Altered leukocyte subsets and immune proteome indicate proinflammatory mechanisms in mastocytosis

Background: Indolent systemic mastocytosis (ISM) is characterized by pathologic accumulation of mast cells. The mechanism behind its phenotypic heterogeneity is not well understood. Interaction of mast cellswith other immune cellsmight cause systemic inflammation and thereby associated symptoms. Objective: We investigated peripheral leukocyte compartments and serum immune proteome in ISM. Methods: Peripheral blood leukocyte phenotyping using flow cytometry in a cohort of 18 adults with ISM and 12 healthy controls. Targeted proteomics was performed to measure 169 proteins associated with inflammation on serum of another 20 ISM patients and 20 healthy controls. Results: Proportions of plasmacytoid dendritic cells and monocytes were significantly decreased while T(H)2 cells were increased in peripheral blood of ISM patients. Furthermore, a shift from naive to memory T cells was observed. Hierarchical clustering of the serum proteome revealed 2 distinct subgroups within ISM patients. In subgroup A (n = 8), 62 proteins were significantly overexpressed, whereas those of subgroup B (n = 12) were comparable to healthy controls. Patients in subgroup A displayed upregulated signaling pathways downstream of Tolllike receptor 4, TNF-alpha, and IFN-gamma. Fatigue was more often present in subgroup A compared to B (75% vs 33% respectively, P = .06). Conclusions: Altered distribution of leukocyte subsets and a proinflammatory proteome were observed in subsequent 2 cohorts of ISM patients. We hypothesize that neoplastic mast cells recruit and activate plasmacytoid dendritic cells, monocytes, and T cells, leading to a vicious cycle of inflammation.

Automated summary

This study observed altered distribution of leukocyte subsets and a proinflammatory proteome in patients with indolent systemic mastocytosis (ISM). The researchers hypothesized that neoplastic mast cells might recruit and activate plasmacytoid dendritic cells, monocytes, and T cells, leading to a vicious cycle of inflammation.