Targeted delivery of DNA using YEE(GalNAcAH)3, a synthetic glycopeptide ligand for the asialoglycoprotein receptor

In vivo gene therapy shows promise as a treatment for both genetic and acquired disorders. The hepatic asialoglycoprotein receptor (ASGPr) binds asialoorosomucoid-polylysine-DNA (ASOR-PL-DNA) complexes and allows targeted delivery to hepatocytes. The tris(N-acetylgalactosamine aminohexyl glycoside) amide of tyrosyl(glutamyl) glutamate [YEE(GalNAcAH)3] has been previously reported to have subnanomolar affinity for the ASGPr. We have used an iodinated derivative of YEE(GalNAcAH)3 linked to polylysine and complexed to the luciferase gene (pCMV-Luc) in receptor-binding experiments to establish the feasibility of substituting ASOR with the synthetic glycopeptide for gene therapy. Scatchard analyses revealed similar Kd values for both ASOR and the glycopeptide. Binding and internalization of 125I-Suc-YEE(GalNAcAH)3 were competitively inhibited with either unlabeled ASOR or glycopeptide. The reverse was also true; 125I-ASOR binding was competed with unlabeled YEE(GalNAcAH)3 suggesting specific binding to the ASGPr by both compounds. Examination of in vivo delivery revealed that the 125I-labeled glycopeptide complex mimicked previous results observed with 125I-ASOR-PL-DNA. CPM in the liver accounted for 96% of the radioactivity recovered from the five major organs (liver, spleen, kidney, heart, and lungs). Cryoautoradiography displayed iodinated glycopeptide complex bound preferentially to hepatocytes rather than nonparenchymal cells. In vitro, as well as in vivo, transfections using the glycopeptide-polylysine-pCMV-luciferase gene complex (YG3-PL-Luc) resulted in expression of the gene product. These data demonstrate that the YEE(GalNAcAH)3 synthetic glycopeptide can be used as a ligand in targeted delivery of DNA to the liver-specific ASGPr.

Identification of functional domains in murine granulocyte-macrophage colony-stimulating factor using monoclonal antibodies to synthetic peptides

Granulocyte-macrophage (GM)-CSF is an important hematopoietic cytokine that regulates proliferation and differentiation of macrophages, neutrophils, and eosinophils. In this study, we generated mAb to five synthetic peptides that correspond to regions along the murine GM-CSF molecule. The ability of anti-peptide mAb to bind to and inhibit biologic activity of murine (m) GM-CSF was determined. mAb with the highest neutralization titers were derived from mice immunized with peptide II, which correspond to amino acids 27 to 38 of mGM-CSF. Immunochemical studies showed that peptide II specifically blocked binding of anti-peptide II mAb to GM-CSF. mAb to two other peptides in the N-terminal half corresponding to residues 7 to 17 and 47 to 58, respectively, of mGM-CSF also inhibited GM-CSF-dependent proliferation and differentiation of murine bone marrow precursors for macrophages and granulocytes. Anti-peptide mAb also inhibited growth of a murine hematopoietic cell line FDCP1 and a murine T cell line HT-2, which was shown to be dependent on GM-CSF for growth in vitro. Biologic activity of both natural and recombinant mGM-CSF was neutralized by anti-peptide mAb. These findings indicate that epitopes in the N-terminal region of mGM-CSF are important for biologic activity, and the epitope defined by peptide II (residues 27 to 38) lies within a particularly important functional domain of the mGM-CSF molecule.

Identification of functional domains in murine granulocyte-macrophage colony-stimulating factor using monoclonal antibodies to synthetic peptides

Granulocyte-macrophage (GM)-CSF is an important hematopoietic cytokine that regulates proliferation and differentiation of macrophages, neutrophils, and eosinophils. In this study, we generated mAb to five synthetic peptides that correspond to regions along the murine GM-CSF molecule. The ability of anti-peptide mAb to bind to and inhibit biologic activity of murine (m) GM-CSF was determined. mAb with the highest neutralization titers were derived from mice immunized with peptide II, which correspond to amino acids 27 to 38 of mGM-CSF. Immunochemical studies showed that peptide II specifically blocked binding of anti-peptide II mAb to GM-CSF. mAb to two other peptides in the N-terminal half corresponding to residues 7 to 17 and 47 to 58, respectively, of mGM-CSF also inhibited GM-CSF-dependent proliferation and differentiation of murine bone marrow precursors for macrophages and granulocytes. Anti-peptide mAb also inhibited growth of a murine hematopoietic cell line FDCP1 and a murine T cell line HT-2, which was shown to be dependent on GM-CSF for growth in vitro. Biologic activity of both natural and recombinant mGM-CSF was neutralized by anti-peptide mAb. These findings indicate that epitopes in the N-terminal region of mGM-CSF are important for biologic activity, and the epitope defined by peptide II (residues 27 to 38) lies within a particularly important functional domain of the mGM-CSF molecule.

In vivo regulation of hemopoiesis by transforming growth factor beta 1: stimulation of GM-CSF- and M-CSF-dependent murine bone marrow precursors

Injection of mice with either natural bovine bone-derived or human recombinant transforming growth factor beta 1 (TGF-beta 1) resulted in a significant increase of the macrophage and macrophage-granulocyte-forming capacity of their macrophage colony-stimulating factor (M-CSF)- and granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent bone marrow precursor cells. The increased potential for generating granulocytes and/or macrophages from bone marrow cells of mice injected with TGF-beta 1 was associated with an increase of the number of M-CSF- and GM-CSF-dependent bone marrow colony-forming units (CFU). The effect was selective, in that in vivo applied TGF-beta 1 did not affect interleukin 3 (IL-3)-dependent CFU. The data suggest that TGF-beta may be useful in recovery of bone marrow granulocyte- and macrophage-forming potentials following depletion caused by chemo- or radiotherapy.

Evaluation in vitro of adriamycin immunoconjugates synthesized using an acid-sensitive hydrazone linker

A novel method for linking Adriamycin (ADM) to monoclonal antibodies is described in which the 13-keto position of the anthracycline is used as the attachment site to the linker arm. A new ADM acylhydrazone derivative, Adriamycin 13-[3-(2-pyridyldithio)propionyl]hydrazone hydrochloride, which contains a pyridyl-protected disulfide, was synthesized and used for conjugation to monoclonal antibodies (MAbs) that were thiolated with N-succinimidyl 3-(pyridyldithiol)propionate or 2-iminothiolane. This resulted in formation of a linker between MAb and drug that contained a disulfide bond. Conjugation conditions were optimized to yield conjugates with high ADM:MAb molar ratios. The final immunoconjugate yields were found to decrease as the ADM:MAb molar ratio of the conjugates increased. Stability studies indicated that ADM was released from the immunoconjugates at mildly acidic pHs ranging from 4.5-6.5. Treatment of immunoconjugates with mild reducing agent dithiothreitol resulted in release of an acylhydrazone derivative of ADM. Flow-cytometric studies showed that the binding activity of various MAbs following conjugation to ADM was preserved at ADM:MAb molar ratios up to 10. Antibody-directed cytotoxicity was demonstrated under several assay conditions using combinations of antigen-positive and antigen-negative cells and binding and nonbinding immunoconjugates. In several experiments, ADM immunoconjugates were more potent than equivalent amounts of unconjugated ADM.

T-cell receptor-CD4 physical association in a murine T-cell hybridoma: induction by antigen receptor ligation

By employing flow cytometric analysis and fluorescence resonance energy transfer (FRET), we examined the physical relationship between the T-cell receptor-CD3 complex (Ti-CD3) and the CD4 molecule on helper T cells. Through the use of an L3T4-negative murine T-cell hybridoma infectant expressing the human CD4 gene and having antigen specificity for HLA-DR, we show that binding of the Ti-CD3 complex with an anti-CD3 monoclonal antibody induces its redistribution proximal to cell-surface CD4. FRET efficiency was 9.4% on cells labeled with rhodaminated anti-CD3 and fluoresceinated anti-CD4. FRET was found to be temperature dependent, since similarly treated cells held at 4 degrees C displayed a FRET efficiency of less than 1%. Energy transfer was evident within 3 min after warming cells to 37 degrees C. Energy transfer was not detected between Ti-CD3 and the abundantly expressed leukocyte common antigen (CD45). Of greater significance was our observation that hybridomas infected with a truncated CD4 gene lacking the cytoplasmic domain failed to transfer energy despite the fact that CD4 was expressed on the cell surface at levels equivalent to or greater than the wild type. These studies suggest that after crosslinking of the Ti-CD3 on CD4+ T cells, a physical association occurs between the antigen receptor complex and CD4 and that the association is dependent upon the presence of the cytoplasmic domain of CD4.

Inhibition of macrophage-induced antigen-specific T-cell proliferation by interferon-gamma

The effects of IFN-gamma on macrophage (M phi)-mediated antigen-specific T-cell proliferation was investigated. A well-defined assay system using purified resident populations of antigen-pulsed peritoneal M phi and immune T cells was used to measure M phi-induced antigen-specific T-cell proliferation. Antibody affinity purified or recombinant IFN-gamma inhibited M phi-induced T-cell proliferation when KLH-pulsed M phi from mice given IFN-gamma prior to KLH were cultured with KLH immune T cells from normal mice. Monoclonal rat anti-IFN-gamma antibody neutralized the inhibitory effect of IFN-gamma. This inhibition of T-cell proliferation occurred despite the fact that these M phi appeared to be activated by IFN-gamma treatment as measured by increased tumoricidal activity. The mechanism for the inhibition was unrelated to class II (Ia) expression, IL-1 secretion, and prostaglandin secretion. These results demonstrate the complex and sensitive role IFN-gamma has in regulating the immune response.

A sensitive immunochemical assay for biologically active MuIFN-gamma

An immunochemical assay for the detection of mouse gamma interferon (MuIFN-gamma) has been established. Using a purified monoclonal antibody (MAb) that neutralizes the antiviral activity of MuIFN-gamma, and a polyclonal antibody (PAb) prepared against affinity-purified MuIFN-gamma, we have developed a double-sandwich enzyme-linked immunosorbent assay (ELISA). The assay is specific for both natural and recombinant MuIFN-gamma and displays only background activity against MuIFN-alpha + beta, recombinant TNF (rTNF), human gamma interferon (HuIFN-gamma) and crude rat spleen cell supernatants. The assay is more sensitive and reproducible than the measurement of hydrogen peroxide (H2O2) release by macrophages, and is capable of detecting both crude and purified MuIFN-gamma down to 0.03 U/ml of antiviral activity, making this assay 10-100 times more sensitive than the conventional antiviral assay. The ELISA detects only biologically active MuIFN-gamma since treatment of the MuIFN-gamma at high temperature or low pH conditions resulted in abolishment of biological activity, as determined by inhibition of cytopathic effect, coincident with a dramatic decrease in ELISA titer.

Gamma interferon as a crucial host defense against Rickettsia conorii in vivo

Gamma interferon (IFN-gamma) plays an important role as a host defense in rickettsial infection. Swiss Webster mice, which are resistant to Rickettsia conorii (Malish 7 strain) infection, were treated with a monoclonal antibody against mouse IFN-gamma. When the antibody-treated mice were inoculated with 12 50% tissue culture infective doses of R. conorii, the mortality was 47% and the morbidity was 100%. None of the control mice, which received the same dose of R. conorii, died or became ill. The enumeration of rickettsiae in organs by direct immunofluorescence in paraffin sections demonstrated higher quantities of rickettsiae in the spleen had liver of IFN-gamma-depleted mice as compared with those of the infected controls. The kinetic analysis of IFN-gamma levels in sera showed depletion in the treated mice. These results indicate that IFN-gamma plays an important role as a host defense in the early stage of rickettsial infection. Survival of some mice despite continued treatment with antibody to IFN-gamma suggests that other immune mechanisms may also be important.

IFN-gamma is not an essential mediator of murine antibody responses in vitro

We have used purified murine gamma-interferon (Mu IFN-gamma) and anti-Mu IFN-gamma monoclonal antibody to study the participation of gamma-interferon (IFN-gamma) in in vitro plaque-forming cell (PFC) responses to antigen. We have studied several supernatants with T-cell replacing factor (TRF) activity as well as helper T-cell dependent anti-sheep red blood cells (SRBC) PFC responses. Our findings demonstrate that neither TRF- nor T-cell mediated responses are critically dependent upon IFN-gamma.

Rapid parasite multiplication rate, rather than immunosuppression, causes the death of mice infected with virulent Plasmodium yoelii

Protective immunity against a lethal malaria challenge infection was passively transferred to naive recipient mice with spleen cells from donor mice bearing a lethal infection with the virulent YM strain of Plasmodium yoelii. Successful transfer of protection was contingent upon the elimination of residual, viable parasites from donor spleen cell suspensions prior to the infusion of cells. Passive transfer experiments failed to detect suppressor cells in the spleens of lethally infected mice because unfractionated spleen cells or T-cell-enriched spleen cells from mice infected with P. yoelii YM did not enhance parasitemias upon infusion into mice infected with cross-reactive nonvirulent P. yoelii 17X. We concluded that a form of protective immunity was generated during the course of virulent infection but that its expression was inconsequential because parasite growth apparently exceeded the capacity of the immune system to clear the infection.

In vitro expression of secondary antitumor immunity by in vitro tumor-sensitized T cells: inhibition by tumor-induced suppressor T cells

In vitro cultivation of memory immune cells from P815- or P388-immune mice with corresponding irradiated tumor cells induced generation of cytolytic T cells (CTL). The induction of CTL generation, as well as the cytolytic activity itself, was tumor-specific. The in vitro generation of CTL from P815- or P388-immune cells was suppressed by spleen cells from mice bearing corresponding progressive tumors (tumor size 15 mm). The tumor-induced suppressor cells suppressed the in vitro generation of CTL, but did not affect their cytolytic function. The suppression was tumor-specific and was mediated by Ly1+2-L3T4+ T cells. Treatment of suppressor cell donors with cyclophosphamide or sublethal gamma-radiation completely abolished the ability of their spleen cells to inhibit the in vitro CTL generation.

Requirement for three distinct lymphokines for the induction of cytotoxic T lymphocytes from thymocytes

The induction of cytotoxic T lymphocytes (CTL) from CTL precursors requires a combination of antigen and lymphokine signals. To investigate lymphokine requirements for CTL generation, we used an assay in which helper T cell and accessory cell-depleted spleen cells or whole thymocytes were cultured with lectin (Con A) and lymphokines. This culture was followed by assessment of lectin-dependent cytolysis. High concentrations of recombinant interleukin 2 (R-IL 2) (100 U/ml) alone were not sufficient for lectin-mediated CTL induction from thymocytes, whereas 20 to 100 U/ml of R-IL 2 alone could induce a significant lectin-mediated CTL response from accessory cell-depleted spleen cells. Using thymocytes as responders, we found purified or recombinant interferon-gamma (IFN-gamma) did not cause cytolytic activity either in the absence of or in the presence of R-IL 2. However, supernatant from Con A-stimulated rat spleen cells (rat Con A SN) in combination with R-IL 2 could induce cytolytic activity, suggesting that several factors are required for CTL induction. Con A SN was fractionated by gel filtration and the fractions were tested for ability to induce CTL. In the presence of a low level of R-IL 2 (5 U/ml), fractions with a Mr of approximately 31,000 could induce CTL, and this activity was referred to as CTL differentiation factor (CDF). The peak fractions containing CDF activity did not have detectable IL 1, IL 2, IFN-gamma, or CSF activity. However, by add-back experiments and the use of blocking antibodies, a monoclonal antibody against the IL 2 receptor or antibodies against murine IFN-gamma, we demonstrated that CTL induction from mature thymocytes (L3T4-, Lyt-2+) requires CDF activity in addition to IL 2 and IFN-gamma.

Biochemical analysis and biological activities of immunoaffinity purified natural murine gamma interferon (MuIFN-gamma)

A rapid one-step procedure for the purification of natural murine gamma interferon (MuIFN-gamma) by immunoaffinity chromatography has been developed. Crude MuIFN-gamma was passed through a column containing immobilized anti-MuIFN-gamma monoclonal antibody, and the column was washed with high salt and detergent. Active MuIFN-gamma was subsequently eluted with ammonium thiocyanate/glycerol (yields of 20-40%). Analysis of the immunopurified interferon by sodium dodecyl sulfate polyacrylamide gel electrophoresis under reducing conditions revealed biologically active bands of about 19.5, and 14 kd. Under nonreducing conditions, three active bands at 35, 19.5, and 14 kd could be seen. Gel filtration of the immunopurified MuIFN-gamma under reducing or nonreducing conditions showed a single major peak of antiviral activity corresponding to a molecular weight of 43 kd. The protein eluted from each band from the SDS-gel, in addition to possessing antiviral activity, was shown to activate macrophages in three assays: macrophage tumoricidal activity, hydrogen peroxide secretion, and expression of la antigen on the surface of exudate macrophages.

Requirement for three distinct lymphokines for the induction of cytotoxic T lymphocytes from thymocytes

The induction of cytotoxic T lymphocytes (CTL) from CTL precursors requires a combination of antigen and lymphokine signals. To investigate lymphokine requirements for CTL generation, we used an assay in which helper T cell and accessory cell-depleted spleen cells or whole thymocytes were cultured with lectin (Con A) and lymphokines. This culture was followed by assessment of lectin-dependent cytolysis. High concentrations of recombinant interleukin 2 (R-IL 2) (100 U/ml) alone were not sufficient for lectin-mediated CTL induction from thymocytes, whereas 20 to 100 U/ml of R-IL 2 alone could induce a significant lectin-mediated CTL response from accessory cell-depleted spleen cells. Using thymocytes as responders, we found purified or recombinant interferon-gamma (IFN-gamma) did not cause cytolytic activity either in the absence of or in the presence of R-IL 2. However, supernatant from Con A-stimulated rat spleen cells (rat Con A SN) in combination with R-IL 2 could induce cytolytic activity, suggesting that several factors are required for CTL induction. Con A SN was fractionated by gel filtration and the fractions were tested for ability to induce CTL. In the presence of a low level of R-IL 2 (5 U/ml), fractions with a Mr of approximately 31,000 could induce CTL, and this activity was referred to as CTL differentiation factor (CDF). The peak fractions containing CDF activity did not have detectable IL 1, IL 2, IFN-gamma, or CSF activity. However, by add-back experiments and the use of blocking antibodies, a monoclonal antibody against the IL 2 receptor or antibodies against murine IFN-gamma, we demonstrated that CTL induction from mature thymocytes (L3T4-, Lyt-2+) requires CDF activity in addition to IL 2 and IFN-gamma.

Monoclonal antibody-mediated inhibition of interferon-gamma-induced macrophage antiviral resistance and surface antigen expression

A monoclonal antibody (MAb) with specificity for murine interferon-gamma (IFN-gamma) was used as a probe for studying the effect of recombinant IFN-gamma (rIFN-gamma) on antiviral activity, Fc receptor expression, and Ia antigen induction in macrophages. Cultures of C3H/HeJ peritoneal exudate macrophages were used to allow direct comparison of all three functions in the same target cell system. Our data provide two major findings: the efficacy of the MAb is very different depending on whether murine fibroblasts or macrophages are used as the target cell in the antiviral assay, i.e., greater than 20 to 100 times more MAb was required to block antiviral activity in macrophage cultures; and 10 to 50 times more MAb was required to inhibit Fc receptor vs Ia antigen expression in response to rIFN-gamma. These latter findings confirm and extend previous observations, which indicate that the induction pathways of two important differentiation markers by IFN-gamma may be dissociable.

Monoclonal antibody-mediated inhibition of interferon-gamma-induced macrophage antiviral resistance and surface antigen expression

A monoclonal antibody (MAb) with specificity for murine interferon-gamma (IFN-gamma) was used as a probe for studying the effect of recombinant IFN-gamma (rIFN-gamma) on antiviral activity, Fc receptor expression, and Ia antigen induction in macrophages. Cultures of C3H/HeJ peritoneal exudate macrophages were used to allow direct comparison of all three functions in the same target cell system. Our data provide two major findings: the efficacy of the MAb is very different depending on whether murine fibroblasts or macrophages are used as the target cell in the antiviral assay, i.e., greater than 20 to 100 times more MAb was required to block antiviral activity in macrophage cultures; and 10 to 50 times more MAb was required to inhibit Fc receptor vs Ia antigen expression in response to rIFN-gamma. These latter findings confirm and extend previous observations, which indicate that the induction pathways of two important differentiation markers by IFN-gamma may be dissociable.

Immunity to Plasmodium yoelii: kinetics of the generation of T and B lymphocytes that passively transfer protective immunity against virulent challenge

Adoptive immunization of A/Tru mice with splenic B cells or T cells from syngeneic donors with a primary, nonvirulent, Plasmodium yoelii (17X) infection confers on these recipients the capacity to resist a challenge infection with a virulent strain (YM) of P. yoelii. Unfractionated spleen cells as well as spleen cells enriched for T or B cells capable of transferring protective immunity were detected as early as Day 7 of the primary nonvirulent infection, and reached peak levels on Day 14. Spleen cells that were harvested from donor animals after resolution of the immunizing infection [on Days 21 or 28] were incapable of transferring protective immunity. The capacity of 7-day immune spleen cells to transfer immunity could be abolished by pretreatment with mitomycin C. In addition, it was found that immunocompetent recipient mice were required for successful adoptive immunization, since thymectomized, irradiated, bone marrow reconstituted mice infused with immune spleen cells failed to survive lethal challenge infections.

Neutralization of lymphokine-mediated antirickettsial activity of fibroblasts and macrophages with monoclonal antibody specific for murine interferon gamma

Lymphokine-mediated inhibition of Rickettsia prowazekii multiplication in L929 fibroblasts was eliminated by treatment of the lymphokine with a monoclonal antibody specific for interferon-gamma. Soluble monoclonal antibody and antibody conjugated to Sepharose beads were equally effective. Macrophage activation to limit the multiplication of Rickettsia conorii was eliminated with antibody-conjugated beads; however, neutralization of the ability to activate macrophages with soluble antibody was not complete and required more antibody than did neutralization of antiviral activity.

Activation of mouse peritoneal macrophages in vitro and in vivo by interferon-gamma

To determine the role of IFN-gamma in the activation of resident mouse peritoneal macrophages, crude macrophage-activating lymphokines were incubated with a monoclonal anti-murine IFN-gamma antibody. This treatment abolished the capacity of mitogen-induced lymphokines to enhance either H2O2 release or activity against the intracellular protozoa Toxoplasma gondii and Leishmania donovani. All macrophage-activating factor detected by these assays was also removed by passing the lymphokines over a Sepharose column to which the monoclonal anti-IFN-gamma antibody had been coupled. Therefore, pure murine rIFN-gamma was tested both in vitro and in vivo as a single activating agent. After 48 hr of pretreatment in vitro with 0.01 to 1 antiviral U/ml, macrophage H2O2-releasing capacity was enhanced an average of 6.4-fold; half-maximal stimulation was induced by 0.03 U/ml. Resident macrophages infected with T. gondii half-maximally inhibited parasite replication after 24 hr of preincubation with 0.14 U/ml of rIFN-gamma, and near complete inhibition was achieved by pretreatment with 100 U/ml. Half-maximal leishmanicidal activity was induced by 0.08 U/ml of rIFN-gamma, and 67 to 75% of intracellular L. donovani amastigotes were killed after macrophages were preincubated with 10 to 100 U/ml. Eighteen hours after parenteral injection of rIFN-gamma, peritoneal macrophages displayed a dose-dependent enhancement of H2O2-releasing capacity and antiprotozoal activity. Half-maximal enhancement required 85 to 250 U or rIFN-gamma given i.p. Peritoneal macrophages were also activated by rIFN-gamma injected i.v. and intramuscularly. These results suggest that, in the mouse model, IFN-gamma is likely to be a primary factor within mitogen-induced lymphokines responsible for activating macrophage oxidative metabolism and antiprotozoal activity, and indicate that rIFN-gamma is a potent activator of these effector functions both in vitro and in vivo. These findings provide a rationale for evaluating rIFN-gamma in the treatment of systemic intracellular infections, and indicate that murine models are appropriate for such studies.

Activation of mouse peritoneal macrophages in vitro and in vivo by interferon-gamma

To determine the role of IFN-gamma in the activation of resident mouse peritoneal macrophages, crude macrophage-activating lymphokines were incubated with a monoclonal anti-murine IFN-gamma antibody. This treatment abolished the capacity of mitogen-induced lymphokines to enhance either H2O2 release or activity against the intracellular protozoa Toxoplasma gondii and Leishmania donovani. All macrophage-activating factor detected by these assays was also removed by passing the lymphokines over a Sepharose column to which the monoclonal anti-IFN-gamma antibody had been coupled. Therefore, pure murine rIFN-gamma was tested both in vitro and in vivo as a single activating agent. After 48 hr of pretreatment in vitro with 0.01 to 1 antiviral U/ml, macrophage H2O2-releasing capacity was enhanced an average of 6.4-fold; half-maximal stimulation was induced by 0.03 U/ml. Resident macrophages infected with T. gondii half-maximally inhibited parasite replication after 24 hr of preincubation with 0.14 U/ml of rIFN-gamma, and near complete inhibition was achieved by pretreatment with 100 U/ml. Half-maximal leishmanicidal activity was induced by 0.08 U/ml of rIFN-gamma, and 67 to 75% of intracellular L. donovani amastigotes were killed after macrophages were preincubated with 10 to 100 U/ml. Eighteen hours after parenteral injection of rIFN-gamma, peritoneal macrophages displayed a dose-dependent enhancement of H2O2-releasing capacity and antiprotozoal activity. Half-maximal enhancement required 85 to 250 U or rIFN-gamma given i.p. Peritoneal macrophages were also activated by rIFN-gamma injected i.v. and intramuscularly. These results suggest that, in the mouse model, IFN-gamma is likely to be a primary factor within mitogen-induced lymphokines responsible for activating macrophage oxidative metabolism and antiprotozoal activity, and indicate that rIFN-gamma is a potent activator of these effector functions both in vitro and in vivo. These findings provide a rationale for evaluating rIFN-gamma in the treatment of systemic intracellular infections, and indicate that murine models are appropriate for such studies.

The glycoprotein nature of murine gamma interferon

Synthesis of murine gamma interferon (MuIFN gamma) by phytohemagglutinin (PHA)-stimulated spleen cells was inhibited in a dose-dependent manner by graded concentrations of tunicamycin or 2-deoxy-glucose, both of which inhibit glycosylation. The homologous (murine) and heterologous (rat) antiviral activities of the MuIFN gamma preparations secreted in the presence of the various concentrations of either glycosylation inhibitor were reduced to similar degrees. MuIFN gamma synthesized in the presence of tunicamycin (tunicamycin-MuIFN gamma) exhibited a lower molecular weight (MW), a lack of binding to immobilized Concanavalin-A (Con A), and different charge properties when compared to MuIFN gamma produced in absence of inhibitor (control-MuIFN gamma). Potent rabbit and rat neutralizing antibodies raised against a control-MuIFN gamma subcomponent, isolated by its specific binding to a Con A affinity column, neutralized the antiviral activity of tunicamycin-MuIFN gamma to the same degree as the immunogen.

Monoclonal antibody to murine gamma interferon inhibits lymphokine-induced antiviral and macrophage tumoricidal activities

Fusion of rat immune spleen cells with mouse myeloma cells resulted in the formation of a stable hybridoma that secretes monoclonal antibody (MAb) directed against murine gamma interferon ( MuIFN -gamma). This MAb specifically neutralized the antiviral activity of a variety of MuIFN -gamma preparations, including a sample produced by recombinant DNA technologies. In contrast, the antiviral activities of a mixture of MuIFN -alpha plus MuIFN -beta, as well as those of rat or human IFN-gamma, were not neutralized by this antibody. The ability of the MAb to inhibit lymphokine-induced macrophage activation was also tested. It was found that in relation to the quantity of antibody needed to completely neutralize antiviral activity, much higher concentrations of MAb were required to abolish the capacity of lymphokine preparations to induce macrophage tumoricidal activity in vitro. The MAb was also coupled to cyanogen bromide-activated Sepharose beads and used as an immunoadsorbent. By reacting lymphokines with MAb coupled to an insoluble matrix, it was possible to show that this immobilized antibody completely and specifically removed from the lymphokine preparations the ability both to invoke macrophage tumoricidal activity and to mediate antiviral activity.

Virulent and nonvirulent forms of Plasmodium yoelii are not restricted to growth within a single erythrocyte type

The present studies were designed to investigate whether the erythrocyte preferences displayed by both virulent and nonvirulent forms of Plasmodium yoelii were fastidious growth requirements of these parasites. When inoculated into mice depleted of reticulocytes by lethal irradiation (900 rad), virulent parasites, which have been reported to grow predominantly in mature erythrocytes, gave rise to high parasitemias which were equivalent to those seen in unirradiated, normal mice. In addition, virulent parasites serially passaged in lethally irradiated mice showed properties of enhanced virulence upon inoculation back into normal mice. When inoculated into lethally irradiated mice, nonvirulent P. yoelii, which were reported to preferentially invade reticulocytes, invaded mature erythrocytes, and the infection progressed at a higher level of parasitemia than in unirradiated, normal mice. The inoculation of virulent parasites into mice made reticulocytemic by pretreatment with phenylhydrazine produced infections marked by the invasion of reticulocytes rather than mature erythrocytes, yet these infections remained lethal for the murine host. When nonvirulent parasites were inoculated into reticulocytemic mice, lethal infections resulted in which the parasites predominantly invaded reticulocytes. These results indicate that both the virulent and nonvirulent forms of P. yoelii possess the ability to invade and proliferate within more than one erythrocyte type and that their apparent erythrocyte preferences are not strict growth requirements.

Two molecular weight species of murine gamma interferon

Concanavalin A (Con A) affinity chromatography was used to concentrate and partially purify a murine gamma interferon (MuIFN gamma) from large volumes of crude MuIFN gamma (specific activity (SA), 10(4) units/mg of protein) produced by mitogen-induced T lymphocytes. Elution of the MuIFN gamma from the immobilized Con A with alpha-methyl-D-mannoside resulted in a 13-fold purification. Further purification of the Con A-bound MuIFN gamma was accomplished by gel filtration chromatography (SA 10(6.7) units/mg of protein) which also demonstrated the molecular weight (MW) to be 38,000 +/- 3000. Molecular weight determinations by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, under both reducing and nonreducing conditions, revealed that the Con A-bound MuIFN gamma may exist as a dimer, consisting of monomers of 20,500 MW. Specific rabbit antiserum raised against the Con A-bound MuIFN gamma neutralized the antiviral activities of crude, Con A-bound and unbound MuIFN gamma fractions, as well as the 20,500 MW MuIFN gamma.

Endotoxin-induced interferon synthesis in macrophage cultures

Pure cultures of murine bone marrow-derived macrophages produce interferon (IFN) after exposure to endotoxin. The levels of endotoxin-induced IFN were enhanced 5- to 20-fold by pretreating (priming) macrophages with murine interferons produced by either NDV-induced L cells, which consisted of a mixture of IFN alpha and IFN beta, or IFN gamma produced by spleen cells stimulated with phytohemagglutinin. Studies conducted on the kinetics of IFN release from endotoxin-induced macrophages demonstrated that peak synthesis occurred within 2-4 hr and was completed 6 hr after the start of treatment. The addition of actinomycin D to macrophages, up to 1 hr after exposure to endotoxin, completely inhibited release of interferon, thus indicating that gene transcription was required for interferon synthesis. The inclusion of cycloheximide in the medium of endotoxin or Poly(I) X Poly(C)-induced macrophages, although inhibiting 90% of protein synthesis, resulted in a superinducing effect, in that induced macrophages treated with cycloheximide produced higher levels of IFN than macrophages not treated with the inhibitor of protein synthesis. Antigenic characterization of macrophage IFNs revealed that endotoxin-induced IFN was neutralized to a higher degree than virus-induced IFNs derived from either macrophages or L cells.

Production and characterization of anti-murine interferon-gamma sera

A partially purified phytohaemagglutinin (PHA)-induced spleen cell murine interferon-gamma (MuIFN-gamma) proved a potent immunogen in a rabbit and rats. Neutralizing anti-MuIFN-gamma activity was detected in rabbit serum following two biweekly subcutaneous inoculations of MuIFN-gamma emulsified in Freund's complete adjuvant. Further biweekly injections of immunogen in Freund's incomplete adjuvant, greatly elevated the serum anti-MuIFN-gamma neutralizing titer. Inbred DA rats also responded with serum neutralizing antibodies for MuIFN-gamma. Rabbit and rat anti-MuIFN-gamma sera neutralized the antiviral activities of MuIFN-gamma preparations produced by T-cells in response to different polyclonal T-cell mitogens or by sensitized T-cells stimulated with specific antigen(s). In addition, the antiviral activity of a rat IFN-gamma on murine cells was neutralized by rabbit anti-MuIFN-gamma serum, but not by the rat anti-MuIFN-gamma serum.

Enhanced production of murine interferon gamma by T cells generated in response to bacterial infection

Spleen cell cultures derived from animals infected 6 d earlier with Listeria monocytogenes produced 10-20-fold more murine interferon gamma (MuIFN gamma) than spleen cells from nonimmune mice in response to stimulation with T cell mitogens. A striking temporal association was found between the enhanced synthesis of MuIFN gamma and the development of anti-Listeria immunity in that both the potential for increased MuIFN gamma production and the generation of Listeria-protective T cells developed and then decayed in unison. Treatment of spleen cells with monoclonal anti-Thy-1.2 plus complement virtually abolished the ability of cells from Listeria-immune mice to synthesize MuIFN gamma. The T cells producing MuIFN gamma were found to be more susceptible to complement-mediated lysis with monoclonal anti-Lyt-1.2 than with monoclonal anti-Lyt-2.2. The production of MuIFN gamma was not affected by treating spleen cells with anti-IgG antisera or with a monoclonal antibody directed against I-A specificities. MuIFN gamma was detected 4 h after the beginning of mitogenic stimulation of spleen cell cultures, and peak levels of MuIFN gamma were reached by 18 h. The IFN synthesized by mitogen-induced spleen cells derived from Listeria-immune mice were relatively labile at pH 2.0 and neutralized by a rabbit anti-MuIFN gamma serum but not by an antiserum having specificities for MuIFN alpha and MuIFN beta. The apparent molecular weight of the MuIFN gamma, as estimated by molecular sieving on a Bio-gel P-60 column, was estimated to be 38,000, and the isoelectric point as determined by chromatofocusing was extremely heterogeneous, ranging between pH 5.0 and pH 7.0.

Dissociation of bactericidal activity from other functions of activated macrophages in exudates induced by thioglycolate medium

Macrophages displayed increased spreading, increased Fc-receptor-mediated phagocytosis, and increased secretion of plasminogen activator when collected from the peritoneal cavities of either Listeria-immune mice challenged intraperitoneally 3 days earlier with Listeria or nonimmune mice injected intraperitoneally 3 days earlier with fluid thioglycolate medium. In contrast, macrophages from the thioglycolate-induced peritoneal exudates were severely impaired in vitro in their ability to destroy Listeria. Injection of thioglycolate markedly interfered with the destruction of sublethal intraperitoneal challenge of Listeria, which resulted in nonimmune animals dying of an overwhelming systemic infection. In animals immune to Listeria, injection of thioglycolate delayed the onset of the expression of immunity to an intraperitoneal challenge of bacteria. The thioglycolate-induced suppression of bactericidal activity was determined to be confined to the site of injection. Results of experiments indicated that the colloidal agar in thioglycolate medium was the cause of the impairment of macrophage bactericidal activity. In addition to the impairment of bactericidal activity induced by agar, additional studies showed that an intraperitoneal injection of colloidal agar (0.075% wt/vol) by itself was a sufficient inflammatory stimulus for the accumulation of a large number of host phagocytic cells.

Subversion of host defense mechanisms by malignant tumors: an established tumor as a privileged site for bacterial growth

Mice carrying any one of three murine tumors in their right hind foot pad were incapable of eliminating an inoculum of the bacterial parasite Listeria monocytogenes from the progressive tumor. In contrast, they were as capable as control mice in efficiently eliminating the organism from their contralateral tumor-free foot pad, and from their lymph nodes and livers. The results serve to show, therefore, that conditions within an established tumor are not only antagonistic to the expression of concomitant anti-tumor immunity, but that they are also antagonistic to the expression of T-cell-mediated anti-bacterial immunity. The possibility was discussed that the tumor contains factors that act pharmacologically to locally suppress the function of sensitized T cells and activated macrophages.

Stimulation of resistance in mice to sporozoite-induced Plasmodium berghei malaria by injections of avian exoerythrocytic forms

Mice received a series of injections of formalin-killed merozoites (FKM) of exoerythrocytic stages of Plasmodium fallax prior to challenge with sporozoites of P. berghei. In one study 4 of 16 FKM-immunized mice never exhibited parasitized erythrocytes after 2 challenges of 10(4) P. berghei sporozoites each, while all control animals died with high parasitemias. FKM-immunized mice were as susceptible as control mice to infections initiated with parasitized erythrocytes. In a second study, 14 of 16 mice immunized via the intravenous (i.v.) or combined intramuscular (i.m.) and i.v. routes were immune to an initial challenge with 10(4) sporozoites, but were susceptible to a second challenge. Three injections of FKM via the i.m. or intraperitoneal routes did not elicit a protective response against sporozoite challenge. Sera harvested from FKM-immunized and control mice prior to challenge produced no visible CSP reaction with P. berghei sporozoites, nor was infectivity of sporozoites altered after incubation in sera, showing that SNA was absent. In additional experiments results were less encouraging. An attempt to repeat the result of the second experiment failed. Each of 5 mice which received the same number of FKM by a similar schedule became infected after sporozoite challenge. In an additional study the immunization schedule was increased from 3 to 7 injections of FKM and 40% of FKM-immunized mice resisted challenge. However, mice which had received FKM prior to sporozoite challenge consistently displayed an increased prepatent period compared with control animals. A department from methods of the more successful studies was necessitated in these later studies in which FKM were harvested from cell cultures maintained for longer periods of time.

Antibodies against Sporozoites of Human and Simian Malaria Produced in Rats

The various methods commonly used for the detection of antimalarial antibodies employ, in nearly all instances, the erythrocytic stages of these parasites as antigen source (1). The antigenic components of the different stages of development of the malaria parasites, however, differ considerably, in spite of the existence of some shared or common antigens (2, 3). Furthermore, the common antigens do not account for all of the antigenic components of the parasites, nor do they include the functional, i.e., protective, antigens of the various developmental stages. This is suggested by the finding that rodents immunized with attenuated sporozoites become totally resistant to an otherwise lethal sporozoite inoculum, but remain fully susceptible to challenge with erythrocytic stages of the same parasite strain (4).

Anti-sporozoite antibodies, i.e., antibodies directed against the infective stages of all malaria parasites, have previously been shown to occur in avian and rodent malaria. In both instances, these antibodies were observed upon immunization of the animals with attenuated, irradiated sporozoites.