Interleukin 3 promotes histamine synthesis in hematopoietic progenitors by increasing histidine decarboxylase mRNA expression.

Interleukin 3 (IL-3) is a potent stimulator of histamine production by cells from murine hematopoietic organs. We demonstrate herein that this phenomenon results from increased histidine decarboxylase (HDC: EC 4.1.1.22) activity in progenitor-enriched bone marrow cells (around 5% of the total bone marrow) isolated from the low density layers of a discontinuous Ficoll gradient. HDC levels are markedly enhanced after a 24 h incubation with IL-3 while a 4 h exposure results only in a slight activation. It results from increased expression of the mRNA coding for HDC, as assessed by Northern blot analysis after a 24 h incubation with IL-3. At the same time point and after a 4 h stimulation, we have evaluated the percentage of cells in this population which express HDC mRNA in response to IL-3, using in situ hybridization with the antisense riboprobe. We have thus established that enhanced HDC mRNA expression occurs in a small immature subset representing from 5 to 8% of the progenitor-enriched bone marrow cells.