Toll-like receptors (TLRs) constitute a family of nonpolymorphic receptors that are devoted to pathogen recognition. In this work, we have explored the impact of TLR ligands (TLR-L) on human hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs). We show that HSCs and HPCs have a comparable pattern of expression of TLR transcripts characterized by the predominance of TLR1, -2, -3, -4 and -6. In longterm cultures of HSCs, HPCs and stromal cells, most TLR-L profoundly inhibited B-cell development while preserving or enhancing the production of myeloid cells. In short-term cultures, the TLR1/2 ligand PAM 3 CSK 4 induced a large proportion of HPCs to express markers of the myelomonocytic lineage. PAM 3 CSK 4 induced only marginal expression of myeloid lineage markers on HSCs but promoted their myeloid commitment as revealed by their acquisition of the phenotype of multi-and bipotential myeloid progenitors and by upregulation of the transcription factors PU.1, C/EBPa and GATA-1. Our results suggest that TLR agonists can bias the lineage commitment of human HSCs and shift the differentiation of lineage-committed progenitors to favor myelopoiesis at the expense of lymphoid B-cell development.

It was recently shown that bacterial thymus-independent (TI) antigens confer long-lasting immunity and generate memory B lymphocytes. However, reactivation of TI memory B cells is repressed in immunocompetent mice, thus raising the issue of the mechanism whereby TI vaccines confer immune protection. Here, we propose an explanation to this apparent paradox by showing that a Streptococcus pneumoniae capsular polysaccharide (PS) generates long-lived bone marrow (BM) plasma cells which frequency can be increased by CpG oligodeoxynucleotides (ODNs). The adjuvant effect of CpG ODNs on the PS3 Ab response is directly targeted to B cells and does not involve B-1a cells. We also demonstrated that BM plasma cells generated in response to the thymus-dependent (TD) form of the PS vaccine have a higher secretion capacity than those produced after immunization with the CpGadjuvanted PS vaccine. Finally, we show that the PS-specific BM plasma cell compartment is sufficient to confer full protection of vaccinated mice against S pneumoniae infection. Altogether, our results show that TI antigens like their TD counterparts can generate both the lymphoid and the plasma cell component of B-cell memory. They also provide a framework for the improvement and widespread usage of TI vaccines. IntroductionDespite advances in antimicrobial therapy, infections with extracellular polysaccharide (PS)-encapsulated bacteria remain an important clinical problem and a primary source of death worldwide. Pathogenic bacteria including Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae express capsular PSs that behave as prototypic thymus-independent (TI) antigens (Ags). These Ags have initially been defined on the basis of their ability to elicit an antibody (Ab) response in T cell-deficient or athymic mice by a mechanism that requires expression of a functional Bruton tyrosine kinase. 1 They are mostly nonpeptidic molecules, which in their great majority, are unable to follow the conventional Agprocessing pathway leading to presentation by MHC class I and II molecules. 2 To overcome systemic infections by encapsulated extracellular bacteria such as S pneumoniae, B cells rapidly generate a protective Ab response against capsular PS. B-1 and marginal zone B cells have been envisioned as key players in the humoral response against TI Ags. 3 More recently, 2 studies, using Borrelia hermsii or capsular PSs from S pneumoniae as immunogens, have shown that B-1b cells are critically involved in bacterial clearance in vaccinated mice. 4,5 It has long been thought that the generation of memory B cells is restricted to thymus-dependent (TD) responses. However, the recent observation that adoptive transfer of B-1b cells from donor mice immunized with whole bacteria can confer long-lasting TI immunity to immunodeficient mice shows that TI Ags generate B-cell memory and that this function can be assigned to the B-1b-cell subset. 5 Nonetheless, the concept of TI B-cell memory is at odds with the fact that, unlike TD Ags, TI Ags fail to...

The CCR4-associated protein CAF1 has been demonstrated to play several roles in the control of transcription and of mRNA decay. To gain further insight into its physiological function, we generated CAF1-deficient mice. They are viable, healthy, and normal in appearance; however, mCAF1 ؊/؊ male mice are sterile. The crossing of mCAF1 ؉/؊ mice gave a Mendelian ratio of mCAF1 ؉/؉ , mCAF1 ؉/؊ , and mCAF1 ؊/؊ pups, indicating that haploid mCAF1-deficient germ cells differentiate normally. The onset of the defect occurs during the first wave of spermatogenesis at 19 to 20 days after birth, during progression of pachytene spermatocytes to haploid spermatids and spermatozoa. Early disruption of spermatogenesis was evidenced by Sertoli cell vacuolization and tubular disorganization. The most mature germ cells were the most severely depleted, but progressively all germ cells were affected, giving Sertoli cell-only tubes, large interstitial spaces, and small testes. This phenotype could be linked to a defect(s) in germ cells and/or to inadequate Sertoli cell function, leading to seminiferous tubule disorganization and finally to a total disappearance of germ cells. The mCAF1-deficient mouse provides a new model of failed spermatogenesis in the adult that may be relevant to some cases of human male sterility.