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Cell surface expression of major histocompatibility complex class II (MHCII) molecules is increased during the maturation of dendritic cells (DCs). This enhances their ability to present antigen and activate naive CD4+ T cells. In contrast to increased cell surface MHCII expression, de novo biosynthesis of MHCII mRNA is turned off during DC maturation. We show here that this is due to a remarkably rapid reduction in the synthesis of class II transactivator (CIITA) mRNA and protein. This reduction in CIITA expression occurs in human monocyte-derived DCs and mouse bone marrow–derived DCs, and is triggered by a variety of different maturation stimuli, including lipopolysaccharide, tumor necrosis factor α, CD40 ligand, interferon α, and infection with Salmonella typhimurium or Sendai virus. It is also observed in vivo in splenic DCs in acute myelin oligodendrocyte glycoprotein induced experimental autoimmune encephalitis. The arrest in CIITA expression is the result of a transcriptional inactivation of the MHC2TA gene. This is mediated by a global repression mechanism implicating histone deacetylation over a large domain spanning the entire MHC2TA regulatory region.

The transcription factor FOXJ1 (alias HFH-4 or FKHL13) of the winged-helix/forkhead family is expressed in cells with cilia or flagella, and seems to be involved in the regulation of axonemal structural proteins. The knockout mouse Foxj1–/– shows abnormalities of organ situs, consistent with random determination of left-right asymmetry, and a complete absence of cilia. The human FOXJ1 gene which maps to chromosome 17q, is thus an excellent candidate gene for Kartagener Syndrome (KS), a subphenotype of Primary Ciliary Dyskinesia (PCD), characterized by bronchiectasis, chronic sinusitis and situs inversus. We have collected samples from 61 PCD fami- lies, in 31 of which there are at least two affected individuals. Two families with complete aciliogenesis, and six families, in which the affected members have microsatellite alleles concordant for a locus on distal chromosome 17q, were screened for mutations in the two exons and intron-exon junctions of the FOXJ1 gene. No sequence abnormalities were observed in the DNAs of the affected individuals of the selected families. These results demonstrate that the FOXJ1 gene is not responsible for the PCD/KS phenotype in the families examined.

The recessive mouse mutation kreisler affects hindbrain segmentation and inner ear development in homozygous mice. The mouse gene affected by the mutation was found to encode a basic domain leucine-zipper (bZIP)-type transcription factor of the Maf-family named kr (Cordes, S.P. and Barsh, G.S. (1994) Cell 79, 1025-1034). The avian bZIP transcription factor mafB, which shows high homology to kr, has been identified as an interaction partner of c-Ets 1 (Sieweke, M.H., Tekotte, M.H., Frampton, J. and Graf, T. (1996) Cell 85, 49-60). Here we demonstrate by Southern blot analysis that mafB is the avian homologue of kr, and present a detailed pattern of its expression during avian and murine embryonic development. Consistent with the kreisler phenotype, mafB is expressed in avians in the tissues which are affected by the mouse mutation: rhombomeres 5 and 6 (r5 and r6) and the neural crest derived from these rhombomeres. However, our analysis reveals a variety of additional expression sites: mafB/kr expression persists in vestibular and acoustic nuclei and is also observed in differentiating neurons of the spinal cord and brain stem. Restricted expression sites are found in the mesonephros, the perichondrium, and in the hemopoietic system. Since these expression sites are conserved between mouse and chicken we reexamined homozygous kreisler mice for unrevealed phenotypes in the hemopoietic system. However, peritoneal macrophages from homozygous kreisler mice were found to be functionally normal and still expressed mafB/kr. Other adult tissues examined from homozygous kreisler mice had also not lost mafB/kr expression. Our results thus indicate that the kreisler mutation involves a tissue specific gene inactivation and suggest additional roles for mafB/kr in later developmental and differentiation processes that are not revealed by the mutation.

The accessory gene regulator ( agr ) is a crucial regulatory component of Staphylococcus aureus involved in the control of bacterial virulence factor expression. We developed a real-time multiplex quantitative PCR assay for the rapid determination of S. aureus agr type. This assay represents a rapid and affordable alternative to sequence-based strategies for assessing relevant epidemiological information.

MHC class II molecules are pivotal for the adaptive immune system, because they guide the development and activation of CD4+ T helper cells. Fulfilling these functions requires that the genes encoding MHC class II molecules are transcribed according to a strict cell-type-specific and quantitatively modulated pattern. This complex gene-expression profile is controlled almost exclusively by a single master regulatory factor, which is known as the class II transactivator. As we discuss here, differential activation of the three independent promoters that drive expression of the gene encoding the class II transactivator ultimately determines the exquisitely regulated pattern of MHC class II gene expression.

Tightly regulated expression of major histocompatibility complex (MHC) class II genes is critical for the immune system. A conserved regulatory module consisting of four cis-acting elements, the W, X, X2 and Y boxes, controls transcription of MHC class II genes. The X, X2, and Y boxes are bound, respectively, by RFX, CREB, and NF-Y to form a MHC class II-specific enhanceosome complex. The latter constitutes a landing pad for recruitment of the transcriptional co-activator CIITA. In contrast to the well defined roles of the X, X2, and Y boxes, the role of the W region has remained controversial. In vitro binding studies have suggested that it might contain a second RFX-binding site. We demonstrate here by means of promoter pull-down assays that the most conserved subsequence within the W region, called the S box, is a critical determinant for tethering of CIITA to the enhanceosome complex. Binding of CIITA to the enhanceosome requires both integrity of the S box and a remarkably stringent spacing between the S and X boxes. Even a 1–2-base pair change in the native S-X distance is detrimental for CIITA recruitment and promoter function. In contrast to current models, binding of RFX to a putative duplicated binding site in the W box is thus not required for either CIITA recruitment or promoter activity. This paves the way for the identification of novel factors mediating the contribution of the S box to the activation of MHC class II promoters.

A T helper 1 (Th1)/Th2 imbalance is thought to contribute to the pathogenesis of autoimmune diseases. The differentiation of T cells into Th1 or Th2 subtypes is under the regulation of several transcription factors. Among these, transcription factor GATA-3 is thought to play an indispensable role in the development of T cells and the differentiation of Th2 cells. To examine how a Th1/Th2 imbalance affects the development of autoimmune disease, GATA-3 was overexpressed in the T lymphocytes of C57BL/6 x BXSB/MpJ-Yaa F(1) (Yaa) mice. Yaa mice developed autoimmune nephritis similarly to BXSB/MpJ-Yaa mice, which are commonly used as a model for Th1-dominant murine lupus. GATA-3 overexpression in T cells improved the 50% mortality incidence time for GATA-3-transgenic Yaa mice (41.6 wk), compared with Yaa mice (30.9 wk), and reduced proteinuria, serum creatinine levels, and the severity of glomerulonephritis in GATA-3-transgenic Yaa mice. GATA-3 overexpression in Yaa mice led to simultaneously elevated Th2 Ig (IgG1) and decreased Th1 Ig (IgG2a and IgG3) production and serum IFN-gamma levels. Although IL-4 production remained unchanged, intracellular cytokine analyses demonstrated that IL-5 was induced and IFN-gamma was suppressed in stimulated T cells from the GATA-3-transgenic Yaa mice. These results indicated that abundant GATA-3 was unable to stimulate complete differentiation of Th2 cells but did counteract the dominance of Th1 cells and alleviated the disease severity in Yaa mice. These data suggest that transcriptional regulation therapy may have potential as an effective strategy for treating autoimmune glomerulonephritis.

In-frame deletion mutagenesis was used to study the roles of two Bradyrhizobium japonicum proteins, HoxX and HoxA, in hydrogenase biosynthesis; based on their sequences, these proteins were previously proposed to be sensor and regulator proteins, respectively, of a two-component regulatory system necessary for hydrogenase transcription. Deletion of the hoxX gene resulted in a strain that expressed only 30 to 40% of wild-type hydrogenase activity. The inactive unprocessed form of the hydrogenase large subunit accumulated in this strain, indicating a role for HoxX in posttranslational processing of the hydrogenase enzyme but not in transcriptional regulation. Strains containing a deletion of the hoxA gene or a double mutation (hoxX and hoxA) did not exhibit any hydrogenase activity under free-living conditions, and extracts from these strains were inactive in gel retardation assays with a 158-bp fragment of the DNA region upstream of the hupSL operon. However, bacteroids from root nodules formed by all three mutant types (hoxX, hoxA, and hoxX hoxA) exhibited hydrogenase activity comparable to that of wild-type bacteroids. Bacteroid extracts from all of these strains, including the wild type, failed to cause a shift of the hydrogenase upstream region used in our assay. It was shown that HoxA is a DNA-binding transcriptional activator of hydrogenase structural gene expression under free-living conditions but not under symbiotic conditions. Although symbiotic hydrogenase expression is still sigma54 dependent, a transcriptional activator other than HoxA functions presumably upstream of the HoxA binding site.

Constitutive major histocompatibility complex (MHC) class II gene expression is tightly restricted to antigen presenting cells and is under developmental control. Cells of the B cell lineage acquire the capacity to express MHC class II genes early during ontogeny and lose this property during terminal differentiation into plasma cells. Cell fusion experiments have suggested that the extinction of MHC class II expression in plasma cells is due to a dominant repression, but the underlying mechanisms are not understood. CIITA was recently identified as an MHC class II transactivator that is essential for MHC class II expression in B lymphocytes. We show here that inactivation of MHC class II genes in plasmocytes is associated with silencing of the CIITA gene. Moreover, experimentally induced expression of CIITA in plasmocytes leads to reexpression of MHC class II molecules to the same level as that observed on B lymphocytes. We therefore conclude that the loss of MHC class II expression observed upon terminal differentiation of B lymphocytes into plasmocytes results from silencing of the transactivator gene CIITA.