The CD69 early activation molecule is overexpressed in human bone marrow mast cells from adults with indolent systemic mast cell disease

We have analysed the quantitative expression of surface CD69 antigen on human mast cells (MC), from both normal and pathological bone marrow (BM) samples, using flow cytometry. Our major aim was to analyse whether CD69 is constitutively expressed by normal BMMC and to explore the possible differences between CD69 expression by BMMC from normal controls and patients suffering from different pathological conditions. The constitutive expression Of surface CD69 was clearly demonstrated in BMMC; however, systemic mast cell disease (SMCD) patients showed significantly higher levels of surface CD69 expression than healthy controls (P < 0.001), chronic lymphocytic leukaemia (P = 0.001), monoclonal gammopathy of unknown significance (P < 0.001), multiple myeloma (P < 0.001) patients, and myelodysplastic syndromes (P = 0.002). Furthermore, almost no overlap between the levels of CD69 expression on BMMC was observed between SMCD cases and the remaining groups of individuals except for the paediatric mastocytosis group (P > 0.05). From the other groups of patients, monoclonal gammopathy of unknown significance (P = 0.04), myelodysplastic syndromes (P = 0.03) and paediatric myelodysplastic (P = 0.003) cases showed a significantly higher expression of surface CD69 as compared to normal subjects. In summary, our findings show that the CD69 antigen is overexpressed in SMCD patients.