Cytologic aspects (May-Grünwald-Giemsa smears) and histamine production of isolated CD34^+/−c-Kit^+/− compartments from PB of patients with mastocytosis and healthy controls. (A) Among healthy donors, cultures of both CD34⁺c-Kit⁺ and CD34⁻c-Kit⁺ cell subsets showed differentiation into mature mast cells in the presence of SCF (top panel), whereas no differentiation was observed in the absence of SCF (data not shown). In patients with proven mastocytosis, bearing either the classic D816V c-Kit mutation or WT c-Kit, similar differentiation into mature mast cells was observed in the presence or absence of SCF (bottom panel). (B) Histamine dosage also supported mast cell differentiation, demonstrating increased histamine levels with or without SCF in both cultured subsets from the patients with mastocytosis, whereas among healthy controls, histamine levels increased only in the presence of SCF.