The mer receptor tyrosine kinase mediates phagocytosis of apoptotic cells and modulates cytokine production; it is also required for prevention of systemic autoimmune disease. Using a mer-specific antibody, we have confirmed the presence of mer on macrophages and now report its expression on NK cells, NKT cells, and dendritic cells (DC). We found that DC do not require mer for ingestion of apoptotic cells, as DC from mer-deficient mice phagocytose apoptotic cells normally. Mer was observed in splenic sections on cells outside follicular areas, probably representing DC and macrophages. Mer apparently participates in NKT-cell antigen-induced signaling, as NKT cells from mer-deficient mice evinced much lower cytokine production after in vivo § -galactosylceramide stimulation; this defect was intrinsic to the mer-deficient NKT cells. Taken together, these studies show mer expression on cells of the innate immune system. Mer, through its binding of lipid antigens, may not only mediate ingestion of apoptotic cells, but also signal events in NK cells, NKT cells, and DC.

Previous studies have shown that patients with deletion of distal human chromosome arm 8p may have congenital heart disease and other physical anomalies. The gene encoding GATA-4, a zinc finger transcription factor implicated in cardiac gene expression and development, localizes to chromosome region 8p23.1. To examine whether GATA-4 deficiency is present in patients with monosomy of 8p23.1 with congenital heart disease, we performed fluorescence in situ hybridization (FISH) with a GATA4 probe on cells from a series of patients with interstitial deletion of 8p23.1. Four individuals with del(8)(p23.1) and congenital heart disease were found to be haploinsufficient at the GATA4 locus by FISH. The GATA4 gene was not deleted in a fifth patient with del(8)(p23.1) who lacked cardiac anomalies. FISH analysis on cells from 48 individuals with congenital heart disease and normal karyotypes failed to detect any submicroscopic deletions at the GATA4 locus. We conclude that haploinsufficiency at the GATA4 locus is often seen in patients with del(8)(p23.1) and congenital heart disease. Based on these findings and recent studies showing that haploinsufficiency for other cardiac transcription factor genes (e.g., TBX5, NKX2-5) causes congenital heart disease, we postulate that GATA-4 deficiency may contribute to the phenotype of patients with monosomy of 8p23.1.

Previous studies have shown that patients with deletion of distal human chromosome arm 8p may have congenital heart disease and other physical anomalies. The gene encoding GATA-4, a zinc finger transcription factor implicated in cardiac gene expression and development, localizes to chromosome region 8p23.1. To examine whether GATA-4 deficiency is present in patients with monosomy of 8p23.1 with congenital heart disease, we performed fluorescence in situ hybridization (FISH) with a GATA4 probe on cells from a series of patients with interstitial deletion of 8p23.1. Four individuals with del(8)(p23.1) and congenital heart disease were found to be haploinsufficient at the GATA4 locus by FISH. The GATA4 gene was not deleted in a fifth patient with del(8)(p23.1) who lacked cardiac anomalies. FISH analysis on cells from 48 individuals with congenital heart disease and normal karyotypes failed to detect any submicroscopic deletions at the GATA4 locus. We conclude that haploinsufficiency at the GATA4 locus is often seen in patients with del(8)(p23.1) and congenital heart disease. Based on these findings and recent studies showing that haploinsufficiency for other cardiac transcription factor genes (e.g., TBX5, NKX2-5) causes congenital heart disease, we postulate that GATA-4 deficiency may contribute to the phenotype of patients with monosomy of 8p23.1.

Monocyte polarization by IFN-γ or IL-4 drives a complex series of cellular responses leading to increased intracellular killing (IFN-γ) or enhanced healing (IL-4) among other functional responses. We studied the effect of IL-4 and IFN-γ polarization on histone modifications at the TNF-α locus in human primary monocytes. IFN-γ polarization markedly increased the expression of TNF-α, whereas IL-4 treatment decreased the expression. We found that IFN-γ alone increased histone H4 acetylation at the TNF-α promoter. The effect of IFN-γ on TNF-α expression was durable upon cytokine washout and even repolarization with IL-4. Concordantly, IFN-γ-mediated H4 acetylation was also durable. IFN-γ recruited activating transcription factor-2 via p38 to the TNF-α promoter, but inhibition of p38 had minimal effect on H4 acetylation. In a novel finding, we found that IFN-γ recruited RNA Pol II to the human TNF-α promoter via ERK signaling, but did so without initiating transcription, leading to a poised condition. These studies provide an important perspective on monocyte polarization. Polarization by IFN-γ has a durable effect on TNF-α expression, and histone acetylation may provide a mechanism for persistence of the effect.

Embryonic stem (ES) cells, derivatives of cells of early mammalian embryos, have turned out to be one of the most powerful tools in developmental and stem cell biology. When injected into embryos, ES cells can contribute to tissues derived from all three germ layers and to the germline. Amazingly, ES cells in culture are able to recapitulate features of embryonic development spontaneously. In addition to previous successes in deriving somatic cell types, recent studies have shown that both mouse and human ES cells can also give rise to primordial germ cells (PGCs) in culture. These mouse germ cells appear to be capable of undergoing meiosis and forming both male and female gametes. Although the full function of these ES-derived germ cells and gametes remains to be demonstrated, these findings open the door for undertaking new types of reproductive studies and novel approaches in regenerative medicine.

IL-23, a heterodimer of IL-12 p40 and IL-23 p19, is critical for an effective immune response to many infections and has been implicated in several autoimmune diseases, however, little is known about the regulation of IL-23 gene expression in monocytes. We found that poly I:C, LPS, flagellin, and zymogen activated significant IL-23 production in primary human monocytes. Using chromatin immunoprecipitation, we found that a distal upstream region of the IL-23 p19 promoter at −601 to −521 underwent extensive histone modifications in response to stimuli. This distal region of the promoter is not highly conserved between species and has not been previously implicated in the regulation of IL-23 expression. Knockdown of CBP markedly decreased IL-23 p19 responses to poly I:C but had a less dramatic effect on LPS responses, confirming different chromatin responses to these two stimuli. Our data suggest that one of the mechanisms regulating IL-23 expression is the regulation of histone modifications at this distal upstream region of the promoter.

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