Combined in vitro differentiation and cell sorting-based isolation of highly pure mouse bone marrow-derived basophils.

Basophils constitute a rare population of granulocytes with key functions in allergies, immunodeficiencies and cancer. The scarcity of basophils in human blood and tissues constitutes a considerable limit for the study of these cells. Interleukin-3 (IL-3) stimulates both the differentiation and the expansion of basophils from bone marrow (BM) precursors by positively regulating the expression of the IL3Ra receptor. We have standardized an in vitro differentiation protocol of mouse basophils (mBaso) from BM precursors through culture in presence of IL-3 for 10 days followed by cell sorting. At the end of the 10-day differentiation, a considerable number of mBaso can be obtained and cell sorting procedures further improved the isolation of an extraordinarily pure (>98 %) and vital FcεR1⁺ CD11c^- c-kit^- mBaso population. Phenotypic analysis of terminally differentiated (day 10) unsorted mBaso cultured for 24 h showed a decrease in basophilic lineage (c-kit^-) and an increase of mastocytic lineage (c-kit⁺) and reduced the expression of basophil markers FcεRI, CD49b and CD200R either in absence of stimuli or following activation with the alarmin IL-33, indicating cell dedifferentiation. In contrast, terminally differentiated and FcεR1⁺ CD11c^- c-kit^- sorted mBaso do not dedifferentiate in mast cells when placed in culture, and responded to IL-33 stimulation by up-regulating the activation marker CD63 without down-modulation of FcεRI and CD200R3. These evidences highlight that in vitro differentiation followed by cell sorting is a useful method to obtain elevated numbers of highly pure mBaso that preserve their lineage markers and thus are suitable for conducting the desired functional studies.