Natural killer (NK) cells provide defense in the early stages of the innate immune response against viral infections by producing cytokines and causing cytotoxicity. The killer immunoglobulin-like receptors (KIRs) on NK cells regulate the inhibition and activation of NK-cell responses through recognition of human leukocyte antigen (HLA) class I molecules on target cells KIR and HLA loci are both highly polymorphic, and some HLA class I products bind and trigger cell-surface receptors specified by KIR genes. Here we report that the activating KIR allele KIR3DS1, in combination with HLA-B alleles that encode molecules with isoleucine at position 80 (HLA-B Bw4-80Ile), is associated with delayed progression to AIDS in individuals infected with human immunodeficiency virus type 1 (HIV-1). In the absence of KIR3DS1, the HLA-B Bw4-80Ile allele was not associated with any of the AIDS outcomes measured. By contrast, in the absence of HLA-B Bw4-80Ile alleles, KIR3DS1 was significantly associated with more rapid progression to AIDS. These observations are strongly suggestive of a model involving an epistatic interaction between the two loci. The strongest synergistic effect of these loci was on progression to depletion of CD4(+) T cells, which suggests that a protective response of NK cells involving KIR3DS1 and its HLA class I ligands begins soon after HIV-1 infection.

NK cell activity is partially controlled through interactions between killer Ig-like receptors (KIR) on NK cells and their respective HLA class I ligands. Independent segregation of HLA and KIR genes, along with KIR specificity for particular HLA allotypes, raises the possibility that any given individual may express KIR molecules for which no ligand is present. Inhibitory receptor genes KIR2DL2/3 and KIR2DL1 were present in nearly all subjects sampled in this study, whereas their respective activating homologs, KIR2DS2 and KIR2DS1, are each present in about half of the subjects. In this work we report that subjects with activating KIR2DS1 and/or KIR2DS2 genes are susceptible to developing psoriatic arthritis, but only when HLA ligands for their homologous inhibitory receptors, KIR2DL1 and KIR2DL2/3, are missing. Absence of ligands for inhibitory KIRs could potentially lower the threshold for NK (and/or T) cell activation mediated through activating receptors, thereby contributing to pathogenesis of psoriatic arthritis.

Advancing pluripotent stem cell technologies for modeling hematopoietic stem cell development and blood therapies requires identifying key regulators of hematopoietic commitment from human pluripotent stem cells (hPSCs). Here, by screening the effect of 27 candidate factors, we reveal two groups of transcriptional regulators capable of inducing distinct hematopoietic programs from hPSCs: panmyeloid (ETV2 and GATA2) and erythro-megakaryocytic (GATA2 and TAL1). In both cases, these transcription factors directly convert hPSCs to endothelium, which subsequently transforms into blood cells with pan-myeloid or erythromegakaryocytic potential. These data demonstrate that two distinct genetic programs regulate the hematopoietic development from hPSCs and that both of these programs specify hPSCs directly to hemogenic endothelial cells. Additionally, this study provides a novel method for the efficient induction of blood and endothelial cells from hPSCs via overexpression of modified mRNA for the selected transcription factors.

ATHSF1 is a heat shock transcription factor (HSF) of Arabidopsis that is constitutively expressed but its activity for DNA binding, trimer formation and transcriptional activation of heat shock (hs) genes is repressed at normal temperatures. In this study the functional properties of chimeric HSF-glucuronidase (GUS) fusion proteins were tested. Ectopic expression of HSF-GUS or GUS-HSF in transgenic Arabidopsis plants resulted in a derepression of HSF functions as shown by trimer formation, specific DNA binding, and the constitutive expression of heat shock proteins (HSPs) at normal temperature. A novel GUS activity-staining protocol was used to show the specific binding of trimeric HSF fusion proteins to DNA and following hs, an interaction between chimeric HSF-GUS and authentic HSF proteins. The chimeric HSFs were insensitive to the negative regulation that counteracts activation of the authentic HSF at normal temperature. Heterotrimer complexes were reconstituted in vitro from recombinant ATHSF1 and HSF-GUS proteins expressed in Escherichia coli and using this protocol, the temperature-dependent activation of wt HSF was monitored in vivo and in vitro. Transgenic plants expressing constitutively active HSF-GUS fusion proteins are also constitutive for HSPs. Approximately 20% of the maximum heat-inducible levels of HSP18 were already present at normal temperature. The level of basic thermotolerance was significantly enhanced in these plants. The results indicate that genetic engineering using protein fusion is a very effective means to derepress the activity of an important regulatory protein in plants, that consequently activates a constitutive hs response in the absence of heat stress and eventually alters the thermotolerance phenotype.

SummaryThe recent identification of hemogenic endothelium (HE) in human pluripotent stem cell (hPSC) cultures presents opportunities to investigate signaling pathways that are essential for blood development from endothelium and provides an exploratory platform for de novo generation of hematopoietic stem cells (HSCs). However, the use of poorly defined human or animal components limits the utility of the current differentiation systems for studying specific growth factors required for HE induction and manufacturing clinical-grade therapeutic blood cells. Here, we identified chemically defined conditions required to produce HE from hPSCs growing in Essential 8 (E8) medium and showed that Tenascin C (TenC), an extracellular matrix protein associated with HSC niches, strongly promotes HE and definitive hematopoiesis in this system. hPSCs differentiated in chemically defined conditions undergo stages of development similar to those previously described in hPSCs cocultured on OP9 feeders, including the formation of VE-Cadherin+CD73−CD235a/CD43− HE and hematopoietic progenitors with myeloid and T lymphoid potential.