Adult mastocytosis: an immunophenotypic and flow-cytometric investigation.

Skin mast cells of five patients with mastocytosis/urticaria pigmentosa and from four normal controls were immunophenotyped with a panel of 17 monoclonal antibodies; peripheral blood mononuclear cells from the patients were similarly labelled and analysed by flow cytometry. Cutaneous mast cells expressed leucocyte common antigen and markers of macrophage/monocyte lineage suggesting a common progenitor in the ontogeny of the two cell types. The mast cells from the patients differed from the controls, expressing HLA-DR in four cases, and this may be a feature of proliferating cells. The patients' peripheral blood T lymphocytes showed a marked increase in the activation markers HLA-DR and CD25 suggesting a contributory role, possibly via cytokines, in driving mast-cell proliferation.