. RESULTS: There was a significant difference between skin tag and control groups regarding mast cell density evaluated by toluidine blue staining (p = 0.003) and mast cell tryptase expression (p = 0.001), where the density was higher in skin tags as compared to normal skin. Mast cells were higher in number using toluidine blue staining in lesions arising in sites other than the head and neck (p = 0.028). High expression of mast cell tryptase was significantly associated with marked collagenosis (p = 0.02) and presence of eosinophils (p = 0.04). CONCLUSION: The present study demonstrates the possible role of mast cells in promoting fibrosis and facilitating the development of skin tags. Mast cells may attract eosinophils to cooperate in inducing more fibrosis in skin tag development.

Purification and characterization of mast cell tryptase and chymase from human tissues.

Mast cells are key effector cells of the allergic response. When stimulated by specific allergen through the high-affinity IgE receptors or through other stimuli, these cells release a number of potent mediators of inflammation. Amongst these are the serine proteases tryptase and chymase. In humans, tryptase is the most abundant mediator stored in mast cells. Chymase is present in more moderate amounts in a subpopulation of mast cells (MC(TC)). This subtype of mast cells predominates in connective tissue, whereas the other major subtype, the MC(T), predominates in mucosal tissue. Both proteases have been shown to act on specific extracellular proteins and peptides, as well as to alter the behavior of various cell types. Inhibitors of tryptase have been found to be efficacious in animal and human models of asthma, and both proteases are currently being investigated as potential targets for therapeutic intervention. Such pharmacological, physiological, and biochemical studies require the availability of purified tryptase and chymase. In this chapter, we shall describe procedures for the purification of tryptase and chymase from human tissues and provide protocols for monitoring purification and characterization of the final product. The preparation of recombinant proteases will not be covered, though some of the procedures described may be readily adapted for their purification from recombinant expression systems. The procedures described here have been developed for the purification of the human proteases and will require some modification if applied to purify mast cell proteases from the tissues of other species.

Extended cleavage specificity of mMCP-1, the major mucosal mast cell protease in mouse-high specificity indicates high substrate selectivity.

Mucosal mast cells are in the mouse predominantly found in the epithelium of the gastrointestinal tract. They express the beta-chymases mMCP-1 and mMCP-2. During nematode infections these intraepithelial mast cells increase in numbers and high amounts of mMCP-1 appear in the jejunal lumen and in the circulation. A targeted deletion of this enzyme leads to decreased ability to expel the intraepithelial nematode Trichinella spiralis. A suggested role for mMCP-1 is alteration of epithelial permeability by direct or indirect degradation of epithelial and endothelial targets, however, no such substrates have yet been identified. To enable a screening for natural substrates we performed a detailed analysis of the extended cleavage specificity of mMCP-1, using substrate phage display technology. In positions P1 and P1' distinct preferences for Phe and Ser, respectively, were observed. In position P2 a high selectivity for large hydrophobic amino acids Phe, Trp and Leu was detected, and in position P2' aliphatic amino acids Leu, Val and Ala was preferred. In positions P3 and P4, N-terminal of the cleaved bond, mMCP-1 showed specificity for aliphatic amino acids. The high selectivity in the P2, P1, P1' and P2' positions indicate that mMCP-1 has a relatively narrow set of in vivo substrates. The consensus sequence was used to screen the mouse protein database for potential substrates. A number of mouse extracellular or membrane proteins were identified and cell adhesion and connective tissue components were a dominating subfamily. This information, including the exact position of potential cleavage sites, can now be used in a more focused screening to identify which of these target molecules is/are responsible for the increased intestinal permeability observed in parasite infected mice.