Basophils and eosinophils share a common differentiation pathway. Factors regulating terminal commitment toward one cell type, however, have so far not been defined. Interleukin-3 (IL-3) is a potent differentiation factor for both human eosinophils and basophils. In the present study, the effects of various recombinant human (rh) growth regulators on IL-3-dependent growth of eosinophils and basophils were studied in a bone marrow (BM) suspension culture system (normal donors, n = 13). We found that type beta transforming growth factors (TGFs) lead to a significant increase in the absolute numbers of basophils in BM cultures grown in the presence of IL-3 (day 14 of culture; IL-3: 133 +/- 20 v IL-3 + TGF-beta 1: 231 +/- 28 x 10(3)/mL [P less than .01]) and to an increase in the total histamine values (IL-3: 72.6 +/- 22.2 v IL-3 + TGF-beta 1: 142.9 +/- 37.3 ng/mL [P less than .015]) compared with rhIL-3 alone. In contrast, type beta TGFs were found to inhibit the IL-3-dependent growth of eosinophils (IL-3: 170.4 +/- 37.2 v IL-3 + TGF-beta 1: 16.7 +/- 5.2 x 10(3)/mL [P less than .01]) and formation of eosinophil cationic protein in the same culture system. The effect of TGF-beta 1 (and TGF-beta 2) on IL-3-dependent differentiation of basophils and eosinophils was dose- and time-dependent (maximum effects observed with 1 to 10 ng/mL of rhTGF-beta 1 or TGF-beta 2) and could be neutralized by an antibody specific for TGF-beta 1. In contrast to the TGFs, interferon-alpha (IFN-alpha) and IFN-gamma were found to downregulate IL-3-dependent formation of both basophils (IL-3: 167 +/- 33 v IL-3 + IFN-alpha: 67 +/- 25 v IL-3 + IFN-gamma: 65 +/- 33 x 10(3)/mL [P less than .01]) and eosinophils (IL-3: 239 +/- 5 v IL-3 + IFN-alpha: 81 +/- 4 v IL-3 + IFN-gamma: 67 +/- 17 x 10(3)/mL [P less than .05]) in our culture system. Type beta TGFs as well as the IFNs failed to directly induce differentiation of human basophils or eosinophils in the absence of other growth factors. Together, these results show that type beta TGFs and IFNs are potent regulators of cytokine-dependent growth and differentiation of human allergic effector cells.

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