The characterization, origin, and kinetics of skin macrophages during inflammation

In Vitro Models Mimicking Immune Response in the Skin

The skin is the first line of defense of our body, and it is composed of the epidermis and dermis with diverse immune cells. Various in vitro models have been investigated to recapitulate the immunological functions of the skin and to model inflammatory skin diseases. The simplest model is a two-dimensional (2D) co-culture system, which helps understand the direct and indirect cell-to-cell interactions between immune and structural cells; however, it has limitations when observing three-dimensional (3D) interactions or reproducing skin barriers. Conversely, 3D skin constructs can mimic the human skin characteristics in terms of epidermal and dermal structures, barrier functions, cell migration, and cell-to-cell interaction in the 3D space. Recently, as the importance of neuro-immune-cutaneous interactions in the inflammatory response is emerging, 3D skin constructs containing both immune cells and neurons are being developed. A microfluidic culture device called "skin-on-a-chip," which simulates the structures and functions of the human skin with perfusion, was also developed to mimic immune cell migration through the vascular system. This review summarizes the in vitro skin models with immune components, focusing on two highly prevalent chronic inflammatory skin diseases: atopic dermatitis and psoriasis. The development of these models will be valuable in studying the pathophysiology of skin diseases and evaluating the efficacy and toxicity of new drugs.

M2-polarized macrophages mediate wound healing by regulating connective tissue growth factor via AKT, ERK1/2, and STAT3 signaling pathways

BACKGROUND

Timely and sufficient M1 recruitment and M2 polarization are necessary for fibrosis during wound healing. The mechanism of how M2 mediates wound healing is worth exploring. Abnormally up-regulated connective tissue growth factor (CTGF) influences multiple organ fibrosis, including cardiac, pulmonary, hepatic, renal, and cutaneous fibrosis. Previous studies reported that M2 contributed to hepatic and renal fibrosis by secreting CTGF. It is worth discussing if M2 regulates fibrosis through secreting CTGF in wound healing.

METHODS AND RESULTS

We established the murine wound model and inhibited macrophages during proliferation phase with clodronate liposomes in vivo. Macrophages depletion led to down-regulation of wound healing rates, collagen deposition, as well as expression of collagen 1/3 and Ki67. M2 was induced by interleukin-4 (IL-4) and measured by flow cytometry in vitro. Secreted pro-fibrotic and anti-fibrotic factors were tested by enzyme-linked immunosorbent assay (ELISA). M2 was polarized, which producing more CTGF, transforming growth factor-beta1 (TGF-β1), and IL-6, as well as less tumor necrosis factor-α (TNF-α) and IL-10. M2 CTGF gene was blocked using siCTGF. Effects of M2 on fibroblasts activities were detected by cell counting kit 8 (CCK8) and cellular wound healing assay. Expressions of related signaling pathway were assessed by western blotting. Blockade of CTGF in M2 deactivated fibroblasts proliferation and migration by regulating AKT, ERK1/2, and STAT3 pathway. Recombinant CTGF restored these effects.

CONCLUSIONS

Our research, for the first time, indicated that M2 promoted wound healing by secreting CTGF, which further mediating proliferation and migration of fibroblasts via AKT, ERK1/2, and STAT3 pathway.

Cell type specific gene expression profiling reveals a role for complement component C3 in neutrophil responses to tissue damage

Tissue damage induces rapid recruitment of leukocytes and changes in the transcriptional landscape that influence wound healing. However, the cell-type specific transcriptional changes that influence leukocyte function and tissue repair have not been well characterized. Here, we employed translating ribosome affinity purification (TRAP) and RNA sequencing, TRAP-seq, in larval zebrafish to identify genes differentially expressed in neutrophils, macrophages, and epithelial cells in response to wounding. We identified the complement pathway and c3a.1, homologous to the C3 component of human complement, as significantly increased in neutrophils in response to wounds. c3a.1^−/− zebrafish larvae have impaired neutrophil directed migration to tail wounds with an initial lag in recruitment early after wounding. Moreover, c3a.1^−/− zebrafish larvae have impaired recruitment to localized bacterial infections and reduced survival that is, at least in part, neutrophil mediated. Together, our findings support the power of TRAP-seq to identify cell type specific changes in gene expression that influence neutrophil behavior in response to tissue damage.

Modulation in the expression of type 1 (CR1/CD35) and type 3 (CR3/CD11b) complement receptors on leukocytes from patients with Visceral leishmaniasis

Visceral leishmaniasis (VL) is an anthropozoonosis endemic in Brazil. We included 20 patients with confirmed diagnosis of VL and 20 healthy individuals to evaluate the expression levels of complement receptor 1 (CR1)/CD35 and CR3/CD11b on leukocytes in the peripheral blood and determine their correlation with the clinical state of patients. CR1/CD35 expression increased on CD11b⁺CD35⁺granulocytes of patients, while CR1/CD35 and CR3/CD11b expression levels increased on CD14⁺CD11b⁺CD35⁺ monocytes. Among patients, those with severe clinical state had higher expression of CR3/CD11b on CD14⁺monocytes. The count of CD19⁺CD35⁺B lymphocytes reduced in the blood samples from patients. These observed changes may indicate the modulation in CR1/CD35 and CR3/CD11b complement receptor expressionlevels on granulocyte and monocyte populations in response to Leishmania sp.

Tissue regeneration promotion effects of phenanthroimidazole derivatives through pro-inflammatory pathway activation

A chemotherapeutic drug exerts favorable antitumor activity and simultaneously exhibits expectable inhibition on wound healing process. Phenanthroimidazole derivatives possess potent anticancer activity. However, only a few studies focused on the discovery of its potential effects on promoting tissue regeneration. In this study, four novel phenanthroimidazole derivatives were synthesized and characterized, and they exhibited evident inhibition on different tumor cells; compound 3 is the most active one. Moreover, 3 can promote wound healing of zebrafish in a dose-dependent manner. Further study demonstrated that 3 promoted the recruitment of inflammatory cells, formation of angiogenesis, and generation of reactive oxygen species and also influenced the motor behavior of zebrafish. Results indicated that 3 can accelerate the occurrence of pro-inflammation, angiogenesis, oxidative stress, and innervation, which play key roles in the facilitation of wound healing. Therefore, 3 can act as a bifunctional drug in inhibiting tumor and promoting tissue regeneration.

Molecular and Cellular Dynamics in the Skin, the Lymph Nodes, and the Blood of the Immune Response to Intradermal Injection of Modified Vaccinia Ankara Vaccine

New vaccine design approaches would be greatly facilitated by a better understanding of the early systemic changes, and those that occur at the site of injection, responsible for the installation of a durable and oriented protective response. We performed a detailed characterization of very early infection and host response events following the intradermal administration of the modified vaccinia virus Ankara as a live attenuated vaccine model in non-human primates. Integrated analysis of the data obtained from in vivo imaging, histology, flow cytometry, multiplex cytokine, and transcriptomic analysis using tools derived from systems biology, such as co-expression networks, showed a strong early local and systemic inflammatory response that peaked at 24 h, which was then progressively replaced by an adaptive response during the installation of the host response to the vaccine. Granulocytes, macrophages, and monocytoid cells were massively recruited during the local innate response in association with local productions of GM-CSF, IL-1β, MIP1α, MIP1β, and TNFα. We also observed a rapid and transient granulocyte recruitment and the release of IL-6 and IL-1RA, followed by a persistent phase involving inflammatory monocytes. This systemic inflammation was confirmed by molecular signatures, such as upregulations of IL-6 and TNF pathways and acute phase response signaling. Such comprehensive approaches improve our understanding of the spatiotemporal orchestration of vaccine-elicited immune response, in a live-attenuated vaccine model, and thus contribute to rational vaccine development.

Quantitative analysis of blood cells and inflammatory factors in wounds

OBJECTIVE

The aim of this study was to quantify blood cells and inflammatory markers, involved in the healing process, in exudates from wounds in different healing phases, to assess these markers in order to identify the inflammatory phase of the wounds.

METHOD

Patients who presented with postsurgical wounds, which closed by first and second intention, and those who presented with pressure ulcers (PUs), which were closed by second intention, were included in the study.

RESULTS

We examined wounds from 37 patients and collected samples from 52 wounds in the inflammatory phase, 30 in the proliferative phase and 29 in the maturation phase. The number of neutrophils and platelets in the exudate collected from wounds in the inflammatory phase was significantly higher (p<0.001), while the number of lymphocytes, was significantly lower in exudate from wounds in the inflammatory phase (p<0.001). Wound c-reactive protein (CRP) and immunoglobulin G (IgG) levels were higher in the inflammatory group (p<0.001). We found a significantly positive correlation between CRP levels and the percentage of neutrophils and monocytes (r=0.346, p=0.004; r=0.293, p=0.015), and a significantly negative correlation between CRP levels and the percentage of lymphocytes (r=-0.503, p<0.001). A stepwise logistic regression analysis was used to identify an optimal combination of these biomarkers. The optimal biomarker combinations were neutrophils + monocytes + platelets + IgG + CRP, with an area under the curve (AUC) of 0.981 [confidence interval (CI) 95%: 0.955-1.000, p<0.001] for the diagnosis of wounds in the inflammatory phase. The optimal cutpoint yielded 96.9 % sensitivity and 94.6 % specificity. The biomarker combination predicted the inflammatory phase and was superior to individual biomarkers.

CONCLUSION

Our findings suggest that the combination of the markers, percentage of neutrophils and monocytes, platelets, CRP and IgG levels could be useful prognostic indicators of the inflammatory phase.

Matrix metalloproteinase 9 modulates collagen matrices and wound repair

Acute and chronic injuries are characterized by leukocyte infiltration into tissues. Although matrix metalloproteinase 9 (Mmp9) has been implicated in both conditions, its role in wound repair remains unclear. We previously reported a zebrafish chronic inflammation mutant caused by an insertion in the hepatocyte growth factor activator inhibitor gene 1 (hai1; also known as spint1) that is characterized by epithelial extrusions and neutrophil infiltration into the fin. Here, we performed a microarray analysis and found increased inflammatory gene expression in the mutant larvae, including a marked increase in mmp9 expression. Depletion of mmp9 partially rescued the chronic inflammation and epithelial phenotypes, in addition to restoring collagen fiber organization, as detected by second-harmonic generation imaging. Additionally, we found that acute wounding induces epithelial cell mmp9 expression and is associated with a thickening of collagen fibers. Interestingly, depletion of mmp9 impaired this collagen fiber reorganization. Moreover, mmp9 depletion impaired tissue regeneration after tail transection, implicating Mmp9 in acute wound repair. Thus, Mmp9 regulates both acute and chronic tissue damage and plays an essential role in collagen reorganization during wound repair.

Inflammation and wound repair

Wound repair requires the integration of complex cellular networks to restore tissue homeostasis. Defects in wound repair are associated with human disease including pyoderma gangrenosum, a heterogeneous disorder that is characterized by unhealed wounds and chronic inflammation of unclear etiology. Despite its clinical importance, there remain significant gaps in understanding how different types of cells communicate to integrate inflammation and wound repair. Recent progress in wound and regenerative biology has been gained by studying genetically tractable model organisms, like zebrafish, that retain the ability to regenerate. The optical transparency and ease of genetic manipulation make zebrafish an ideal model system to dissect multi-cellular and tissue level interactions during wound repair. The focus of this review is on recent advances in understanding how inflammation and wound repair are orchestrated and integrated to achieve wound resolution and tissue regeneration using zebrafish.

Fibroblast-specific protein 1/S100A4-positive cells prevent carcinoma through collagen production and encapsulation of carcinogens

Stromal restraints to cancer are critical determinants of disease but they remain incompletely understood. Here, we report a novel mechanism for host surveillance against cancer contributed by fibroblast-specific protein 1 (FSP1)+ /S100A4+ fibroblasts. Mechanistic studies of fibrosarcoma formation caused by subcutaneous injection of the carcinogen methylcholanthrene (MCA) had suggested that IFN-γ receptor signaling may restrict MCA diffusion by inducing expression of collagen (foreign body reaction). We tested the hypothesis that this reaction encapsulated MCA and limited carcinogenesis by determining whether its ability to induce fibrosarcomas was impaired in the absence of proliferating fibroblasts. We found that FSP1+ /S100A4+ fibroblasts accumulated around the carcinogen where they produced collagens, encapsulating MCA and protecting epithelial cells from DNA damage. Ablation of these cells at the site of MCA injection by local administration of ganciclovir in FSP-TK transgenic mice altered tumor morphology to an epithelial phenotype, indicating that, in the absence of encapsulating fibroblasts, MCA targeted epithelial cells. Notably, we showed that destruction of the fibrous capsule around the MCA by local injection of collagenase induced rapid tumor development in mice that were otherwise durably tumor free. Our findings demonstrate that the FSP1+ /S100A4+ fibroblasts prevent epithelial malignancy and that collagen encapsulation of carcinogens protects against tumor development. Together, this study provides a novel mechanism for host surveillance against cancer.

Psoriasis

Psoriasis is a common relapsing and remitting immune-mediated inflammatory disease that affects the skin and joints. This review focuses on current immunogenetic concepts, key cellular players, and axes of cytokines that are thought to contribute to disease pathogenesis. We highlight potential therapeutic targets and give an overview of the currently used immune-targeted therapies.

Skin immune sentinels in health and disease

Human skin and its immune cells provide essential protection of the human body from injury and infection. Recent studies reinforce the importance of keratinocytes as sensors of danger through alert systems such as the inflammasome. In addition, newly identified CD103(+) dendritic cells are strategically positioned for cross-presentation of skin-tropic pathogens and accumulating data highlight a key role of tissue-resident rather than circulating T cells in skin homeostasis and pathology. This Review focuses on recent progress in dissecting the functional role of skin immune cells in skin disease.

Vascular endothelial cell distribution and adhesion molecule expression in xanthoma

BACKGROUND

The migration of circulating monocytes into the dermis is considered to be essential for both the initiation and the progression of xanthoma. The contribution of vascular endothelial cells to the migration process is unclear.

METHODS

Twenty cases of xanthelasma and six cases of tuberous xanthoma lesions were analyzed using immunohistochemical staining.

RESULTS

Xanthoma lesions contained up to 25-fold more von Willebrand factor-stained endothelial cells than normal skin. The prevalence of E-selectin-positive endothelial cells increased by up to threefold more in xanthoma lesions than in normal skin. In contrast, the prevalence of intercellular cell adhesion molecule-1 (ICAM-1) decreased up to 3.5-fold more in xanthoma lesions than in normal skin. In xanthoma lesions, almost all ICAM-1-positive endothelial cells co-expressed with E-selectin but many endothelial cells, which only expressed E-selectin, were also found in the lesions and the ratio of macrophages to endothelial cells was higher (10:1) than that in normal skin (5:1).

CONCLUSIONS

Endothelial cells proliferate and express E-selectin rather than ICAM-1 under a microenvironment in which macrophages predominate rather than endothelial cells, thereby promoting macrophage migration into xanthoma lesions.

Enhanced healing of full-thickness burn wounds using di-rhamnolipid

The aim of this study was to investigate the properties of di-rhamnolipid [alpha-L-rhamnopyranosyl-(1-2)-alpha-L-rhamnopyranosyl-3-hydroxydecanoyl-3-hydroxydecanoic acid, also referred to as di-rhamnolipid BAC-3] relating to the process of cutaneous wound healing. Di-rhamnolipid was prepared in a eucerin ointment and applied topically on full-thickness burn wounds in normal Sprague-Dawley rats covering 5% of the total body surface area. The rate of wound closure was measured over the period of 45 days. The collagen content was evaluated microscopically, by performing densitometric analysis on Verhoeff's stained histopathological slides of wound biopsies taken at the end of 45th day of di-rhamnolipid treatment. Di-rhamnolipid toxicity was assessed with the subcutaneous multi-dose study in Swiss-Webster mice. The treatment of full-thickness-burn wounds with topical 0.1% di-rhamnolipid accelerated the closure of wounds on day 21 of the treatment by 32% compared to the control (p < 0.05). On day 35, the wounds closed in all animals-treated with 0.1% di-rhamnolipid ointment while some rats in the control group had open wounds on days 35 and even 45. Histologic comparisons have shown that di-rhamnolipid significantly decreased collagen content in burn wounds (47.5%, p < 0.05) as compared to the vehicle-treated (control) wounds. Di-rhamnolipid was well-tolerated. The results of this study raise the possibility of potential efficacy of di-rhamnolipid in accelerating normal wound healing and perhaps in overcoming defects associated with healing failure in chronic wounds.

Different mechanisms of adhesion molecule expression in human dermal microvascular endothelial cells by xanthoma tissue-mediated and copper-mediated oxidized low density lipoproteins

BACKGROUND

Oxidation of low density lipoprotein (LDL) has been implicated in infiltration of foam cells derived from circulating monocytes. Monocyte adhesion to endothelial cells and migration into dermis are essential steps for infiltration of foam cells.

OBJECTIVE

We investigated the role of adhesion molecules contributing to the process of monocyte adhesion to human dermal microvascular endothelial cells (HDMEC). Special attention was paid to the signal transduction for adhesion molecule expression induced by two distinct types of oxidized LDL.

METHODS

HDMEC were incubated with xanthoma tissue-modified LDL (x-LDL), a model of extravasated LDL oxidized in xanthoma lesions, or Cu(2+)-treated LDL (Cu-LDL), a model of oxidized LDL. Adhesion of U937 cells, a human monocytic leukemia cell line, to HDMEC and expression of endothelial cell adhesion molecules on HDMEC were examined. Signal transduction pathways for the adhesion molecule expression were evaluated by employing specific inhibitors.

RESULTS

x-LDL induced adhesion of U937 cells to HDMEC through vascular cell adhesion molecule-1 (VCAM-1) and E-selectin by activating tyrosine kinase pathway. Cu-LDL up-regulated the adhesion through not only VCAM-1 and E-selectin but also intercellular cell adhesion molecule-1 (ICAM-1) by activating G(i) protein pathway.

CONCLUSION

Extravasated and oxidized LDL in xanthoma lesions contributes to foam cell recruitment by activating tyrosine kinase pathway and inducing adhesion of monocytes to HDMEC through VCAM-1 and E-selectin. Cu-LDL, on the other hand, activates G(i) protein pathway and induces the adhesion through ICAM-1, VCAM-1 and E-selectin.

The future of nutrition and wound healing

Nutrition is vital to all bodily processes. During wound healing, it is essential that nutrients are available as they form the building blocks for tissue repair. Nutrition may therefore affect healing due to an overall deficiency of intake, either due to non-availability or due to inability of the patient to absorb sufficiently to meet their requirements. Alternatively, deficiencies of specific nutrients may also inhibit healing and on the converse some additives, not normally present in large quantity in the diet, may have beneficial effects. This review considers the nutritional factors affecting wound healing and some developments that may alter the future of therapy.

In vitro and in vivo biocompatibility of chitosan-xanthan polyionic complex

A novel hydrogel, CHITOXAN(TM) (CH-X), has potential as a vehicle for controlled drug delivery. The hydrogel is obtained by complexation of two polysaccharides, chitosan and xanthan. In the present work we investigated the biocompatibility of the complex using in vitro and in vivo models. The cytotoxic effects of CH-X microspheres as well as their degradation products at different concentrations were assessed on fibroblasts (fibroblast cell line L-929) using 3-(4,5-dimethylthiazole-2yl)-2,5-triphenyl tetrazolium) (MTT). The test is based on mitochondrial dehydrogenase cell activity as an indicator of cell viability. Interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) cytokines as well as nitric oxide (NO) production by macrophages (macrophage cell line J-774) were examined as indicators of cell activation. In vivo biocompatibility assessment was performed for 1 to 12 weeks. This study was performed using tablets obtained after compression of CH-X particles implanted at the subcutaneous level in male Wistar rats. CH-X biocompatibility and degradation were investigated using histological studies. Light and transmission electron microscopy (TEM) analyses were used to determine the foreign-body reaction and phagocytosis of the implants by macrophages. Fibroblast exposition to CH-X particles and degradation products did not show cytotoxic effects as measured by MTT test. TNF-alpha production was dependent on CH-X particles concentration, whereas IL-1beta production was found to be dose independent. CH-X extract products stimulated TNF-alpha secretion when used at the highest concentration (10 mg/mL), notably after 28 days' degradation time. No effect was observed on IL-1beta production when CH-X extracts were used in comparison to the control. The effects of CH-X particles on NO secretion were similar as on TNF-alpha. Histological studies showed that CH-X tablets broke down into particles which progressively degraded into smaller fragments. A significant fraction of the fragments was ingested by the macrophages after 12 weeks of implantation. Light microscopy studies showed a weak foreign-body reaction as a function of time and the fibrous layer thickness decreased with time of implantation.

Acceleration of full-thickness wound healing in normal rats by the synthetic thrombin peptide, TP508

Thrombin is an essential factor in hemostasis, inflammation, and tissue repair. The synthetic thrombin peptide, TP508, binds to high-affinity thrombin receptors and mimics cellular effects of thrombin at sites of tissue injury. Treatment of full-thickness excisional wounds in normal rats with a single topical application of 0.1 microg TP508 (14 pmol/cm2) reproducibly accelerates wound closure, yielding wounds that on average close 39% more than controls by day 7 (p < 0.001). Wounds treated with 1.0 microg TP508 are 35% and 43% (p < 0.001) smaller than controls on day 7 and 10, respectively. The early rate of closure is approximately 40% greater in TP508-treated than vehicle-treated wounds (20 versus 14 mm2/day) and remains higher through day 7. Breaking strength after closure is slightly greater (15-23%) in wounds treated with TP508 than with saline alone. Histologic comparisons show that TP508 enhances recruitment of inflammatory cells to the wound site within 24 hours post-injury. TP508 treatment also augments revascularization of injured tissue, as evidenced at day 7 by the larger size of functional vessels in the granulation tissue and by the directed development of blood vessels to wounds. These studies raise the possibility that TP508 may be clinically useful in management of open wounds.

Immuno-inflammatory cell dynamics during cutaneous wound healing

The process of wound healing begins with an inflammatory reaction that is principally dependent on cellular immune elements. Although the involvement in wound healing of leucocytes that mediate nonspecific immunity (e.g. neutrophils and macrophages) is well known, the participation of cells which prime the immune reaction, i.e. the lymphocytes, requires further investigation. This study was performed to examine the temporal sequence and kinetics of these cells during cutaneous wound repair. The model selected was a full-thickness skin excisional wound made on the flanks of female Wistar rats. At time points ranging from 3 h to 2 wk wound samples were processed for polyester wax-embedding. Target antigens were identified and monitored quantitatively in sections stained immunohistochemically. Monoclonal antibodies against neutrophils, macrophages, pan T cells and cytotoxic populations of lymphocytes were used. The results showed that these cells are involved in the process of wound healing in a distinctive dynamic pattern. The accumulation of CD3+ T lymphocytes in the wound bed was mainly associated with the phase of granulation tissue formation. Intraepithelial CD3+ T lymphocytes were detected in considerable numbers within the regenerating epidermis. The cytotoxic cell populations (OX8+) were classified morphologically into the cytotoxic/suppressor subset of T cells and NK cells. The OX8+ T cells were shown to have a kinetic pattern similar to CD3+ T lymphocytes but of a lower magnitude. The accumulation of OX8+ NK cells was confined to the early inflammatory phase of repair. It is concluded that CD3+ T lymphocytes as well as OX8+ cytotoxic populations of the immune system are involved in the process of cutaneous wound healing in temporal sequences which suggest that they may be involved in its modulation.

The origin and mode of fibroblast migration and proliferation in granulation tissue

The factors which regulate the properties of granulation tissue remain uncertain. The key cells in granulation tissue are fibroblasts and their role was investigated in rat skin excisional wounds. Full thickness wounds in 28 Hooded Lister rats were made and traced. On days 1 to 7, animals in groups of 4 received colchicine 1 mg/kg subcutaneously, 4 h before being killed. Wound sections were stained to locate and count mitotic cells. All wounds healed with a normal coefficient of contraction. The fibroblasts' mitotic indices (% of mitotic cells) were calculated. Dermis: 0.1% vs. 2.9% (control vs. test P < 0.001, paired t-test); fascia; 0.07% vs. 5.6% (control vs. test P < 0.001); granulation tissue: 9.7%. Granulation tissue fibroblasts come mainly from the adjacent fascia although the dermis may have an initial role. Once they are in the wound replication is extremely rapid. This study highlights for the first time the rapidity of fibroblastic migration and proliferation in excisional wounds, and suggests that future therapeutic interventions to control granulation tissue should consider these kinetics.

Macrophage and microglia-like cells in the avian inner ear

Recent studies suggest that macrophages may influence early stages of the process of hair cell regeneration in lateral line neuromasts; numbers of macrophages were observed to increase prior to increases in hair cell progenitor proliferation, and macrophages have the potential to secrete mitogenic growth factors. We examined whether increases in the number of leukocytes present in the in vivo avian inner ear precede the proliferation of hair cell precursors following aminoglycoside insult. Bromodeoxyuridine (BrdU) immunohistochemistry was used to identify proliferating cells in chicken auditory and vestibular sensory receptor epithelia. LT40, an antibody to the avian homologue of common leukocyte antigen CD45, was used to label leukocytes within the receptor epithelia. Macrophages and, surprisingly, microglia-like cells are present in normal auditory and vestibular sensory epithelia. After hair cell loss caused by treatment with aminoglycosides, numbers of macrophage and microglia-like cells increase in the sensory epithelium. The increase in macrophage and microglia-like cell numbers precedes a significant increase in sensory epithelial cell proliferation. The results suggest that macrophage and microglia-like cells may play a role in releasing early signals for cell cycle progression in damaged inner ear sensory epithelium.

Effect of chemical structure of hydrogels on the adhesion and phenotypic characteristics of human monocytes such as expression of galectins and other carbohydrate-binding sites

The reactivity of diverse immune aspects to the presence of synthetic polymers represents one of the most important aspects of implantable device biocompatibility. In this report, we show the effect of the chemical structure of a synthetic polymer support on monocyte adhesion and selected phenotypic characteristics in vitro as a model for the initial steps of non-self-recognition of an implant. The extent of monocyte adhesion was significantly influenced by the support chemistry. The highest level of monocyte adhesion was observed on a surface copolymer of 2-hydroxyethyl methacrylate with dimethyl aminoethyl methacrylate relative to results of experiments in which poly(2-hydroxyethyl methacrylate) or the copolymer of 2-hydroxyethyl methacrylate with the sodium salt of methacrylic acid was used. Cell adhesion to the polymers tested and to glass was accompanied by enhanced expression of the carbohydrate-binding sites tested for asialoglycoprotein beta-galactosides such as galectins, beta-N-acetylgalactosamine, alpha-mannoside, specific lectin for heparin as well as the lymphokine-macrophage migration inhibitory factor in the monocytes tested. These results suggest the importance of monocyte adhesion to the biomaterial surface for their development into macrophages and further non-self-recognition of the implanted device.

Macrophage recruitment during limb development and wound healing in the embryonic and foetal mouse

Macrophages play a pivotal role in the adult inflammatory response to wounding. They are directly responsible for cellular debridement and, by providing a source of growth factors and cytokines, they recruit other inflammatory and fibroblastic cells and influence cell proliferation and tissue remodelling. In this paper we investigate the role of macrophages in clearing areas of programmed cell death in the developing embryo and also their role in embryonic and foetal wound healing. Immunocytochemistry using the monocyte/macrophage-specific monoclonal antibody, F4/80, reveals a close association between areas of programmed cell death in the remodelling interdigital regions of the mouse footplate and of F4/80-positive cells, suggesting that monocyte-derived macrophages, and not locally recruited fibroblastic cells, as previously believed, are responsible for phagocytosing and clearing areas of interdigital apoptosis. Our studies of wound healing reveal that macrophages are not recruited to, and therefore cannot be playing an active role in the healing of, excisional wounds made in the mouse embryo at any stage up until E14.5. Beyond this transition stage we see a significant recruitment of macrophages within 12 hours of wounding. We find that macrophages can be attracted to wounds in earlier embryos if the wound results in significant cell death such as after burning.

Bone marrow cell response following induction of acute inflammation in different strains of mice

The magnitude of the macrophage inflammatory response differs among inbred mouse strains. Mice of the A/J strain respond poorly to sterile inflammatory stimuli while those of the C57BL/6 strain show a strong response. Inflammatory macrophages found at the site of inflammation are the product of bone marrow (BM) myeloid stem cells. Mice of the A/J strain were found to have half the number of BM nucleated cells per femur than those of the C57BL/6 strain. The lower BM cellularity may be one reason for the poor macrophage inflammatory response observed in A/J mouse strain. Using A x B/B x A recombinant inbred mouse strains, we determined that the number of nucleated cells per femur found in normal mice was not a determining factor of the magnitude of the macrophage inflammatory response. One additional explanation for the poor macrophage inflammatory response in mice of the A/J strain is their deficiency in the C5 component of complement. Using a C5-sufficient A/J.C5 congenic strain, we have previously shown that the presence of C5 on the A/J background improved their inflammatory response. We compared A/J and A/J.C5 mouse strains to determine whether or not C5 had an impact on the BM cell response to inflammatory stimulus. The presence of C5 on the A/J background could contribute to the improvement of the inflammatory response in mice of the A/J.C5 strain by inducing a greater number of nucleated cells to exit the BM compartment early following induction of inflammation.

The magnitude of macrophage inflammatory response does not directly depend on ability of bone marrow cells to respond to interleukin-3 in mice of different strains

The multicolony stimulating factor Interleukin-3 (IL-3) has a role in regulating the proliferation, differentiation, and survival of myeloid stem cells and committed progenitor cells within each of the myeloid lineages. It has been referred to as an emergency factor appearing following triggering of an inflammatory response. The ability of bone marrow (BM) stem cells to respond to a stimulus such as IL-3 in vitro may reflect the in vivo capacity of BM stem cells to generate newly BM-derived macrophages being recruited to an inflammatory site. Both parameters, namely the BM cell response to in vitro IL-3 treatment and the magnitude of the macrophage inflammatory response vary among inbred mouse strains. Mice of the A/J strain are known to have weak macrophage inflammatory response to a phlogistic agent and their BM cells are hyporesponsive to IL-3 exposure. In contrast, mice of the C57BL/6 strain mount a high macrophage inflammatory reaction to a stimulus, and their BM cells strongly proliferate in response to the presence of IL-3. Thus, we examined whether or not the type of BM cell response to IL-3 (i.e., A/J- or C57BL/6-like) determines the magnitude of the macrophage inflammatory response using the A x B/B x A recombinant inbred (RI) mouse strain system. The two traits were found not to cosegregate, suggesting that they are not linked. The continuous strain distribution pattern of the magnitude of the macrophage inflammatory response obtained in mice of the A x B/B x A RI strains implies that this trait is under the control of several genes.

The acute inflammatory response to lipopolysaccharide in CNS parenchyma differs from that in other body tissues

Acute inflammation is important for defence against infection, wound repair and the mediation of auto-immune tissue destruction. Myelomonocytic recruitment in acute inflammation is a stereotyped and non-specific response to tissue insult which begins within 2 h. In this study, lipopolysaccharide was injected into the murine CNS and other body sites of mice to compare the inflammatory responses. Doses of lipopolysaccharide which induced typical myelomonocytic recruitment in skin and the choroid plexus had no effect in CNS parenchyma, apart from the morphological activation of local resident microglia. The CNS parenchymal response proceeded independently of that in the choroid plexus-cerebral ventricles and had three distinct and unique phases. Initially there was minimal neutrophil exudation and a two-day delay before any increase in macrophage-microglial cell number. Next, there was a rapid increase in macrophage-microglial cell numbers during the third day, mainly due to recruitment of blood monocytes. During this phase, leukocyte recruitment was restricted to monocytes which rapidly adopted the arborized microglial phenotype. Monocytes migrated through an intact blood-brain barrier independent of changes in solute permeability. Finally, there was a florid myelomonocytic reaction predominantly in the white matter, one week after intracerebral injection of 2 micrograms lipopolysaccharide. At this time, the leukocyte reaction disrupted the blood-brain barrier, mononuclear phagocytes expressed macrophage morphology and abundant major histocompatibility complex Class II antigen, and T lymphocytes were present. Myelomonocytic entry into the CNS was partially inhibited by prior blockade of the type 3 complement receptor, known to mediate leukocyte adhesion to endothelium elsewhere. The processes which lead to rapid myelomonocytic recruitment in other tissues are absent in CNS parenchyma. Understanding the molecular mechanisms responsible could have considerable significance both for CNS pathophysiology as well as possible anti-inflammatory therapeutic application elsewhere in the body.

The CNS acute inflammatory response to excitotoxic neuronal cell death

Acute inflammation is a stereotyped non-specific response to tissue injury which results in the recruitment of neutrophils and monocytes within minutes. In this study the myelomonocytic and microglial reaction to neuronal destruction following unilateral hippocampal injection of kainic acid neurotoxin was investigated. Despite extensive acute neuronal necrosis and notwithstanding a leaky blood-brain-barrier, there is no neutrophil recruitment and a 2-day delay before any increase in macrophage-microglial cell numbers. Resident microglia are capable of reversible upregulation to an activated morphology and the macrophage-microglial reaction is seen not only at the injection site, but also at distant sites related to the axonal pathways and synaptic terminals of the killed neurons.

The kinetics and morphological characteristics of the macrophage-microglial response to kainic acid-induced neuronal degeneration

Outside the nervous system myelomonocytic cells are known to play an important role in the inflammatory response and tissue repair after injury. In this study we have examined the myelomonocytic response to neuronal destruction following unilateral injection of the excitotoxin kainic acid into the mouse hippocampus. Intrahippocampal injection of kainate induces rapid, synchronous neuronal death. There is no neutrophil recruitment and a delay of at least 48 h before macrophage-microglial cell numbers increase. The microglial reaction in the injected hippocampus consists of altered morphology, a 6-9-fold increase in mononuclear phagocyte cell numbers and enhanced expression of the macrophage-specific plasma membrane antigen, F4/80, assessed immunohistochemically and by Western blotting. Microglia also respond at distant sites related to the projection pathway and terminals of killed pyramidal cells but the reaction varies in cell numbers, kinetics and morphology. The absence of neutrophil recruitment and the delay in an increase in macrophage or microglial cells shows that the CNS differs from other sites in the body with regard to the kinetics and nature of the myelomonocytic cell inflammatory response. The role of mononuclear phagocytes in tissue repair in the CNS remains to be defined.

Macrophage and smooth muscle cell proliferation in atherosclerotic lesions of WHHL and comparably hypercholesterolemic fat-fed rabbits

Lesions of atherosclerosis were analyzed at varying stages of development in Watanabe heritable hyperlipidemic (WHHL) and comparably hypercholesterolemic fat-fed (FF) rabbits for the capacity to incorporate thymidine into proliferating cells within both the intima and the underlying media. An identical inverse relationship between the intimal/medial ratio (which reflects both lesion size and severity) and the labeling index was observed for both the WHHL and FF rabbits. Analysis of the spatial distribution of the labeled cells within each lesion revealed the highest rates of thymidine incorporation in cells situated within the superficial areas and lateral margins of the lesions. Up to 12% of the labeled cells were foam cells, which were predominantly located immediately beneath the endothelium and within the lateral margins. Some labeled macrophages were also observed within the necrotic core of advanced lesions. There were no differences in the labeling indexes at differing sites in the aorta, providing lesions of comparable size were compared. Simultaneous thymidine autoradiography and immunostaining with cell type-specific monoclonal antibodies revealed that approximately 30% of the labeled cells were macrophages and 45% were smooth muscle cells in advanced lesions from both WHHL and FF rabbits.

Reversal of impaired wound healing in irradiated rats by platelet-derived growth factor-BB

This study examined the potential influence of platelet-derived growth factor-BB homodimers (PDGF-BB) on surgical incisions in irradiated animals with depressed wound healing. Rats were irradiated with either 800 rads total body or 2,500 rads surface irradiation. Parallel dorsal skin incisions were made 2 days later, and PDGF-BB was applied topically a single time to one of two incisions. In total body-irradiated rats, bone marrow-derived elements were severely depressed, wound macrophages were virtually eliminated, and PDGF-BB treatment was ineffective. However, in surface-irradiated rats, PDGF-BB treatment recruited macrophages into wounds and partially reversed impaired healing on day 7 (p less than 0.005) and day 12 (p less than 0.001). PDGF-BB-treated wounds were 50 percent stronger than the paired control wounds. The results suggest PDGF requires bone marrow-derived cells, likely wound macrophages, for activity and that it may be useful as a topical agent in postirradiation surgical incisions.

Quantitative immunocytochemical characterization of four murine macrophage-like cell lines

The aim of the present study was to obtain quantitative data on the expression of seven cell-surface antigens by the murine macrophage-like cell lines WEHI-3, P388-D1, J774.1, and PU5-1.8, and to compare these data with those obtained for various mononuclear phagocytes. Binding of monoclonal antibodies F4/80, M1/70, 2.4.G.2., 30.G.12, M3/38, M3/84, and 59AD2.2 to cells from these four cell lines was detected by the biotin-avidin immunoperoxidase staining method and quantified by cytophotometry. The results are expressed as the percentage cells expressing a given antigen and the mean specific integrated absorbance per 0.25 micron2 cell-surface area. The results revealed that the phenotypes of the four macrophage-like cell lines differ markedly. Expression of the cell antigens by the cells of the various cell lines did not follow a normal distribution. Although the cell lines divide continuously and have certain characteristics in common with mature mononuclear phagocytes, none of the macrophage-like cell lines accurately resembles any of the mononuclear phagocyte populations. The strongest correlations for membrane were found between on the one hand WEHI-3 and P388-D1 cells and monoblasts and promonocytes (P greater than 0.011) on the other. P388-D1, J774.1 and PU5-1.8 cells expressed four of the six antigens to the same extent as skin macrophages (P greater than 0.012). With respect to expression of antigens recognized by antibodies 2.4.G.2., 30.G.12, M3/38, and M3/84 PU5-1.8 cells resembled activated peritoneal macrophages (P greater than 0.031). It is concluded that WEHI-3 is the most immature cell line, followed by the P388-D1 cell line, while J774.1, and PU5-1.8 are the most mature cell lines.

Monocyte production during inflammation

The majority of the resident macrophages in non-inflamed organs and serous cavities derive from circulating monocytes, but a small proportion originate from immature mononuclear phagocytes that only divide once in the tissues and originate from the bone marrow as well. During an acute inflammation the number of circulating monocytes increases, and a large proportion of these cells migrate to the site of inflammation and differentiate into exudate macrophages. The monocyte production during an acute inflammation is controlled by humoral factor, FIM, which is a protein that is synthesized and secreted by macrophages at the site of inflammation.