A role for BAFF during myelopoiesis (153.25)

Abstract

Abstract B cell activating factor (BAFF) is expressed in several tissues including the bone marrow (BM). Although BAFF is important for B cell homeostasis and survival, its effects on other leukocytes has not been elucidated. While studying the role of BAFF in rabbit, we discovered that BAFF binds peripheral blood myeloid cells and MHC Class IIneg CD14neg myeloperoxidase (MPO)pos myeloid progenitors (MP) in the BM. Addition of BAFF to co-cultures of unfractionated rabbit BM cells with the murine BM stroma cell line, OP9 stimulated proliferation of rabbit cells resulting in an increase in the total cell number compared to co-cultures lacking BAFF. In addition, BAFF increased the percentage of CD14pos myeloid cells including macrophages in these co-cultures. To determine if BAFF plays a role in human myelopoiesis, we examined Lineageneg CD13pos MP from cord blood (CB) for BAFF binding and expression of BAFF receptors. We found that a small number of these cells express BAFF receptor and bind BAFF. To elucidate the function of BAFF binding to MP, we cultured MP sorted from CB with thrombopoietin, stem cell factor (SCF), and Flt-3L or with SCF and Flt-3L in the presence or absence of BAFF. Total cell number and the number of myeloid cells expressing CD14, CD15, or Class II was not statistically different in cultures containing or lacking BAFF. Experiments to elucidate the function of BAFF binding to MP cells are ongoing. These data suggest a novel role for BAFF in myelopoiesis.