Systemic expression of rat soluble retinal antigen induces resistance to experimental autoimmune uveoretinitis.

To assess the role of sequestration in the maintenance of the immune privilege of the retina, retrovirally mediated gene transfer was used to express a defined, specific retinal autoantigen, rat soluble retinal Ag (S-Ag), in a systemic, nonsequestered manner. In this study we report the stable, long term transduction of rat retinal S-Ag into PBMC. Tolerance to S-Ag was assayed by challenging the S-Ag chimeric animals with S-Ag peptides in CFA and monitoring the time course and severity of experimental autoimmune uveoretinitis (EAU). The resulting data showed a correlation between the incidence of S-Ag chimerism and the loss of susceptibility to EAU. The development of resistance to EAU induction supports the hypothesis that Ag sequestration contributes to retinal immune privilege.     

Inhibition of experimental autoimmune uveitis by retinal photoreceptor antigens coupled to spleen cells.

Experimental autoimmune uveitis (EAU) and experimental autoimmune pinealitis (EAP) are CD4+ T cell-mediated inflammatory diseases of the uveal tract and retina of the eye and of the pineal gland. EAU and EAP can be induced by several retinal autoantigens including S-antigen (S-Ag) and interphotoreceptor retinoid binding protein (IRBP). In this study we investigated the effect of intravenous administration of S-Ag and IRBP coupled to syngeneic spleen cells on the development of EAU and EAP. Injection of S-Ag or IRBP coupled to spleen cells 5 days prior to immunization with native S-Ag or IRBP, respectively, was effective in preventing the induction of EAU and EAP in LEW rats. Conversely, LEW rats receiving S-Ag-coupled spleen cells and challenged with IRBP or LEW rats receiving IRBP-coupled spleen cells and challenged with S-Ag developed a severe EAU within 10 days to 2 weeks following immunization, as did all control animals receiving sham-coupled spleen cells and challenged with the two retinal antigens. The results show that the administration of retinal autoantigens coupled to spleen cells effectively protects against the development of EAU when animals are subsequently challenged with the tolerizing antigen but not when challenged with another unrelated pathogenic retinal autoantigen.     

Enhanced tumour growth in the rat liver after selective elimination of Kupffer cells

The evidence that Kupffer cells are capable of controlling metastatic growth in the liver in vivo is largely circumstantial. The best approach when studying natural cytotoxicity activities of Kupffer cells is to investigate the effect of Kupffer cell elimination on tumour growth. Until now it has not been possible to eliminate Kupffer cells without affecting other cell populations. We have recently developed a new method to eliminate Kupffer cells selectively: intravenous injection of liposome-encapsulated (dichloromethylene)bisphosphonate (Cl₂MDP-liposomes) leads to effective elimination of all Kypffer cells, without affecting non-phagocytic cells. Wag/Rij rats were injected with Cl₂MDP-liposomes. After 48 h, rats were inoculated with syngeneic CC531 colon carcinoma cells by injection in the portal system. The results show a strongly enhanced tumour growth in the liver of the Cl₂MDP-liposometreated rats. In these animals, livers were almost completely replaced by tumour and had increased in weight, whereas in the control groups only a few (four to eight) small (1-mm) tumour nodules were found. These data show that selective elimination of Kupffer cells results in enhanced tumour growth in the liver, implying that Kupffer cells play a crucial role in controlling tumour growth in the liver.     

Liposomal muramyl dipeptide therapy of experimental M5076 liver metastases in mice

Summary The effectiveness ofN-acetylmuramyl-l-alanyl-d-isoglutamine (MDP) or of liposomes containing a lipophilic MDP derivative, MDP-glyceroyldipalmitate MDP-GDP in inhibiting the growth of M5076 reticulum cell sarcoma liver metastases in C57BL/6 mice has been determined. MDP (100 µg) or liposomal MDP-GDP (2.5 µmol containing 1 µg) were equally effective in inhibiting liver metastatic growth when given as a single treatment 3 days before tumor cell injection. Therapeutic treatment, initiated 3 days after tumor cell injection and continued for a period of 2 weeks, failed to inhibit metastatic growth. Activation of thioglycollate-elicited peritoneal macrophages or Kupffer cells in vitro with MDP or liposomal MDP-GDP resulted in the expression of tumoricidal activity against M5076 tumor cells. Adoptive cellular therapy with four injections of 2 × 10⁶ macrophages was ineffective: activation of the macrophages with either MDP or liposomal MDP-GDP prior to injection was effective in inhibiting liver metastatic growth. Incorporation of the macrophage toxin dichlorodimethylene diphosphonate within liposomes containing MDP-GDP abolished the ability of such liposomes to induce macrophage or Kupffer cell tumoricidal activity in vitro as well as the antitumor activity when administered 3 days before tumor cell challenge.     

Effect of Macrophage Elimination Using Liposome-Encapsulated Dichloromethylene Diphosphonate on Tissue Distribution of Liposomes

Abstract

Effect of macrophage elimination using liposomal dichloromethylene diphosphonate (C1₂MDP)1 on tissue distribution of different types of liposomes was examined in mice. Intravenously administration into mice with CI2MDP encapsulated in liposomes composed of phosphatidylcholine, cholesterol and phosphatidylserine exhibits a temporary blockade of liver and spleen function for liposome uptake. At a low dose of 90 (ig/mouse, the liposome uptake by the liver was significantly decreased. Such decrease was accompanied by an increase in liposome accumulation in either spleen or blood depending on liposome composition and size. Direct correlation between the administration dose of liposomal CI2MDP and the liposome circulation time in blood was also obtained even for liposomes with an average diameter of more than 500 nm. These results indicate that temporary elimination of macrophages of the liver and spleen using liposomal CI2MDP may prove to be useful to enhance the drug delivery efficiency of liposomes.     

Intraocular trafficking of lymphocytes in locally induced experimental autoimmune uveoretinitis (EAU)

Experimental autoimmune uveoretinitis (EAU) was induced in naive Lewis rats by intravitreal adoptive transfer of 10(6) long-term S-antigen (S-Ag)-specific syngeneic T-lymphocyte lines of helper/inducer phenotype (ThS). These cells were stimulated with the T-cell mitogen concanavalin A (Con A) in culture for 48 hr and subsequently labeled with tritiated thymidine. Lymph node cells (LNC) cultured in parallel were used as controls. Histopathology and light microscopic autoradiography of the ocular tissue was performed at several time points to analyze the cell migration in relation to the development of EAU. The disappearance of both types of lymphocytes from the vitreous was similar and large numbers of host leukocytes were attracted into the vitreous. However, significantly more S-Ag-specific cells penetrated the retina and induced EAU (P less than 0.008). These results suggest that the development of EAU by intravitreal injection of S-Ag-specific T lymphocytes occurs by the migration of antigen-specific cells into the retina and recognition of the specific antigen, with subsequent release of soluble mediators that interact with the host effector cells, ultimately leading to specific photoreceptor damage.     

The Role of Lipoprotein-Associated Phospholipase A? in a Murine Model of Experimental Autoimmune Uveoretinitis

Macrophage activation is, in part, regulated via hydrolysis of oxidised low density lipoproteins by Lipoprotein-Associated phospholipase A₂ (Lp-PLA₂), resulting in increased macrophage migration, pro-inflammatory cytokine release and chemokine expression. In uveitis, tissue damage is mediated as a result of macrophage activation; hence inhibition of Lp-PLA₂ may limit macrophage activation and protect the tissue. Utilising Lp-PLA₂ gene-deficient (KO) mice and a pharmacological inhibitor of Lp-PLA₂ (SB-435495) we aimed to determine the effect of Lp-PLA₂ suppression in mediating retinal protection in a model of autoimmune retinal inflammation, experimental autoimmune uveoretinitis (EAU). Following immunisation with RBP-3 (IRBP) 1–20 or 161–180 peptides, clinical disease was monitored and severity assessed, infiltrating leukocytes were enumerated by flow cytometry and tissue destruction quantified by histology. Despite ablation of Lp-PLA₂ enzyme activity in Lp-PLA₂ KO mice or wild-type mice treated with SB-435495, the number of infiltrating CD45⁺ cells in the retina was equivalent to control EAU animals, and there was no reduction in disease severity. Thus, despite the reported beneficial effects of therapeutic Lp-PLA₂ depletion in a variety of vascular inflammatory conditions, we were unable to attenuate disease, show delayed disease onset or prevent progression of EAU in Lp-PLA₂ KO mice. Although EAU exhibits inflammatory vasculopathy there is no overt defect in lipid metabolism and given the lack of effect following Lp-PLA₂ suppression, these data support the hypothesis that sub-acute autoimmune inflammatory disease progresses independently of Lp-PLA₂ activity.     

Benefits of oat beta-glucan on respiratory infection following exercise stress: role of lung macrophages

Exercise stress is associated with an increased risk for upper respiratory tract infection (URTI). We have shown that consumption of the soluble oat fiber beta-glucan (ObetaG) can offset the increased risk for infection and decreased macrophage antiviral resistance following stressful exercise; however, the direct role of macrophages is unknown. This study examined the effect of macrophage depletion on the benefits of orally administered ObetaG on susceptibility to infection (morbidity, symptom severity, and mortality) following exercise stress. CL(2)MDP (Ex- H(2)O-CL(2)MDP, Ex-ObetaG-CL(2)MDP, Con-H(2)O-CL(2)MDP, Con-ObetaG-CL(2)MDP)-encapsulated liposomes were administered intranasally to deplete macrophages, and PBS (Ex-H(2)O-PBS, Ex-ObetaG-PBS, Con-H(2)O-PBS, Con-ObetaG-PBS)-encapsulated liposomes were given to macrophage-intact groups. Ex mice ran to volitional fatigue on a treadmill for 3 consecutive days, and ObetaG mice were fed a solution of 50% ObetaG in their drinking water for 10 consecutive days before infection. Fifteen minutes following the final bout of Ex or rest, mice were intranasally inoculated with 50 microl of a standardized dose of herpes simplex virus-1. Ex increased morbidity (P < 0.001) and symptom severity (P < 0.05) but not mortality (P = 0.09). The increase in morbidity and symptom severity was blocked by ObetaG consumption for 10 consecutive days before exercise and infection [morbidity (P < 0.001) and symptom severity (P < 0.05)]. Depletion of macrophages negated the beneficial effects of ObetaG on reducing susceptibility to infection following exercise stress, as evidenced by an increase in morbidity (P < 0.01) and symptom severity (P < 0.05). Results indicate that lung macrophages are at least partially responsible for mediating the beneficial effects of ObetaG on susceptibility to respiratory infection following exercise stress.     

Comparison of protection from homologous cell-free vs cell-associated SIV challenge afforded by inactivated whole SIV vaccines

This study attempted to determine if SIV vaccines could protect against challenge with peripheral blood mononuclear cells (PBMCs) from an SIV infected rhesus monkey. Mature Macaca mulatta were vaccinated four times with formalin inactivated SIV_mac32H administered in MDP adjuvant (n = 8) or SIV_mac32H ISCOM vaccine (n = 8). Controls included animals vaccinated with measles virus in MDP adjuvant (n = 4) or ISCOM (n = 4) preparations. Of each group, half were challenged intravenously (IV) with ten MID₅₀ of the cell-free SIV_mac32H (11-88) SIV stock and half were challenged with ten MID₃₀ of PBMCs from the SIV_mac32H infected macaque 1XC. All SIV vaccinated animals challenged with the 11-88 cell free stock of SIV_mac32H were protected, whereas only half of the SIV vaccinated monkeys receiving the same infectious dose of the 1XC cell stock were protected.     

Selective immunosuppression of activated T cells with the chimeric toxin IL-2-PE40. Inhibition of experimental autoimmune uveoretinitis

A characteristic of activated T lymphocytes is the expression of high affinity IL-2R. We studied a new method of selective immunosuppression directed against activated T cells by using a chimeric recombinant protein (IL-2-PE40) composed of IL-2 fused to a modified Pseudomonas exotoxin lacking its cell recognition domain. As a model of T cell-mediated disease, we used experimental autoimmune uveoretinitis (EAU) produced in Lewis rats by active immunization with the retinal S-Ag. The treatment protocol consisted of i.p. injection of IL-2-PE40 at 0.25 micrograms/g every 12 h. Controls were PBS, PE40, or IL-2-PE40asp553 a mutant form of the molecule with reduced activity. Treatment with IL-2-PE40 resulted in a significant reduction of the incidence and severity of EAU over controls. The analysis of the effect of i.p. injection of IL-2-PE40 on the popliteal draining lymph nodes of immunized animals showed a marked reduction in the lymphocytes content. Transfer experiments demonstrated that IL-2-PE40 prevented the development of EAU effector T cells. Interestingly, although activated B cells were reported to express IL-2R, there was no significant reduction of antibody production against the immunizing Ag under IL-2-PE40 treatment, suggesting sparing of the B cells.     

Development of pulmonary intravascular macrophage function in newborn lambs.

We sought to determine whether pulmonary intravascular macrophages are involved in pulmonary vascular sensitivity to intravenously injected particles in sheep. We estimated that newborn lambs have few of these macrophages at birth but develop a 10-fold greater density within 2 wk. Awake, chronically instrumented newborn lambs showed no change in pulmonary vascular driving pressure (pulmonary arterial minus left atrial pressure) after injection of either liposomes [2 +/- 3 (SD) cmH2O; n = 5] or Monastral blue particles (3 +/- 2 cmH2O; n = 6) and showed no net pulmonary production of thromboxane B2, the stable metabolite of the vasoconstrictor thromboxane A2. In contrast, five of those lambs 2 wk later showed both an increase in pulmonary vascular driving pressure after injection of liposomes and Monastral blue (20 +/- 16 and 25 +/- 15 cmH2O, respectively; P < 0.05) and net pulmonary production of thromboxane B2 (171 +/- 103 and 429 +/- 419 pg/ml plasma, respectively; P < 0.05). Older lambs (n = 5) had higher pulmonary uptakes than newborn lambs (n = 6) of radioactive liposomes (47 +/- 13 vs. 12 +/- 10%; P < 0.01) and Monastral blue (53 +/- 6 vs. 21 +/- 10%; P < 0.05). We conclude that pulmonary intravascular macrophages are responsible for the sensitivity of sheep to intravenous foreign particles and are essential for a cascade of processes leading to microvascular injury.     

Macrophage Depletion Impairs Corneal Wound Healing after Autologous Transplantation in Mice

Purpose

Macrophages have been shown to play a critical role in the wound healing process. In the present study, the role of macrophages in wound healing after autologous corneal transplantation was investigated by depleting local infiltrated macrophages.

Methods

Autologous corneal transplantation model was used to induce wound repair in Balb/c mice. Macrophages were depleted by sub-conjunctival injections of clodronate-containing liposomes (Cl₂MDP-LIP). The presence of CD11b⁺ F4/80⁺ macrophages, α-smooth muscle actin⁺ (α-SMA⁺) myofibroblasts, CD31⁺ vascular endothelial cells and NG₂ ⁺ pericytes was examined by immunohistochemical and corneal whole-mount staining 14 days after penetrating keratoplasty. Peritoneal macrophages were isolated from Balb/c mice and transfused into conjunctiva to examine the recovery role of macrophages depletion on wound healing after autologous corneal transplantation.

Results

Sub-conjunctival Cl₂MDP-LIP injection significantly depleted the corneal resident phagocytes and infiltrated macrophages into corneal stroma. Compared with the mice injected with PBS-liposome, the Cl₂MDP-LIP-injected mice showed few inflammatory cells, irregularly distributed extracellular matrix, ingrowth of corneal epithelium into stroma, and even the detachment of donor cornea from recipient. Moreover, the number of macrophages, myofibroblasts, endothelial cells and pericytes was also decreased in the junction area between the donor and recipient cornea in macrophage-depleted mice. Peritoneal macrophages transfusion recovered the defect of corneal wound healing caused by macrophages depletion.

Conclusions

Macrophage depletion significantly impairs wound healing after autologous corneal transplantation through at least partially impacting on angiogenesis and wound closure.     

Antigen-directed retention of an autoimmune T-cell line

We have used the T-cell-mediated, organ-specific autoimmune disease model of experimental autoimmune uveoretinitis (EAU) in the Lewis rat to study antigen-directed retention of autoimmune T helper cells in the target organ. We have compared the migration into the eye of two T-helper-cell lines: ThS, specific for retinal S antigen (S-Ag), that is uveitogenic to normal syngenic recipients, and ThP, specific to purified protein derivative of tuberculin (PPD), that is non-uveitogenic. The retention of adoptively transferred 51Cr-labeled ThS and ThP was studied up to the stage of disease induction in unprimed animals, during the acute stage of EAU induced by active immunization with S-Ag, and during the acute stage of a uveitis induced by a nonocular antigen (bovine serum albumin, BSA). Low numbers of cells from the two lymphocyte lines were detected in the eyes of unprimed animals, with no obvious increase of ThS over ThP, despite induction of EAU in the recipient animals by the injected ThS cells. In S-Ag-induced EAU many more ThS accumulated in the eye than ThP. In BSA uveitis both T-cell lines accumulated in the eye to the same extent, but more than in control noninflamed eyes. These results demonstrate the presence of increased antigen-specific retention of circulating autoimmune T helper lymphocytes during the acute stage of an ocular antigen-specific, but not ocular antigen nonspecific, inflammation. Since detectable accumulation of ThS cells in the eye was not a prerequisite for the induction of EAU, this phenomenon appears to be the result, rather than the cause, of the autoimmune process.     

Expression of S-antigen in retina, pineal gland, lens, and brain is directed by 5'-flanking sequences.

S-antigen (S-Ag) is an abundant protein of the retina and pineal gland that elicits experimental autoimmune uveitis and pinealocytis in several animal species. To study the elements regulating the expression of S-Ag, we generated transgenic mice expressing the chloramphenicol acetyl transferase (CAT) gene under the control of a 1.3-kilobase pair 5'-flanking segment of the mouse S-Ag gene. While all of the transgenic mice expressed CAT activity in the retina, in some animals CAT activity was also detected in the pineal gland, lens, and brain. Immunoblotting, polymerase chain reaction-mediated detection of RNA, and immunocyto-staining of transgenic tissues with antibodies to CAT and S-Ag established that the profile of expression of the transgene corresponded to that of S-Ag; both proteins were detectable in retinal photoreceptor cells, pinealocytes, lens fiber and epithelial cells, the cerebellum, and the cerebral cortex. These results indicate that S-Ag is expressed in a wider spectrum of the cell types than previously recognized and that a 1.3-kilobase pair S-Ag promoter segment contains sufficient information to direct appropriate tissue-specific gene expression in transgenic mice.     

Elimination of phagocytic cells in the spleen after intravenous injection of liposome-encapsulated dichloromethylene diphosphonate

Summary Dichloromethylene diphosphonate can be used for temporary elimination of macrophages in the spleen when administered after entrapment in liposomes. No comparable effect on the macrophages of the spleen was observed with free dichloromethylene diphosphonate or in the case of empty liposomes. Marginal metallophils on the boundary between white pulp and marginal zone as well as macrophages in the marginal zone and red pulp disappeared from the spleen within one day and remained largely absent for about a week. After this time cells reappeared slowly, and at approximately four weeks after injection their presence in the spleen did not differ from that in control animals. Marginal metallophils and macrophages in the spleen were demonstrated by use of enzyme-histochemical methods and by their capacity to ingest carbon particles.     

Depletion and repopulation of macrophages in spleen and liver of rat after intravenous treatment with liposome-encapsulated dichloromethylene diphosphonate

Summary Rats received a single intravenous injection with liposome-encapsulated dichloromethylene diphosphonate (Cl2MDP). This treatment resulted in the elimination of macrophages in spleen and liver within 2 days. Macrophages ingest the liposomes and are destroyed by the drug, which is released from the liposomes after disruption of the phospholipid bilayers under the influence of lysosomal phospholipases. Repopulation of macrophages in spleen and liver was studied at different time intervals after treatment. Macrophages in the liver (Kupffer cells) and red pulp macrophages in the spleen were the first cells to reappear, followed by marginal metallophilic macrophages and marginal-zone macrophages in the spleen. Different markers of the same cell did not reappear simultaneously. On the other hand, the same marker (recognized by the monoclonal antibody ED2) reappeared much more rapidly in the liver than in the spleen. The present results in the rat were different from those earlier obtained in the mouse. Red pulp macrophages were the first cells and marginal zone macrophages were the last cells to repopulate the spleen in both rodents after treatment with Cl2MDP liposomes. However, there was much more overlap in the repopulation kinetics of splenic macrophage subpopulations in the rat, when compared with the mouse.     

Effects of Cl2MDP-encapsulating liposomes in a murine model of Pseudomonas aeruginosa-induced sepsis

Pseudomonas aeruginosa is a pathogen that frequently causes acute lung injury, bacteremia and sepsis in critically ill patients. As tissue macrophages are a major producer of inflammatory mediators that contribute to septic physiology, and are essential for eliminating bacteria from the circulation, we investigated the role of tissue macrophages in the generation of both inflammatory and anti-inflammatory cytokines in septic shock by using our mouse model of P. aeruginosa pneumonia. To see the effects of tissue macrophage depletion, we intravenously injected dichloromethylene-diphosphonate (Cl2MDP)-encapsulating liposomes in mice. Two days after the liposome injection, we instilled cytotoxic P. aeruginosa (PA103) into the lung that disseminates and causes septic shock. After the infection, we collected blood and bronchoalveolar lavage fluids. The samples were then analyzed for TNF-alpha, MIP-2, and IL-10 concentration. We compared these results to control mice that received either liposomes without Cl2MDP or phosphate buffered saline alone. Plasma TNF-alpha, MIP-2, and IL-10 levels were significantly decreased in the tissue macrophage-depleted mice compared to the control groups of mice. Although depletion of tissue macrophages by Cl2MDP-liposome administration did not affect the severity of bacteremia or the survival of infected mice, these results imply that tissue macrophages have a major role in the production of both proinflammatory and anti-inflammatory cytokines in the circulation and in the causing septic physiology associated with P. aeruginosa pneumonia.     

Inhibition of Alveoloar Bone Loss During Maturation of the Rat

The effects of dichloromethylene diphosphonate (C1₂MDP) on previously described maturational bone loss were quantified in 24 Wistar rats. Four groups of six animals each were treated daily from 18 to 28 weeks of age with a subcutaneous injection of a 0.1, 1.0 or 10mg/kg dose of C1₂MDP or were sham treated with 0.9% NaC1. Prior to sacrifice, all animals were double-labeled with tetracycline. The interdental bone between first and second maxillary molars was evaluated on decalcified stained sections and on undecalcified ground sections by digitizing morphometry. No significant differences in periodontal ligament width, bone height, osteoclast numbers or tetracycline labeled surface were detected. Significantly greater bone area (p<0.01) and bone width (p<0.005), and significantly fewer osteoblasts/mm of bone surface (p<0.001) were measured in rats treated with 10 mg/kg doses of C1₂MDP; and a dose response was demonstrated. It was concluded that C1₂MDP prevented interdental bone loss by inhibiting bone resorption, and that bone formation may have been indirectly reduced through a coupling mechanism.     

Clodronate liposomes improve metabolic profile and reduce visceral adipose macrophage content in diet-induced obese mice

Background

Obesity-related adipose inflammation has been thought to be a causal factor for the development of insulin resistance and type 2 diabetes. Infiltrated macrophages in adipose tissue of obese animals and humans are an important source for inflammatory cytokines. Clodronate liposomes can ablate macrophages by inducing apoptosis. In this study, we aim to determine whether peritoneal injection of clodronate liposomes has any beneficial effect on systemic glucose homeostasis/insulin sensitivity and whether macrophage content in visceral adipose tissue will be reduced in diet-induced obese (DIO) mice.

Methodology/Principal Findings

Clodronate liposomes were used to deplete macrophages in lean and DIO mice. Macrophage content in visceral adipose tissue, metabolic parameters, glucose and insulin tolerance, adipose and liver histology, adipokine and cytokine production were examined. Hyperinsulinemic-euglycemic clamp study was also performed to assess systemic insulin sensitivity. Peritoneal injection of clodronate liposomes significantly reduced blood glucose and insulin levels in DIO mice. Systemic glucose tolerance and insulin sensitivity were mildly improved in both lean and DIO mice treated with clodronate liposomes by intraperitoneal (ip) injection. Hepatosteatosis was dramatically alleviated and suppression of hepatic glucose output was markedly increased in DIO mice treated with clodronate liposomes. Macrophage content in visceral adipose tissue of DIO mice was effectively decreased without affecting subcutaneous adipose tissue. Interestingly, levels of insulin sensitizing hormone adiponectin, including the high molecular weight form, were significantly elevated in circulation.

Conclusions/Significance

Intraperitoneal injection of clodronate liposomes reduces visceral adipose tissue macrophages, improves systemic glucose homeostasis and insulin sensitivity in DIO mice, which can be partially attributable to increased adiponectin levels.     

In situ activation of murine macrophages by liposomes containing lymphokines

Murine alveolar and peritoneal macrophages harvested after injection of lymphokines encapsulated within multilamellar phospholipid vesicles (liposomes) were tumoricidal in vitro. The state and degree of activation depended on the route of liposome administration. Activation of peritoneal macrophages was achieved by intraperitoneal injection of liposomes and alveolar macrophages were activated by injecting liposomes intravenously but not intraperitoneally. The in vivo rendering of macrophages with tumoricidal properties might be useful toward destruction of tumor cells in vivo.