Porous Implants Modulate Healing and Induce Shifts in Local Macrophage Polarization in the Foreign Body Reaction

The foreign body reaction (FBR) to implanted materials is of critical importance when medical devices require biological integration and vascularization to support their proper function (e.g., transcutaneous devices, implanted drug delivery systems, tissue replacements, and sensors). One class of materials that improves FBR outcomes is made by sphere-templating, resulting in porous structures with uniform, interconnected 34 μm pores. With these materials we observe reduced fibrosis and increased vascularization. We hypothesized that improved healing is a result of a shift in macrophage polarization, often measured as the ratio of M1 pro-inflammatory cells to M2 pro-healing cells. In this study, macrophage polarity of 34 μm porous implants was compared to non-porous and 160 μm porous implants in subcutaneous mouse tissue. Immunohistochemistry revealed that macrophages in implant pores displayed a shift towards an M1 phenotype compared to externalized cells. Macrophages in 34 μm porous implants had up to 63% greater expression of M1 markers and up to 85% reduction in M2 marker expression (p < 0.05). Macrophages immediately outside the porous structure, in contrast, showed a significant enrichment in M2 phenotypic cells. This study supports a role for macrophage polarization in driving the FBR to implanted materials.     

Corticosteroids and the Generalized Shwartzman Reaction: Mechanisms of Sensitization in the Rabbit

An analysis of the effects of adrenal cortical steroids on the response of the vascular system to bacterial endotoxin has shown that glucocorticoids (cortisone, triamcinolone) are capable of preparing the system for the generalized Shwartzman reaction. On the other hand, the mineralocorticoid desoxycorticosterone acetate does not have this capability. The mechanism of preparation by glucocorticoids has been studied. Administering insulin, with maintenance of normal blood sugar, had no effect on the extent of glomerular capillary thrombosis. Blockade, however, of α-adrenergic receptor sites by Dibenzyline caused a significant reduction of the thrombosis. In addition, cortisone-treated animals did not require exogenous stimulation of α-adrenergic receptor sites by norepinephrine to localize thrombi in the glomerular capillaries when Hageman factor was activated (by ellagic acid) and fibrinolysis inhibited (by ε-aminocaproic acid). It is concluded that glucocorticoids prepare for the generalized Shwartzman reaction by increasing the sensitivity of the microcirculation to stimulation of α-adrenergic receptor sites.     

Induction of the Generalized Shwartzman Reaction in Pregnant and Nonpregnant Rats by Colchicine

The intravenous injection of colchicine (2 mg/kg body weight) into pregnant rats on the last 4 to 5 days of gestation induced disseminated intravascular coagulation, occluding glomerular capillaries with fibrin thrombi, typical of the generalized Shwartzman reaction. Thrombi did not form earlier than 9 hours after the injection of colchicine, whereas in the endotoxin-induced generalized Shwartzman reaction, thrombi were already observed 2½ hours after the injection of endotoxin. The colchicine-induced generalized Shwartzman reaction could also be produced in hysterectomized “pregnant” rats. A single injection of colchicine into nonpregnant rats did not induce disseminated intravascular coagulation. If, however, fibrinolysis was inhibited with ε-aminocaproic acid, the colchicine-induced generalized Shwartzman reaction could also be elicited in nonpregnant rats. In this regard fibrinolysis inhibition represents one mechanism by which pregnancy prepares for the generalized Shwartzman reaction.     

Failure of Cobra Venom Factor to Prevent the Generalized Shwartzman Reaction and Loss of Renal Cortical Fibrinolytic Activity

Previous studies have shown that renal cortical fibrinolytic activity is absent in rabbits given one or two injections of endotoxin. Using a fibrin slide technic, we have studied the effect of endotoxin on cortical fibrinolytic activity in rabbits depleted of terminal complement components (C3-C9) by cobra venom factor. The loss of cortical fibrinolytic activity induced by endotoxin is not prevented by pretreatment with cobra venom factor. Additionally, this complement depletion did not prevent development of glomerular fibrin deposition, cortical necrosis or thrombocytopenia in the generalized Shwartzman reaction.     

Prevention of the Generalized Shwartzman Reaction and Endotoxin Lethality by Polymyxin B Localized in Tissues

Pretreatment with multiple doses of polymyxin B and colistimethate was evaluated as to its ability to sequester sufficient antibiotic in tissues to neutralize the effects of endotoxin in three animal models. Animals were challenged with endotoxin 24, 48, or 72 h after the last dose of antibiotic when there was minimal or not detectable drug in serum. Pretreatment with polymyxin B was successful in preventing the generalized Shwartzman reaction in rabbits and reducing endotoxin lethality in mice; however, large doses (20 mg per kg per day for 2 or 4 days) were required. Prolongation by more than 24 h of the interval between the last dose of polymyxin B and endotoxin challenge resulted in reduction or loss of protection. Dogs were unable to tolerate the high polymyxin B dosage which was protective in the mouse and rabbit. Lower, nontoxic doses of polymyxin B in dogs did not prevent endotoxin shock and lethality, even when challenged as soon as 1 h after the last dose. Pretreatment with colistimethate was ineffective in all three animal models.     

Placental Products Induce Suppressor Cells of Graft Versus Host Reaction

ABSTRACT: Cells from mice alloimmunized in the presence of placental extract were coinjected with cells from mice conventionally alloimmunized in the footpad of virgin female recipients. The contralateral footpad received a control twice the dose of cells from alloimmunized mice. Cells from the popliteal lymph nodes were harvested on day 3, and pulsed in vitro for measurement of proliferative capacity with ³H thymidine. The response of lymph nodes was compared (homo- vs contralateral). The cells from mice alloimmunized with placental extract in conjunction with alloantigens displayed a marked suppressive capacity of the local graft versus host (GVH) potential of cells from mice conventionally alloimmunized. It is suggested that this local GVH assay represents a quick, objective assay for suppressor-cell induction by placental products.     

Antibody-coated Sheep Erythrocytes Suppress the Ability of Polyclonal B-Cell Activators to Induce Plaque-forming Cells against Sheep Erythrocytes

The primary immune response to untreated sheep erythrocytes (SRBC) in vitro was suppressed by the addition of antibody-coated SRBC. A mixture of SRBC and antibody-coated SRBC also suppressed the induction of anti-SRBC plaque-forming cells by the polyclonal B cell activators lipopolysaccharide, purified protein derivative of tuberculin, and native dextran. Injection of a mixture of SRBC and antibody-coated SRBC into mice led to an increased response to SRBC. It seems plausible from the in vitro findings that the Fc part of antibodies complexed to an antigen can exert a negative signal on antigen-specific B cells that cannot be overcome by positive signals delivered by polyclonal B cell activators.     

Ureteral blockade sensitizes to the generalized Shwartzman reaction.

Renal cortical necrosis (RCN) has been reported in the normal kidney of patients with a contralateral ureteral occlusion (UO). So far, studies have examined the mechanisms protecting the affected kidney from glomerular thrombosis and cortical necrosis; but to the authors' knowledge, none has ever investigated the potential role of UO on the occurrence of the associated disseminated intravascular coagulation (DIC) episode leading to RCN. Female rats with a ligature of the right or left ureter were given injections, at different times after surgery, of 400 micrograms Salmonella typhosa 0901 endotoxin. Other experimental groups included normal and sham-operation rats and animals with a unilateral nephrectomy or with one kidney rendered ischemic by complete ligature of the renal vessels and of the ureter. All the animals were sacrificed 4 hours after endotoxin, and kidney sections stained with PTAH were examined for the presence of fibrin thrombi. Glomerular thrombosis was never observed in any hydronephrotic kidney, but occurred with a low incidence (16%) in the contralateral organ in the group given endotoxin the second day after UO. The incidence and severity of glomerular capillary thrombosis gradually increased in the normal kidney as the delay between surgery and endotoxin was prolonged; the incidences (P less than 0.01) were 45% and 83%, respectively, after 6 and 10 days. Endotoxin failed totally to initiate the lesion 1 day after UO as well as in normal, sham-operation and unilaterally nephrectomized rats, and in animals with combined UO and ligature of the renal circulation. We conclude that the perfused hydronephrotic kidney liberates a factor(s) that sensitizes to DIC and glomerular thrombosis, typical of the generalized Shwartzman reaction.     

Expression of Fas and Fas Ligand on Mouse Renal Tubular Epithelial Cells in the Generalized Shwartzman Reaction and Its Relationship to Apoptosis

Previously we reported that the consecutive injection of lipopolysaccharide (LPS) into LPS-sensitized mice for the generalized Shwartzman reaction (GSR) appeared to induce the injury of renal tubular epithelial cells via apoptosis. The aim of this study was to characterize the mechanism of renal tubular epithelial cell injury in GSR. The expression of Fas and Fas ligand was immunohistochemically detected on renal tubular epithelial cells from GSR-induced mice, although neither Fas nor Fas ligand was found in cells from untreated control mice or in cells from mice receiving a single injection of LPS. GSR-induced renal tubular epithelial cell injury was produced in neither Fas-negative MRL-lpr/lpr mice nor Fas ligand-negative MRL-gld/gld mice. The administration of anti-gamma interferon antibody together with a preparative injection of LPS prevented the expression of Fas and Fas ligand and the apoptosis of renal tubular epithelial cells. A provocative injection of tumor necrosis factor alpha into LPS-sensitized mice augmented Fas and Fas ligand expression and the apoptosis of renal tubular epithelial cells. The administration of tumor necrosis factor alpha to interleukin-12-sensitized mice resulted in Fas and Fas ligand expression and the apoptosis. Sensitization with interleukin-12 together with anti-gamma interferon antibody did not cause the apoptosis of renal tubular epithelial cells. It was suggested that the Fas/Fas ligand system probably plays a critical role in the development of renal tubular epithelial cell injury through apoptotic cell death.     

Sensitization to the generalized Shwartzman reaction by catechol-O-methyltransferase inhibitors.

The generalized Shwartzman reaction (GSR) was produced by a single injection of endotoxin in male rats pretreated with catechol-o-methyltransferase (COMT) inhibitors (tropolone, pyrogallol). Such a result was not obtained with inhibitors (pargyline, phenelzine, isocarboxazide) of the monoamine oxidase (MAO). The inhibitors of the COMT were found to enhance the action of endotoxin on the coagulation system such as evidenced by the increased consumptions of Hageman factor, fibrinogen, and platelets. Tropolone-treated rabbits did not require exogenous stimulation of alpha-adrenergic receptor sites by norepinephrine to localize thrombi in the glomerular capillaries when Hageman factor was activated by ellagic acid and fibrinolysis inhibited by epsilon-amino-caproic acid. It is concluded that interference with the degradation of circulating catecholamines results in sensitization to the generalized Shwartzman reaction.     

LPS and Poly I:C Induce Chromatin Modifications at a Novel Upstream Region of the IL-23 p19 Promoter

IL-23, a heterodimer of IL-12 p40 and IL-23 p19, is critical for an effective immune response to many infections and has been implicated in several autoimmune diseases, however, little is known about the regulation of IL-23 gene expression in monocytes. We found that poly I:C, LPS, flagellin, and zymogen activated significant IL-23 production in primary human monocytes. Using chromatin immunoprecipitation, we found that a distal upstream region of the IL-23 p19 promoter at -601 to -521 underwent extensive histone modifications in response to stimuli. This distal region of the promoter is not highly conserved between species and has not been previously implicated in the regulation of IL-23 expression. Knockdown of CBP markedly decreased IL-23 p19 responses to poly I:C but had a less dramatic effect on LPS responses, confirming different chromatin responses to these two stimuli. Our data suggest that one of the mechanisms regulating IL-23 expression is the regulation of histone modifications at this distal upstream region of the promoter.     

Inefficiency of Isoprenaline to Induce Drinking in the Goat

Isoprenaline, which acts as a potent dipsogen in water-satiated rats and dogs, did not elicit water intake when infused intravenously at 0.1 or 0.3 μg/kg min^-1 in non-hydrated goats. Even the low dose of the drug caused a marked reduction of parotid salivary flow. The possibility is discussed that reduced salivary secretion might be the particular effect which makes isoprenaline dipsogenic in prandially drinking species. The intravenous infusion of isoprenaline at the high dose level caused an inhibition of the water diuresis of hydrated goats, concomitant with reduced renal Na⁺ excretion and a marked, sustained fall in the arterial blood pressure. Significant amounts of ADH were recovered from the urine secreted during the antidiuresis. This ADH-release was apparently not due to central β-adrenergic stimulation since no inhibition of the water diuresis was observed during intraventricular infusions of isoprenaline. Rather, the ADH-release appears to have been secondary to the isoprenaline-induced fall in arterial blood pressure.     

Immunomodulation of the mother during pregnancy

The concept that the immune responsiveness of the mother is reduced during pregnancy arose from studies which appeared to show that immune response to certain antigens is reduced during pregnancy (1, 2). Various substances claimed to have immunosuppressive or immunomodulating effect include alpha fetoprotein, placental proteins, early pregnancy factor (EPF), human chorionic gonadotropin (HCG), corticosteroids, estrogens, androgens and progesterone (2). To summarise a body of literature, there is very little change in the immune competence of the mother during pregnancy. This makes sense, as generalized immunosuppression would be a risky way to ensure the survival of the fetus. Immune enhancement and subsequent immunomodulation of the mother is likely to be the mechanism operative during pregnancy. It is conceivable that the overall immune response in pregnancy could be the net result of an interplay of various interactions that may be operating to ensure non-rejection of the antigenically alien fetus while at the same time preventing a state of excessive immunosuppression. Such a dynamic homeostatic mechanism appears to be important for the successful completion of pregnancy.