To characterize the transcriptional program that governs terminal granulocytic differentiation in vivo, we performed comprehensive microarray analyses of human bone marrow populations highly enriched in promyelocytes (PMs), myelocytes/ metamyelocytes (MYs), and neutrophils (bm-PMNs). These analyses identified 11 310 genes involved in differentiation, of which 6700 were differentially regulated, including previously unidentified effector proteins and surface receptors of neutrophils. Differentiation of PMs toward MYs was accompanied by a marked decline of proliferative and general cellular activity as defined by down-regulation of E2 promoter binding factor (E2F) target genes; cyclin dependent kinases 2, 4, and 6; and various metabolic, proteasomal, and mitochondrial genes. Expression patterns of apoptosis genes indicated death control by the p53 pathway in PMs and by death receptor pathways in bm-PMNs. Effector proteins critical for host defense were expressed successively throughout granulocytic differentiation, whereas receptors and receptor ligands essential for the activation of the host defense program were terminally up-regulated in bm-PMNs. The up-regulation of ligandreceptor pairs, which are defined inducers as well as target genes of nuclear factor-B (NF-B), suggests a constitutive activation of NF-B in bm-PMNs by autocrine loops. Overall IntroductionPolymorphonuclear neutrophilic granulocytes (neutrophils/PMNs) constitute the most abundant population of white blood cells and are essential players in innate immune defense of mammalian hosts against microorganisms. Once neutrophils have migrated to sites of infection, they recognize microorganisms and their products to initiate a first line of defense using a number of distinct mechanisms. These defense mechanisms include phagocytosis, generation of reactive oxygen intermediates, and the release of antimicrobial granule proteins for killing and degradation of microorganisms. 1,2 Neutrophils are short-lived cells, which are continuously generated from hematopoietic stem cells (HSCs) in the bone marrow (BM) by a process called granulopoiesis. The hallmark of early granulopoiesis is the successive commitment of pluripotent HSCs via multipotent common myeloid progenitors (CMPs) and bipotent granulocyte-macrophage progenitors (GMPs) toward unipotent progenitors restricted to the granulocytic lineage. 3,4 Once the progenitors are committed to the granulocytic lineage, they initiate terminal granulopoiesis and differentiate into mature neutrophils. Terminal granulopoiesis gives rise to a series of morphologically distinct stages, which are readily identified by their characteristic nuclear shape and their content of granules. At the myeloblast/ promyelocyte (MB/PM) stages the cells still proliferate and generate primary granules with their constituting proteins. At the myelocyte/metamyelocyte (MC/MM) stages, cell proliferation and expression of primary granule proteins stop concomitantly with the successive generation of secondary and tertiary granules and the...

Multiple myeloma (MM) is an incurable B-cell malignancy characterized by accumulation of malignant plasma cells in bone marrow (BM) and recurrent or persistent infections. Tolllike receptors (TLRs) are essential in the host defense against infections and today 10 human TLRs (TLR1-TLR10) and one TLR-homolog (RP105) have been characterized. B cells express several TLRs (mainly TLR1, 6, 7, 9, 10 and RP105) and TLRinitiated responses in B cells include proliferation, antiapoptosis effect and plasma cell (PC) differentiation. The present study was designed to analyze the role of TLRs in MM. We show that frequent expressions of TLRs were detected in cell lines from MM patients (minimum six TLRs in each). In comparison, only few TLRs (mainly TLR1 and or RP105) were found expressed in PCs from BM of healthy donors. In addition, TLR-specific ligands induce increased proliferation and survival of the MM cell lines, partially due to an autocrine interleukin-6 production. Importantly, we demonstrate that also PC from MM patients proliferates in response to TLR-specific ligands. In conclusion, TLR-ligands may contribute to increased growth and survival of MM cells in MM patients.

No abstract