Changes in bone marrow-derived myeloid cells from thermally injured rats reflect changes in the progenitor cell population

[Current place of cultured epithelial autografts in the management of massive burns and future prospects: Literature review]

Cultured Epithelial Autografts (CEAs), developed at the end of the 1970s from in vitro culture amplification of keratinocytes, have led to a therapeutic revolution in the treatment of major burns. The areas of improvement of the cultures initially involved the manufacturing processes (culture media, support matrices, etc.) and then clinical applications (use of a largely expanded allogeneic or autologous dermal bed). These advances have enabled burn centers (BC) using CEAs to obtain very satisfactory percentages of graft integration and survival of major burns patients. However, since CEAs are not without major drawbacks (fragility, high rate of infection, high cost, unstable scars), these pitfalls have restricted their use worldwide. As of 2014, CEAs produced by Genyzme Tissue Repair are no longer available in Europe, which has considerably reduced an indispensable therapeutic arsenal for severe and extensive burns. To overcome these therapeutic limitations, current research is focusing on techniques combining surgery, tissue engineering and cell therapy. The advent of regenerative medicine, based on the use of stem cells, in particular mesenchymal stem cells (MSC), can contribute to an improvement in the management of these massively burned patients (optimization of the environmental medium, attenuation of the systemic inflammatory response and the immunosuppressive effects of the burn, acceleration of tissue regeneration, etc.). Cell therapy, therefore, offers alternatives to CEAs, which must imperatively retain their place in the therapeutic arsenal, namely an effective emergency coverage technique that can be improved.

Chronic stress induces persistent low-grade inflammation

INTRODUCTION

This study sought to determine if the systemic cytokine profile of rodents subjected to chronic restraint stress leads to persistent low-grade inflammation.

METHODS

Male Sprague-Dawley rats were subjected to restraint stress for a total of seven or fourteen days. Urine norepinephrine (NE), plasma interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), C-reactive protein (CRP) were assessed with ELISA. Liver expression of IL-6 and TNF-α were assessed with real time PCR.

RESULTS

Chronic stress at 7 and 14 days sequentially increased plasma acute phase reactants (NE, IL-6, TNF-α, and CRP), liver IL-6 expression, hematopoietic progenitor cell mobilization, and decreased erythroid progenitor colony growth. Weight gain was reduced by chronic stress compared to each models' naïve counterpart.

CONCLUSIONS

Combining this model with trauma and sepsis models will allow evaluation of the contribution of persistent inflammation in disease progression and outcomes.

Innate Immune Cell Recovery Is Positively Regulated by NLRP12 during Emergency Hematopoiesis

With enhanced concerns of terrorist attacks, dual exposure to radiation and thermal combined injury (RCI) has become a real threat with devastating immunosuppression. NLRP12, a member of the NOD-like receptor family, is expressed in myeloid and bone marrow cells and was implicated as a checkpoint regulator of inflammatory cytokines, as well as an inflammasome activator. We show that NLRP12 has a profound impact on hematopoietic recovery during RCI by serving as a checkpoint of TNF signaling and preventing hematopoietic apoptosis. Using a mouse model of RCI, increased NLRP12 expression was detected in target tissues. Nlrp12^-/- mice exhibited significantly greater mortality, an inability to fight bacterial infection, heightened levels of proinflammatory cytokines, overt granulocyte/monocyte progenitor cell apoptosis, and failure to reconstitute peripheral myeloid populations. Anti-TNF Ab administration improved peripheral immune recovery. These data suggest that NLRP12 is essential for survival after RCI by regulating myelopoiesis and immune reconstitution.

Homologous lactoferrin triggers mobilization of the myelocytic lineage of bone marrow in experimental mice

The effects of lactoferrin (LF), an iron binding protein, on myelopoiesis have been studied extensively in vitro and in vivo in human and murine models over the past three decades. Due to the lack of high-quality homologous LFs, however, the conclusions are still unequivocal. Recently, both human and murine LFs have become available as recombinant products expressed in Chinese hamster ovary (CHO) cell lines showing mammalian type of glycosylation, thus apparently species compatible. In this study, we present the effects of homologous recombinant mouse LF (rmLF) on myelopoiesis in CBA mice. The myelocytic lineage has been assessed by their appearance in circulating blood and bone marrow, and induction of relevant mediators of inflammation. Intravenous injection of rmLF (100 μg/mouse) resulted in a significantly increased number of myelocytic cells in the circulating blood after 24 h. Mouse serum transferrin, used as a control protein, showed no stimulatory effect. The increase in output of neutrophil precursors, neutrophils, and eosinophils was correlated with a twofold increase of leukocyte concentrations. The analysis of the bone marrow sections confirmed increased myelopoiesis. The alterations in the bone marrow cell composition were statistically significant regarding mature neutrophils (10.8% vs. 27.7%), metamyelocytes (11.4% vs. 16.0%), and myelocytes (2.4% vs. 4.0%). The mobilization of the myelocytic cells in the bone marrow and the increased output of these cells into circulation were accompanied by elevated serum concentrations of interleukin-6 at 6 h and haptoglobin at 24 h following administration of rmLF. In conclusion, the homologous LF elicits significant and transient myelopoiesis in experimental mice.

Persistent inflammation and immunosuppression: a common syndrome and new horizon for surgical intensive care

Surgical intensive care unit (ICU) stay of longer than 10 days is often described by the experienced intensivist as a "complicated clinical course" and is frequently attributed to persistent immune dysfunction. "Systemic inflammatory response syndrome" (SIRS) followed by "compensatory anti-inflammatory response syndrome" (CARS) is a conceptual framework to explain the immunologic trajectory that ICU patients with severe sepsis, trauma, or emergency surgery for abdominal infection often traverse, but the causes, mechanisms, and reasons for persistent immune dysfunction remain unexplained. Often involving multiple-organ failure (MOF) and death, improvements in surgical intensive care have altered its incidence, phenotype, and frequency and have increased the number of patients who survive initial sepsis or surgical events and progress to a persistent inflammation, immunosuppression, and catabolism syndrome (PICS). Often observed, but rarely reversible, these patients may survive to transfer to a long-term care facility only to return to the ICU, but rarely to self-sufficiency. We propose that PICS is the dominant pathophysiology and phenotype that has replaced late MOF and prolongs surgical ICU stay, usually with poor outcome. This review details the evolving epidemiology of MOF, the clinical presentation of PICS, and our understanding of how persistent inflammation and immunosuppression define the pathobiology of prolonged intensive care. Therapy for PICS will involve innovative interventions for immune system rebalance and nutritional support to regain physical function and well-being.

Injury-induced GR-1+ macrophage expansion and activation occurs independently of CD4 T-cell influence

Burn injury initiates an enhanced inflammatory condition referred to as the systemic inflammatory response syndrome or the two-hit response phenotype. Prior reports indicated that macrophages respond to injury and demonstrate a heightened reactivity to Toll-like receptor stimulation. Since we and others observed a significant increase in splenic GR-1 F4/80 CD11b macrophages in burn-injured mice, we wished to test if these macrophages might be the primary macrophage subset that shows heightened LPS reactivity. We report here that burn injury promoted higher level TNF-α expression in GR-1, but not GR-1 macrophages, after LPS activation both in vivo and ex vivo. We next tested whether CD4 T cells, which are known to suppress injury-induced inflammatory responses, might control the activation and expansion of GR-1 macrophages. Interestingly, we found that GR-1 macrophage expansion and LPS-induced TNF-α expression were not significantly different between wild-type and CD4 T cell-deficient CD4(-/-) mice. However, further investigations showed that LPS-induced TNF-α production was significantly influenced by CD4 T cells. Taken together, these data indicate that GR-1 F4/80 CD11b macrophages represent the primary macrophage subset that expands in response to burn injury and that CD4 T cells do not influence the GR-1 macrophage expansion process, but do suppress LPS-induced TNF-α production. These data suggest that modulating GR-1 macrophage activation as well as CD4 T cell responses after severe injury may help control the development of systemic inflammatory response syndrome and the two-hit response phenotype.

Mobilization of endothelial progenitor cells into the circulation in burned patients

BACKGROUND

Bone marrow-derived endothelial progenitor cells (EPCs) have been detected in the peripheral blood of patients following thermal injury. EPCs migrate to sites of active neovascularization in response to mediators released after trauma, contributing to wound healing. The aim was to characterize levels and kinetics of EPCs in burned patients, then relate these to key mobilizing factors, vascular endothelial growth factor (VEGF) and the chemokine (C-X-C motif) ligand 12 (CXCL 12), and compare them with those in healthy subjects.

METHODS

The study included 19 adult patients with superficial or full-thickness burns and 50 blood donor volunteer controls. EPCs, identified by cell surface markers CD45(dim/-), CD133+, CD144+ and VEGF receptor 2, were quantified by four-colour flow cytometry. Plasma VEGF and CXCL12 were measured using enzyme-linked immunosorbent assay.

RESULTS

Burned patients showed a rapid rise in EPC levels within 24 h, a ninefold increase compared with controls, returning to basal levels by 72 h. Body surface area burned correlated strongly with the degree of mobilization. EPC levels correlated significantly with rises in plasma VEGF and CXCL12.

CONCLUSION

Thermal injury induced a rapid rise in EPCs that was proportional to the extent of the burn and significantly correlated with levels of angiogenic cytokines. Such cytokines may be used to stimulate EPCs as a future therapeutic target in burned patients.

A Survey of Current Rehabilitation Trends for Burn Injuries to the Head and Neck

Burn injuries to the face and neck present a unique challenge to the burn team and must be treated with considerable care and vigilance by the rehabilitation team to prevent potential contractures that may occur. Standard guidelines for treatment of the head and neck have not been established. This article presents the results of a comprehensive survey that examined the similarities and differences in the rehabilitation techniques used in various burn centers for the treatment of these injuries. The results obtained from the survey responses demonstrate several similarities in treatment throughout the continuum of care, revealing the potential for the development of a uniform rehabilitation protocol for the treatment of burn injuries to the face and neck.

Stimulation of hematopoiesis by the Fms-like tyrosine kinase 3 ligand restores bacterial induction of Th1 cytokines in thermally injured mice

Patients with large burn injuries are susceptible to opportunistic infections due to impaired functions of multiple effector cells of innate immunity and acquired immunity, including macrophages, dendritic cells (DC), natural killer (NK) cells, and T cells. The ability of a host to produce Th1 cytokines, such as gamma interferon (IFN-gamma) and interleukin-12 (IL-12), upon infectious challenge is also impaired after burn injury. Stimulation of hematopoiesis, to regenerate new immune cells, may be an effective strategy for improving resistance to infections after severe burn trauma. Fms-like tyrosine kinase 3 ligand (Flt3L) is a hematopoietic cytokine that stimulates the expansion and differentiation of NK cells and DC. Using a mouse model, we tested the hypothesis that Flt3L treatments after burn injury stimulate the production of functional effector cells of innate immunity and restore appropriate Th1 cytokine responses to Pseudomonas aeruginosa, a common source of pneumonia and wound infections in burn victims. Flt3L increased splenic cellularity in sham (uninjured) and burned mice and increased the numbers of NK cells (DX5(+)) and DC (CD11c(+)). In response to P. aeruginosa, significant increases in the serum IFN-gamma levels and the numbers of splenic IFN-gamma-producing DC, NK cells, and T cells were observed in Flt3L-treated burned mice compared to the values obtained for untreated burned mice. The splenic levels of IL-12 and IL-15 mRNAs and the IL-12 and IL-15 receptors were also increased. In addition, Flt3L treatment restored the ability of splenic cultures prepared from burned mice to produce IFN-gamma and IL-12 after in vitro challenge with P. aeruginosa. Flt3L may have potential for restoring NK cell and DC functions and improving immunity after burn injury.