KIT mutation in mast cells and other bone marrow hematopoietic cell lineages in systemic mast cell disorders: a prospective study of the Spanish Network on Mastocytosis (REMA) in a series of 113 patients.

Despite the relevance of the c-kit/stem cell factor (SCF) signaling pathway in mast cell (MC) diseases, the exact frequency of KIT mutations in different compartments of bone marrow (BM) hematopoietic cells of individuals with systemic mastocytosis (SM), and its different diagnostic categories, remains unknown. In this study, we prospectively analyzed the presence of KIT mutations in fluorescence-activated cell-sorting (FACS)- purified populations of BM MCs (n = 113) and other BM cell compartments (n = 67) from adults with SM. Our results show the presence of D816V KIT mutation in virtually all adults (93%) with indolent and aggressive forms of SM, except well-differentiated SM (29%), while other KIT mutations were rarely (< 3%) detected. In around one-third of patients with mutated MCs, the KIT mutation was also detected in CD34+ hematopoietic cells and eosinophils, and, to a lesser extent, in monocytic, neutrophil-lineage BM precursor cells and lymphocytes. Most patient with poor-prognosis SM (81%) carried the KIT mutation in 2 or more BM myeloid cell populations, while this was detected in a smaller proportion (27%) of indolent cases. These results would support the notion that KIT mutation is a hallmark of adult SM where it targets a pluripotent hematopoietic stem cell, and may contribute to explaining previously observed discrepancies in the literature.

The effects of thyroid hormones on circulating markers of cell-mediated immune response, as studied in patients with differentiated thyroid carcinoma before and during thyroxine withdrawal.

OBJECTIVE: To address the influence of thyroid hormones on circulating markers of cell-mediated immune response in an in vivo human model. SUBJECTS AND DESIGN: Twenty-two patients with stage I differentiated thyroid carcinoma were studied on the last day of thyroxine suppressive treatment, 4-7 days after withdrawal, and the day before whole body scanning. Three patients were excluded because of residual disease. Twenty euthyroid individuals served as controls. Serum thyrotrophin and thyroid hormones were measured by an immunometric assay, circulating cytokines by enzyme-linked immuno-sorbent assay and lymphoid populations by flow cytometry. RESULTS: Thyroid function in patients changed from subclinical or mild hyperthyroidism at the first visit, to a situation of normal circulating levels of free thyroxine and triiodothyronine at the second, ending in a state of overt hypothyroidism. Thyroxine suppressive treatment in patients increased serum interleukin-18 concentrations (IL-18, mean+/-s.d., 280+/-122 vs 183+/-106 pg/ml, F = 3.192, P = 0.029), soluble interleukin-2 receptor levels (sIL-2R, 4368+/-1480 vs 2564+/-846 pg/ml, F = 21.324, P < 0.001), and the percentage of natural killer (NK) cells in peripheral blood (15.9+/-8.6 vs 10.5+/-3.6%, F = 4.977, P = 0.004) compared with controls. After thyroxine withdrawal, serum levels of IL-18, sIL-2R and the percentage of NK cells decreased progressively. CONCLUSION: Our present results suggest that thyroid hormones modulate the cell-mediated immune response in humans.

Systemic mastocytosis associated with acute myeloid leukemia: case report and implications for disease pathogenesis.

Mastocytosis may be associated with clonal nonmast cell lineage hematologic diseases, including myelodysplastic syndromes, myeloproliferative disorders, and acute myeloid leukemia. Here we present a patient with the simultaneous diagnosis of mastocytosis and an acute myeloid leukemia, M2 subtype in the French-American-British classification, with t(8;21) carrying a population of immature mast cell precursors, and discuss this presentation in the context of a potential pathogenetic cellular link between this leukemia and mastocytosis.

Immunophenotypic analysis of mast cells in mastocytosis: When and how to do it. Proposals of the Spanish Network on Mastocytosis (REMA).

BACKGROUND: Mastocytosis is a term used for a heterogeneous group of disorders characterized by an abnormal proliferation and accumulation of mast cells (MCs) in one or multiple tissues including skin, bone marrow, liver, spleen, and lymph nodes, among others. METHODS: In recent years, multiparameter flow cytometric studies have shown that pathologic MCs from patients with mastocytosis display unique aberrant immunophenotypic characteristics as compared with normal MCs. RESULTS: Among other features, pathologic MCs show aberrant expression of CD25 and CD2 antigens and abnormally high levels of the CD11c and CD35 complement receptors, the CD59 complement regulatory molecule, the CD63 lysosomal membrane antigen, and the CD69 early-activation antigen. In addition, MCs from mastocytosis express abnormally low levels of CD117 and unexpectedly high light scatter and autofluorescence characteristics. CONCLUSIONS: These aberrant immunophenotypic features are of great relevance for the assessment of tissue involvement in mastocytosis with consequences in the diagnosis, classification, and follow-up of the disease and in its differential diagnosis with other entities. In this paper we provide the reader with information for the objective and reproducible identification of pathologic MCs by using quantitative multiparametric flow cytometry, information for their phenotypic characterization, and the criteria currently used for a correct interpretation of the immunophenotypic results obtained.

Overexpression of complement receptors and related antigens on the surface of bone marrow mast cells in patients with systemic mastocytosis.

Depending on their stage of maturation and other factors, mast cell (MC) subsets differ from each other in terms of the expression of complement-associated antigens. This study analysed the expression of various complement-related cell surface antigens (CD11b/CR3, CD11c/CR4, CD35/CR1, CD55/DAF, CD59/MIRL, CD88/C5aR) on bone marrow mast cells (BMMC) in patients suffering from systemic mastocytosis (SM), other haematological diseases and non-haematological disorders (control groups). Expression of complement-associated cell surface antigens was analysed by flow cytometry. There were clear immunophenotypic differences between BMMC obtained from patients with SM and those from the control subjects: the percentage of patients expressing surface CD11c, CD35 and CD88 was significantly higher in patients with SM (76%, 100%, 54%) than in the control subjects (58%, 11%, 18%) (P < 0.05). In addition, the levels of CD11c, CD35 and CD88 expressed per MC (sites per cell) were significantly higher (P < 0.05) in SM than in the control group. Expression of the complement regulatory molecules CD55 and CD59 was detected in BMMC in all patients analysed. However, the levels of CD59 per BMMC were higher in patients with SM as compared with the control subjects, which could help to explain the formation of BMMC aggregates in the former group of individuals. Together, our results showed that BMMC in systemic mastocytosis overexpressed the cell surface membrane receptors involved in binding of complement components and complement-mediated cell activation. Whether this pathological expression of complement receptors is of pathophysiological significance remains to be determined.

Abnormal expression of CD antigens in mastocytosis.

Human mast cells are myeloid cells derived from human pluripotential CD34+ stem cells. Normal mast cells exhibit a myeloid immunophenotype characterized by the expression of CD117, CD33 and Fc epsilon RI in the absence of reactivity for CD14, CD15 and lymphoid-lineage-associated antigens. Multiparametric flow-cytometric studies have shown that mast cells from mastocytosis display unique immunophenotypic characteristics, including coexpression of CD2 and CD25 antigens together with abnormally high levels of the activation-related antigens CD35, CD63 and CD69 among others. Such aberrant immunophenotypic features are of great relevance in the diagnosis and differential diagnosis of the disease, flow-cytometric immunophenotyping of mast cells representing the most sensitive method for the diagnosis of tissue involvement in mastocytosis. From the pathogenetic point of view, the immunophenotypical patterns described suggest the existence of profound changes regarding the adhesion and activation status of mast cells in mastocytosis and may represent a useful tool for a better understanding of some pathophysiological aspects of the disease.