Identification of a putative invertebrate helical cytokine similar to the ciliary neurotrophic factor/leukemia inhibitory factor family by PSI-BLAST-based approach

Most of our knowledge of helical cytokine-like molecules in invertebrates relies on functional assays and similarities at the physicochemical level. It is hard to predict helical cytokines in invertebrates based on sequences from mammals and vertebrates, because of their long evolutionary divergence. In this article, we collected 12 kinds of fish cytokines and constructed their respective consensus sequences using hidden Markov models; then, the conserved domains region of each consensus sequence were further extracted by the SMART tool, and used as the query sequence for PSI-BLAST analysis in Drosophila melanogaster. After two filtering processes based on the properties of helical cytokines, we obtained one protein named CG14629, which shares 25% identities/46% positives to fish M17 cytokine in the half length of the N-terminus. Considering the homology between M17 and LIF/CNTF (leukemia inhibitory factor/ciliary neurotrophic factor), and the close relationship between Dome, the putative cytokine receptor in Drosophila cells, and LIFR/CNTFR (LIF receptor/CNTF receptor), the results suggest that CG14629 is a good candidate for the helical cytokine ortholog in D. melanogaster.

Induction of the CTLA-4 gene in human lymphocytes is dependent on NFAT binding the proximal promoter

CTLA-4 is a member of the costimulatory family, has homology to CD28, and binds the B7 family of ligands. Unlike CD28, CTLA-4 ligation transmits a negative signal in T cells. CTLA-4 expression, while inducible in most T cells, is expressed constitutively on T cells with a regulatory phenotype. The mechanism controlling CTLA-4 expression in human T cells is poorly characterized, thus we sought to better understand the mechanism of activation of the CTLA-4 gene. By cloning the 5' upstream promoter and creating promoter-deletion reporter constructs, we show that the proximal promoter is critical for activating the CTLA-4 gene. Within this region, we identify a NFAT consensus sequence that binds NFAT with high affinity that differs from other NFAT sequences and does not recruit AP-1. Analysis of the chromatin proteins in the native CTLA-4 gene shows that this promoter region becomes associated with acetylated histones by chromatin immunoprecipitation assays. In addition, NFAT1 binds to the promoter of the CTLA-4 gene after stimulation by chromatin immunoprecipitation. The functional requirement of the NFAT site for CTLA-4 transcription was demonstrated by mutations in the NFAT site that abolished the activity of the promoter. Furthermore, inhibitors of NFAT suppressed CTLA-4 gene expression, indicating that NFAT plays a critical role in regulating the induction of the CTLA-4 gene in lymphocytes. The identification of NFAT as a critical regulator of the CTLA-4 gene suggests that targeting NFAT function may lead to novel approaches to modulate the CTLA-4 gene to control the immune response.

Forkhead Box P3 Regulates TLR10 Expression in Human T Regulatory Cells

Although functionally relevant TLRs can be expressed on human T regulatory (Treg) cells, little is known about the transcriptional control of their expression. We hypothesized that the transcription factor forkhead box P3 (FOXP3) regulates the expression of TLR family members in human Treg cells. Using primary human T cells and a reporter assay in Jurkat T cell lines, we dissected the regulation of TLR10, a TLR highly expressed in human Treg cells. We determined that TLR10 was expressed in human Treg cells through quantitative PCR, Western blotting, and flow cytometry. DNA binding of FOXP3 to a suspected cis-regulatory region in proximity to the transcription start site of TLR10 was established through EMSA and chromatin immunoprecipitation. Transcriptional control of TLR10 by FOXP3 was determined through luciferase reporter assays in Jurkat T cell lines. Relevance of FOXP3 to TLR10 gene transcription in primary T cells was established through the transfection of primary CD4(+)CD25(-)FOXP3(-) T cells with a FOXP3 expression vector, which resulted in prompt production of TLR10 mRNA. Enhanced expression of TLR10 protein in primary Treg cells was induced in a calcium-dependent fashion through TCR activation. The suspected promotional cooperation between FOXP3 and NF-AT was established in the abolition of the luciferase signal upon transfection of a mutant FOXP3 devoid of NF-AT-binding activity. These results suggest that human Treg cells express TLR10, and this expression is regulated through a cooperative complex of FOXP3 and NF-AT.

Development of a synthetic consensus sequence scrambled antigen HIV-1 vaccine designed for global use

Induction of high levels of broadly reactive cytotoxic T lymphocytes (CTL) remains a promising approach for an effective HIV-1 vaccine. We have developed a novel genetic-based vaccine strategy that encodes consensus overlapping peptide sets from all HIV-1 proteins scrambled together. This synthetic scrambled antigen vaccine (SAVINE) strategy has significant advantages, e.g. capacity to encode more antigens safely and is very flexible compared to traditional isolate-based strategies. The SAVINE vaccine strategy is clearly immunogenic, being able to restimulate a range of human HIV-1 specific responses in vitro and induce HIV-1 specific immunity in vivo in mice. Interestingly, different in vivo delivery strategies affected the resulting immunity and immunodominance pattern in mice. This platform strategy could be used for other infections and cancers where T cell responses are important for protection.

High degree of inter-clade cross-reactivity of HIV-1-specific T cell responses at the single peptide level

OBJECTIVES

To determine HIV-1-specific T cell responses in clade B infected individuals recognizing the clade A, B and C consensus sequences in order to assess the degree of inter-clade cross-reactivity of these immune responses at the single epitope level.

METHODS

HIV-1-specific T cell responses were assessed cross-sectionally in 27 chronically HIV-1-infected individuals from a population infected mainly with clade B viral strains, using an interferon-gamma Elispot assay with a total of 1230 overlapping peptides spanning the entire amino acid sequence of the clade A, B and C 2001 consensus sequences.

RESULTS

No significant difference was observed between the total magnitude or breadth of T cell responses recognizing either the clade A, B or C consensus sequences. However, at the single peptide level, 194 T cell responses were identified that recognized only one of the three different clade-specific peptide variants (A: B: C, 34: 105: 55), 125 T cell responses recognized two of the three peptide variants (AB: AC: BC, 71: 15: 39) and 166 T cell responses (34%) were cross-reactive with all three different peptide variants. Peptides recognized in all three consensus sequence variants had a significantly lower entropy (P < 0.0001) and a significantly higher inter-clade homology (P < 0.0001).

CONCLUSIONS

Viral epitopes within regions of low HIV-1 clade B diversity and high inter-clade homology can be recognized in the clade A, B and C variants and indicate a wide degree of cross-isolate and cross-clade recognition by HIV-1-specific T cells. These regions may therefore be of particular relevance for the design of HIV-1 vaccines.

Divergent and convergent evolution after a common-source outbreak of hepatitis C virus

The genomic sequences of viruses that are highly mutable and cause chronic infection tend to diverge over time. We report that these changes represent both immune-driven selection and, in the absence of immune pressure, reversion toward an ancestral consensus. Sequence changes in hepatitis C virus (HCV) structural and nonstructural genes were studied in a cohort of women accidentally infected with HCV in a rare common-source outbreak. We compared sequences present in serum obtained 18–22 yr after infection to sequences present in the shared inoculum and found that HCV evolved along a distinct path in each woman. Amino acid substitutions in known epitopes were directed away from consensus in persons having the HLA allele associated with that epitope (immune selection), and toward consensus in those lacking the allele (reversion). These data suggest that vaccines for genetically diverse viruses may be more effective if they represent consensus sequence, rather than a human isolate.

HIV-1 MN Env 15-mer peptides better detect HIV-1 specific CD8 T cell responses compared with consensus subtypes B and M group 15-mer peptides

OBJECTIVE

To compare the ability of three Env (15-mer) peptide sets derived from the HIV-1 MN, the subtype B consensus, and the group M consensus to detect HIV-1 specific interferon (IFN)-gamma responses in HIV-1 subtype B infected subjects.

METHODS

Peripheral blood mononuclear cells were obtained from 17 HIV-1 subtype B seropositive and 5 HIV-1 seronegative subjects. Peptide matrices comprising each peptide set were used in IFN-gamma Elispot assays to screen for T cell epitopes. Following matrix deconvolution, individual peptides were analyzed by IFN-gamma intracellular cytokine-staining to confirm and characterize the responding cells.

RESULTS

HIV specific IFN-gamma responses were detected in 17 of 17 HIV-1 seropositive and none of 5 HIV-1 seronegative subjects by Elispot. Within the 17 HIV-1 seropositives, 16, 14, and 11 subjects responded to MN, B consensus, and group M env peptides, respectively. Responses were confirmed by intracellular cytokine analysis in 14 subjects and were in the CD3CD8 compartment. Cross-recognition of 'equivalent' peptides (i.e., peptides mapping to the same sequence region from the three peptide sets) was observed in 9 of 17 subjects. Peptide set specific responses to individual peptides were also observed; 11, 1, and 1 subjects demonstrated peptide set specific responses to MN, B consensus, and consensus group M, respectively.

CONCLUSION

MN derived Env peptides were better able to detect HIV-1 specific CD8 T cell responses, many of which were not detectable by the equivalent clade or group consensus peptides. No single peptide set detected all the IFN-gamma responses within an individual. These results demonstrate the importance of reagent selection for monitoring of HIV responses in HIV-1 infected individuals and subsequently vaccine recipients.

Cellular immune selection with hepatitis C virus persistence in humans

Hepatitis C virus (HCV) infection frequently persists despite substantial virus-specific cellular immune responses. To determine if immunologically driven sequence variation occurs with HCV persistence, we coordinately analyzed sequence evolution and CD8+ T cell responses to epitopes covering the entire HCV polyprotein in subjects who were followed prospectively from before infection to beyond the first year. There were no substitutions in T cell epitopes for a year after infection in a subject who cleared viremia. In contrast, in subjects with persistent viremia and detectable T cell responses, we observed substitutions in 69% of T cell epitopes, and every subject had a substitution in at least one epitope. In addition, amino acid substitutions occurred 13-fold more often within than outside T cell epitopes (P < 0.001, range 5-38). T lymphocyte recognition of 8 of 10 mutant peptides was markedly reduced compared with the initial sequence, indicating viral escape. Of 16 nonenvelope substitutions that occurred outside of known T cell epitopes, 8 represented conversion to consensus (P = 0.015). These findings reveal two distinct mechanisms of sequence evolution involved in HCV persistence: viral escape from CD8+ T cell responses and optimization of replicative capacity.

Transmission and accumulation of CTL escape variants drive negative associations between HIV polymorphisms and HLA

Human immunodeficiency virus (HIV)-1 amino acid sequence polymorphisms associated with expression of specific human histocompatibility leukocyte antigen (HLA) class I alleles suggest sites of cytotoxic T lymphocyte (CTL)-mediated selection pressure and immune escape. The associations most frequently observed are between expression of an HLA class I molecule and variation from the consensus sequence. However, a substantial number of sites have been identified in which particular HLA class I allele expression is associated with preservation of the consensus sequence. The mechanism behind this is so far unexplained. The current studies, focusing on two examples of “negatively associated” or apparently preserved epitopes, suggest an explanation for this phenomenon: negative associations can arise as a result of positive selection of an escape mutation, which is stable on transmission and therefore accumulates in the population to the point at which it defines the consensus sequence. Such negative associations may only be in evidence transiently, because the statistical power to detect them diminishes as the mutations accumulate. If an escape variant reaches fixation in the population, the epitope will be lost as a potential target to the immune system. These data help to explain how HIV is evolving at a population level. Understanding the direction of HIV evolution has important implications for vaccine development.

Functionally-inactive and immunogenic Tat, Rev and Nef DNA vaccines derived from sub-Saharan subtype C human immunodeficiency virus type 1 consensus sequences

The efficacy of cellular immune responses elicited by HIV vaccines is dependent on their strength, durability and antigenic breadth. The regulatory proteins are abundantly expressed early in the viral life cycle and CTL recognition may bring about early killing of infected cells. We synthesised DNA vaccine constructs that encode consensus HIV-1 subtype C Tat, Rev and Nef proteins. Proteins carrying inactivating mutations were tested for functional activity and highly expressing, inactive Tat, Rev and Nef mutants were identified and their reading frames fused into a TatRevNef cassette. Single- and polygene Tat, Rev and/or Nef constructs were immunogenic in BALB/c mice. These constructs may serve to increase the antigenic breadth for an HIV-1 vaccine that is relevant for sub-Saharan Africa.

Identifying MHC class I epitopes by predicting the TAP transport efficiency of epitope precursors

We are able to make reliable predictions of the efficiency with which peptides of arbitrary lengths will be transported by TAP. The pressure exerted by TAP on Ag presentation thus can be assessed by checking to what extent MHC class I (MHC-I)-presented epitopes can be discriminated from random peptides on the basis of predicted TAP transport efficiencies alone. Best discriminations were obtained when N-terminally prolonged epitope precursor peptides were included and the contribution of the N-terminal residues to the score were down-weighted in comparison with the contribution of the C terminus. We provide evidence that two factors may account for this N-terminal down-weighting: 1) the uncertainty as to which precursors are used in vivo and 2) the coevolution in the C-terminal sequence specificities of TAP and other agents in the pathway, which may vary among the various MHC-I alleles. Combining predictions of MHC-I binding affinities with predictions of TAP transport efficiency led to an improved identification of epitopes, which was not the case when predictions of MHC-I binding affinities were combined with predictions of C-terminal cleavages made by the proteasome.

IFN-stimulated gene 15 is synergistically activated through interactions between the myelocyte/lymphocyte-specific transcription factors, PU.1, IFN regulatory factor-8/IFN consensus sequence binding protein, and IFN regulatory factor-4: characterization of a new subtype of IFN-stimulated response element

Type I IFNs cause the induction of a subset of genes termed IFN-stimulated genes (ISGs), which harbor a specific DNA element, IFN-stimulated response element (ISRE). This ISRE confers the responsiveness to the IFN signal through the binding of a family of transcription factors designated IFN regulatory factors (IRFs). Some IRFs can bind to the DNA alone, such as IRF-1, which elicits transcriptional activation, or IRF-2, which leads to transcriptional repression. In addition, these factors associate with IRF-8/IFN consensus sequence binding protein (ICSBP), an immune cell-restricted IRF, and the assembled heterocomplexes lead to synergistic repression of ISRE elements. ISG15 is a prototype ISG that contains a well-characterized ISRE. Here we show that PU.1, an ETS member essential for myeloid/lymphoid cell differentiation, forms heterocomplexes with the immune-restricted IRFs, IRF-8\/ICSBP and IRF-4, which lead to transcriptional activation of ISG15. These data allowed the characterization of a subset of ISREs designated ETS/IRF response element (EIRE), which are differentially regulated in immune cells. EIREs are unique in their ability to recruit different factors to an assembled enhanceosomes. In nonimmune cells the factors will mainly include IRF members, while cell type-restricted factors, such as PU.1, IRF-8\/ICSBP, and IRF-4, will be recruited in immune cells. IRF heterocomplex formation leads to transcriptional repression, and conversely, PU.1/IRFs heterocomplex formation leads to transcriptional activation. The fact that IRF-8\/ICSBP is an IFN-gamma-induced factor explains why some of the EIREs are also induced by type II IFN. Our results lay the molecular basis for the unique regulation of ISGs, harboring EIRE, in immune cells.

Antibody responses against B-cell epitopes of the hypervariable region 1 of hepatitis C virus in self-limiting and chronic human hepatitis C followed-up using consensus peptides

A rare collection of serum samples from patients with hepatitis C virus (HCV) infection followed up from the onset of clinical symptoms was acquired. RNA corresponding to the hypervariable region 1 (HVR1) of E2 protein of HCV isolated from nine patients was reverse-transcribed, amplified, sequenced, and HVR1 amino acid sequences were deduced. These sequences and a selection of HVR1 amino acid sequences of matching HCV genotypes from protein and translated DNA sequence databanks were used to create the HVR1 amino acid consensus. The degenerated peptides mimicking N- and C-termini of the consensus were synthesized. Most (76%) of 17 patients followed up for the period from 1 week to a minimum of 7 months from the onset of acute symptoms developed antibodies reacting with peptides representing N- and/or C- termini of HVR1. Antibody recognition of the consensus HVR1 peptides indicates that the variability of HVR1 sequence on the protein level is limited with certain conserved structure(s) being untouched. A tendency was observed for a slower development of anti-HVR1 antibody response in patients developing chronic HCV, as compared to those with self-limiting HCV infection.

Src homology 2 domain-containing protein-tyrosine phosphatases, SHP-1 and SHP-2, are required for platelet endothelial cell adhesion molecule-1/CD31-mediated inhibitory signaling

Platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) is a newly assigned member of the Ig immunoreceptor tyrosine-based inhibitory motif superfamily, and its functional role is suggested to be an inhibitory receptor that modulates immunoreceptor tyrosine-based activation motif-dependent signaling cascades. To test whether PECAM-1 is capable of delivering inhibitory signals in B cells and the functional requirement of protein-tyrosine phosphatases (PTPs) for this inhibitory signaling, we generated chimeric Fc gamma RIIB1-PECAM-1 receptors containing the extracellular and transmembrane portions of murine Fc gamma RIIB1 and the cytoplasmic domain of human PECAM-1. These chimeric receptors were stably expressed in chicken DT40 B cells either as wild-type or mutant cells deficient in SHP-1(-/-), SHP-2(-/-), SHIP(-/-), or SHP-1/2(-/-) and then assessed for their ability to inhibit B cell Ag receptor (BCR) signaling. Coligation of wild-type Fc gamma RIIB1-PECAM-1 with BCR resulted in inhibition of intracellular calcium release, suggesting that the cytoplasmic domain of PECAM-1 is capable of delivering an inhibitory signal that blocks BCR-mediated activation. This PECAM-1-mediated inhibitory signaling correlated with tyrosine phosphorylation of the Fc gamma RIIB1-PECAM-1 chimera, recruitment of SHP-1 and SHP-2 PTPs by the phosphorylated chimera, and attenuation of calcium mobilization responses. Mutational analysis of the two tyrosine residues, 663 and 686, constituting the immunoreceptor tyrosine-based inhibitory motifs in PECAM-1 revealed that both tyrosine residues play a crucial role in the inhibitory signal. Functional analysis of various PTP-deficient DT40 B cell lines stably expressing wild-type chimeric Fc gamma RIIB1-PECAM-1 receptor indicated that cytoplasmic Src homology 2-domain-containing phosphatases, SHP-1 and SHP-2, were both necessary and sufficient to deliver inhibitory negative regulation upon coligation of BCR complex with inhibitory receptor.

Mapping of the region of complement receptor (CR) 1 required for Plasmodium falciparum rosetting and demonstration of the importance of CR1 in rosetting in field isolates

The malaria parasite Plasmodium falciparum induces a number of novel adhesion properties in the erythrocytes that it infects. One of these properties, the ability of infected erythrocytes to bind uninfected erythrocytes to form rosettes, is associated with severe malaria and may play a direct role in the pathogenesis of disease. Previous work has shown that erythrocytes deficient in complement receptor (CR) 1 (CR1, CD35; C3b/C4b receptor) have greatly reduced rosetting capacity, indicating an essential role for CR1 in rosette formation. Using deletion mutants and mAbs, we have localized the region of CR1 required for the formation of P. falciparum rosettes to the area of long homologous repeat regions B and C that also acts as the binding site for the activated complement component C3b. This result raises the possibility that C3b could be an intermediary in rosetting, bridging between the infected erythrocyte and CR1. We were able to exclude this hypothesis, however, as parasites grown in C3-deficient human serum formed rosettes normally. We have also shown in this report that rosettes can be reversed by mAb J3B11 that recognizes the C3b binding site of CR1. This rosette-reversing activity was demonstrated in a range of laboratory-adapted parasite strains and field isolates from Kenya and Malawi. Thus, we have mapped the region of CR1 required for rosetting and demonstrated that the CR1-dependent rosetting mechanism occurs commonly in P. falciparum isolates, and could therefore be a potential target for future therapeutic interventions to treat severe malaria.

IFN-gamma up-regulates IL-18 gene expression via IFN consensus sequence-binding protein and activator protein-1 elements in macrophages

Constitutive IL-18 expression is detected from many different cells, including macrophages, keratinocytes, and osteoblasts. It has been known that IL-18 gene expression is regulated by two different promoters (p1 promoter and p2 promoter). When RAW 264.7 macrophages were treated with IFN-gamma, IL-18 gene expression was increased in a dose- and time-dependent manner. IFN-gamma activated the inducible promoter 1, but not the constitutive promoter 2. Mutagenesis studies indicated that an IFN consensus sequence-binding protein (ICSBP) binding site between -39 and -22 was critical for the IFN-gamma inducibility. EMSA using an ICSBP oligonucleotide probe showed that IFN-gamma treatment increased the formation of DNA-binding complex, which was supershifted with anti-IFN regulatory factor-1 Ab and anti-ICSBP Ab. Another element, an AP-1 site between -1120 and -1083, was important. EMSA using an AP-1-specific oligonucleotide demonstrated that IFN-gamma or LPS treatment increased the AP-1-binding activity. The addition of anti-c-Jun Ab or anti-c-Fos Ab to IFN-gamma- or LPS-treated nuclear extracts resulted in the reduction of AP-1 complex or the formation of a supershifted complex. Taken together, these results indicate that IFN-gamma increased IL-18 gene expression via ICSBP and AP-1 elements.

An IFN-gamma-inducible transcription factor, IFN consensus sequence binding protein (ICSBP), stimulates IL-12 p40 expression in macrophages

IL-12 is a cytokine that links innate and adaptive immunity. Its subunit p40 is induced in macrophages following IFN-gamma/LPS stimulation. Here we studied the role for IFN consensus sequence binding protein (ICSBP), an IFN-gamma/LPS-inducible transcription factor of the IFN regulatory factor (IRF) family in IL-12 p40 transcription. Macrophage-like cells established from ICSBP-/- mice did not induce IL-12 p40 transcripts, nor stimulated IL-12 p40 promoter activity after IFN-gamma/LPS stimulation, although induction of other inducible genes was normal in these cells. Transfection of ICSBP led to a marked induction of both human and mouse IL-12 p40 promoter activities in ICSBP+/+ and ICSBP-/- cells, even in the absence of IFN-gamma/LPS stimulation. Whereas IRF-1 alone was without effect, synergistic enhancement of promoter activity was observed following cotransfection of ICSBP and IRF-1. Deletion analysis of the human promoter indicated that the Ets site, known to be important for activation by IFN-gamma/LPS, also plays a role in the ICSBP activation of IL-12 p40. A DNA affinity binding assay revealed that endogenous ICSBP is recruited to the Ets site through protein-protein interaction. Last, transfection of ISCBP alone led to induction of the endogenous IL-12 p40 mRNA in the absence of IFN-gamma and LPS. Taken together, our results show that ICSBP induced by IFN-gamma/LPS, acts as a principal activator of IL-12p40 transcription in macrophages.

Protein-protein and DNA-protein interactions affect the activity of lymphoid-specific IFN regulatory factors

IFN regulatory factors (IRFs) constitute a family of transcription factors that are involved in IFN signaling and the development and differentiation of the immune system. Targeted gene disruption studies in mice assigned their primary role to the immune system. Two lymphoid-specific IRF members, IFN consensus sequence binding protein (ICSBP) and IRF-4, bind target DNA with greater efficiency following interaction with two transcription factors, PU.1 and E47, leading to transcriptional synergy. PU.1 and E47 are essential for proper differentiation and maturation of lymphoid cells. In addition, ICSBP interacts with two IRF members, IRF-1 and IRF-2, which also have central roles in the regulation of cell-mediated immunity. Previously, we identified a region in ICSBP, termed the IRF association domain (IAD), that is conserved in all IRFs (excluding IRF-1 and IRF-2) and is essential for its interactions with other IRF proteins. Here we show that the IAD is an independent module used by ICSBP and IRF-4 for protein-protein interactions. In addition, an IAD of IRF-2 (IAD2), necessary for interaction with ICSBP, was identified and found to be conserved in IRF-1. The IAD2 shares similar characteristics with the PEST domain that is essential for the interaction of PU.1 with IRF-4. We also show that the ICSBP DNA binding domain is indispensable for the formation of DNA binding heterocomplexes and transcriptional activity. Therefore, our results shed light on the molecular mechanisms that affect IRF activities in the immune system via discrete functional domains.

Regulation of complement activation by C-reactive protein: targeting the complement inhibitory activity of factor H by an interaction with short consensus repeat domains 7 and 8-11

C-reactive protein (CRP) is a major acute phase protein whose functions are not totally clear. In this study, we examined the interaction of CRP with factor H (FH), a key regulator of the alternative pathway (AP) of complement. Using the surface plasmon resonance technique and a panel of recombinantly expressed FH constructs, we observed that CRP binds to two closely located regions on short consensus repeat (SCR) domains 7 and 8-11 of FH. Also FH-like protein 1 (FHL-1), an alternatively spliced product of the FH gene, bound to CRP with its most C-terminal domain (SCR 7). The binding reactions were calcium-dependent and partially inhibited by heparin. In accordance with the finding that CRP binding sites on FH were distinct from the C3b binding sites, CRP preserved the ability of FH to promote factor I-mediated cleavage of C3b. We propose that the function of CRP is to target functionally active FH and FHL-1 to injured self tissues. Thereby, CRP could restrict excessive complement attack in tissues while allowing a temporarily enhanced AP activity against invading microbes in blood.

Regulation of apoptosis in myeloid cells by interferon consensus sequence-binding protein

Mice with a null mutation of the gene encoding interferon consensus sequence-binding protein (ICSBP) develop a disease with marked expansion of granulocytes and macrophages that frequently progresses to a fatal blast crisis, thus resembling human chronic myelogenous leukemia (CML). One important feature of CML is decreased responsiveness of myeloid cells to apoptotic stimuli. Here we show that myeloid cells from mice deficient in ICSBP exhibit reduced spontaneous apoptosis and a significant decrease in sensitivity to apoptosis induced by DNA damage. In contrast, apoptosis in thymocytes from ICSBP-deficient mice is unaffected. We also show that overexpression of ICSBP in the human U937 monocytic cell line enhances the rate of spontaneous apoptosis and the sensitivity to apoptosis induced by etoposide, lipopolysaccharide plus ATP, or rapamycin. Programmed cell death induced by etoposide was specifically blocked by peptides inhibitory for the caspase-1 or caspase-3 subfamilies of caspases. Studies of proapoptotic genes showed that cells overexpressing ICSBP have enhanced expression of caspase-3 precursor protein. In addition, analyses of antiapoptotic genes showed that overexpression of ICSBP results in decreased expression of Bcl-X(L). These data suggest that ICSBP modulates survival of myeloid cells by regulating expression of apoptosis-related genes.

Differential expression of the RTP/Drg1/Ndr1 gene product in proliferating and growth arrested cells

Using a differential display method to identify differentiation-related genes in human myelomonocytic U937 cells, we cloned the cDNA of a gene identical to Drg1 and homologous to other recently discovered genes, respectively human RTP and Cap43 and mouse Ndr1 and TDD5 genes. Their open reading frames encode proteins highly conserved between mouse and man but which do not share homology with other know proteins. Conditions in which mRNAs are up-regulated suggest a role for the protein in cell growth arrest and terminal differentiation. We raised antibodies against a synthetic peptide reproducing a characteristic sequence of the putative polypeptide chain. These antibodies revealed a protein with the expected 43 kDa molecular mass, up-regulated by phorbol ester, retinoids and 1,25-(OH)2 vitamin D3 in U937 cells. It was increased in mammary carcinoma MCF-7 cells treated by retinoids and by the anti-estrogen ICI 182,780 but not by 4-hydroxytamoxifen. The mouse Drg1 homologous protein was up-regulated by retinoic acid in C2 myogenic cells. The diversity of situations in which expression of RTP/Drg1/Ndr1 has now been observed shows that it is widely distributed and up-regulated by various agents. Here we show that ligands of nuclear transcription factors involved in cell differentiation are among the inducers of this novel protein.

Regulation of IFN consensus sequence binding protein expression in murine macrophages

Recent work has demonstrated that the transcription factor, IFN consensus sequence binding protein (ICSBP), plays a critical role in the capacity of mice to control infection with Toxoplasma gondii and Leishmania major, agents that require highly activated macrophages for their elimination. In this report the regulation of ICSBP mRNA and protein were analyzed in murine macrophages stimulated with LPS and/or IFN-gamma. Like induction of leishmaniacidal activity, LPS and IFN-gamma synergize to induce ICSBP mRNA and protein. Deletion analysis of the ICSBP promoter identified regions that were IFN-gamma responsive, regions that mediate the ability of LPS and IFN-gamma to activate this promoter synergistically, as well as regions that normally repress ICSBP transcription. Finally, exogenous expression of ICSBP, found in previous studies to down-regulate MHC I gene expression, failed to repress basal or IFN-gamma-induced ICSBP transcription. This demonstrates that ICSBP can selectively suppress the expression of IFN-responsive genes. These findings extend in a significant way our understanding of the regulation of ICSBP by LPS and IFN-gamma and provide important clues as to its role in macrophage activation.

Two human neonatal IgM antibodies encoded by different variable-region genes bind the same linear peptide: evidence for a stereotyped repertoire of epitope recognition

Two monoclonal IgM Abs have been produced from lymphocytes isolated from two human umbilical cord bloods. These mAbs recognize a conformational epitope present in a CNBr digestion fraction of lactoferrin. Linear epitopes recognized by each mAb were selected from several phage display peptide libraries. In each case, phages displaying a peptide with a motif defined by [WF],G,[EQS],N were recovered. Phages displaying that motif bound equally well to either mAb but did not bind to control IgM. A peptide bearing this motif competed with the phage-displayed peptides for binding to either mAb. The same peptide also competes with a component of the CNBr digestion fraction of lactoferrin for Ab binding in ELISA. The Abs use different families of VH, JH, and VK gene cassettes but use the same JK cassette. All segments are virtually identical to their germline gene counterparts. This work provides further evidence that certain innate specificities are stereotyped among individuals.

Identification of a domain in human factor H and factor H-like protein-1 required for the interaction with streptococcal M proteins

The plasma protein factor H (FH) inhibits the alternative pathway of complement activation. Previous work has shown that FH binds to group A streptococci and that the interaction does not interfere with the complement-inhibitory capacity of FH. In this work, we report a molecular analysis of this interaction. In absorption experiments with human plasma, M protein-expressing group A streptococci bound both FH and FH-like protein-1 (FHL-1), an active 42-kDa splice product of the FH-gene transcript comprising the first 7 of its 20 short consensus repeat (SCR) domains. rFHL-1 also bound to M protein-expressing streptococci, but rFH fragments containing SCR 1-5 or SCR 1-6 did not. rFHL-1 bound to purified M5 protein with an affinity that was higher than the value calculated for the interaction between FH and M5 protein. The binding of radiolabeled rFHL-1 to immobilized M5 was blocked completely by unlabeled rFHL-1, but was inhibited only partially by SCR 1-6, emphasizing the importance of SCR 7 for the interaction. In experiments with the FH-related proteins FHR-3 and FHR-4, only the former bound to M protein-expressing streptococci, again pointing to an involvement of SCR 7, since FHR-3, but not FHR-4, contains a domain that is similar to SCR 7. Finally, the interaction between rFHL-1 and purified M5 protein was inhibited by heparin, which binds FH via SCR 7. Together, these data indicate that the interaction between streptococcal M proteins and FH or FHL-1 requires SCR 7.

Identification of the second heparin-binding domain in human complement factor H

Complement factor H (fH) regulates activation of the alternative pathway of C, reducing the amount of C3b deposited on sialic acid-rich surfaces. Heparin binding has been used as a model for examining the sialic acid-binding characteristics of fH. We have previously shown that of the 20 short consensus repeat (SCR) modules of fH, SCR 7 contains an important heparin binding site, but other SCRs also play a role in heparin binding. To localize the other sites, we prepared recombinant truncated and SCR deletion mutants of fH and tested them by heparin-agarose affinity chromatography. The 5 C-terminal SCRs were found to contain a heparin binding site as an SCR 7 deletion mutant of the N terminal 15 SCRs did not bind heparin, but a construct consisting of SCRs 16-20 was shown to bind heparin. Double deletion of SCRs 7 and 20 from fH abrogated binding to heparin, indicating that SCR 20 contains a heparin binding site. This finding was confirmed with the observation that attachment of SCR 20 to a group of nonbinding SCRs produced a heparin-binding protein. A protein consisting of SCRs 19 and 20 did not bind heparin, whereas SCRs 18-20 did, indicating that, although SCR 20 contains a heparin binding site, at least two nonspecific adjacent SCRs are required. fH-related protein-3 (FHR-3) possesses an SCR homologous to SCR 7 of fH and bound heparin, whereas FHR-4, which lacks such an SCR, did not. Thus, fH contains two separate heparin binding sites, which are located in SCRs 7 and 20.

Antibody binding to individual short consensus repeats of decay-accelerating factor enhances enterovirus cell attachment and infectivity

Decay-accelerating factor (DAF), a widely expressed membrane complement-regulatory protein, is utilized as a cellular receptor by many human enteric pathogens. We show here that the binding of two enteroviruses to individual short consensus repeats (SCR) of DAF on the cell surface is greatly augmented by mAb binding to an alternate SCR: Coxsackievirus A21 binding to the SCR1 of DAF is increased by Ab binding to SCR3 and, conversely, Echovirus 7 binding to SCR3 is enhanced severalfold by Ab binding to SCR1. These Ab-induced increases in viral binding also resulted in increased viral infectivity. Using purified soluble DAF in a solid phase assay it was found that Ab binding to SCR1 is increased greatly in the presence of an Ab against SCR3 and, reciprocally, Ab against SCR1 greatly increases Ab binding to SCR3. In contrast to the results obtained with the larger viral particles, however, this reciprocal Ab-induced enhancement of binding is not seen when measuring Ab binding to membrane-bound DAF SCR on the cell surface. These findings provide a possible explanation for functional differences between membrane-bound and soluble DAF with implications for a potential role for DAF-binding molecules in regulating DAF function. This is the first demonstration of enhancement of viral infectivity mediated by Ab against the viral receptor.

Interferon consensus sequence binding protein-deficient mice display impaired resistance to intracellular infection due to a primary defect in interleukin 12 p40 induction

Mice lacking the transcription factor interferon consensus sequence binding protein (ICSBP), a member of the interferon regulatory factor family of transcription proteins, were infected with the intracellular protozoan, Toxoplasma gondii. ICSBP-deficient mice exhibited unchecked parasite replication in vivo and rapidly succumbed within 14 d after inoculation with an avirulent Toxoplasma strain. In contrast, few intracellular parasites were observed in wild-type littermates and these animals survived for at least 60 d after infection. Analysis of cytokine synthesis in vitro and in vivo revealed a major deficiency in the expression of both interferon (IFN)-gamma and interleukin (IL)-12 p40 in the T. gondii exposed ICSBP-/- animals. In related experiments, macrophages from uninfected ICSBP-/- mice were shown to display a selective impairment in the mRNA expression of IL-12 p40 but not IL-1alpha, IL-1beta, IL-1Ra, IL-6, IL-10, or TNF-alpha in response to live parasites, parasite antigen, lipopolysaccharide, or Staphylococcus aureus. This selective defect in IL-12 p40 production was observed regardless of whether the macrophages had been primed with IFN-gamma. We hypothesize that the impaired synthesis of IL-12 p40 in ICSBP-/- animals is the primary lesion responsible for the loss in resistance to T. gondii because IFN-gamma-induced parasite killing was unimpaired in vitro and, more importantly, administration of exogenous IL-12 in vivo significantly prolonged survival of the infected mice. Together these findings implicate ICSBP as a major transcription factor which directly or indirectly regulates IL-12 p40 gene activation and, as a consequence, IFN-gamma-dependent host resistance.

Interferon (IFN) consensus sequence-binding protein, a transcription factor of the IFN regulatory factor family, regulates immune responses in vivo through control of interleukin 12 expression

Mice with a null mutation of the gene encoding interferon consensus sequence-binding protein (ICSBP) develop a chronic myelogenous leukemia-like syndrome and mount impaired responses to certain viral and bacterial infections. To gain a mechanistic understanding of the contributions of ICSBP to humoral and cellular immunity, we characterized the responses of control and ICSBP-/- mice to infection with influenza A (flu) and Leishmania major (L. major). Mice of both genotypes survived infections with flu, but differed markedly in the isotype distribution of antiflu antibodies. In sera of normal mice, immunoglobulin (Ig)G2a antibodies were dominant over IgG1 antibodies, a pattern indicative of a T helper cell type 1 (Th1)-driven response. In sera of ICSBP-/- mice, however, IgG1 antibodies dominated over IgG2a antibodies, a pattern indicative of a Th2-driven response. The dominance of IgG1 and IgE over IgG2a was detected in the sera of uninfected mice as well. A seeming Th2 bias of ICSBP-deficient mice was also uncovered in their inability to control infection with L. major, where resistance is known to be dependent on IL-12 and IFN-gamma as components of a Th1 response. Infected ICSBP-deficient mice developed fulminant, disseminated leishmaniasis as a result of failure to mount a Th1-mediated curative response, although T cells remained capable of secreting IFN-gamma and macrophages of producing nitric oxide. Compromised Th1 differentiation in ICSBP-/- mice could not be attributed to hyporesponsiveness of CD4(+) T cells to interleukin (IL)-12; however, the ability of uninfected and infected ICSBP-deficient mice to produce IL-12 was markedly impaired. This indicates that ICSBP is a deciding factor in Th responses governing humoral and cellular immunity through its role in regulating IL-12 expression.

AML1A and AML1B can transactivate the human IL-3 promoter

The AML1 gene encodes several transcription factors, including AML1A and AML1B, which bind to DNA via a TGT/cGGT consensus sequence that is found in several promoters, including the human IL-3 promoter. We performed cotransfection experiments in T cells, and demonstrated that although AML1A lacks a putative transactivation domain, it can transactivate the IL-3 promoter nearly as effectively as AML1B, a known activator. A consensus AML1 binding site (TGTGGT), located in the previously identified DNase I footprint region A of the human IL-3 promoter (extending from bp -165 to -128), and a sequence similar to the consensus binding site (TGTGGG), located in footprint region B (bp -55 to -42), specifically bind AML1 proteins in gel shift assays. The affinity for the TGTGGG sequence was much less than that for the TGTGGT sequence, and mutating the TGTGGG sequence did not alter the IL-3 promoter activity, whereas mutation of the consensus binding site decreased the basal promoter activity and nearly eliminated transactivation by AML1A and AML1B. The AML1/ETO fusion protein, generated by the t(8;21) translocation, repressed IL-3 promoter activity, although the AML1 portion of AML1/ETO (amino acids 1-177) lacked transcriptional regulatory activity and did not bind to DNA in vitro. The 60- to 177-amino acid portion of AML1 readily bound DNA, suggesting that the first 59 amino acids may function as an inhibitory domain for DNA binding. Demonstration of the transactivation by AML1A and localization of a putative inhibitory binding domain suggest additional complexity within this family of transcription factors.

The B cell antigen receptor complex: mechanisms and implications of tyrosine kinase activation

The B cell receptor is a multimeric receptor complex whose constituent chains appear to mediate distinct and possibly interrelated functions. In this review we have focused on how one chain, immunoglobulin (Ig)-alpha, may function to activate tyrosine kinases and the consequences of that activation. The cytoplasmic domain of Ig-alpha contains a consensus sequence, the antigen recognition homology 1 (ARH 1) motif, which is found in Ig-beta and other antigen recognition receptor associated chains. We argue that this conserved structure reflects an underlying conserved mechanism of secondary effector activation. Our data also indicates that the specificity of each motif (i.e., the elements which restrict secondary effector binding to particular motifs) is encoded within divergent sequences found in each ARH 1 motif. In the particular case of kinase activation by Ig-alpha, the subsequent phosphorylation of multiple tyrosines on Ig-alpha, Ig-beta, CD19, CD22 and possibly other functionally related chains form recruitment sites for a myriad of secondary signal transducers. In this model, proximal tyrosine kinases and phosphatases do not function so much to mediate the linear transfer of information as to establish and modulate an interrelated network of signal transducers capable of driving complicated cellular responses.

The hemagglutinins of duck and human H1 influenza viruses differ in sequence conservation and in glycosylation

We determined the deduced amino acid sequences of two H1 duck influenza A virus hemagglutinins (HAs) and found that the consensus sequence of the HA, determined directly from virus recovered from the intestinal tract, remains unchanged through many generations of growth in MDCK cells and chicken embryos. These two duck viruses differ from each other by 5 amino acids and from A/Dk/Alberta/35/1976 (F. J. Austin, Y. Kawaoka, and R. G. Webster, J. Gen. Virol. 71:2471-2474, 1990) by 9 and 12 amino acids, most of which are in the HA1 subunit. They are antigenically similar to each other but different from the Alberta virus. We compared these H1 duck HAs with the HAs of human isolates to identify structural properties of this viral glycoprotein that are associated with host range. By comparison to the human H1 HAs, the duck virus HA sequences are highly conserved as judged by the small fraction of nucleotide differences between strains which result in amino acid substitutions. However, the most striking difference between these duck and human HAs is in the number and distribution of glycosylation sites. Whereas duck and swine viruses have four and five conserved glycosylation sites per HA1 subunit, none of which are on the tip of the HA, all human viruses have at least four additional sites, two or more of which are on the tip of the HA. These findings stress the role of glycosylation in the control of host range and suggest that oligosaccharides on the tip of the HA are important to the survival of H1 viruses in humans but not in ducks or swine.

Immunological reactivity of a human immunodeficiency virus type I derived peptide representing a consensus sequence of the GP120 major neutralizing region V3

To reduce the opportunities for human immunodeficiency virus type 1 (HIV-1) to evade vaccine induced immunity, the development of subunit vaccines must focus on the characterization of immunogenic epitopes, which are major targets for the immune system. The most dominant site for elicitation of neutralising immune response is located on the external envelope glycoprotein gp120 within the third variable domain (V3). To overcome virus type specificity of antibodies directed to the V3-domain we designed a 36 amino acids long gp120/V3-consensus peptide (V3-C36) based on published biological data and sequence comparisons of various HIV-1 virus isolates. This peptide contains a conserved core sequence which is suggested to form a surface-exposed beta-turn. This peptide also includes T-cell epitopes defined in mice and humans, an ADCC-epitope and two highly conserved cysteine residues which were oxidized to form a cystine derivate, thus allowing correct peptide folding. In ELISA-tests, this peptide reacts with at least 90% of randomly selected sera of European and African patients infected with HIV-1 and is recognized by three different HIV-1/V3 "type-specific" antisera (MN, RF, IIIB-strain). Using this peptide as immunogen in rabbits, antisera could be raised with highly cross-reactive and HIV-1/IIIB strain neutralizing properties. Moreover, HTLV/HIV-1/IIIB specific cytotoxic T-lymphocytes (CTLs) of BALB/c mice infected with a gp120 recombinant vaccinia virus recognized the central 16- and 12-mer peptides of the V3-C36 consensus peptide in cytolytic assays, indicating perfect compatibility of the consensus peptide with the IIIB-primed CTLs. The DNA-sequence encoding the V3-consensus loop region might be an important component in newly designed recombinant subunit vaccines. In addition, due to its broad serological reactivity, the V3-consensus peptide might play an important role in special diagnostic purposes.

Cloning of the non-neuronal intermediate filament protein of the gastropod Aplysia californica; identification of an amino acid residue essential for the IFA epitope

We describe the isolation and characterization of a full-length cDNA corresponding to the larger non-neuronal (nn) intermediate filament (IF) protein of the gastropod Aplysia californica. Comparison of the sequences of the nn-IF proteins from Aplysia californica and Helix aspersa shows a strong evolutionary drift. At a 72% sequence identity level, the IF proteins of Opisthobranchia and Pulmonata show a larger distance than vimentins from Xenopus and mammals. The sequence comparison of the two snail proteins provides an important step in understanding the epitope of the monoclonal antibody IFA mapped by previous studies to the consensus sequence at the carboxy-terminal end of the rod domain of IF proteins. We identify for the first time in a naturally occurring IF protein a single amino acid exchange which leads to the loss of the epitope. The consensus sequence YRKLLEGEE present in IFA-positive proteins such as the Helix IF protein is changed in the IFA-negative Aplysia protein only by the conservative substitution of the arginine (R) by a lysine (K). Thus, the IFA epitope is not a necessity of IF structure, and its presence or absence on different IF proteins reflects only small changes in an otherwise conserved consensus sequence. Consequently, lack of IFA reactivity does not exclude the presence of IF. This result predicts that IF are much more universally expressed in lower eukaryotes than currently expected from immunological results with the monoclonal antibody IFA.