Enhancers with cooperative Notch binding sites are more resistant to regulation by the Hairless co-repressor

Notch signaling controls many developmental processes by regulating gene expression. Notch-dependent enhancers recruit activation complexes consisting of the Notch intracellular domain, the Cbf/Su(H)/Lag1 (CSL) transcription factor (TF), and the Mastermind co-factor via two types of DNA sites: monomeric CSL sites and cooperative dimer sites called Su(H) paired sites (SPS). Intriguingly, the CSL TF can also bind co-repressors to negatively regulate transcription via these same sites. Here, we tested how synthetic enhancers with monomeric CSL sites versus dimeric SPSs bind Drosophila Su(H) complexes in vitro and mediate transcriptional outcomes in vivo. Our findings reveal that while the Su(H)/Hairless co-repressor complex similarly binds SPS and CSL sites in an additive manner, the Notch activation complex binds SPSs, but not CSL sites, in a cooperative manner. Moreover, transgenic reporters with SPSs mediate stronger, more consistent transcription and are more resistant to increased Hairless co-repressor expression compared to reporters with the same number of CSL sites. These findings support a model in which SPS containing enhancers preferentially recruit cooperative Notch activation complexes over Hairless repression complexes to ensure consistent target gene activation.

Cell signaling provides a basic means of communication during development. Many signaling pathways, including the Notch pathway, convert extracellular signals into changes in gene expression via transcription factors that bind specific DNA sequences. Importantly, the Notch pathway transcription factor can either form activating complexes upon Notch activation to stimulate gene expression or repression complexes with co-repressors to inhibit gene expression. Prior studies showed that the Notch activation complex binds DNA as either an independent complex on monomer binding sites or as two cooperative complexes (dimer) on paired binding sites. In this study, we used synthetic biology to examine how these two types of DNA sites impact the binding of Notch activation versus repression complexes and the output of Notch target gene expression. Our studies reveal that unlike the Notch activation complex, the repression complex does not cooperatively bind dimer sites. Moreover, our findings support the model that the enhanced stability of the Notch activation complex on dimer sites makes target genes with dimer sites less sensitive to the repression complex than target genes with only monomer sites. Thus, our studies reveal how target genes with different binding sites differ in sensitivity to the ratio of Notch activation to repression complexes.

Effective immunization of mice against cutaneous leishmaniasis using an intrinsically adjuvanted synthetic lipopeptide vaccine

Two peptides representing predicted T-cell epitopes of gp63, a major surface glycoprotein of the parasite Leishmania major, were used in vaccines tested in a murine model of cutaneous leishmaniasis. Either subcutaneous or intraperitoneal immunization in saline with a peptide representing gp63 amino acids 467-482 (p467) significantly protected CBA mice against the development of severe cutaneous lesions only when the peptide was intrinsically adjuvanted by covalently adding a lauryl-cysteine moiety (LC-p467) to its amino terminus during synthesis. In marked contrast, administration of p467 alone, cysteinyl-p467 or gp63 protein in saline resulted in some disease exacerbation. Splenic cells of LC-p467 immunized mice stimulated in vitro with LC-p467 displayed strong proliferative responses and secretion of IL-2, IFN-tau and GM-CSF (but not IL-4 and IL-10) suggesting that immunization with the lipopeptide induced the TH1 type cytokine responses associated with cell-mediated immunity. The safety, efficacy, ease of production and standardization of such lipopeptide vaccines suggest that they have significant potential for the development of vaccines for humans against leishmaniasis or other parasitic or viral diseases that require cell-mediated immunity for protection.

Imbalance of immune responses in patients with chronic and widespread fungal skin infection

Fungal infections of the skin are caused by dermatophyte fungi. Infections can be acute and inflammatory or chronic and non-inflammatory; it is believed that cell-mediated immunity is the cornerstone of host defence and is instrumental in the eradication of the infection. We describe here parameters of the immune response of a group of patients who although not immunocompromised, suffered from widespread and chronic infections. All patients lacked a specific delayed-type hypersensitivity (DTH) response; however, their in vitro lymphocyte proliferation in response to Trichophyton rubrum extract and to other fungal antigens was normal. The patients were not atopic by clinical history, and yet had high levels of non-specific IgE and of T. rubrum-specific IgG4. Taken together, the results of this study suggest that the group of patients studied suffered from an immune imbalance which has characteristics of a Th2-type response.

Changing patterns of cutaneous leishmaniasis in Israel and neighbouring territories

The most frequent form of cutaneous leishmaniasis (CL) in Israel and the neighbouring territories is due to Leishmania major, which is endemic mainly in the Jordan Valley and in the Rift Valley. CL due to L. tropica is much less common, and in the past only sporadic cases have been reported. In this study we present data obtained during the years 1988-1992 regarding CL in the area. Our clinic has diagnosed a total of 371 leishmaniasis cases, most of whom acquired the infection in the Jordan Valley, mainly during June and July. About one-third of the patients had single lesions, and one-third more than 5 lesions. We also describe an outbreak of leishmaniasis in Kfar Adumim, a village 15 km east of Jerusalem, where leishmaniasis was previously unknown. Parasites were characterized by the polymerase chain reaction and by immunostaining, and found to be both L. tropica and L. major. The localization of the homes of the affected people on a slope where hyraxes were abundant suggests that these animals might have been involved in the transmission of L. tropica in this area.

Antigen presentation by epidermal Langerhans cells in experimental cutaneous leishmaniasis

Cutaneous leishmaniasis is a disease induced by intradermal injection of leishmania promastigotes. Since the first cells the parasite encounters are those of the skin, the involvement of this organ in the early immune response might be relevant to the outcome of the disease. In this study we examined the ability of epidermal langerhans cells (LC) to become infected in vivo and to function as antigen presenting cells during the early hours of infection with Leishmania major. Our experiments showed that LC from mice injected with parasites can present antigen to a leishmania-specific T cell line when LC are obtained as early as four h after infection. The stimulation was specific, since LC from leishmania injected mice did not present antigen to an ovalbumin-specific T cell line nor did LC from ovalbumin-injected mice present antigen to the leishmania specific T cell line. Despite the ability of epidermal LC cells to present antigen, no parasites were detected in the epidermis, suggesting that these cells are not directly involved in establishing an infection.

Idiotypic cross-reactivity of immunoglobulins expressed in Waldenström's macroglobulinemia, chronic lymphocytic leukemia, and mantle zone lymphocytes of secondary B-cell follicles

Monoclonal antibodies (MoAbs) specific for autoantibody-associated cross-reactive idiotypes (CRIs) of Waldenström's IgM react frequently with the surface Ig (slg) expressed by leukemia cells of patients with chronic lymphocytic leukemia (CLL). Evaluation of the molecular basis for this cross-reactivity indicates that such CRIs are encoded by conserved antibody variable region genes (V genes) that have undergone little or no somatic hypermutation. We find that such anti-CRI MoAbs stain a subpopulation of cells within the mantle zones surrounding the germinal centers of normal human tonsil. In contrast, MoAbs specific for variable region subgroup determinants react with cells in both the mantle zones and germinal centers of secondary B-cell follicles. To test whether mantle zone B cells not reactive with existing anti-CRI MoAbs may express slg bearing as-yet-unrecognized CRIs present on Igs produced by neoplastic cells of some patients with Waldenström's macroglobulinemia or CLL, we immunized mice with purified Waldenström's IgM that have been characterized for their variable region subgroups using subgroup-specific antisera raised against synthetic peptides. The supernatants of hybridomas generated from the splenocytes of immunized mice were screened for their ability to stain a subpopulation of mantle zone lymphocytes in human tonsil. With this approach, two new anti-CRI MoAbs were identified, designated OAK1 and VOH3. OAK1 binds to a CRI present on a subset of kappa light chains of the VK1 subgroup. VOH3 recognizes a CRI determinant(s) present on a subset of antibody heavy chains of the VH3 subgroup. Flow cytometric analyses demonstrated that OAK1 specifically binds leukemia cells from 5 to 20 patients (25%) with kappa light chain expressing CLL. In addition, VOH3 reacted with the leukemia cells from 1 of 17 (6%) patients tested. The success of these methods demonstrates that the variable regions of the Igs produced by mantle zone B cells share idiotypic determinants with Igs expressed in B-cell CLL (B-CLL) and Waldenström's macroglobulinemia.

Correlation between the biologic functions and the generation of lymphokines in T cell clones

We have recently reported that various murine T cell clones produce IL-1. Based on this observation we have analyzed in the present study the correlation between the biological functions and the generation of different lymphokines in (T,G)-A--L specific CD4+ clones. One subset of clones--the "helper clones"--were found to provide help to primed B cells, in vitro. These cells could be shown to produce IL-1, IL-2, and B cell stimulatory factor 1 (IL-4) activities and to express mRNA encoding for these three cytokines. The second subset of clones, termed "proliferative clones", were unable to help B cells in vitro but expressed vigorous Ag-dependent proliferations. These cells did not express IL-1, IL-2, or IL-4 activities. They produced another lymphokine(s) which may be granulocyte-macrophage-CSF, or some other factor recognized by the HT2 cell line. This study further substantiates the link between T cell activities and lymphokine repertoire with a special emphasis on the potential role(s) of T cell-derived IL-1.

Correlation between the biologic functions and the generation of lymphokines in T cell clones

We have recently reported that various murine T cell clones produce IL-1. Based on this observation we have analyzed in the present study the correlation between the biological functions and the generation of different lymphokines in (T,G)-A--L specific CD4+ clones. One subset of clones--the "helper clones"--were found to provide help to primed B cells, in vitro. These cells could be shown to produce IL-1, IL-2, and B cell stimulatory factor 1 (IL-4) activities and to express mRNA encoding for these three cytokines. The second subset of clones, termed "proliferative clones", were unable to help B cells in vitro but expressed vigorous Ag-dependent proliferations. These cells did not express IL-1, IL-2, or IL-4 activities. They produced another lymphokine(s) which may be granulocyte-macrophage-CSF, or some other factor recognized by the HT2 cell line. This study further substantiates the link between T cell activities and lymphokine repertoire with a special emphasis on the potential role(s) of T cell-derived IL-1.

Mode of action of antigen-specific T-cell helper factors secreted by a T-cell line and clones

Antigen-specific T-cell helper factors were secreted from a (T,G)-A--L specific T-cell line and clones. The factors were released upon antigenic stimulation and could be induced by a low or a high dose of antigen. The factors secreted upon low-dose stimulation possessed the antigenic specificity of the secreting cells, while the high dose-induced factors had a broader antigenic specificity and could react with the closely related polypeptide (Phe,G)-A--L, even when the cells were restricted to (T,G)-A--L. Both the low dose- as well as the high dose-induced factors could not trigger antibody production in the presence of a non-relevant antigen, and did not collaborate with B cells immunized with a non-related antigen for the production of antibodies. The helper factors, like their secreting cells, were H-2-restricted in the collaboration with B cells. In contrast to the helper cells, however, they did not require accessory cells for triggering the B cells in the process of antibody production. Some preparations of helper factors were found to be inactive. The helper activity could be restored by IL-2. Thus, IL-2 is an additional essential factor required for the antigen-specific collaboration of B cells and T-cell helper factors.

Functional requirements of (Phe, G)-A--L-specific T-cell clones of (H-2b X H-2k)F1 origin

T-cell clones specific for the synthetic polypeptide antigen poly(LPhe, LGlu)-poly(DLAla)--poly(LLys) of (C57BL/6 X C3H/HeJ)F1 origin were tested for their biological activities. One group of clones was restricted in its proliferative response to the H-2b haplotype, the second to the H-2k haplotype, and the third to the F1 unique Ia determinants. All the clones which proliferated in response to antigen secreted interleukin-2 (IL-2) following stimulation. The H-2 restriction of the IL-2 secretion was the same as that of the proliferation. Two of the clones tested, C.6 and C.10, could provide help to B cells in antibody production. However, the genetic restriction profile of the helper activity was less stringent than that for the proliferative response. Thus, C.6, which proliferated in the presence of F1 antigen-presenting cells only, could help B cells and accessory cells of C3H/HeJ. C.10, which was restricted in its proliferative response to the H-2b haplotype, could collaborate with B cells and accessory cells of the H-2k haplotype as well. The antibody response of both clones was restricted to the parental or F1 strains.

Analysis of the biological functions and fine specificity of (T,G)-A--L specific T cell clones

Two T cell lines, TPB1 and TPB2, specific for the synthetic polypeptide antigen (T,G)-A--L, were established from (T,G)-A--L primed lymph node cells of C3H.SW(H-2b) mice. Both lines proliferated in the presence of (T,G)-A--L, helped in antibody production in vitro, and secreted IL2 upon stimulation with antigen. The lines differed in the fine specificity of their responses to antigenic stimulation. The line with the broader specificity TPB2 was cloned by limiting dilution, and its derived clones were analyzed. No efficient manifestation of both proliferative activity and helper function could be detected in a single clone. Most of the clones were highly specific to (T,G)-A--L, although 2 of them cross-reacted with the closely related polypeptide (Phe,G)-A--L. Individual clones could trigger B cells for the production of antibodies of the IgM and IgG classes. All helper clones secreted (T,G)-A--L specific helper factors. No correlation was found between efficient secretion of IL2 by the clones and their other biological functions.

Establishment and biological activity of a proliferative anti-idiotype-activated T cell line

Antisera were raised in rabbits against a monoclonal antibody (McAb 103) of C3H.SW origin which is specific to the synthetic polypeptide (T,G)-A-L and was shown to express the major idiotypic determinants of conventional anti-(T,G)-A-L antibodies. Antibodies were purified and were shown in a binding assay to recognize McAb 103 as well as C3H.SW anti-(T,G)-A-L antibodies. C57BL/6 mice were immunized with the purified rabbit anti-McAb 103 (Ra 103) and their lymph nodes were studied in a proliferation assay. Proliferation was observed in the presence of both Ra 103 and (T,G)-A-L, although the latter stimulated the cells to a lesser extent, suggesting the induction in vivo of (T,G)-A-L-specific clones in low frequency. A T cell line was established from these lymph node cells. The line is kept in continuous growth in the presence of IL-2 and periodic triggering with Ra 103. A significant proliferative response was obtained with Ra 103 only. This proliferation could be almost completely inhibited by either McAb 103 or by conventional anti-(T,G)-A-L antibodies of C3H.SW origin, indicating the cross reaction between the idiotypes expressed on the T cell line and the (T,G)-A-L-specific antibodies. No proliferation could be detected in the presence of either normal rabbit IgG or rabbit anti-mouse IgG. Thus, the T cell line TId 103 allows the analysis of the role of idiotype in T cell recognition and regulation.

Antigen presentation by proliferating thymic macrophages to A (T,G)-A-L specific T cell line in an H-2 restricted manner

Long-term cultures of murine homogeneous populations of Ia-bearing thymus-derived murine macrophages were tested for their ability to present antigen to a (T,G)-A-L specific IL-2-dependent continuous T cell line. Thymus-derived macrophages, with and without pretreatment for Ia induction, triggered efficiently antigen-specific T cell proliferation in an MHC restricted way. This experimental system, consisting of two normal proliferating homogeneous populations of macrophages and antigen specific T cells, provides an ideal tool for studying the mechanism of antigen presentation to T cells and for elucidation of the role of macrophages in T-B cell collaboration for antibody production.