Lipopolysaccharide and polyribonucleotide activation of macrophages: implications for a natural triggering signal in tumor cell killing

Toll-Like Receptor Ligands and Interferon-γ Synergize for Induction of Antitumor M1 Macrophages

Tumor-associated macrophages may either promote or suppress tumor growth depending on their activation status. Interferon-γ (IFN-γ) has been identified as a key factor for inducing tumoricidal M1 phenotype in macrophages. However, it remains unclear whether IFN-γ is sufficient or if additional stimuli are required. Here, we tested IFN-γ and a panel of toll-like receptor (TLR) agonists for the ability to activate murine macrophages toward a tumoricidal M1 phenotype. The following TLR ligands were used: TLR1/TLR2 agonist Pam3CSK4, TLR2/TLR6 agonist lipotechoic acid, TLR3 agonist poly(I:C), TLR4 agonist lipopolysaccharide (LPS), TLR5 agonist flagellin, TLR7 agonist CL264, and TLR9 agonist CpG. We used an in vitro growth inhibition assay to measure both cytotoxic and cytostatic activity of mouse macrophages against Lewis lung carcinoma (LLC) and MOPC315 plasmacytoma tumor cells. Production of nitric oxide (NO) and cytokines by activated macrophages was quantified. We found that IFN-γ alone was not able to render macrophages tumoricidal. Similarly, macrophage activation with single TLR agonists was inefficient. In sharp contrast, IFN-γ was shown to synergize with TLR agonists for induction of macrophage tumoricidal activity and production of both NO and pro-inflammatory cytokines (TNF-α, IL-12p40, and IL-12p70). Furthermore, IFN-γ was shown to suppress macrophage IL-10 secretion induced by TLR agonists. NO production was necessary for macrophage tumoricidal activity. We conclude that two signals from the microenvironment are required for optimal induction of antitumor M1 macrophage phenotype. Combination treatment with IFN-γ and TLR agonists may offer new avenues for macrophage-based cancer immunotherapy.

Autoregulation by interferons provides an endogenous 'priming' signal for LPS-responsive macrophages

RT-PCR technology was used to evaluate endogenous levels of IFN-α, β, and γ mRNA in macrophages derived from LPS-responsive (C3H/OuJ) and LPS-hyporesponsive (C3H/HeJ) mice. IFN mRNA levels were found to be consistently higher in the LPS-responsive macrophages. That these IFNs may be part of an autocrine loop is supported by the observations that treatment of macrophages, in vitro, with IFN-α or IFN-β induces IFN-γ mRNA and, conversely, that exogenous IFN-γ treatment results in increased detection of both IFN-a and IFN-β mRNA species. In vitro 'priming' of LPS-hyporesponsive macrophages with either IFN-α or IFN-γ causes these cells to be activated by a polyI:C triggering signal, in a manner equivalent to that seen for LPS-'primed' C3H/OuJ macrophages. Thus, low levels of endogenous IFNs, which induce each other bidirectionally, may provide a replenishable source of 'primed' macrophages, that are more plentiful in Lpsn mice and that are capable of being 'triggered' to functional maturity during an immune response.

Mycobacterium tuberculosis conserved hypothetical protein rRv2626c modulates macrophage effector functions

Secretory proteins of Mycobacterium tuberculosis are the major immunomodulators of the host immune response. Open reading frame (ORF) Rv2626c, encoding a conserved hypothetical protein eliciting a strong humoral immune response in patients with tuberculosis (TB), was shown to be up-regulated upon infection in mice under hypoxic conditions. We now show that recombinant Rv2626c protein (rRv2626c) can bind to the surface of murine macrophages and elicit the type-1 immune response, as manifested by nitric oxide (NO) secretion and expression of inducible nitric oxide synthase (iNOS). Significant induction of pro-inflammatory cytokines [interleukin (IL)-12 and tumour necrosis factor (TNF)-alpha] was evident upon stimulation of murine macrophages, as well as peripheral blood mononuclear cells (PBMCs) isolated from patients with active TB disease, with rRv2626c. Stimulation with rRv2626c also enhanced the expression of costimulatory molecules such as B7-1, B7-2 and CD40 on murine macrophages. We further show that the production of NO and pro-inflammatory cytokines in response to rRv2626c is mediated by the transcription factor nuclear factor (NF)-kappaB, and this was further confirmed using pyrrolidine dithiocarbamate (PDTC), a specific pharmacological inhibitor of NF-kappaB. Rv2626c therefore appears to modulate macrophage effector functions by eliciting both innate and adaptive immune responses, suggesting its possible use as a vaccine candidate.

Early development of primary biliary cirrhosis in female C57BL/6 mice because of poly I:C administration

BACKGROUND

Primary biliary cirrhosis (PBC) is one of the organ-specific autoimmune diseases characterized by destruction of the biliary epithelial cells, cholestasis, liver cirrhosis, and liver failure. With the postulation that induction of the autoimmune process might induce PBC-like cholangitis, here we used polyinosinic polycytidylic acid (poly I:C), an inducer of type-1 interferon (IFN), to generate an autoimmune cholangitis animal model.

METHODS

Female C57BL/6 mice were injected with 5 mg/kg of poly I:C twice a week for 28 consecutive weeks. Liver specimens were collected to evaluate the degree of cell infiltration. Autoantibodies, including antimitochondrial antibody (AMA), were assayed by immunofluorescence, enzyme-linked immunosorbent assay (ELISA) and immunoblotting. IFN-alpha was estimated in the sera by an ELISA method. Poly I:C injection induced IFN-alpha.

RESULTS

Mononuclear cells were detected at the portal areas 8 weeks after the start of poly I:C injection, which progressed up to 16 weeks. Autoantibodies, including AMA, were detected in the sera from all poly I:C-injected mice.

CONCLUSIONS

In conclusion, we show an early development of a PBC-like cholangitis in a genetically susceptible mouse strain because of poly I:C administration. This model would be helpful to study PBC immunopathogenesis and to evaluate the effectiveness of newly developed therapeutic regimens for PBC.

APOE genotype-specific differences in human and mouse macrophage nitric oxide production

Individuals expressing an APOE4 genotype demonstrate increased Alzheimer's disease (AD) neuropathology and a decreased onset age. The APOE4 gene may act by modulating the CNS immune response. Using human monocyte-derived macrophages (MDM), we show a significantly greater increase in NO production during immune activation in MDM from APOE4 AD patients compared to normal, age-matched individuals or to AD patients with an APOE 3/3 genotype. Microglia and peritoneal macrophages from APOE4 targeted replacement mice demonstrate a similar increase in NO compared to the APOE3 targeted replacement mice. The enhanced macrophage responsiveness and the increased production of NO in APOE4 AD patients may predispose the CNS to an increased potential for nitration and nitrosation, consistent with the redox imbalance and neuroinflammatory state seen in AD.

A novel autoimmune pancreatitis model in MRL mice treated with polyinosinic:polycytidylic acid

In this study we established a new animal model for exploring the pathogenesis of autoimmune pancreatitis. We have found previously that MRL/Mp-+/+(MRL/+) mice develop pancreatitis spontaneously by an autoimmune mechanism but only when they are more than 34 weeks old. Because this disease might be a model of multi-factorial diseases controlled by genetic and environmental factors, beginning at 6 weeks old, we injected polyinosinic:polycytidylic acid (poly I:C) into MRL/+ mice and in addition, into MRL/Mp mice bearing the Fas deletion mutant gene, lpr (MRL/lpr). Poly I:C induced chronic severe pancreatitis in all the MRL/+ mice and to a lesser extent in the MRL/lpr mice by 18 weeks of age. There was no pancreatitis in control mice of both strains at the same age. Other than chronic pancreatitis, no severe autoimmune diseases were observed in MRL/+ mice. Immunohistochemical examinations revealed predominant infiltration of CD4+ T cells and Mac-2+ activated macrophages in the pancreatic lesions. Splenic expression of the mRNAs for TNF-alpha and IL-10, which is known to suppress the development of pancreatitis, were increased in both strains of mice. These findings suggest that an MRL strain of mice treated with poly I:C might be a good model for developing new approaches to the study of the pathogenesis of autoimmune pancreatitis.

Apolipoprotein E acts to increase nitric oxide production in macrophages by stimulating arginine transport

Previous studies have shown that apolipoprotein E (apoE) plays a role in immune function by modulating tissue redox balance. Using a mouse macrophage cell line (RAW 264.7), we have examined the mechanism by which apoE regulates nitric oxide (NO) production in macrophages. ApoE potentiates NO production in immune activated RAW cells in combination with lipopolysaccharide or polyinosinic:polycytidylic acid (PIC), agents known to induce expression of inducible nitric oxide synthase mRNA and protein. The effect is not observed with apolipoprotein B or heat-inactivated apoE. The combination of PIC plus apoE produced more NO than the level expected from an additive effect of PIC and apoE alone. Furthermore, this increase was observed at submaximal extracellular arginine concentrations, suggesting that apoE altered arginine (substrate) availability. Examination of [(3)H]arginine uptake across the cell membrane demonstrated that arginine uptake was increased by PIC but further increased by PIC plus apoE. Treatment of RAW cells with apoE was associated with an increased apparent V(max) and decreased affinity for arginine as well as a switch in the induction of mRNA for subtypes of cationic amino acid transporters (CAT). Treatment of RAW cells with PIC plus apoE resulted in the loss of detectable CAT1 mRNA and expression of CAT2 mRNA. Regulation of arginine availability is a novel action of apoE on the regulation of macrophage function and the immune response.

Double-stranded RNA-induced inducible nitric-oxide synthase expression and interleukin-1 release by murine macrophages requires NF-kappaB activation

The effects of double-stranded RNA (synthetic polyinosinic-polycytidylic acid; poly(I-C)) on macrophage expression of inducible nitric-oxide synthase (iNOS), production of nitric oxide, and release of interleukin-1 (IL-1) were investigated. Individually, poly(I-C), interferon-gamma (IFN-gamma), and lipopolysaccharide (LPS) stimulate nitrite production and iNOS expression by RAW 264.7 cells. In combination, the effects of poly(I-C) + IFN-gamma are additive, while poly(I-C) does not further potentiate LPS-induced nitrite production. These results suggest that poly(I-C) and LPS may stimulate iNOS expression by similar signaling pathways, which may be independent of pathways activated by IFN-gamma. LPS-induced iNOS expression is associated with the activation of NF-kappaB. We show that inhibition of NF-kappaB by pyrrolidinedithiocarbamate prevents poly(I-C) + IFN-gamma-, poly(I-C) + LPS-, and LPS-induced iNOS expression, nitrite production and IkappaB degradation by RAW 264.7 cells. The effects of poly(I-C) on iNOS expression appear to be cell-type specific. Poly(I-C), alone or in combination with IFN-gamma, does not stimulate, nor does poly(I-C) potentiate, IL-1-induced nitrite production by rat insulinoma RINm5F cells. In addition, we show that the combination of poly(I-C) + IFN-gamma stimulates iNOS expression, nitrite production, IkappaB degradation, and the release of IL-1 by primary mouse macrophages, and these effects are prevented by pyrrolidinedithiocarbamate. These findings indicate that double-stranded RNA, in the presence of IFN-gamma, is a potent activator of macrophages, stimulating iNOS expression, nitrite production, and IL-1 release by a mechanism which requires the activation of NF-kappaB.

Effects of vanadium upon polyl:C-induced responses in rat lung and alveolar macrophages

Hosts exposed to vanadium (V) display a subsequent decrease in their resistance to infectious microorganisms. Our earlier studies with rats inhaling occupationally relevant levels of V (as, ammonium metavanadate, NH4VO3) indicated that several nascent/inducible functions of pulmonary macrophages (PAM) were reduced. In the present study, V-exposed rats were examined to determine whether some of the same effects might also occur in situ. Rats were exposed nose-only to air or 2 mg V/m3 (as NH4VO3) for 8 h/d for 4 d, followed, 24 h later, by intratracheal (it) instillation of polyinosinic:polycytidilic acid (polyl:C) or saline. Analysis of lavaged lung cells/fluids after polyl:C instillation indicated that total lavageable cell/neutrophil numbers and protein levels, while significantly elevated in both exposure groups (as well as in saline-treated V-exposed rats), were always greater in V-exposed hosts. Exposure to V also affected the inducible production of interleukin 6 (IL-6) and interferon gamma (IFN gamma), but apparently not that of tumor necrosis factor-alpha (TNF alpha) or IL-1. Although polyl:C induced significant increases in lavage fluid IL-6 and IFN gamma levels in both exposure groups, levels were greater in V-exposed rats. If calculated with respect to total lavaged protein, however, V-exposed rats produced significantly less cytokine. Following polyl:C instillation, there were no marked exposure-related differences in basal or stimulated superoxide anion production by pooled lavaged cells or PAM specifically. With V-exposed rats, pooled cells recovered 24 h after saline instillation displayed reduced production (in both cases) compared to the air control cells; PAM-specific production was affected only after stimulation. In both exposure groups, polyl:C caused decreased superoxide production in recovered cells. Though less apparent with pooled cells, there was a time post polyl:C instillation-dependent decrease in stimulated PAM-specific superoxide production; this effect was greater in PAM from V-exposed rats than in PAM from air controls. Phagocytic activity of PAM from rats in both exposure groups was significantly increased by polyl:C instillation, although total activity in cells obtained from V-exposed rats was always significantly lower compared to air control cells. Our results indicate that short-term, repeated inhalation of occupationally relevant levels of V by rats modulates pulmonary immunocompetence. Modified cytokine production and PAM functionality in response to biological response modifiers (such as lipopolysaccharide, IFN gamma, or polyl:C) may be, at least in part, responsible for the increases in bronchopulmonary disease in humans occupationally exposed to V.

Autocrine induction of macrophage synthesis of complement subcomponent C1q by endogenous interferon-alpha/beta

Peritoneal macrophages (M phi) constitutively synthesize and secrete interferon-alpha (IFN-alpha) and IFN-beta, as well as complement subcomponent C1q. Because exogenous interferon-gamma (IFN-gamma) stimulates Mø synthesis of C1q, our purpose was to determine if endogenous secretion of IFN-alpha/beta regulated the constitutive level of endogenous C1q mRNA synthesis in an autocrine fashion. Both exogenous IFN-alpha and IFN-beta effectively substituted for IFN-gamma in stimulating M phi C1q mRNA expression in a dose-dependent fashion by northern blot analysis. Neutralizing anti-INF-alpha/beta antibodies inhibited M phi constitutive C1q mRNA synthesis by approximately twofold and abrogated the feedback stimulatory effects of exogenous C1q on C1q mRNA expression. Paraffin oil-elicited inflammatory M phi displayed distinctively different constitutive levels of C1q mRNA expression from thioglycollate brothelicited M phi, which was correlated with their relative levels of secretory IFN-alpha/beta by ELISA. Exogenous IFN-alpha/beta also restored C1q mRNA synthesis of AKR mouse M phi with low constitutive C1q mRNA expression. The cumulative results support the concept that constitutive synthesis of C1q by M phi is regulated by the endogenous synthesis and secretion of IFN-alpha/beta, which appears to act in an autocrine fashion.

Triggering effects of BCG vaccine on antitumor and interleukin-1 secretory activity of T cell lymphokine-primed macrophages

By using an in vitro model, this work demonstrates that BCG (Bacillus Calmette-Guerin) vaccine is able to trigger activation of T cell lymphokine-primed murine macrophages (Mo) for both tumoricidal cytotoxicity and interleukin-1 (IL-1) secretion. The results presented support the view that BCG vaccine may essentially activate primed, but not intact Mo; and that macrophage-mediated both antitumor and immunostimulatory effects of BCG vaccine observed in the body may be largely defined by functional activity of T-lymphocytes responsible for antigen-induced production of macrophage-activating lymphokines.

Functional switching of macrophage responses to tumor necrosis factor-alpha (TNF alpha) by interferons. Implications for the pleiotropic activities of TNF alpha

Recent work conducted in our laboratory has been directed towards understanding the role of TNF alpha in stimulating the synthesis of two macrophage gene products, namely IGF-1, a growth factor implicated in wound repair and fibrosis, and complement component factor B (Bf), an alternative pathway complement component. The expression of these proteins is induced by hyaluronic acid and poly (I:C), respectively, although TNF alpha plays a requisite role in the expression of both proteins. The objective of this study was to determine the mechanism governing the dichotomy in the expression of IGF-1 and Bf by TNF alpha. First, we questioned if the diversity in IGF-1 and Bf synthesis was regulated at the level of TNF receptor usage. Second, based on earlier findings that IFNs contribute to the initiation of Bf expression, we determined if IFNs modulate the response of macrophages to TNF alpha. Our data show that differences in TNF receptor usage cannot fully explain the dichotomy in the expression of IGF-1 and Bf. However, prior exposure to IFN-beta or IFN-gamma was found to be a dominant factor controlling the expression of these proteins, suppressing IGF-1, and enhancing Bf. These findings indicate that IFNs mediate a functional "switch" in the response of macrophages to TNF alpha and suggest that the pattern of cytokine expression by diverse macrophage stimuli is an important determinant of the eventual responses of macrophages to TNF alpha.

Involvement of protein kinase C in macrophage activation by poly(I.C)

The expression of cytocidal activity is initiated by the interaction of macrophages with priming [e.g., interferon (IFN)] and triggering stimuli (polyinosinic-polycytidylic acid). We have shown that the triggering step can be initiated in a Ca(2+)-dependent fashion and hypothesized that protein kinase C (PKC) may couple the Ca2+ signal to the expression of a gene product, Bf, that accompanies the expression of macrophage cytocidal activity. Exposure of IFN-primed macrophages to polyinosinic-polycytidylic acid in the presence of the PKC inhibitors H-7 or sphingosine or after downregulation of PKC with phorbol myristate acetate markedly inhibited Bf synthesis. Western blots of macrophage lysates revealed the presence of the alpha-, delta-, and zeta-isozymes of PKC, and all were found to be downregulated by phorbol myristate acetate. Inhibition of PKC also prevented the increase in IFN-beta mRNA levels and partially blocked the response to IFN-beta. These data suggest that the alpha-, delta-, and zeta-isozymes of PKC are involved in signaling leading to Bf expression and that the level of involvement is restricted to the induction and response to IFN-beta.

Priming of human monocytes for enhanced lipopolysaccharide responses: expression of alpha interferon, interferon regulatory factors, and tumor necrosis factor

Culture of human monocytes with either granulocyte-macrophage colony-stimulating factor or gamma interferon (IFN-gamma) results in a primed state, during which these cells express heightened responses to bacterial lipopolysaccharide (LPS). The production of IFN-alpha in response to LPS by human monocytes has an absolute requirement for priming. Tumor necrosis factor (TNF) expression is also greatly enhanced in primed monocytes after LPS stimulation, but unlike IFN-alpha, TNF is readily expressed in unprimed monocytes as well. In an effort to determine the molecular events associated with IFN-alpha induction in this system, freshly isolated human monocytes were primed by culture with either IFN-gamma or granulocyte-macrophage colony-stimulating factor and then treated with LPS; expression of IFN-alpha subtype 2 (IFN-alpha 2), IFN regulatory factors (IRFs), and TNF was assessed by Northern (RNA blot) analysis. IRF-1 mRNA is expressed at high levels in monocytes and is regulated by both LPS and priming cytokines, but its expression alone does not correlate with the induction of IFN-alpha 2 expression. IRF-2 mRNA is expressed in a more gradual manner following LPS stimulation, implying a possible feedback mechanism for inhibiting IFN-alpha expression. However, nuclear run-on analysis indicates that IFN-alpha 2 is not transcriptionally modulated in this system, in striking contrast to TNF, which is clearly regulated at the transcriptional level. In addition, IFN-alpha 2 mRNA accumulation is superinduced when primed monocytes are treated with LPS plus cycloheximide, while TNF mRNA is relatively unaffected. The results demonstrate that priming can affect subsequent LPS-induced gene expression at different levels in human monocytes.

Inhibitor of C1q secretion suppresses the macrophage response to lipid A for nitric oxide but not for TNF production: evidence for a role of C1q in autocrine binding of TNF

Studies were designed to further define the modulatory role of complement subcomponent C1q in macrophage activation by Lipid A to mediate production of TNF and cytotoxic nitric oxide (NO). Pretreatment of macrophages for 24 h with 2.5 mM 3,4,dehydro-D,L-proline (DHP), an inhibitor of C1q secretion, suppressed their response to Lipid A activation for cytotoxicity of P815 tumor targets which correlated with a corresponding decrease in NO production. In contrast, DHP-pretreated macrophages displayed an increase in the release of TNF in response to Lipid A as compared to untreated controls. Time kinetic studies indicated that DHP-pretreated macrophages produced higher sustained levels of TNF activity during 1 to 24 h culture with Lipid A than did untreated control macrophages. This was confirmed by increased TNF mRNA expression in response to Lipid A by DHP-treated cells. DHP-pretreated macrophages had reduced levels of cell surface C1q as determined by cytofluorometric analysis of the binding of FITC-labeled anti-C1q, F(ab')2. Macrophages were also found to have reduced binding capacity for phycoerythrin-labeled rTNF (PE-TNF) by cytofluorometric analysis following DHP treatment. Exposure of DHP-pretreated macrophage to soluble C1q at 4 degrees C restored their reduced binding of PE-TNF. C1q was confirmed to bind to macrophages at 4 degrees C as detected by FITC anti-C1q, F(ab')2 and such C1q binding promoted a corresponding increased binding of PE-TNF. Macrophages which were plated over immobilized C1q were also markedly enhanced in their binding of PE-TNF probe. Our results indicate that the inhibition of macrophage secretion of C1q by DHP pretreatment, was accompanied by an increased TNF mRNA expression and release with a decrease in NO generation following Lipid A activation. Since TNF binding to DHP-treated macrophages was reconstituted by the binding of exogenous C1q to the cells, it appears that C1q may be involved in the modulation of autocrine binding of TNF for subsequent generation of cytotoxic NO.

Microbial cell-wall contaminants in peptides: a potential source of physiological artifacts

Microbial cell-wall products (MCWP) such as endotoxins are easily introduced into peptides produced under standard laboratory conditions. Because these products stimulate the induction of cytokines and other mediators, which, in turn, trigger a broad range of physiological responses. MCWP in peptide preparations are potential sources of artifacts. This brief tutorial outlines the physical/chemical nature of MCWP, some of their sources, their physiological effects, and a simple method to control for them in some peptide preparations.

Transmembrane-mediated changes in [Ca2+] are involved in the signaling pathway leading to macrophage cytocidal differentiation: implications of localized changes in intracellular [Ca2+] and of interferon priming on Ca2+ utilization

Macrophage cytocidal activation requires the sequential impingement on the macrophage of a priming stimulus (interferon [IFN] alpha, beta, or gamma) and a triggering stimulus (such as polyinosinic acid:polycytidylic acid [poly [I:C]] or bacterial lipopolysaccharide). The mechanism of progression from the IFN-primed state to the cytocidal state is poorly understood. By quantifying the level of expression of a gene product (complement component factor B [Bf]) associated with cytocidal activation and through the use of phenotypically distinct populations of macrophages (unprimed and IFN-primed), we have investigated the functional necessity of changes in intracellular concentration of free calcium ions ([Ca2+]i) in signaling the transition from the primed to the cytocidal state. Elevating the [Ca2+]i by incubation of unprimed macrophages with the calcium ionophore, ionomycin, failed to induce the expression of Bf. By contrast, Bf was expressed at high levels when IFN-primed macrophages were exposed to ionomycin, suggesting that priming induced within the macrophages the capacity to respond to a nonspecific change in [Ca2+]i. Quantification of the [Ca2+]i in response to exposure to ionomycin revealed an initial transient elevation, followed by a secondary sustained component. No differences in these changes were observed between unprimed and IFN-primed macrophages. We therefore questioned if changes in [Ca2+]i were also implicated in the transition between the primed and the cytocidal state using the ligand, poly [I:C]. In contrast to ionomycin, incubation of IFN-primed macrophages with poly [I:C] did not sustain measurable increases in [Ca2+]i, yet fully stimulated the transition from the IFN primed to the cytocidal state. However, incubation of IFN-primed macrophages with poly [I:C] in the presence of 1) a Ca2+/ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid buffer calculated to clamp the extracellular concentration of free calcium ions to a value approximately equal to the resting [Ca2+]i; 2) the calcium channel blocker verapamil; or 3) the intracellular Ca2+ antagonists (W-7, W-13, and TMB-8) substantially inhibited the induction of Bf. Collectively, these data support the following conclusions. First, that changes in [Ca2+]i comprise an important element in the induction of progression from the IFN-primed to the cytocidal state. Second, the failure to detect global changes in [Ca2+]i in response to the ligand, poly [I:C], suggests that changes in [Ca2+]i or Ca2+ movement may occur in either a spatially restricted or in an asynchronous cyclical fashion and are not detected by population fluorescence measurements. Third, the source of the relevant Ca2+ is extracellular. Fourth, our findings suggest that priming influences macrophage functional responses at a locus that is distal to the changes in [Ca2+]i, thereby potentially allowing signaling processes to be utilized to initiate different cellular responses.

An hypothesis concerning optimal therapy in HIV disease

Ampligen, a mismatched double stranded RNA, is hypothesized to be an ideal base therapy for HIV disease to which other agents, such as the nucleoside analogue, AZT, can be advantageously added. The unique properties of Ampligen which support this hypothesis include activation of immune cells, inhibition of virus replication by inducing an antiviral cellular state and inhibition of growth of neoplastic cells. Ampligen is synergistic with other agents being used or being tested for use in HIV disease and is without toxicity.

Inhibition of Ehrlichia risticii infection in murine peritoneal macrophages by gamma interferon, a calcium ionophore, and concanavalin A

Ehrlichia risticii incubated with mouse peritoneal macrophages elicited with thioglycolate broth survived and replicated, thereby allowing examination of the effects of several immunopotentiating agents. Treatment of the macrophages with recombinant murine gamma interferon (rMuIFN-gamma) in vitro at 1 day before or 3 h after infection made the macrophages resistant to infection with E. risticii, and macrophages treated with rMuIFN-gamma at 1 to 3 days after infection developed the capacity to eradicate intracellular E. risticii. Similar effects were seen with macrophages treated with the Ca2+ ionophore A23187 before or after E. risticii infection in vitro. Concanavalin A treatment before or 3 h after infection caused the macrophages to become resistant to infection with E. risticii but could confer neither ehrlichiacidal nor ehrlichiastic activity to them once infection had been established for more than 1 day. Bacterial products such as lipopolysaccharide and muramyl dipeptide were less or not at all effective, respectively, in conferring antiehrlichial activity to macrophages. Finally, protein kinase C activator, phorbol myristate acetate, and recombinant tumor necrosis factor did not induce any antiehrlichial activity in macrophages when the macrophages were treated either before or after infection.

Cellular response to double-stranded RNA

The study of double-stranded RNA (dsRNA) encompasses a variety of fields. Basic research in this area has contributed to a greater mechanistic understanding of gene induction, tumor cell growth arrest, the establishment of antiviral states, and immunomodulation. Because of the possible clinical value of these molecules, physicians are now exploring the use of synthetic dsRNA to treat patients with cancer, HIV-1 disease, and immune dysfunction. Continued studies of the mechanisms of action of dsRNA are likely to suggest an even wider scope of clinical applications.

Influence of the cytocidal macrophage phenotype on the degradation of acetylated low density lipoproteins: dual regulation of scavenger receptor activity and of intracellular degradation of endocytosed ligand

The appearance of lipid-laden macrophages is a characteristic feature in the development of the atherosclerotic plaque. The functional status of macrophages located within the intima of atherosclerotic lesions is as yet unknown; nevertheless, macrophages are known to be exceedingly responsive to their environment and can differentiate to different functional states. The objective of this study was to determine the influence of two definable macrophage functional states, namely the IFN-primed state and the cytocidal state, on the capacity of macrophages to bind and degrade lipoproteins. We report that priming of macrophages with IFN-beta or IFN-gamma failed to influence the ability of macrophages to degrade native low density lipoprotein or acetylated low density lipoprotein (AcLDL). However, challenge with stimuli that induce expression of the cytocidal state (poly[I:C] and LPS) resulted in a marked inhibition of the capacity of the cells to degrade both lipoproteins. The poly[I:C]-induced inhibition of 125I-AcLDL degradation was accompanied by a proportional decrease in the binding of the ligand to its receptor which Scatchard analysis revealed was due to a decrease in receptor number rather than a change in receptor affinity for 125I-AcLDL. However, in addition to the down-regulation of receptor activity, the degradation of endocytosed 125I-AcLDL was also suppressed in macrophages that had been exposed to poly[I:C]. This latter observation suggests that the degradation of endocytosed lipid is also regulated at a second, previously unidentified level, independent of the availability of cell surface ligand receptors. We speculate that this down-regulation in the intracellular hydrolysis of endocytosed lipid may account for the observed accumulation of 125I-AcLDL in these cells.

Immunostimulation circumvents diabetes in NOD/Lt mice

Diabetes susceptibility in non-obese diabetic (NOD) mice may entail faulty activation of immunoregulatory cells resulting from cytokine deficiencies. Depletion of T cells prevents disease onset in these mice. Since we had previously shown that IL-2 treatment in vivo restored the ability of NOD/Lt mice to produce self-restricted suppressor T cells (Ts) in a syngeneic mixed lymphocyte reaction (SMLR), we investigated the possibility that diabetes could be circumvented by treatment with immunostimulatory agents that increase cytokine production. By 20 weeks of age, 75% of vehicle-treated NOD/Lt female controls had become glycosuric, while glycosuria developed in only 17% of NOD/Lt females injected with human recombinant interleukin-2 (rIL-2, 250 U twice weekly) beginning at 6 weeks of age. Treatment of mice with Poly [I:C] alone [50 micrograms twice weekly, an inducer of Interferon (IFN) alpha/beta] or in conjunction with rIL-2 was even more effective, completely preventing glycosuria for 20 weeks. However, therapeutic effects required continuous administration of the immunostimulants since pancreatic insulin content declined and severity of insulitis increased following cessation of treatment. IL-2 treatment increased transcription of interleukin-1 (IL-1) mRNA in peritoneal macrophages and increased lipopolysaccharide (LPS)-stimulated IL-1 secretion in comparison to controls. In the presence of stimulators from IL-2-treated mice, T lymphocytes isolated from both controls and IL-2-treated NOD/Lt mice proliferated in a SMLR and acquired Ts function. Peritoneal macrophages from Poly [I:C]-treated mice exhibited increased IFN alpha gene transcription and LPS-stimulated IL-1 secretion. T cells isolated from Poly [I:C]-treated mice were capable of suppressing NOD-Lt T cell responses to alloantigens in a mixed lymphocyte culture without prior activation in a SMLR. Thus, Poly [I:C] treatment may recruit a different population of regulatory cells than those elicited by treatment with IL-2. However, the mechanisms by which autoreactive T-cell clones may be regulated by these two treatments in NOD/Lt mice may be synergistic. These results indicate that in addition to T-cell depletion protocols, diabetes in NOD mice can be prevented by treatment with immunostimulatory agents.

Modifications of glycosylation patterns in macrophages upon activation

Activated macrophages, in contrast to inflammatory and resident macrophages, are able to inhibit the growth of intracellular pathogens and tumor cells. In order to understand the adaptative changes which allow macrophages to express antitumor activity, we compared, among several parameters, the glycoproteins of cytotoxic and non-cytotoxic macrophages. After activation of mouse peritoneal macrophages by two stimuli applied in a sequence (trehalose dimycolate in vivo, lipopolysaccharide in vitro), we observed that: (1) surface sialic acid residues (labeled by tritiated borohydride after treatment of intact cells in culture by periodate) were reduced by 37%; (2) total sialic acid, as measured by an adaptation to HPLC of the thiobarbituric assay, was reduced by 30%. Variations in the intensity of the labeling after periodate/borohydride treatment were especially pronounced for a few high-molecular-weight glycoproteins. Analysis of glycopeptides indicated that the reduction of sialylation was accompanied by a slight increase in the relative importance of high mannose-type oligosaccharides (glycopeptides sensitive to endoglycosidase H or retained on concanavalin A-Sepharose) but did not affect the ratio of the various anionic species separated on QAE-Sephadex. A reduced sialylation of glycans after activation may facilitate interactions of macrophages with microbes and tumor cells.

Triggering of interferon gamma-primed macrophages by various known complement activators for nonspecific tumor cytotoxicity

Five known complement activators were evaluated for their capacity to directly activate murine macrophages and to trigger activation of lymphokine primed macrophages for nonspecific tumor cytotoxicity. Bacterial lipopolysaccharide (LPS), Lipid A, polyinosinic-polycytidylic acid, cobra venom factor (CVF), and zymosan directly activated macrophages in a dose-dependent fashion at high concentrations. Subactivating concentrations of each of these agents were found to effectively trigger macrophages which were preprimed either by macrophage-activating factor or by murine recombinant interferon gamma for enhanced tumoricidal activity. An Fc receptor blockade with opsonized sheep erythrocytes abrogated LPS-mediated direct activation and triggering of interferon gamma-primed macrophages, but had no inhibitory effect on direct activation or triggering by CVF for nonspecific tumor cytotoxicity. This study characterizes the capacity of a diverse group of known complement activators to serve as second signal triggers for culmination of the activation process of interferon-primed macrophages for nonspecific tumoricidal activity. These findings suggest that complement activators may directly activate macrophages by stimulation of interferon beta production by macrophages for self-priming and, as we have shown, act as self-triggers. The putative role of macrophage-associated complement components in the activation process is discussed.

Activation of mouse macrophages for migration inhibition and for tumor cytotoxicity is mediated by interferon-gamma priming and triggering by various agents

The requirements for activation of C3HeB/FeJ mouse peritoneal macrophages to mediate migration inhibition from capillary tubes was compared with those conditions prerequisite for nonspecific tumor cytotoxicity. Both in vitro assays for macrophage activation were found to require a two-stage process that involved priming by murine recombinant interferon-gamma (IFN-gamma) and triggering by subactivating concentrations of bacterial lipopolysaccharide (LPS), Lipid A, Polyinosinic-polycytidylic acid (poly I:C), or cobra venom factor (CVF). A dose-related increase in both migration inhibition and tumor cytotoxicity was shown with increasing concentrations of IFN-gamma (3.0-50.0 U/ml) in synergistic combination with an LPS trigger. IFN-gamma alone produced low levels of migration inhibition or tumor cytotoxicity, only at higher concentrations, that was not attributable to LPS contamination. The concentrations of the various agents required for direct activation or triggering of IFN-gamma-primed macrophages were approximately 2- to 10-fold greater for migration inhibition than for tumor cytotoxicity. Our results indicate that the two-signal process of priming and triggering for mediating mouse macrophage nonspecific tumoricidal activity is also operative in migration inhibition from capillary tubes. Thus, under defined conditions with purified lymphokines, the migration inhibition assay appears to be a reliable alternate in vitro correlate of macrophage activation by IFN-gamma.