No abstract

One of the major advances in the histological diagnosis of bone marrow (BM) involvement in mastocytosis has been the specific immunohistochemical detection of tryptase on most cells (MC), which has shown to be of great diagnostic value, especially in cases of malignant mastocytosis. On the other hand, recent studies have clearly shown that bone marrow mast cells can be specifically identified and accurately enumerated using multiparametric flow cytometry, which allow a systematic analysis of the immunophenotypic characteristics of bone marrow mast cells. Once this flow cytometric approach was applied for the analysis of BMMC from mastocytosis patients clear immunophenotypical differences were found between BMMC from normal individuals and adults with mastocytosis. The most characteristic immunophenotypic feature, both in malignant and adult indolent systemic mast cell disease, being the coexpression of CD2 and CD25 antigens, never present in normal bone marrow mast cells and, which constitute an aberrant hallmark of bone marrow mast cells in adult mastocytosis. Furthermore, bone mast cells from mastocytosis display a higher reactivity for CD35, CD63, and CD69 activation-associated antigens. Based on these results it could be concluded that the use of multiparametric flow cytometric immunophenotyping of BMMC in adult patients suffering from cutaneous mastocytosis can be of great utility for the diagnosis of BM involvement; additionally, this might also help to establish the real incidence of BM involvement in cutaneous mastocytosis.

Summary.We have analysed the quantitative expression of surface CD69 antigen on human mast cells (MC), from both normal and pathological bone marrow (BM) samples, usinḡ ow 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 signi®cantly higher levels of surface CD69 expression than healthy controls (P < 0´001), chronic lymphocytic leukaemia (P 0´001), monoclonal gammopathy of unknown signi®cance (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 signi®cance (P 0´04), myelodysplastic syndromes (P 0´03) and paediatric mastocytosis (P 0´003) cases showed a signi®cantly higher expression of surface CD69 as compared to normal subjects.In summary, our ®ndings show that the CD69 antigen is overexpressed in SMCD patients.

The immunophenotypic identification and enumeration of human bone marrow mast cells represents a clear demonstration of the utility of flow cytometry for rare‐event analysis. The basic approach can be applied to a variety of specimens, including bone marrow, peripheral blood, ascitic fluid, and lymphoid tissue such as adenoids. Special emphasis is placed on markers with potential utility for distinguishing between normal, reactive, and pathological mast cells. From the clinical aspect, immunophenotypic analysis of mast cells may have great utility in supporting the diagnosis of tissue involvement in mastocytosis.