Generation of a considerable number of functional mast cells with a high basal level of FcepsilonRI expression from cord blood CD34+ cells by co-culturing them with bone marrow stromal cell line under serum-free conditions

The number of mast cells (MC) that can be obtained from tissue is limited, making it difficult to study the role of MC. Cultured MC derived from cord blood (CB)-CD34(+) cells proliferate well compared with those derived from adult CD34(+) cells; however, they have been reported to be phenotypically or functionally immature regardless of culture system. For example, very few cells express FcepsilonRI. To resolve this problem, we addressed the effect of human bone marrow stromal cell line on the development of cultured MC. CB-CD34(+) (1 x 10(4)) cells were cultured for 8 weeks in a serum-free medium containing rhIL-6 and rhSCF with or without a human bone marrow stromal cell line, namely, co-culture and liquid culture, and were compared in various regards. MC were basically determined by metachromatic staining of granules. The number of MC obtained (60.3 +/- 15.8 x 10(5) versus 2.0 +/- 1.0 x 10(5)), percentage of FcepsilonRI(+) cells (29.3 +/- 9.4% versus 1.9 +/- 0.8%), histamine content (9.7 +/- 2.8 pg/cell versus 5.8 +/- 2.3 pg/cell), and IgE-mediated histamine release (46 +/- 10% versus 17 +/- 7%) were higher (P < 0.01 and P < 0.05) in the co-culture than in the liquid culture. When CB-CD34(+) cells were developed in liquid culture with the co-culture supernatant (CM), a significant increase (P < 0.01) in the percentage of FcepsilonRI(+) cells and in cell number was observed but these values were lower than those of co-cultured MC. We concluded that this co-culture system was useful for obtaining a considerable number of mature MC with a high basal level of functional FcepsilonRI expression from CB-CD34(+) cells. Yet unknown humoral factors in CM may partly mediate this effect.