Induction of endotoxin tolerance inhibits alloimmune responses

Modulation of allograft immune responses by Porphyromonas gingivalis lipopolysaccharide administration in a rat model of kidney transplantation

Periodontitis is a chronic inflammatory disease that affects the periodontal tissues. Although it is associated with various systemic diseases, the impact of periodontitis on kidney transplantation (KT) outcomes, particularly allograft rejection, remains unclear. This study investigated the effect of periodontitis on transplant immunity, specifically examining Porphyromonas gingivalis-derived lipopolysaccharide (LPS-PG). In vitro experiments revealed that LPS-PG increased regulatory T cells (Tregs) in Lewis rat spleen cells. In a mixed lymphocyte reaction assay, concentrations of interferon-γ, indicative of alloreactivity, were lower than in controls when LPS-PG was added to the culture and when LPS-PG-administered Lewis rat spleen cells were used as responders. In a rat KT model, LPS-PG administration to recipients promoted mild tubulitis and low serum creatinine and blood urea nitrogen levels 5 days post-KT compared with PBS-administered controls. Furthermore, LPS-PG-administered recipients had an elevated Treg proportion in their peripheral blood and spleen cells, and increased infiltrating Tregs in kidney allografts, compared with controls. The elevated Treg proportion in peripheral blood and spleen cells had a significant negative correlation with serum creatinine, suggesting elevated Tregs modulated allograft rejection. These findings suggest that periodontitis might modulate alloimmune reactivity through LPS-PG and Tregs, offering insights to refine immunosuppressive strategies for KT recipients.

TCR repertoire landscape reveals macrophage-mediated clone deletion in endotoxin tolerance

BACKGROUND

Endotoxin tolerance (ET) is a protective mechanism in the process of sepsis, septic shock, and their sequelae including uncontrolled inflammation. Accumulating evidence has shown that peripheral T cells contribute to the induction of ET. However, what and how T-cell development contributes to ET inductions remain unclear.

METHODS

Mice were intraperitoneally injected with LPS at a concentration of 5 mg/kg to establish an LPS tolerance model and were divided into two groups: a group examined 72 h after LPS injection (72-h group) and a group examined 8 days after LPS injection (8-day group). Injection of PBS was used as a control. We performed high-throughput sequencing to analyze the characteristics and changes of CD4⁺SP TCRβ CDR3 repertoires with respect to V direct to J rearrangement during the ET induction. Moreover, the proportion and proliferation, as well as surface molecules such as CD80 and CD86, of F4/80⁺ macrophages were analyzed using FCM. Furthermore, ACT assay was designed and administered by the tail vein into murine LPS-induced mouse model to evaluate the role of F4/80⁺ macrophages on the development of CD4⁺SP thymocytes in ET condition.

RESULTS

We found that the frequency and characteristics of the TCRβ chain CDR3 changed obviously under condition of ET, indicating the occurrence of TCR rearrangement and thymocyte diversification. Moreover, the absolute numbers of F4/80⁺ macrophages, but not other APCs, were increased in thymic medulla at 72-h group, accompanied by the elevated function-related molecules of F4/80⁺ macrophages. Furthermore, adoptively transferred OVA_332-339 peptide-loaded macrophages into Rag-1^-/- mice induced the clone deletion of OVA-specific CD4⁺SP, thereby ameliorating the pathology in lung tissue in LPS challenge.

CONCLUSIONS

These data reveal that the frequency and characteristics of the TCRβ chain CDR3 undergo dynamic programming under conditions of LPS tolerance. Furthermore, the peripheral macrophages may be a key factor which carry peripheral antigen to thymic medulla and affect the negative selection of T-cell population, thereby contributing to the formation of ET. These results suggest that the clone selection in thymus in ET may confer protection against microbial sepsis.

Redox regulation of the immune response

The immune-inflammatory response is associated with increased nitro-oxidative stress. The aim of this mechanistic review is to examine: (a) the role of redox-sensitive transcription factors and enzymes, ROS/RNS production, and the activity of cellular antioxidants in the activation and performance of macrophages, dendritic cells, neutrophils, T-cells, B-cells, and natural killer cells; (b) the involvement of high-density lipoprotein (HDL), apolipoprotein A1 (ApoA1), paraoxonase-1 (PON1), and oxidized phospholipids in regulating the immune response; and (c) the detrimental effects of hypernitrosylation and chronic nitro-oxidative stress on the immune response. The redox changes during immune-inflammatory responses are orchestrated by the actions of nuclear factor-κB, HIF1α, the mechanistic target of rapamycin, the phosphatidylinositol 3-kinase/protein kinase B signaling pathway, mitogen-activated protein kinases, 5' AMP-activated protein kinase, and peroxisome proliferator-activated receptor. The performance and survival of individual immune cells is under redox control and depends on intracellular and extracellular levels of ROS/RNS. They are heavily influenced by cellular antioxidants including the glutathione and thioredoxin systems, nuclear factor erythroid 2-related factor 2, and the HDL/ApoA1/PON1 complex. Chronic nitro-oxidative stress and hypernitrosylation inhibit the activity of those antioxidant systems, the tricarboxylic acid cycle, mitochondrial functions, and the metabolism of immune cells. In conclusion, redox-associated mechanisms modulate metabolic reprogramming of immune cells, macrophage and T helper cell polarization, phagocytosis, production of pro- versus anti-inflammatory cytokines, immune training and tolerance, chemotaxis, pathogen sensing, antiviral and antibacterial effects, Toll-like receptor activity, and endotoxin tolerance.

Induction of Endotoxin Tolerance Delays Acute Rejection in a Hindlimb Transplantation Model in Rats

BACKGROUND

Acute rejection is seen in 85 percent of composite vascular allogeneic transplants despite long-term immunosuppression. Recently, it was reported that the induction of endotoxin tolerance prolonged heart allograft survival in mice. However, it produced side effects in all the animals secondary to the inflammatory reaction. Galactomannan has shown endotoxin tolerance without this side effect in vitro. The authors hypothesized that galactomannan-induced endotoxin tolerance delays acute rejection in vascular allogeneic transplantation without the side effects produced by lipopolysaccharide.

METHODS

Twenty-four rat hindlimb transplants were divided into four groups according to the preconditioning received: control, lipopolysaccharide (0.16 ml/kg), galactomannan 72 hours before (galactomannan-72) (8 ml/kg), and galactomannan 24 hours before (galactomannan-24) (8 ml/kg). Median acute rejection time, weight loss, and diarrheal episodes were monitored. Blood samples were collected at 0, 7, 21, 30, 45, and 60 days. Plasma cytokines (i.e., tumor necrosis factor alpha, interferon gamma), peripheral chimerism, and lymphocyte percentages were analyzed.

RESULTS

Median allograft survival was 40 days (range, 40 to 44 days) in the control group, 68 days (range, 61 to 71 days) in the lipopolysaccharide group, and 70 days (range, 69 to 73 days) in both galactomannan groups (p = 0.001). Weight loss was higher in the lipopolysaccharide group (p < 0.001), as was the 83.3 percent rate of diarrheal episodes (control, 0 percent, p = 0.015; galactomannan-72, 0 percent, p = 0.015; and galactomannan-24, 16.7 percent, p = 0.02). Preconditioned rats had higher peripheral blood chimerism (lipopolysaccharide, 2.30 ± 0.13 percent; galactomannan-72, 2.63 ±1.46 percent; and galactomannan-24, 2.47 ± 0.19 percent) compared to the control group (2.06 ± 0.36 percent) (lipopolysaccharide, p = 0.04; galactomannan-72, p = 0.002; and galactomannan-24, p = 0.002).

CONCLUSIONS

Induction of endotoxin tolerance delays acute rejection in the rat hindlimb transplantation model. Galactomannan preconditioning has no lipopolysaccharide side effects and was equally effective in delaying acute rejection.

CLINICAL RELEVANCE STATEMENT

The contributions of this experimental work are very incipient. Although the use of galactomannan in clinical practice requires more studies to assess its safety, there is no doubt that immunomodulation may be one of the responses that solve the problem of long-term immunosuppression.

Myalgic encephalomyelitis or chronic fatigue syndrome: how could the illness develop?

A model of the development and progression of chronic fatigue syndrome (myalgic encephalomyelitis), the aetiology of which is currently unknown, is put forward, starting with a consideration of the post-infection role of damage-associated molecular patterns and the development of chronic inflammatory, oxidative and nitrosative stress in genetically predisposed individuals. The consequences are detailed, including the role of increased intestinal permeability and the translocation of commensal antigens into the circulation, and the development of dysautonomia, neuroinflammation, and neurocognitive and neuroimaging abnormalities. Increasing levels of such stress and the switch to immune and metabolic downregulation are detailed next in relation to the advent of hypernitrosylation, impaired mitochondrial performance, immune suppression, cellular hibernation, endotoxin tolerance and sirtuin 1 activation. The role of chronic stress and the development of endotoxin tolerance via indoleamine 2,3-dioxygenase upregulation and the characteristics of neutrophils, monocytes, macrophages and T cells, including regulatory T cells, in endotoxin tolerance are detailed next. Finally, it is shown how the immune and metabolic abnormalities of chronic fatigue syndrome can be explained by endotoxin tolerance, thus completing the model.

Immunotherapy using lipopolysaccharide-stimulated bone marrow-derived dendritic cells to treat experimental autoimmune encephalomyelitis

Lipopolysaccharide (LPS) produced by Gram-negative bacteria induces tolerance and suppresses inflammatory responses in vivo; however, the mechanisms are poorly understood. In this study we show that LPS induces apoptosis of bone marrow-derived dendritic cells (DCs) and modulates phenotypes of DCs. LPS treatment up-regulates expression of tolerance-associated molecules such as CD205 and galectin-1, but down-regulates expression of Gr-1 and B220 on CD11c(+) DCs. Moreover, LPS treatment regulates the numbers of CD11c(+) CD8(+) , CD11c(+) CD11b(low) and CD11c(+) CD11b(hi) DCs, which perform different immune functions in vivo. Our data also demonstrated that intravenous transfer of LPS-treated DCs blocks experimental autoimmune encephalomyelitis (EAE) development and down-regulates expression of retinoic acid-related orphan receptor gamma t (ROR-γt), interleukin (IL)-17A, IL-17F, IL-21, IL-22 and interferon (IFN)-γ in myelin oligodendrocyte glycoprotein (MOG)-primed CD4(+) T cells in the peripheral environment. These results suggest that LPS-induced apoptotic DCs may lead to generation of tolerogenic DCs and suppress the activity of MOG-stimulated effector CD4(+) T cells, thus inhibiting the development of EAE in vivo. Our results imply a potential mechanism of LPS-induced tolerance mediated by DCs and the possible use of LPS-induced apoptotic DCs to treat autoimmune diseases such as multiple sclerosis.

Heat preconditioning ameliorates hepatocyte viability after cold preservation and rewarming, and modulates its immunoactivity

BACKGROUND

Heat preconditioning significantly preserved liver graft function after cold preservation in animal experimental model. The elevation of heat shock protein 70 (HSP70) was claimed to play a critical role in protecting grafts against cold preservation-induced hepatocyte apoptosis. However, little is known about whether HSP70 also plays an immunomodulatory role in cold preserved cells. This study aimed at investigating the relationship between HSP70 protein and the immunoactivity in response to lipopolysaccharide (LPS) stimulation.

METHODS AND RESULTS

A normal rat hepatocyte cell line was preserved with University of Wisconsin (UW) solution, Ringer's lactate solution (RL), and phosphate-buffered saline (PBS) at 4 degrees C. No significant morphological alteration was noted in UW-preserved cells after 24 h through phase-contrast microscopic observation and fluorescent viability stain. Western blotting showed a two-fold increase in the ratio of HSP70/Bax proteins in cells after 24 h of UW preservation. Heat preconditioning significantly enhanced the recovery of lactate dehydrogenase (LDH) activity in both RL- and UW-preserved cells that were stored for a period of 12 h or less. Moreover, heat preconditioning promoted HSP70 and NF-kappaB p50 nuclear translocation and suppressed the LPS-induced nuclear p50 accumulation in cells before UW preservation. Immunofluorescent stain revealed that the LPS-induced p50 protein redistribution to nuclear membrane might contribute to NF-kappaB activation, while heat preconditioning and UW cold preservation completely abrogated the p50 intranuclear redistribution. Thus NF-kappaB p50 might be responsible for the endotoxin tolerance induction.

CONCLUSIONS

These findings strongly suggest that heat preconditioning not only preserves hepatocyte viability after cold preservation and rewarming, but also ameliorates its immunoactivity.

Tolerogenic dendritic cells and the quest for transplant tolerance

In recent years, there has been a shift from the perception of dendritic cells (DCs) solely as inducers of immune reactivity to the view that these cells are crucial regulators of immunity, which includes their ability to induce and maintain tolerance. Advances in our understanding of the phenotypical and functional plasticity of DCs, and in our ability to manipulate their development and maturation in vitro and in vivo, has provided a basis for the therapeutic harnessing of their inherent tolerogenicity. In this Review, we integrate the available information on the role of DCs in the induction of tolerance, with a focus on transplantation.