Unfolded Von Willebrand Factor Binds Protein S and Reduces Anticoagulant Activity

Protein S (PS), the critical plasma cofactor for the anticoagulants tissue factor (TF) pathway inhibitor (TFPI) and activated protein C (APC), circulates in two functionally distinct pools: free (anticoagulant) or bound to complement component 4b-binding protein (C4BP) (anti-inflammatory). Acquired free PS deficiency is detected in several viral infections, but its cause is unclear. Here, we identified a shear-dependent interaction between PS and von Willebrand Factor (VWF) by mass spectrometry. Consistently, plasma PS and VWF comigrated in both native and agarose gel electrophoresis. The PS/VWF interaction was blocked by TFPI but not APC, suggesting an interaction with the C-terminal sex hormone binding globulin (SHBG) region of PS. Microfluidic systems, mimicking arterial laminar flow or disrupted turbulent flow, demonstrated that PS stably binds VWF as VWF unfolds under turbulent flow. PS/VWF complexes also localized to platelet thrombi under laminar arterial flow. In thrombin generation-based assays, shearing plasma decreased PS activity, an effect not seen in the absence of VWF. Finally, free PS deficiency in COVID-19 patients, measured using an antibody that binds near the C4BP binding site in SHBG, correlated with changes in VWF, but not C4BP, and with thrombin generation. Our data suggest that PS binds to a shear-exposed site on VWF, thus sequestering free PS and decreasing its anticoagulant activity, which would account for the increased thrombin generation potential. As many viral infections present with free PS deficiency, elevated circulating VWF, and increased vascular shear, we propose that the PS/VWF interaction reported here is a likely contributor to virus-associated thrombotic risk.

R-DOTAP Cationic Lipid Nanoparticles Outperform Squalene-Based Adjuvant Systems in Elicitation of CD4 T Cells after Recombinant Influenza Hemagglutinin Vaccination

It is clear that new approaches are needed to promote broadly protective immunity to viral pathogens, particularly those that are prone to mutation and escape from antibody-mediated immunity. Prototypic pathogens of this type are influenza and SARS-CoV-2, where the receptor-binding protein exhibits extremely high variability in its receptor-binding regions. T cells, known to target many viral proteins, and within these, highly conserved peptide epitopes, can contribute greatly to protective immunity through multiple mechanisms but are often poorly recruited by current vaccine strategies. Here, we have studied a promising novel pure enantio-specific cationic lipid 1,2-dioleoyl-3-trimethylammonium-propane (R-DOTAP), which was previously recognized for its ability to generate anti-tumor immunity through the induction of potent cytotoxic CD8 T cells. Using a preclinical mouse model, we have assessed an R-DOTAP nanoparticle adjuvant system for its ability to promote CD4 T cell responses to vaccination with recombinant influenza protein. Our studies revealed that R-DOTAP consistently outperformed a squalene-based adjuvant emulsion, even when it was introduced with a potent TLR agonist CpG, in the ability to elicit peptide epitope-specific CD4 T cells when quantified by IFN-γ and IL-2 ELISpot assays. Clinical testing of R-DOTAP containing vaccines in earlier work by others has demonstrated an acceptable safety profile. Hence, R-DOTAP can offer exciting opportunities as an immune stimulant for next-generation prophylactic recombinant protein-based vaccines.

Abstract B24: Development of targeted T-cell cancer immunotherapies based on a novel enantiomeric cationic lipid that promotes antigen cross-presentation and upregulation of type I interferons

The enantiomeric cationic lipid R-DOTAP nanoparticle platform (Versamune®) was reported (Gandhapudi et. al. 2019, J. Immunol.) to promote cross presentation of multi-epitope human papilloma virus (HPV) antigens and upregulation of Type I interferons, leading to induction of high levels of antigen-specific cytolytic polyfuctional CD8+ T-cells in vivo and complete regression of TC-1 tumors in preclinical models. In two ongoing Phase 2 human clinical trials (ASCO 2022), the early data in a group of the first 60 patients receiving PDS0101 (Versamune® plus HPV16 peptide mix) and who had previously failed standard of care suggests translation of the established mechanism of action into humans resulting in the induction of tumor-specific, clinically effective immune responses. In refractory and difficult-to-treat HPV-related cancers, improved patient survival and tumor shrinkage has been demonstrated. In this study we demonstrate expansion of the Versamune® platform to the treatment of non-viral associated cancers. We have developed Versamune® based drug formulations containing novel multi-epitope peptide sequences of the TARP (T-Cell receptor gamma chain Alternate Reading frame Protein) antigen expressed in 100% of adult and pediatric AML (acute myelogenous leukemia), over 90% of prostate cancers and over 50% of breast cancers. We have also developed Versamune® based drug formulations containing modified sequences of novel Mucin 1 oncoprotein (MUC1) agonist peptide antigens that are over expressed in multiple solid tumors. Using humanized HLA-A2 transgenic mice, we show that the Versamune® platform similarly promotes cross presentation of the non-viral antigens resulting in equally high levels of antigen-specific CD8+ T-cells as observed with HPV. These data demonstrate superior immunogenicity in breadth and potency of vaccine-induced immune responses, supporting progression of the targeted T-cell immunotherapies into human clinical trials.

Citation Format: Siva K Gandhapudi, Karuna Sundarapandiyan, Martin Ward, Afsheen Fatima, Mania Dorrani, Mary Banoub, Joe Dervan, Lauren Wood, Greg Conn, Jerold G Woodward. Development of targeted T-cell cancer immunotherapies based on a novel enantiomeric cationic lipid that promotes antigen cross-presentation and upregulation of type I interferons [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy; 2022 Oct 21-24; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(12 Suppl):Abstract nr B24.

R-DOTAP (Versamune): A novel enantiospecific cationic lipid nanoparticle that induces CD4 and CD8 cellular immune responses to whole protein and tumor-specific peptide antigens

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Background: Immunotherapy approaches are limited in their ability to induce antigen-specific CD8+ T cells in vivo able to recognize and kill tumor cells. We developed a novel immunotherapy approach using enantiomerically pure, R-DOTAP cationic lipid nanoparticles and tumor-derived T cell antigens, and previously demonstrated that R-DOTAP formulations efficiently prime cytotoxic T cells through enhanced cross presentation and induction of type I interferons.[1] A phase I clinical trial of a R-DOTAP HPV16 peptide formulation confirmed induction of strong in vivo HPV-specific CD8+ cytolytic T-cells without associated systemic toxicities. In this study, we assessed R-DOTAP nanoparticle formulations containing whole protein (ovalbumin) or long multi-epitope peptides from the tumor antigen TARP (T-cell alternate reading frame protein): a 58-residue protein overexpressed in prostate and breast cancers, documented to be immunogenic in humans. Methods: R-DOTAP formulations were prepared containing ovalbumin (OVA) or TARP peptides. C57BL/6K mice were immunized with 10 μg/mouse of OVA plus R-DOTAP, CFA or sucrose on Days 0, 15 and 30. OVA-specific cellular and humoral responses following vaccination were assessed by measuring splenic CD4 and CD8 T cell IFN-γ production and circulating OVA-specific antibodies in serum. HLA-A2 transgenic mice (AAD mice) were vaccinated with long, multi-epitope TARP peptides delivered as an R-DOTAP admixture or with CFA or sucrose on Days 0 and 7. Antigen-specific T cell responses were measured by IFN-γ ELISpot assay. Results: OVA R-DOTAP formulations induced strong antigen-specific effector CD4 and CD8 immune and memory responses detected 7 and 30 days, respectively, following vaccination as well as OVA-specific antibody responses. In TARP peptide vaccinated mice, R-DOTAP formulations were able to present multiple CD8 T cell epitopes and stimulate responses that were superior to CFA. Conclusions: Our results suggest that R-DOTAP is a versatile immune activating therapy that can be formulated with long, multi-epitope tumor-derived peptides or whole proteins. R-DOTAP formulations induce quantitatively robust antigen-specific CD4 and CD8 T cells in vivo compared to well-established immune stimulants. Reference: 1.Gandhapudi SK, Ward M, Bush JP et al. Antigen Priming with Enantiospecific Cationic Lipid Nanoparticles Induces Potent Antitumor CTL Responses through Novel Induction of a Type I IFN Response. J Immunol 2019;202:3524-3536

Antigen Priming with Enantiospecific Cationic Lipid Nanoparticles Induces Potent Antitumor CTL Responses through Novel Induction of a Type I IFN Response

Certain types of cationic lipids have shown promise in cancer immunotherapy, but their mechanism of action is poorly understood. In this study, we describe the properties of an immunotherapeutic consisting of the pure cationic lipid enantiomer R-1,2-dioleoyl-3-trimethyl-ammonium-propane (R-DOTAP) formulated with modified viral or self-peptide Ags. R-DOTAP formulations with peptide Ags stimulate strong cross-presentation and potent CD8 T cell responses associated with a high frequency of polyfunctional CD8 T cells. In a human papillomavirus tumor model system, a single s.c. injection of tumor-bearing mice with R-DOTAP plus human papillomavirus Ags induces complete regression of large tumors associated with an influx of Ag-specific CD8 T cells and a reduction of the ratio of regulatory/Ag-specific CD8 T cells. R-DOTAP also synergizes with an anti-PD1 checkpoint inhibitor, resulting in a significant inhibition of B16 melanoma tumor growth. We found that R-DOTAP stimulates type I IFN production by dendritic cells in vivo and in vitro. s.c. injection of R-DOTAP results in an IFN-dependent increase in draining lymph node size and a concomitant increase in CD69 expression. Using knockout mice, we show that type I IFN is required for the induction of CD8 T cell activity following administration of R-DOTAP plus Ag. This response requires Myd88 but not TRIF or STING. We also show that R-DOTAP stimulates both TLR7 and 9. Collectively, these studies reveal that R-DOTAP stimulates endosomal TLRs, resulting in a Myd88-dependent production of type I IFN. When administered with Ag, this results in potent Ag-specific CD8 T cell responses and antitumor activity.

mPGES1-Dependent Prostaglandin E2 (PGE2) Controls Antigen-Specific Th17 and Th1 Responses by Regulating T Autocrine and Paracrine PGE2 Production

The integration of inflammatory signals is paramount in controlling the intensity and duration of immune responses. Eicosanoids, particularly PGE₂, are critical molecules in the initiation and resolution of inflammation and in the transition from innate to acquired immune responses. Microsomal PGE synthase 1 (mPGES1) is an integral membrane enzyme whose regulated expression controls PGE₂ levels and is highly expressed at sites of inflammation. PGE₂ is also associated with modulation of autoimmunity through altering the IL-23/IL-17 axis and regulatory T cell (Treg) development. During a type II collagen-CFA immunization response, lack of mPGES1 impaired the numbers of CD4⁺ regulatory (Treg) and Th17 cells in the draining lymph nodes. Ag-experienced mPGES1^-/- CD4⁺ cells showed impaired IL-17A, IFN-γ, and IL-6 production when rechallenged ex vivo with their cognate Ag compared with their wild-type counterparts. Additionally, production of PGE₂ by cocultured APCs synergized with that of Ag-experienced CD4⁺ T cells, with mPGES1 competence in the APC compartment enhancing CD4⁺ IL-17A and IFN-γ responses. However, in contrast with CD4⁺ cells that were Ag primed in vivo, exogenous PGE₂ inhibited proliferation and skewed IL-17A to IFN-γ production under Th17 polarization of naive T cells in vitro. We conclude that mPGES1 is necessary in vivo to mount optimal Treg and Th17 responses during an Ag-driven primary immune response. Furthermore, we uncover a coordination of autocrine and paracrine mPGES1-driven PGE₂ production that impacts effector T cell IL-17A and IFN-γ responses.

Reduced T cell-dependent humoral immune response in microsomal prostaglandin E synthase-1 null mice is mediated by nonhematopoietic cells

Microsomal PGE synthase-1 (mPGES-1) is an inducible enzyme that specifically catalyzes the conversion of PGH2 to PGE2. We showed that mPGES-1 null mice had a significantly reduced incidence and severity of collagen-induced arthritis compared with wild-type (WT) mice associated with a marked reduction in Abs to type II collagen. In this study, we further elucidated the role of mPGES-1 in the humoral immune response. Basal levels of serum IgM and IgG were significantly reduced in mPGES-1 null mice. Compared with WT mice, mPGES-1 null mice exhibited a significant reduction of hapten-specific serum Abs in response to immunization with the T cell-dependent (TD) Ag DNP-keyhole limpet hemocyanin. Immunization with the T cell-independent type 1 Ag trinitrophenyl-LPS or the T cell-independent type 2 Ag DNP-Ficoll revealed minimal differences between strains. Germinal center formation in the spleen of mPGES-1 null and WT mice were similar after immunization with DNP-keyhole limpet hemocyanin. To determine whether the effect of mPGES-1 and PGE2 was localized to hematopoietic or nonhematopoietic cells, we generated bone marrow chimeras. We demonstrated that mPGES-1 deficiency in nonhematopoietic cells was the critical factor for reduced TD Ab production. We conclude that mPGES-1 and PGE2-dependent phenotypic changes of nonhematopoietic/mesenchymal stromal cells play a key role in TD humoral immune responses in vivo. These findings may have relevance to the pathogenesis of rheumatoid arthritis and other autoimmune inflammatory diseases associated with autoantibody formation.

Heat shock transcription factor 1 is activated as a consequence of lymphocyte activation and regulates a major proteostasis network in T cells critical for cell division during stress

Heat shock transcription factor 1 (HSF1) is a major transcriptional regulator of the heat shock response in eukaryotic cells. HSF1 is evoked in response to a variety of cellular stressors, including elevated temperatures, oxidative stress, and other proteotoxic stressors. Previously, we demonstrated that HSF1 is activated in naive T cells at fever range temperatures (39.5°C) and is critical for in vitro T cell proliferation at fever temperatures. In this study, we demonstrated that murine HSF1 became activated to the DNA-binding form and transactivated a large number of genes in lymphoid cells strictly as a consequence of receptor activation in the absence of apparent cellular stress. Microarray analysis comparing HSF1(+/+) and HSF1(-/-) gene expression in T cells activated at 37°C revealed a diverse set of 323 genes significantly regulated by HSF1 in nonstressed T cells. In vivo proliferation studies revealed a significant impairment of HSF1(-/-) T cell expansion under conditions mimicking a robust immune response (staphylococcal enterotoxin B-induced T cell activation). This proliferation defect due to loss of HSF1 is observed even under nonfebrile temperatures. HSF1(-/-) T cells activated at fever temperatures show a dramatic reduction in cyclin E and cyclin A proteins during the cell cycle, although the transcription of these genes was modestly affected. Finally, B cell and hematopoietic stem cell proliferation from HSF1(-/-) mice, but not HSF1(+/+) mice, were also attenuated under stressful conditions, indicating that HSF1 is critical for the cell cycle progression of lymphoid cells activated under stressful conditions.

Lipid nanocapsule as vaccine carriers for his-tagged proteins: evaluation of antigen-specific immune responses to HIV I His-Gag p41 and systemic inflammatory responses

The purpose of this study was to design novel nanocapsules (NCs) with surface-chelated nickel (Ni-NCs) as a vaccine delivery system for histidine (His)-tagged protein antigens. Ni-NCs were characterized for binding His-tagged model proteins through high-affinity non-covalent interactions. The mean diameter and zeta potential of the optimized Ni-NCs were 214.9 nm and -14.8 mV, respectively. The optimal binding ratio of His-tagged Green Fluorescent Protein (His-GFP) and His-tagged HIV-1 Gag p41 (His-Gag p41) to the Ni-NCs was 1:221 and 1:480 w/w, respectively. Treatment of DC2.4 cells with Ni-NCs did not result in significant loss in the cell viability up to 24h (<5%). We further evaluated the antibody response of the Ni-NCs using His-Gag p41 as a model antigen. Formulations were administered subcutaneously to BALB/c mice at day 0 (prime) and 14 (boost) followed by serum collection on day 28. Serum His-Gag p41-specific antibody levels were found to be significantly higher at 1 and 0.5 μg doses of Gag p41-His-Ni-NCs (His-Gag p41 equivalent) compared with His-Gag p41 (1 μg) adjuvanted with aluminum hydroxide (AH). The serum IgG2a levels induced by Gag p41-His-Ni-NCs (1 μg) were significantly higher than AH adjuvanted His-Gag p41. The Ni-NCs alone did not result in the elevation of systemic IL-12/p40 and CCL5/RANTES inflammatory cytokine levels upon subcutaneous administration in BALB/c mice. In conclusion, the proposed Ni-NCs can bind His-tagged proteins and have the potential to be used as antigen delivery system capable of generating strong antigen-specific antibodies at doses much lower than with aluminum-based adjuvant and causing no significant elevation of systemic pro-inflammatory IL-12/p40 and CCL5/RANTES cytokines.

Tresyl-based conjugation of protein antigen to lipid nanoparticles increases antigen immunogenicity

The present studies were aimed at investigating the engineering of NPs with protein-conjugated-surfactant at their surface. In order to increase the immunogenicity of a protein antigen, Brij 78 was functionalized by tresyl chloride and then further reacted with the primary amine of the model proteins ovalbumin (OVA) or horseradish peroxide (HRP). The reaction yielded Brij 78-OVA and Brij 78-HRP conjugates which were then used directly to form NP-OVA or NP-HRP using a one-step warm oil-in-water microemulsion precursor method with emulsifying wax as the oil phase, and Brij 78 and the Brij 78-OVA or Brij 78-HRP conjugate as surfactants. Similarly, Brij 700 was conjugated to HIV p24 antigen to yield Brij 700-p24 conjugate. The utility of these NPs for enhancing the immune responses to protein-based vaccines was evaluated in vivo using ovalbumin (OVA) as model protein and p24 as a relevant HIV antigen. In separate in vivo studies, female BALB/c mice were immunized by subcutaneous (s.c.) injection with NP-OVA and NP-p24 formulations along with several control formulations. These results suggested that with multiple antigens, covalent attachment of the antigen to the NP significantly enhanced antigen-specific immune responses. This facile covalent conjugation and incorporation method may be utilized to further incorporate other protein antigens, even multiple antigens, into an enhanced vaccine delivery system.

Lipid Nanoparticles with Accessible Nickel as a Vaccine Delivery System for Single and Multiple His-tagged HIV Antigens

Lipid-based nanoparticles (NPs) with a small amount of surface-chelated nickel (Ni-NPs) were developed to easily formulate the human immunodeficiency virus (HIV) his-tagged Tat (his-Tat) protein, as well as to formulate and co-deliver two HIV antigens (his-p24 and his-Nef) on one particle. Female BALB/c mice were immunized by subcutaneous injection with his-Tat/Ni-NP formulation (1.5 μg his-Tat/mouse) and control formulations on day 0 and 14. The day 28 anti-Tat specific immunoglobulin G titer with his-Tat/Ni-NPs was significantly greater than that with Alum/his-Tat. Furthermore, splenocytes from his-Tat/Ni-NP-immunized mice secreted significantly higher IFN-γ than those from mice immunized with Alum/his-Tat. Although Ni-NPs did not show better adjuvant activity than Tat-coated anionic NPs made with sodium dodecyl sulfate (SDS/NPs), they were less toxic than SDS/NPs. The initial results indicated that co-immunization of mice using his-p24/his-Nef/Ni-NP induced greater antibody response compared to using Alum/his-p24/his-Nef. Co-delivery of two antigens using Ni-NPs also increased the immunogenicity of individual antigens compared to delivery of a single antigen by Ni-NPs. In conclusion, Ni-NPs are an efficient delivery system for HIV vaccines including both single antigen delivery and multiple antigen co-delivery.

Heat shock factor 1 is activated in lymphoid cells as a consequence of antigen recognition and is critical for cell cycle progression during an immune response (33.25)

Heat shock factor 1 (HSF1) is the dominant transcription factor controlling the cellular response to a variety of cellular stress signals. We now demonstrate that HSF1 becomes activated to the DNA binding form and trans-activates a large number of genes in lymphoid cells strictly as a consequence of receptor activation in the apparent absence of stress. Furthermore, this activation stabilizes cell cycle progression, becoming increasingly critical in the face of stress. EMSA assays revealed the DNA binding form of HSF1 in activated lymphocytes, but not in naïve cells at 37oC. Microarray analysis comparing WT and KO gene expression in T cells activated at 37oC revealed a diverse set of 307 genes significantly regulated by HSF1 in non-stressed T cells. HSF1-/- T or B cells proliferated normally under benign conditions of anti-CD3 or LPS stimulation in vitro. However, proliferation was severely compromised under conditions mimicking a robust immune response (SEB induced T cell activation) or stress (39oC). Western blotting revealed that the block in proliferation was associated with an inability to up-regulate cyclin A resulting in a block in cell cycle progression. Finally, hematopoetic stem cell proliferation from HSF1-/- mice, but not WT mice was also attenuated at elevated temperatures, indicating that HSF1 is a major regulator of hematopoetic cell cycle progression under stress.

Defective generation of a humoral immune response is associated with a reduced incidence and severity of collagen-induced arthritis in microsomal prostaglandin E synthase-1 null mice

Microsomal PGE synthase-1 (mPGES-1) is an inducible enzyme that acts downstream of cyclooxygenase and specifically catalyzes the conversion of PGH(2) to PGE(2). The present study demonstrates the effect of genetic deletion of mPGES-1 on the developing immunologic responses and its impact on the clinical model of bovine collagen-induced arthritis. mPGES-1 null and heterozygous mice exhibited decreased incidence and severity of arthritis compared with wild-type mice in a gene dose-dependent manner. Histopathological examination revealed significant reduction in lining hyperplasia and tissue destruction in mPGES-1 null mice compared with their wild-type littermates. mPGES-1 deficient mice also exhibited attenuation of mechanical nociception in a gene dose-dependent manner. In addition, mPGES-1 null and heterozygous mice showed a marked reduction of serum IgG against type II collagen, including subclasses IgG1, IgG2a, IgG2b, IgG2c, and IgG3, compared with wild-type mice, which correlated with the reduction in observed inflammatory features. These results demonstrate for the first time that deficiency of mPGES-1 inhibits the development of collagen-induced arthritis, at least in part, by blocking the development of a humoral immune response against type II collagen. Pharmacologic inhibition of mPGES-1 may therefore impact both the inflammation and the autoimmunity associated with human diseases such as rheumatoid arthritis.

HSF1 is necessary for reactive oxygen species (ROS) homeostasis and proliferation in T cells at fever temperatures. (87.47)

HSF1 is a major heat and stress inducible transcription factor in eukaryotic cells responsible for the regulation of a variety of genes involved in maintenance of cellular homeostasis. We have previously shown that HSF1 is activated at physiologic fever temperatures (39oC) in T cells vs. much higher, non-physiologic temperatures (42oC) in most other cell types. T cells from HSF1−/− mice proliferate normally at 37oC, but are severely inhibited at 39oC. These T cells are blocked at the G1-S phase transition of the cell cycle. T cells normally increase ROS levels as a result of activation. Antioxidants which block ROS increases also inhibit proliferation. We found that fever temperatures also inhibited the normal activation induced increase of ROS in T cells within 2h. Wild type T cells can overcome this inhibition in ROS generation within 5h and go on to proliferate normally. In contrast, HSF1−/− T cells were unable to overcome this dysregulation and failed to proliferate. Thus, fever temperature causes a dysregulation in ROS homeostasis in T cells and HSF1 is critical in restoring this regulation.

Preparation and Characterization of Nickel Nanoparticles for Binding to His-tag Proteins and Antigens

PURPOSE

The purpose of these studies was to prepare nanoparticles (NPs) with a small amount of surface-chelated nickel for obtaining enhanced binding of histidine-tagged (his-tag) proteins compared to non-histidine-tagged protein binding to charged nanoparticles.

MATERIALS AND METHODS

NPs were prepared from oil-in-water microemulsion precursors using emulsifying wax, 3 mM Brij 78 and 0.1 mM DOGS-NTA-Ni lipid (referred to as Ni-NPs). The amount of lipid entrapped in the NPs was quantitated by atomic emission spectroscopy (AES). The Ni-NPs were investigated for binding to two his-tag proteins, green fluorescent protein (GFP) and his-tag HIV-1 Gag p24. In vivo studies in mice were carried out to evaluate the immune responses obtained to his-tag Gag p24 bound to Ni-NPs.

RESULTS

AES studies demonstrated that approximately 5% of the DOGS-NTA-Ni lipid used was entrapped in the NPs. The optimal binding ratio his-tag GFP and his-tag Gag p24 to Ni-NPs was found to be 1:33.7 and 1:35.4 w/w, respectively. This interaction was stable at 37 degrees C in PBS, pH 7.4 over 4 h and the interaction of his-tag GFP with the Ni-NPs was enhanced compared to control NPs prepared with no Ni on the surface (NTA-NPs). The in vivo studies demonstrated enhanced serum IgG and IgG2a responses to his-tag Gag p24 bound to Ni-NPs compared to protein adjuvanted with Alum or adsorbed on the surface of control NTA-NPs.

CONCLUSIONS

Ni-NPs can be used to bind strongly to his-tag proteins. This system was demonstrated to have potential applications in vaccine delivery for enhancing immune responses to protein-based vaccines.

HIV-1 Tat-coated nanoparticles result in enhanced humoral immune responses and neutralizing antibodies compared to alum adjuvant

HIV-1 Tat has been identified as an attractive target for vaccine development and is currently under investigation in clinical trials as both a therapeutic and preventative vaccine for HIV-1. It is well known that protein based vaccines produce poor immune responses by themselves and therefore require adjuvants to enhance immune responses. We have previously reported on the use of anionic nanoparticles (NPs) for enhancing cellular and humoral immune responses to Tat (1-72). The purpose of this study was to further evaluate the immune response of HIV-1 Tat (1-72) coated on anionic nanoparticles compared to alum using various doses of Tat (1-72). Nanoparticles were effective at generating comparable antibody titers at both 1 and 5 microg doses of Tat (1-72), whereas the antibody titers significantly decreased at the lower dose of Tat (1-72) using alum. Anti-sera from Tat (1-72) immunized mice reacted greatest to the N-terminal and basic regions of Tat, with the NP groups showing stronger reactivity to these regions compared to alum. Moreover, the anti-sera from all Tat (1-72) immunized groups contained Tat-neutralizing antibodies and were able to significantly inhibit Tat-mediated long terminal repeat (LTR) transactivation.

Strong T cell type-1 immune responses to HIV-1 Tat (1–72) protein-coated nanoparticles

A significant emphasis has been placed on the development of adjuvants and/or delivery systems to improve both antibody production and cell-mediated immune responses. We previously reported on a novel anionic nanoparticle, which led to enhanced humoral and T helper type-1 (Th1) biased immune responses in mice when coated with cationized model antigen. Tat (1-72) is a conserved regulatory HIV-1 protein. It was hypothesized that HIV vaccine strategies employing Tat (1-72) may be a promising approach. Although previous reports have suggested that Tat (1-86) may be immunosuppressive, it was demonstrated in this present study that Tat (1-72) was not immunosuppressive when co-administered to mice with ovalbumin (OVA). Tat (1-72) was coated on novel anionic nanoparticles. BALB/c mice were immunized with Tat (5 microg)-coated nanoparticles (15 microg) by subcutaneous injection on days 0 and 14. Antibody and cytokine release were determined on day 28 and compared to Tat (5 microg) adjuvanted with Alum (15 microg) as a Th2 control, Tat (5 microg) adjuvanted with Lipid A (50 microg) as a Th1 control. Immunization of BALB/c mice with Tat-coated nanoparticles resulted in antibody levels (IgG and IgM) comparable to those elicited from Tat and Alum. However, Tat-coated nanoparticles led to a Th1 biased immune response. The IFN-gamma release from splenocytes with Tat-coated nanoparticles was comparable to that from mice immunized with Tat and Lipid A, and 3.3-fold greater than that from mice immunized with Tat and Alum. These studies warrant further investigation of these nanoparticles to enhance both antibody and cellular-based immune responses.

Lowered temperature set point for activation of the cellular stress response in T-lymphocytes

The induction of heat shock protein gene expression in response to stress is critical for the ability of organisms to cope with and survive exposure to these stresses. However, most studies on HSF1-mediated induction of hsp70 gene expression have utilized immortalized cell lines and temperatures above the physiologically relevant range. For these reasons much less is known about the heat shock response as it occurs in mammalian cells within tissues in the intact organism. To gain insight into this area we determined the temperature thresholds for activation of HSF1 DNA binding in different mouse tissues. We have found that HSF1 DNA binding activity and hsp70 synthesis are induced in spleen cells at significantly lower temperatures relative to cells of other tissues, with a temperature threshold for activation (39 degrees C) that is within the physiological range for fever. Furthermore, we found that the lowered temperature set point for induction of the stress response in spleen is specific to T-lymphocytes residing within this tissue and is not exhibited by B-lymphocytes. This lowered threshold is also observed in T-lymphocytes isolated from lymph nodes, suggesting that it is a general property of T-lymphocytes, and is seen in different mouse strains. Fever is an early event in the immune response to infection, and thus activation of the cellular stress response in T-lymphocytes by fever temperatures could serve as a way to give these cells enough time to express hsps in anticipation of their function in the coming immune response. The induced hsps likely protect these cells from the stressful conditions that can exist during the immune response, for example increasing their protection against stress-induced apoptosis.

In vivo behavior of peptide-specific T cells during mucosal tolerance induction: antigen introduced through the mucosa of the conjunctiva elicits prolonged antigen-specific T cell priming followed by anergy

The mucosa of the conjunctiva is an important site of entry for environmental Ags as well as Ags emanating from the eye itself. However, very little is known about T cell recognition of Ag introduced through this important mucosal site. We have characterized the in vivo process of CD4 T cell recognition of Ag delivered via the conjunctival mucosa. Application of soluble OVA to the conjunctiva of BALB/c mice induced potent T cell tolerance. APC-presenting OVA peptide in vivo was only found in the submandibular lymph node and not in other lymph nodes, spleen, or nasal-associated lymphoid tissue. Similarly, in TCR transgenic DO11. 10 adoptive transfer mice, OVA-specific CD4+ T cell clonal expansion was only observed in the submandibular lymph node following conjunctival application of peptide. These experiments thus define a highly specific lymphatic drainage pathway from the conjunctiva. OVA-specific T cell clonal expansion peaked at day 3 following initiation of daily OVA administration and gradually declined during the 10-day treatment period, but remained elevated compared with nontreated adoptive transfer mice. During this period, the T cells expressed activation markers, and proliferated and secreted IL-2 in vitro in response to OVA stimulation. In contrast, these cells were unable to clonally expand in vivo, or proliferate in vitro following a subsequent OVA/CFA immunization. These results suggest that Ag applied to a mucosal site can be efficiently presented in a local draining lymph node, resulting in initial T cell priming and clonal expansion, followed by T cell anergy.

Bactericidal activity and postantibiotic effect of levofloxacin against anaerobes

The bactericidal activity and postantibiotic effect (PAE) of levofloxacin against nine anaerobes were determined. Levofloxacin at concentrations of the MIC and twice the MIC was bactericidal at 24 h to five of nine and nine of nine strains, respectively. The PAE of levofloxacin following a 2-h exposure ranged from 0.06 to 2.88 h.

Interleukin-3 and granulocyte-macrophage colony-stimulating factor enhance the generation and function of dendritic cells

Dendritic cells, well-known for their potent antigen-presenting activity, are generally present at very low frequency in the spleens of naive mice. We examined the ability of mice to generate functional dendritic cells (DC) following exposure to the cytokines interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Tumours secreting these cytokines provided a continuous stimulus resulting in a greatly increased number and frequency of DC in the spleen. These cells were purified by conventional DC isolation techniques and were found to exhibit many of the characteristics of DC from unmanipulated mice, including high allo-stimulatory activity in mixed lymphocyte reactions and expression of many similar cell surface markers. Using ovalbumin-peptide specific class I- and class II-restricted hybridomas containing the lacZ reporter gene, we found that these cytokine-generated DC had a greatly increased efficacy in the uptake and processing of particulate antigen. These cells appear to have retained the ability to ingest antigen that is generally associated with immature DC, but also exhibit the peptide/major histocompatibility complex (MHC)-presenting capabilities of mature DC. Development of an assay to measure the activity of a single DC revealed that these dual activities were the properties of the majority of the cytokine-generated DC. These findings indicate that exposure in vivo to the cytokines IL-3 and GM-CSF can result in the generation of large numbers of DC with increased capability of stimulating T cells. Thus, these cells may be important in vivo in the process of cross-priming and the subsequent generation of tumour-reactive cytotoxic T lymphocytes (CTL).

In-vitro activity of a new oral streptogramin, RPR 106972, alone and in combination with rifampicin or ciprofloxacin against Legionella spp

The in-vitro activity of RPR 106972, a new oral streptogramin, was compared with that of erythromycin, ciprofloxacin, and rifampicin against 45 Legionella spp. While rifampicin was the most active of all agents tested, RPR 106972 demonstrated activity comparable to that of erythromycin and ciprofloxacin. Usually, indifference was seen when RPR 106972 was tested in combination with rifampicin or ciprofloxacin.

Peptide-specific T cell clonal expansion in vivo following immunization in the eye, an immune-privileged site

To visualize the primary antigen-specific T cell response to Ag introduced into the eye, we have used an adoptive transfer system in which a limiting number of OVA peptide (323-339)-specific T cells from a TCR-transgenic mouse were transferred into nonirradiated, syngeneic recipients and then tracked in vivo by staining for FACS analysis or immunohistochemistry with the clonotypic mAb KJ1-26. Following posterior chamber injection of Ag, KJ1-26+ cells accumulated primarily in the draining, submandibular lymph node (LN) within 3 days. Although reduced in number, by day 6 these cells were primarily in the paracortical regions and were able to proliferate and secrete IL-2 in response to Ag stimulation. In contrast, following i.v. injection of Ag, the KJ1-26+ cells accumulated in the paracortical regions of the LN to a comparable degree, but did not proliferate or secrete IL-2. The day 3 accumulation of KJ1-26+ cells in the submandibular LN was inhibited if the eye was removed within 5 h after injection of Ag. In the spleen, foci of KJ1-26+ cells were observed in the periarteriolar lymphoid sheaths at day 3; these were not observed to the same degree following other forms of immunization. These results demonstrate that the submandibular LN is the primary site for early clonal expansion of antigen-specific T cells following intraocular Ag administration and that these cells show changes consistent with immunity rather than tolerance.

Peptide-specific T cell clonal expansion in vivo following immunization in the eye, an immune-privileged site

To visualize the primary antigen-specific T cell response to Ag introduced into the eye, we have used an adoptive transfer system in which a limiting number of OVA peptide (323-339)-specific T cells from a TCR-transgenic mouse were transferred into nonirradiated, syngeneic recipients and then tracked in vivo by staining for FACS analysis or immunohistochemistry with the clonotypic mAb KJ1-26. Following posterior chamber injection of Ag, KJ1-26+ cells accumulated primarily in the draining, submandibular lymph node (LN) within 3 days. Although reduced in number, by day 6 these cells were primarily in the paracortical regions and were able to proliferate and secrete IL-2 in response to Ag stimulation. In contrast, following i.v. injection of Ag, the KJ1-26+ cells accumulated in the paracortical regions of the LN to a comparable degree, but did not proliferate or secrete IL-2. The day 3 accumulation of KJ1-26+ cells in the submandibular LN was inhibited if the eye was removed within 5 h after injection of Ag. In the spleen, foci of KJ1-26+ cells were observed in the periarteriolar lymphoid sheaths at day 3; these were not observed to the same degree following other forms of immunization. These results demonstrate that the submandibular LN is the primary site for early clonal expansion of antigen-specific T cells following intraocular Ag administration and that these cells show changes consistent with immunity rather than tolerance.

Transgenic expression of IFN-gamma in the murine lens results in multiple ocular abnormalities and an early but self-limited inflammatory response

The anterior chamber of the eye is known to be an immune privileged site, due to both local and systemic effects on the immune response. Injection of IFN-gamma into the anterior chamber (AC) overcomes the suppression of antigen-specific delayed hypersensitivity responses normally seen in the eye. Transgenic mice expressing increased IFN-gamma in the lens under the alpha A-crystallin promoter were produced to determine whether the proinflammatory effects of IFN-gamma would abolish immune privilege and promote loss of tolerance as has been seen in non-immune privileged tissues. Two alpha C/IFN-gamma transgenic lines are described which demonstrate multiple ocular and lenticular abnormalities some of which are developmental in origin and others that may be secondary to the inflammatory effects of IFN-gamma. A significant inflammatory cell infiltrate which is observed in the AC and vitreous from birth to 4 weeks of age, consists initially of macrophage and polymorphonuclear leukocytes and then CD4+ T lymphocytes. However, the infiltrate is essentially resolved by 6 weeks of age. Therefore, although lens-specific expression of IFN-gamma results in early loss of immune privilege, chronic uveitis does not occur probably due to the lack of continued IFN-gamma expression.

Characterization of human T-cell responses to Yersinia enterocolitica superantigen

We reported that antigenic preparations from Yersinia enterocolitica stimulate murine T cells in a manner consistent with that of superantigens. As a consequence we examined whether Y. enterocolitica antigenic preparations stimulate human T-cell cultures. Human T cells, enriched from peripheral blood lymphocytes, were stimulated to proliferate in the presence of Y. enterocolitica cytoplasmic and membrane preparations. This activity has also been shown to be sensitive to protease treatment, indicating the presence of a protein, and when separated by ion-exchange chromatography a single peak of activity is resolved. Furthermore, this proliferation was inhibited, in a dose-dependent manner, by the presence of antibodies directed against MHC class II antigens, indicating a requirement for these molecules. When these cells were stained with a panel of V beta-specific antibodies to determine if there was an enrichment of a particular V beta-bearing T-cell subset after stimulation, results indicate a significant enrichment of T cells bearing V beta 3, V beta 12, V beta 14, and V beta 17 over controls. Taken together, these data are consistent with a Y. enterocolitica product acting as a superantigen for human T cells.

Lens-specific expression of a major histocompatibility complex class I molecule disrupts normal lens development and induces cataracts in transgenic mice

PURPOSE

Lens epithelial tissue does not normally express major histocompatibility complex (MHC) class I molecules. In addition, the mechanism of self-tolerance to intraocular antigens is unknown. To study the effect of class I expression in the lens, transgenic mice were produced that express an allo-MHC class I molecule under the alpha A-crystallin proximal promoter.

METHODS

p alpha Dd was generated by fusion of the H-2Dd structural gene to the alpha A-crystallin proximal promoter. Transgenic mice were produced, and founder lines were identified by Southern blot hybridization. Eyes from transgenic mice were cryostat sectioned and stained for Dd expression or fixed in paraformaldehyde and stained for histologic analysis. Lens RNA was isolated by acid phenol extraction, and transgene expression was analyzed by nuclease protection.

RESULTS

The transgenic mice demonstrated dose-dependent, nonimmunologic lens defects consistent within a given line. In the highest expressing lines, ocular defects, including microphthalmia and cataract formation, were observed. Many adult mice from these lines demonstrated lens capsule rupture and a Dd-specific inflammatory response. Inflammation did not occur in mice with intact lens capsules.

CONCLUSIONS

Overexpression of H-2Dd in the lens had serious nonimmunologic consequences on lens development and cataract formation. In addition, the high copy number mice revealed at least a partial loss of immunologic tolerance on lens capsule rupture. The lack of an inflammatory response in transgenic mice with intact lens capsules suggests that the physical barrier of the lens capsule is one mechanism of maintaining immune privilege.

Transcription of the murine class II Eb gene is regulated primarily at the level of transcriptional initiation

The constitutive and inducible expression of MHC class II genes is known to be regulated by multiple upstream promoter elements. Transient transfection assays implicate the proximal promoter region as both necessary and sufficient for appropriate tissue-specific and inducible expression. However, transgenic mouse experiments suggest that additional control regions are important. In this study we tested the hypothesis that additional regulation of class II expression occurred at the level of RNA polymerase II elongation. Nuclear run-on analysis using single-stranded probes spanning the entire Eb gene was performed on a variety of class II-positive, class II-negative, and class II-inducible cell lines. The results demonstrate that, while there is not an even distribution of RNA polymerase along the gene, there is no evidence for a regulated block in elongation. These data further support the idea that the primary mechanism of class II gene regulation is at the level of transcriptional initiation.

Characterization of MHC induction by Mycoplasma fermentans (incognitus strain)

Mycoplasma fermentans (incognitus strain) is a recently identified new human pathogen and suspected cofactor in acquired immune deficiency syndrome. Because this organism appears to exert strong immunosuppressive properties of its own, we decided to investigate whether it was capable of inducing MHC class II expression, as we have observed for other species of mycoplasma. In this report we demonstrate that M. fermentans (incognitus strain) is capable of producing factors that increase MHC class II expression as well as MHC class I expression on the myelomonocytic cell line, WEHI-3 cells. We also present data showing that these mycoplasmal factors induce small, although significant, increases in MHC class I and II antigens on a mouse glioma cell line, G26-20, and MHC class II expression on the human monocyte cell lines, U-937 and HL-60. Using nuclear run-on analysis, we show that the mycoplasma-induced increase in MHC expression is at least partially due to an increase in transcription of the MHC genes. Furthermore, we show that the factor that mediates this activity is sensitive to protease treatment, indicating that it is, at least in part, protein. These results demonstrate that M. fermentans (incognitus strain) is capable of modulating the expression of immunologically important MHC genes in both murine and human cell lines, which may prove to be an important factor in the pathogenesis of this organism.

Two regions of the H-2 Dd promoter are responsive to dimethylsulfoxide in line 1 cells by a mechanism distinct from IFN-gamma

The line 1 lung carcinoma is a spontaneous BALB/c tumor deficient in class I Ag expression at the protein and mRNA levels. Exposure of line 1 cells to 3% DMSO or IFN-gamma increases class I Ag protein and mRNA dramatically. We have examined the regulation of class I Ag induction by DMSO in line 1 cells. We found DMSO induces class I Ag expression in line 1 cells by a mechanism distinct from IFN, because the kinetics of class I Ag induction by these agents were dramatically different, 7 days vs 3 days, and DMSO did not act through an IFN second messenger. At the molecular level, class I H chain transcription in line 1 cells was low. Treatment with 3% DMSO or IFN-gamma increased H chain transcription four-fold and sevenfold, respectively, indicating that class I H chain expression is regulated at the level of transcription in line 1 cells. Using reporter gene constructs, we mapped the regions in the Dd H chain promoter that increase H chain expression after DMSO treatment of line 1 cells. Two regions of the Dd promoter, D1, from -210 to -133 bp, and D2, from -125 to -61 bp, were found to be independently responsive to DMSO. These regions were also responsive to IFN-gamma in line 1 cells. However, consistent with our cellular results, DMSO and IFN induction of class I H chain expression differed at the molecular level as determined by D1 point mutations that diminished IFN-gamma responsiveness but did not alter induction by DMSO. Thus, DMSO appears to regulate class I transcription through multiple regions of the class I H chain promoter in line 1 cells by a mechanism distinct from IFN-gamma.

Two regions of the H-2 Dd promoter are responsive to dimethylsulfoxide in line 1 cells by a mechanism distinct from IFN-gamma

The line 1 lung carcinoma is a spontaneous BALB/c tumor deficient in class I Ag expression at the protein and mRNA levels. Exposure of line 1 cells to 3% DMSO or IFN-gamma increases class I Ag protein and mRNA dramatically. We have examined the regulation of class I Ag induction by DMSO in line 1 cells. We found DMSO induces class I Ag expression in line 1 cells by a mechanism distinct from IFN, because the kinetics of class I Ag induction by these agents were dramatically different, 7 days vs 3 days, and DMSO did not act through an IFN second messenger. At the molecular level, class I H chain transcription in line 1 cells was low. Treatment with 3% DMSO or IFN-gamma increased H chain transcription four-fold and sevenfold, respectively, indicating that class I H chain expression is regulated at the level of transcription in line 1 cells. Using reporter gene constructs, we mapped the regions in the Dd H chain promoter that increase H chain expression after DMSO treatment of line 1 cells. Two regions of the Dd promoter, D1, from -210 to -133 bp, and D2, from -125 to -61 bp, were found to be independently responsive to DMSO. These regions were also responsive to IFN-gamma in line 1 cells. However, consistent with our cellular results, DMSO and IFN induction of class I H chain expression differed at the molecular level as determined by D1 point mutations that diminished IFN-gamma responsiveness but did not alter induction by DMSO. Thus, DMSO appears to regulate class I transcription through multiple regions of the class I H chain promoter in line 1 cells by a mechanism distinct from IFN-gamma.

Yersinia enterocolitica produces superantigenic activity

We have recently observed that antigenic preparations from Yersinia enterocolitica are capable of inducing strong proliferative responses in normal murine spleen cell cultures. As a consequence of this observation, we evaluated whether Yersinia-derived Ag possess superantigenic activity. Stimulatory activity can be found in culture supernatants, as well as membrane and cytoplasmic fractions of Y. enterocolitica. Cell depletion studies indicate that the primary responding cell is a CD4+ T cell, which requires the presence of APC for responsiveness to Y. enterocolitica Ag. Furthermore, these APC must express MHC class II Ag, as evidenced by the fact that either antibody depletion of class II+ APC or addition of anti-class II antibodies (that block class II Ag on the surface of APC) eliminates the proliferative response. Evaluation of TCR usage by BALB/c T cells responsive to Y. enterocolitica revealed that those T cells bearing V beta 3, 6, and 11 and possibly 7 and 9 were expanded after exposure to Y. enterocolitica Ag preparations. By using a panel of T cell hybridomas, we have shown that hybridomas bearing V beta 3, 7, 8.1, 9, and 11 but not 2, 8.2, 8.3, and 13 respond to Yersinia. When cytoplasmic fractions of Y. enterocolitica were subjected to column chromatography, proliferative activity was enriched approximately 27-fold, and the elution characteristics of the active material suggest that it possesses hydrophobic regions and is, therefore, probably membrane associated. These data indicate that Y. enterocolitica produces antigenic material that has properties consistent with those of T cell superantigens.

Yersinia enterocolitica produces superantigenic activity

We have recently observed that antigenic preparations from Yersinia enterocolitica are capable of inducing strong proliferative responses in normal murine spleen cell cultures. As a consequence of this observation, we evaluated whether Yersinia-derived Ag possess superantigenic activity. Stimulatory activity can be found in culture supernatants, as well as membrane and cytoplasmic fractions of Y. enterocolitica. Cell depletion studies indicate that the primary responding cell is a CD4+ T cell, which requires the presence of APC for responsiveness to Y. enterocolitica Ag. Furthermore, these APC must express MHC class II Ag, as evidenced by the fact that either antibody depletion of class II+ APC or addition of anti-class II antibodies (that block class II Ag on the surface of APC) eliminates the proliferative response. Evaluation of TCR usage by BALB/c T cells responsive to Y. enterocolitica revealed that those T cells bearing V beta 3, 6, and 11 and possibly 7 and 9 were expanded after exposure to Y. enterocolitica Ag preparations. By using a panel of T cell hybridomas, we have shown that hybridomas bearing V beta 3, 7, 8.1, 9, and 11 but not 2, 8.2, 8.3, and 13 respond to Yersinia. When cytoplasmic fractions of Y. enterocolitica were subjected to column chromatography, proliferative activity was enriched approximately 27-fold, and the elution characteristics of the active material suggest that it possesses hydrophobic regions and is, therefore, probably membrane associated. These data indicate that Y. enterocolitica produces antigenic material that has properties consistent with those of T cell superantigens.

Differential induction of bone marrow macrophage proliferation by mycoplasmas involves granulocyte-macrophage colony-stimulating factor

We have studied the ability of three different Mycoplasma species to induce proliferation of bone marrow-derived macrophages (BMM). We observed a significant mitogenic effect when BMM cells from BALB/c, DBA/2J, SJL, and C57BL/6 mice were incubated with membranes derived from Mycoplasma arginini or M. arthritidis but not when they were incubated with an equivalent amount of M. pulmonis membrane. We also determined that pretreatment of mycoplasma membrane preparations with papain eliminated the ability of these preparations to induce BMM proliferation. To determine whether these membrane fractions acted indirectly by stimulating the production of soluble factors known to stimulate proliferation of BMM cells, we performed blocking studies with antibodies directed against colony-stimulating factor 1 (CSF-1), interleukin-3 (IL-3), and granulocyte-macrophage colony-stimulating factor. Our results indicate that antibodies directed against either CSF-1 or IL-3 failed to block mycoplasma-initiated proliferation of BMM cells. However, when anti-GM-CSF was added to proliferative cultures at the time of initiation, we saw a dose-dependent reduction of mycoplasma-initiated proliferation. We conclude that the ability of mycoplasma membranes to initiate the proliferation of BMM is not shared by all species of mycoplasma and that it involves the production of GM-CSF by an as yet undetermined cell.

Evidence that IFN-gamma does not affect MHC class II gene expression at the post-transcriptional level in a mouse macrophage cell line

Mouse class II major histocompatibility complex genes have been shown to be regulated at the level of transcription for both tissue-specific and inducible expression. In particular, IFN-gamma induction of the class II genes has been shown to occur at the transcriptional level, although the role that additional post-transcriptional mechanisms of regulation may play in this induction is not known. To evaluate IFN-gamma effects on transcriptional and post-transcriptional events of class II gene expression, we examined the rate of decline of class II transcription, steady-state mRNA, and cell surface protein following the removal of IFN-gamma from maximally stimulated WEHI-3 cells (an IFN-gamma inducible, myelomonocytic cell line). We determined that transcription of class II genes almost completely returned to baseline levels eight hours after removal of IFN-gamma. However, the steady-state level of class II mRNA's required 4 days, and membrane Ia expression required 5 days to return to baseline levels. This decay was linear and allowed us to determine a half-life value of 16-20 h for class II transcripts. These data demonstrate that, following removal of IFN-gamma from fully stimulated cells, transcription of the class II genes declined rapidly, but mRNA was quite long-lived. We also assessed the class II mRNA stability in unstimulated WEHI-3 cells and the B-cell lymphoma. A20/2J, by actinomycin D treatment and northern blot analysis. In agreement with the IFN-gamma washout experiments, transcripts from all four class II genes were quite long-lived in these cell types, with a half-life greater than ten hours. These data support the concept that IFN-gamma acts primarily at the level of class II transcription and argues against IFN-gamma playing a major role in post-transcriptional modulation of class II expression.

Negative trans-acting factors extinguish Ia expression in B cell-L 929 somatic cell hybrids

Numerous studies have implicated trans-acting factors in the regulation of MHC class II gene expression. Some of these factors have been shown to act by inducing the expression of class II genes while others have been demonstrated to downregulate such expression. These reports have dealt almost exclusively with the role of trans-acting factors in the regulation of class II gene expression in hematopoietic-derived cells. We decided to extend these studies to the role trans-acting factors play in nonhematopoietic-derived (NHD) cells. In order to address this question we made somatic cell hybrids between the NHD Ltk- cell line and normal B cells to determine if the existence of positive trans-acting factors from the B cell would lead to the expression of Ltk- class II genes in the resultant hybrid. Our results clearly indicate that not only was there no induction of Ltk- class II gene expression in the hybrids, but there was a loss of B cell class II gene expression as well. These results suggest that Ltk- cells possess negative trans-acting factors that appear to predominate over the positive trans-acting factors possessed by B cells. We have further extended these studies to test the MHC-inducing activity of IFN-gamma and IL-4 on these hybrids. Our results indicate that the hybrids responded to IFN-gamma with an increase in class I but not class II expression for both fusion partners. Furthermore, neither B cell nor L cell class II genes were induced by IL-4. Taken together, these results indicate that Ltk- cells possess negative trans-acting factors that not only maintain the Ia- phenotype of these cells, but also block the action of positive trans-acting factors from B cells.

MHC class II transcription in different mouse cell types. Differential requirement for protein synthesis between B cells and macrophages

Although the MHC class II genes are known to be regulated transcriptionally, the relative rates of transcription of the four classical class II genes in different cell types have not been investigated. Using nuclear transcriptional analysis, we have investigated the transcriptional rates of the class II genes in the macrophage cell line WEHI-3, normal bone marrow-derived macrophages, L-929 cells, and two different B cell lymphoma lines. Kinetic analysis of class II transcription in IFN-gamma-treated WEHI-3 cells revealed a 4-h delay, followed by a rapid increase in transcription over the next 20 h. A significant basal level of class II transcription, apparent in bone marrow derived macrophages, was also further enhanced by IFN-gamma treatment. None of the class II genes were transcribed in L cells, whereas all class II genes were transcribed constitutively in the B cell lines. In both B cell lines and macrophages, the four class II genes were found to be transcribed at different rates from one another, but the only gene showing a consistent pattern in multiple experiments was A-alpha, always showing the highest rate. We also investigated the effect of protein synthesis inhibition on class II transcription. Cycloheximide treatment of WEHI-3 cells did not inhibit IFN-gamma-induced transcription of the class II genes within 8 h, suggesting that IFN-gamma acts on pre-existing trans-acting factors, rather than inducing their synthesis. In contrast, treatment of B cells with cycloheximide for 8 h significantly reduced class II transcription, suggesting that, in B cells, continuous synthesis of a labile trans-acting factor is required for constitutive expression. These data support the notion that class II expression in B cells is mediated by trans-acting factors distinct from those found in macrophages.

MHC class II transcription in different mouse cell types. Differential requirement for protein synthesis between B cells and macrophages

Although the MHC class II genes are known to be regulated transcriptionally, the relative rates of transcription of the four classical class II genes in different cell types have not been investigated. Using nuclear transcriptional analysis, we have investigated the transcriptional rates of the class II genes in the macrophage cell line WEHI-3, normal bone marrow-derived macrophages, L-929 cells, and two different B cell lymphoma lines. Kinetic analysis of class II transcription in IFN-gamma-treated WEHI-3 cells revealed a 4-h delay, followed by a rapid increase in transcription over the next 20 h. A significant basal level of class II transcription, apparent in bone marrow derived macrophages, was also further enhanced by IFN-gamma treatment. None of the class II genes were transcribed in L cells, whereas all class II genes were transcribed constitutively in the B cell lines. In both B cell lines and macrophages, the four class II genes were found to be transcribed at different rates from one another, but the only gene showing a consistent pattern in multiple experiments was A-alpha, always showing the highest rate. We also investigated the effect of protein synthesis inhibition on class II transcription. Cycloheximide treatment of WEHI-3 cells did not inhibit IFN-gamma-induced transcription of the class II genes within 8 h, suggesting that IFN-gamma acts on pre-existing trans-acting factors, rather than inducing their synthesis. In contrast, treatment of B cells with cycloheximide for 8 h significantly reduced class II transcription, suggesting that, in B cells, continuous synthesis of a labile trans-acting factor is required for constitutive expression. These data support the notion that class II expression in B cells is mediated by trans-acting factors distinct from those found in macrophages.

Induction of class II MHC antigen expression in macrophages by Mycoplasma species

Several different Mycoplasma species have been shown to act as mitogens for either T or B cells and as stimulators of macrophage tumoricidal activity. In this report, we show that at least five different species of Mycoplasma are capable of inducing class II MHC expression on macrophages. We have observed significant induction of class II MHC surface expression on the myelomonocytic cell line, WEHI-3, as early as 24 h after deliberate infection of cultures, reaching maximal levels by 4 days. This induction was also apparent at the mRNA level as assessed by Northern blot analysis by using A alpha, E alpha, and A beta probes. However, unlike many other previously described MHC-inducing agents, mycoplasmas failed to induce class I MHC expression at either the cell surface or mRNA levels. Kinetic analysis revealed that induction of class II mRNA by mycoplasmas was slower than induction by IFN-gamma requiring 24 h rather than 8 h for significant increases to be noted. Induction by mycoplasmas does not require the presence of live organisms and remains active after heat treatment of 90 degrees C for 30 min. We have also demonstrated that mycoplasma infection of primary bone marrow macrophage cultures leads to the induction of both class I and class II genes and, as in the case of WEHI-3, this induction does not require the presence of live organisms. These data indicate that several Mycoplasma species have the capacity to induce class II MHC expression in WEHI-3 and both class I and class II MHC expression in bone marrow macrophage cultures in the absence of any T cell products.

Induction of class II MHC antigen expression in macrophages by Mycoplasma species

Several different Mycoplasma species have been shown to act as mitogens for either T or B cells and as stimulators of macrophage tumoricidal activity. In this report, we show that at least five different species of Mycoplasma are capable of inducing class II MHC expression on macrophages. We have observed significant induction of class II MHC surface expression on the myelomonocytic cell line, WEHI-3, as early as 24 h after deliberate infection of cultures, reaching maximal levels by 4 days. This induction was also apparent at the mRNA level as assessed by Northern blot analysis by using A alpha, E alpha, and A beta probes. However, unlike many other previously described MHC-inducing agents, mycoplasmas failed to induce class I MHC expression at either the cell surface or mRNA levels. Kinetic analysis revealed that induction of class II mRNA by mycoplasmas was slower than induction by IFN-gamma requiring 24 h rather than 8 h for significant increases to be noted. Induction by mycoplasmas does not require the presence of live organisms and remains active after heat treatment of 90 degrees C for 30 min. We have also demonstrated that mycoplasma infection of primary bone marrow macrophage cultures leads to the induction of both class I and class II genes and, as in the case of WEHI-3, this induction does not require the presence of live organisms. These data indicate that several Mycoplasma species have the capacity to induce class II MHC expression in WEHI-3 and both class I and class II MHC expression in bone marrow macrophage cultures in the absence of any T cell products.

Induction of class I and class II MHC antigen expression on murine bone marrow-derived macrophages by IL-4 (B cell stimulatory factor 1)

We have studied the effects of IL-4 (B cell stimulatory factor 1) on the expression of MHC gene products in normal bone marrow-derived macrophages, peritoneal macrophages, and the myelomonocytic cell line WEHI-3. Using both IL-4-containing T cell supernatant and rIL-4, we have observed significant induction of both class I and class II MHC surface expression (about 1.5- to 4-fold increase) in 2-, 3-, and 4-day cultures of bone marrow-derived macrophages. This induction was also apparent at the mRNA level as assessed by Northern blot analysis using A beta, E alpha, and class I probes. Kinetic analysis revealed that induction of class II mRNA by IL-4 was slower than induction by IFN-gamma, requiring 48 h before a significant increase was noted. The magnitude of MHC induction by IL-4 was not as great as that seen with IFN-gamma, which was found to increase surface expression of MHC antigens two- to eightfold. IL-4 also differs from IFN-gamma in the repertoire of macrophages responsive to it. IL-4 was unable to induce class I or class II expression in either thioglycolate-elicited peritoneal macrophages or WEHI-3 cells whereas IFN-gamma induced MHC antigen expression on both cell types under the same conditions. These data demonstrate that IL-4 is capable of inducing both class I and class II MHC gene products in some, but not all, macrophages.

Induction of class I and class II MHC antigen expression on murine bone marrow-derived macrophages by IL-4 (B cell stimulatory factor 1)

We have studied the effects of IL-4 (B cell stimulatory factor 1) on the expression of MHC gene products in normal bone marrow-derived macrophages, peritoneal macrophages, and the myelomonocytic cell line WEHI-3. Using both IL-4-containing T cell supernatant and rIL-4, we have observed significant induction of both class I and class II MHC surface expression (about 1.5- to 4-fold increase) in 2-, 3-, and 4-day cultures of bone marrow-derived macrophages. This induction was also apparent at the mRNA level as assessed by Northern blot analysis using A beta, E alpha, and class I probes. Kinetic analysis revealed that induction of class II mRNA by IL-4 was slower than induction by IFN-gamma, requiring 48 h before a significant increase was noted. The magnitude of MHC induction by IL-4 was not as great as that seen with IFN-gamma, which was found to increase surface expression of MHC antigens two- to eightfold. IL-4 also differs from IFN-gamma in the repertoire of macrophages responsive to it. IL-4 was unable to induce class I or class II expression in either thioglycolate-elicited peritoneal macrophages or WEHI-3 cells whereas IFN-gamma induced MHC antigen expression on both cell types under the same conditions. These data demonstrate that IL-4 is capable of inducing both class I and class II MHC gene products in some, but not all, macrophages.

Analysis of the equine lymphocyte antigen system by Southern blot hybridization

Fourteen Standardbred horses homozygous for one of six equine lymphocyte antigen (ELA) specificities (A1, A3, A4, A5, A6, or A10) were analyzed by Southern blot hybridization using DNA probes derived from the mouse major histocompatibility complex (MHC). Total genomic DNA from peripheral lymphocytes was digested with the restriction enzymes Hind III, Pvu II, or Eco RI. Twenty-three to thirty-three bands were generated for individual horses with the class I cDNA probe. The resulting band patterns revealed 12-14 nonpolymorphic fragments, which is consistent with the highly conserved Qa/Tla genes seen in other species. The remaining 10-19 bands displayed significant polymorphism; no two animals had identical band patterns when studied with all three enzymes. The polymorphism was markedly decreased between animals of the same ELA serotypes. Unique bands were identified in both A1 horses and all four A6 animals. Pvu II digestions of lymphocyte DNA were hybridized with mouse MHC class II probes. A cDNA probe for the E alpha gene revealed only a single nonpolymorphic band. In contrast, a cDNA probe for the H-2 A alpha locus displayed three to five strong bands in each animal with polymorphism that was most pronounced between horses of different ELA serotypes. Genomic DNA probes for A beta and E beta genes both revealed multiple polymorphic bands. However, cross-hybridization between these two probes prevented distinction between A beta and E beta equivalent loci. The reduced polymorphism evident within ELA specificities is consistent with the concept that the equine lymphocyte antigen system includes two families of closely linked MHC genes.

Further characterization of low density mononuclear cells: FACS-assisted analysis of human MLR stimulators

Previously, we reported that all of the potent stimulators of the allogeneic mixed leukocyte reaction (MLR) are contained in a heterogeneous low density fraction of human peripheral blood mononuclear (PBM) cells. We have further characterized human MLR stimulators by staining them with highly specific monoclonal antibodies, and then analyzing and separating them with the fluorescence-activated cell sorter. These studies revealed two populations of low density cells with potent allogeneic stimulatory activity. One population is a monocyte subset that reacts with anti-OKM1, MO.2, and expresses C3b as well as Fc-IgG receptors. The second population exhibits even greater stimulatory capacity and does not express any of these monocyte markers. Moreover, these cells are not phagocytic and do not react with alpha-naphthyl esterase. They comprise approximately 10% of the low density fraction or 0.5% of PBM. These cells are most likely lymphoid dendritic cells, described in various species as potent MLR stimulators. In contrast to the allogeneic MLR, only the low density cell type exhibiting dendritic cell characteristics induced a potent autologous MLR.

Further characterization of low density mononuclear cells: FACS-assisted analysis of human MLR stimulators

Previously, we reported that all of the potent stimulators of the allogeneic mixed leukocyte reaction (MLR) are contained in a heterogeneous low density fraction of human peripheral blood mononuclear (PBM) cells. We have further characterized human MLR stimulators by staining them with highly specific monoclonal antibodies, and then analyzing and separating them with the fluorescence-activated cell sorter. These studies revealed two populations of low density cells with potent allogeneic stimulatory activity. One population is a monocyte subset that reacts with anti-OKM1, MO.2, and expresses C3b as well as Fc-IgG receptors. The second population exhibits even greater stimulatory capacity and does not express any of these monocyte markers. Moreover, these cells are not phagocytic and do not react with alpha-naphthyl esterase. They comprise approximately 10% of the low density fraction or 0.5% of PBM. These cells are most likely lymphoid dendritic cells, described in various species as potent MLR stimulators. In contrast to the allogeneic MLR, only the low density cell type exhibiting dendritic cell characteristics induced a potent autologous MLR.

Distinct epitopes are recognized by cytolytic T lymphocyte clones on the same class I molecule: direct demonstration using DNA-transfected targets and long-term cytolytic T cell clones

By producing long-term, stable, cytolytic T lymphocyte clones and utilizing targets expressing only a single gene product derived from the stimulator mouse strain, we have been able to directly demonstrate that T cells recognize distinct epitopes expressed on a single H-2 molecule. These multiple determinants are distinguishable by inhibition patterns with monoclonal antibodies (mAb). When two T cell clones, P-2.14 and P-2.17, are tested on an L cell transfected with the Dp gene (lambda 12a), the T cells kill the transfected targets as well as blasts derived from Dp mouse strains. mAb 7-16.10 inhibits recognition and killing of Dp targets by both P-2.14 and P-2.17. This mAb recognizes a private specificity H-2.m22. Interestingly mAb 11-20.3 which also recognizes the H-2.m22 specificity inhibits clone P-2.14 but not P-2.17. The mAb 7-16.10, however, competes with 11-20.3 for binding to the surface of L cells expressing the Dp gene. Thus the two T cells must recognize an overlapping specificity. Other mAb which bind to the H-2Dp molecule are unable to inhibit either of these two cytolytic T cell clones. Paradoxically, any of the mAb when tested individually are sufficient to inhibit the polyclonal response derived from in vitro mixed lymphocyte culture. Therefore, by using targets expressing only a single H-2 molecule derived by DNA-mediated gene transfer and cytolytic T cell clones we have been able to directly demonstrate the presence of multiple epitopes on a single molecule and define their inhibition with mAb directed to that same molecule.

Production and characterization of T cell clones specific for mouse hepatitis virus, strain JHM: in vivo and in vitro analysis

Mouse hepatitis virus, strain JHM, is a coronavirus capable of inducing both acute and chronic central nervous system disease. To characterize the cell-mediated immune response directed toward JHMV antigens, we have generated and analyzed the properties of four T cell clones reactive to JHMV antigens. All four clones are of the Ly-1+2- phenotype and show an antigen-specific, I-Ab-restricted proliferative response that is dependent on antigen-presenting cells (APC). The fine specificity of I-A restriction was revealed by their differential recognition of JHMV antigen in the context of mutant I-A molecules present on B6.C-H-2bm12 APC. Two clones were unable to recognize JHMV antigen presented on bm12 APC, whereas a third clone showed an equivalent response with both bm12 and wild type B6 APC. In the analysis of the viral specificity, three of the clones showed distinct cross-reactions with MHV-2 and very little if any cross-reaction with MHV-A59. In addition, three of three clones tested responded well to sucrose gradient-purified, UV-inactivated JHMV, indicating that their specificity is directed toward virus structural rather than nonstructural proteins. Finally, two of the clones were analyzed for their ability to induce a DTH reaction when injected together with antigen into the footpads of various mouse strains. Consistent with the in vitro data, both clones produced a marked DTH response only in those strains carrying the I-Ab genotype. These data demonstrate, both in vivo and in vitro, that at least one component of the cell-mediated immune response to JHMV is characterized by an Ly-1+2-, I-A-restricted T cell specific for JHMV structural proteins.