Early emergence of CD19-negative human antibody secreting cells at the plasmablast to plasma cell transition

Long-lived human plasma cells (PCs) play central roles in immunity and autoimmunity and are enriched amongst the subpopulation of CD19-negative human PCs. However, whether human CD19-negative PCs are necessarily ″aged″ cells that have gradually lost CD19 expression is not known. Assessing peripheral blood samples at steady state and during the acute response to influenza vaccination in healthy donors we identify the presence of phenotypic CD19-negative plasmablasts, the proliferative precursor state to mature PCs, and demonstrate by ELISpot that these are antibody-secreting cells (ASCs). During the acute response to influenza vaccination CD19-positive, CD19-low and CD19-negative ASCs secrete vaccine-specific antibody and show linked IGHV repertoires. To address precursor/product relationships we employ in vitro models which mimic both T-dependent and T-independent differentiation finding that the CD19-negative state can be established at the plasmablast to PC transition, that CD19-negative PCs increase as a percentage of surviving PCs in vitro, and that CD19-negative and CD19-positive PCs can be maintained independently. These data provide proof-of-principle for the view that newly generated ASCs can acquire a mature PC phenotype accompanied by loss of CD19 expression at an early stage of differentiation and that ″aging″ is not an obligate requirement for a CD19-negative state to be established

Network analysis identifies proinflammatory plasma cell polarization for secretion of ISG15 in human autoimmunity

Plasma cells (PCs) as effectors of humoral immunity produce Igs to match pathogenic insult. Emerging data suggest more diverse roles exist for PCs as regulators of immune and inflammatory responses via secretion of factors other than Igs. The extent to which such responses are preprogrammed in B-lineage cells or can be induced in PCs by the microenvironment is unknown. In this study, we dissect the impact of IFNs on the regulatory networks of human PCs. We show that core PC programs are unaffected, whereas PCs respond to IFNs with distinctive transcriptional responses. The IFN-stimulated gene 15 (ISG15) system emerges as a major transcriptional output induced in a sustained fashion by IFN-α in PCs and linked both to intracellular conjugation and ISG15 secretion. This leads to the identification of ISG15-secreting plasmablasts/PCs in patients with active systemic lupus erythematosus. Thus, ISG15-secreting PCs represent a distinct proinflammatory PC subset providing an Ig-independent mechanism of PC action in human autoimmunity

An extended set of PRDM1/BLIMP1 target genes links binding motif type to dynamic repression

The transcriptional repressor B lymphocyte-induced maturation protein-1 (BLIMP1) regulates gene expression and cell fate. The DNA motif bound by BLIMP1 in vitro overlaps with that of interferon regulatory factors (IRFs), which respond to inflammatory/immune signals. At such sites, BLIMP1 and IRFs can antagonistically regulate promoter activity. In vitro motif selection predicts that only a subset of BLIMP1 or IRF sites is subject to antagonistic regulation, but the extent to which antagonism occurs is unknown, since an unbiased assessment of BLIMP1 occupancy in vivo is lacking. To address this, we identified an extended set of promoters occupied by BLIMP1. Motif discovery and enrichment analysis demonstrate that multiple motif variants are required to capture BLIMP1 binding specificity. These are differentially associated with CpG content, leading to the observation that BLIMP1 DNA-binding is methylation sensitive. In occupied promoters, only a subset of BLIMP1 motifs overlap with IRF motifs. Conversely, a distinct subset of IRF motifs is not enriched amongst occupied promoters. Genes linked to occupied promoters containing overlapping BLIMP1/IRF motifs (e.g. AIM2, SP110, BTN3A3) are shown to constitute a dynamic target set which is preferentially activated by BLIMP1 knock-down. These data confirm and extend the competitive model of BLIMP1 and IRF interaction

Reprogramming Primordial Germ Cells into Pluripotent Stem Cells

Background: Specification of primordial germ cells (PGCs) results in the conversion of pluripotent epiblast cells into monopotent germ cell lineage. Blimp1/Prmt5 complex plays a critical role in the specification and maintenance of the early germ cell lineage. However, PGCs can be induced to dedifferentiate back to a pluripotent state as embryonic germ (EG) cells when exposed to exogenous signaling molecules, FGF-2, LIF and SCF. Methodology and Principal Findings: Here we show that Trichostatin A (TSA), an inhibitor of histone deacetylases, is a highly potent agent that can replace FGF-2 to induce dedifferentiation of PGCs into EG cells. A key early event during dedifferentiation of PGCs in response to FGF-2 or TSA is the down-regulation of Blimp1, which reverses and apparently relieves the cell fate restriction imposed by it. Notably, the targets of Blimp1, which include c-Myc and Klf-4, which represent two of the key factors known to promote reprogramming of somatic cells to pluripotent state, are up-regulated. We also found early activation of the LIF/Stat-3 signaling pathway with the translocation of Stat-3 into the nucleus. By contrast, while Prmt5 is retained in EG cells, it translocates from the nucleus to the cytoplasm where it probably has an independent role in regulating pluripotency. Conclusions/Significance: We propose that dedifferentiation of PGCs into EG cells may provide significant mechanistic insights on early events associated with reprogramming of committed cells to a pluripotent state

A novel Alzheimer disease locus located near the gene encoding tau protein

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordAPOE ε4, the most significant genetic risk factor for Alzheimer disease (AD), may mask effects of other loci. We re-analyzed genome-wide association study (GWAS) data from the International Genomics of Alzheimer's Project (IGAP) Consortium in APOE ε4+ (10 352 cases and 9207 controls) and APOE ε4- (7184 cases and 26 968 controls) subgroups as well as in the total sample testing for interaction between a single-nucleotide polymorphism (SNP) and APOE ε4 status. Suggestive associations (P<1 × 10-4) in stage 1 were evaluated in an independent sample (stage 2) containing 4203 subjects (APOE ε4+: 1250 cases and 536 controls; APOE ε4-: 718 cases and 1699 controls). Among APOE ε4- subjects, novel genome-wide significant (GWS) association was observed with 17 SNPs (all between KANSL1 and LRRC37A on chromosome 17 near MAPT) in a meta-analysis of the stage 1 and stage 2 data sets (best SNP, rs2732703, P=5·8 × 10-9). Conditional analysis revealed that rs2732703 accounted for association signals in the entire 100-kilobase region that includes MAPT. Except for previously identified AD loci showing stronger association in APOE ε4+ subjects (CR1 and CLU) or APOE ε4- subjects (MS4A6A/MS4A4A/MS4A6E), no other SNPs were significantly associated with AD in a specific APOE genotype subgroup. In addition, the finding in the stage 1 sample that AD risk is significantly influenced by the interaction of APOE with rs1595014 in TMEM106B (P=1·6 × 10-7) is noteworthy, because TMEM106B variants have previously been associated with risk of frontotemporal dementia. Expression quantitative trait locus analysis revealed that rs113986870, one of the GWS SNPs near rs2732703, is significantly associated with four KANSL1 probes that target transcription of the first translated exon and an untranslated exon in hippocampus (P≤1.3 × 10-8), frontal cortex (P≤1.3 × 10-9) and temporal cortex (P≤1.2 × 10-11). Rs113986870 is also strongly associated with a MAPT probe that targets transcription of alternatively spliced exon 3 in frontal cortex (P=9.2 × 10-6) and temporal cortex (P=2.6 × 10-6). Our APOE-stratified GWAS is the first to show GWS association for AD with SNPs in the chromosome 17q21.31 region. Replication of this finding in independent samples is needed to verify that SNPs in this region have significantly stronger effects on AD risk in persons lacking APOE ε4 compared with persons carrying this allele, and if this is found to hold, further examination of this region and studies aimed at deciphering the mechanism(s) are warranted

BLIMP-1 and STAT3 counterregulate microRNA-21 during plasma cell differentiation

Abstract During cellular differentiation, mRNA transcription and translation require precise coordination. The mechanisms controlling this are not well defined. IL-21 is an important regulator of plasma cell differentiation, and it controls the master regulator of plasma cell differentiation, B lymphocyte-induced maturation protein-1 (BLIMP-1), via STAT3 and IRF4. Among the other targets of STAT3 is microRNA-21 (miR-21). miR-21 is the most frequently deregulated microRNA in malignancy, including B cell lymphomas, and it has oncogenic potential downstream of STAT3. However, the regulation and function of miR-21 during plasma cell differentiation are not characterized. In contrast to the induction of miR-21 observed in response to STAT3 activation in other systems, we demonstrate that miR-21 is repressed during IL-21–driven plasma cell differentiation. We explored the molecular basis for this repression and identify primary miR-21 transcription as a direct target of BLIMP-1–dependent repression, despite continued STAT3 activation and phospho-STAT3 binding to the primary miR-21 promoter. Thus, STAT3 and BLIMP-1 constitute an incoherent feed-forward loop downstream of IL-21 that can coordinate microRNA with mRNA expression during plasma cell differentiation.</jats:p