Human/severe combined immunodeficient mouse chimeras. An experimental in vivo model system to study the regulation of human endothelial cell-leukocyte adhesion molecules

Blank Spots in the Map of Human Skin: The Challenge for Xenotransplantation

Most of the knowledge about human skin homeostasis, development, wound healing, and diseases has been accumulated from human skin biopsy analysis by transferring from animal models and using different culture systems. Human-to-mouse xenografting is one of the fundamental approaches that allows the skin to be studied in vivo and evaluate the ongoing physiological processes in real time. Humanized animals permit the actual techniques for tracing cell fate, clonal analysis, genetic modifications, and drug discovery that could never be employed in humans. This review recapitulates the novel facts about mouse skin self-renewing, regeneration, and pathology, raises issues regarding the gaps in our understanding of the same options in human skin, and postulates the challenges for human skin xenografting.

Implantation of engineered human microvasculature to study human infectious diseases in mouse models

Animal models for studying human pathogens are crucially lacking. We describe the implantation in mice of engineered human mature microvasculature consisting of endothelial and perivascular cells embedded in collagen hydrogel that allows investigation of pathogen interactions with the endothelium, including in vivo functional studies. Using Neisseria meningitidis as a paradigm of human-restricted infection, we demonstrated the strength and opportunities associated with the use of this approach.

Mouse Models for Human Skin Transplantation: A Systematic Review

Immunodeficient mouse models with human skin xenografts have been developed in the past decades to study different conditions of the skin. Features such as follow-up period and size of the graft are of different relevance depending on the purpose of an investigation. The aim of this study is to analyze the different mouse models grafted with human skin. A systematic review of the literature was performed in line with the PRISMA statement using MEDLINE/PubMed databases from January 1970 to June 2020. Articles describing human skin grafted onto mice were included. Animal models other than mice, skin substitutes, bioengineered skin, postmortem or fetal skin, and duplicated studies were excluded. The mouse strain, origin of human skin, graft dimensions, follow-up of the skin graft, and goals of the study were analyzed. Ninety-one models were included in the final review. Five different applications were found: physiology of the skin (25 models, mean human skin graft size 1.43 cm2 and follow-up 72.92 days), immunology and graft rejection (17 models, mean human skin graft size 1.34 cm2 and follow-up 86 days), carcinogenesis (9 models, mean human skin graft size 1.98 cm2 and follow-up 253 days), skin diseases (25 models, mean human skin graft size 1.55 cm2 and follow-up 86.48 days), and would healing/scars (15 models, mean human skin graft size 2.54 cm2 and follow-up 129 days). The follow-up period was longer in carcinogenesis models (253 ± 233.73 days), and the skin graft size was bigger in wound healing applications (2.54 ± 3.08 cm2). Depending on the research application, different models are suggested. Careful consideration regarding graft size, follow-up, immunosuppression, and costs should be analyzed and compared before choosing any of these mouse models. To our knowledge, this is the first systematic review of mouse models with human skin transplantation.

Colonization of dermal arterioles by Neisseria meningitidis provides a safe haven from neutrophils

The human pathogen Neisseria meningitidis can cause meningitis and fatal systemic disease. The bacteria colonize blood vessels and rapidly cause vascular damage, despite a neutrophil-rich inflammatory infiltrate. Here, we use a humanized mouse model to show that vascular colonization leads to the recruitment of neutrophils, which partially reduce bacterial burden and vascular damage. This partial effect is due to the ability of bacteria to colonize capillaries, venules and arterioles, as observed in human samples. In venules, potent neutrophil recruitment allows efficient bacterial phagocytosis. In contrast, in infected capillaries and arterioles, adhesion molecules such as E-Selectin are not expressed on the endothelium, and intravascular neutrophil recruitment is minimal. Our results indicate that the colonization of capillaries and arterioles by N. meningitidis creates an intravascular niche that precludes the action of neutrophils, resulting in immune escape and progression of the infection.

Experimental Evidence of Bacterial Colonization of Human Coronary Microvasculature and Myocardial Tissue during Meningococcemia

Meningococcal septic shock is associated with profound vasoplegia, early and severe myocardial dysfunction, and extended skin necrosis responsible for a specific clinical entity designated purpura fulminans (PF). PF represents 90% of fatal meningococcal infections. One characteristic of meningococcal PF is the myocardial dysfunction that occurs in the early phase of sepsis. Furthermore, hemodynamic studies have shown that the prognosis of meningococcal sepsis is directly related to the degree of impairment of cardiac contractility during the initial phase of the disease. To gain insight into a potential interaction of Neisseria meningitidis with the myocardial microvasculature, we modified a previously described humanized mouse model by grafting human myocardial tissue to SCID mice. We then infected the grafted mice with N. meningitides Using the humanized SCID mouse model, we demonstrated that N. meningitidis targets the human myocardial tissue vasculature, leading to the formation of blood thrombi, infectious vasculitis, and vascular leakage. These results suggest a novel mechanism of myocardial injury in the course of severe N. meningitidis sepsis that is likely to participate in primary myocardial dysfunction.

Invasive meningococcal disease: a disease of the endothelial cells

Neisseria meningitidis is an extracellular pathogen, which, once in the bloodstream, has the ability to form microcolonies on the apical surface of endothelia. Pathogen interaction with microvessels is mediated by bacterial type IV pili and two receptors on endothelial cells: CD147 and the β2-adrenoceptor. CD147 facilitates the adhesion of diplococci to the endothelium, whereas the β2-adrenoceptor facilitates cell signaling, and crossing of the blood-brain barrier. In this review, we discuss how meningococcal interaction with endothelial cells is responsible for the specific clinical features of invasive meningococcal infection such as meningitis, and a peripheral thrombotic/vascular leakage syndrome possibly leading to purpura fulminans.

Vascular endothelial-targeted therapy combined with cytotoxic chemotherapy induces inflammatory intratumoral infiltrates and inhibits tumor relapses after surgery

Surgery is the most effective therapy for cancer in the United States, but disease still recurs in more than 40% of patients within 5 years after resection. Chemotherapy is given postoperatively to prevent relapses; however, this approach has had marginal success. After surgery, recurrent tumors depend on rapid neovascular proliferation to deliver nutrients and oxygen. Phosphatidylserine (PS) is exposed on the vascular endothelial cells in the tumor microenvironment but is notably absent on blood vessels in normal tissues. Thus, PS is an attractive target for cancer therapy after surgery. Syngeneic mice bearing TC1 lung cancer tumors were treated with mch1N11 (a novel mouse chimeric monoclonal antibody that targets PS), cisplatin (cis), or combination after surgery. Tumor relapses and disease progression were decreased 90% by combination therapy compared with a 50% response rate for cis alone (P = .02). Mice receiving postoperative mch1N11 had no wound-related complications or added systemic toxicity in comparison to control animals. Mechanistic studies demonstrated that the effects of mch1N11 were associated with a dense infiltration of inflammatory cells, particularly granulocytes. This strategy was independent of the adaptive immune system. Together, these data suggest that vascular-targeted strategies directed against exposed PS may be a powerful adjunct to postoperative chemotherapy in preventing relapses after cancer surgery.

Target cells in graft-versus-host disease: implications for cancer therapy

Acute graft-versus-host disease (GVHD) conceptually may be divided into three evolutionary stages: allostimulation, effector cell homing to specific tissues, and cellular targeting and injury. Surprisingly, little is known regarding the targeting stage of GVHD. Recently, we have learned that epithelial target cell injury is mediated by specific subpopulations of effector T cells that may be identified based on Vbeta family expansion during allostimulation. Antibody probes specific for these Vbeta families have permitted precise identification of effector cell homing patterns. In squamous epithelium, allospecific T cells selectively home to basal cell layer subpopulations that express cytokeratin 15 (CK15) and that undergo target cell injury via apoptosis. Interestingly, these target cells coincide with basal layer subpopulations that have properties of epithelial stem cells and that normally express an apoptosis-resistant genomic profile. Accordingly, epithelial cell injury in GVHD appears to involve selective targeting of stem-cell subpopulations via conversion from an anti-apoptotic to a pro-apoptotic phenotype. Understanding of the mechanism(s) of this conversion could facilitate development of translationally relevant approaches to shielding target cells from injury in GVHD. Moreover, determination of how putative apoptosis-resistant stem cells may be rendered vulnerable to immune-mediated targeting has implications potentially relevant to more directed immunotherapeutic approaches focused at elimination of neoplastic (cancer) stem cells.

Possible early prediction of preterm birth by determination of novel proinflammatory factors in midtrimester amniotic fluid

Interferon-gamma-inducible T cell-alpha chemoattractant (ITAC) is a chemokine, directing activated T lymphocytes toward sites of inflammation. ADAM-8 (A disintegrin and metalloprotease-8) is a glycoprotein expressed in cells promoting inflammation. Elastase, a protease targeting at the degradation of intra- or extracellular proteins, is inhibited by secretory leukocyte proteinase inhibitor (SLPI), which protects against microbial invasion. Adhesion molecules (soluble intercellular adhesion molecule--sICAM-1 and soluble vascular cell adhesion molecule-sVCAM--1) serve as markers of inflammation or tissue damage. We hypothesized that elevated midtrimester amniotic fluid concentrations of above substances, and decreased levels of SLPI could possibly be useful predictors of asymptomatic intra-amniotic inflammation and/or infection, eventually resulting in preterm labor and delivery. The study involved 312 women undergoing midtrimester amniocentesis. Thirteen cases, progressing to preterm delivery (<37 weeks), were matched with 21 controls (delivering >37 weeks) for age, parity, and gestational age at amniocentesis. Amniotic fluid levels of the above substances were measured by enzyme-linked immunosorbent assay (ELISA). Only amniotic fluid ITAC and ADAM-8 levels were significantly higher (P=0.005 and P < 0.02, respectively) in women delivering at <37 weeks than at >37 weeks. SLPI concentrations significantly increased in women going into labor without ruptured membranes irrespective of pre- or term delivery (P < 0.007, P < 0.001, respectively) and correlated with elastase (r=0.508, P < 0.002). In conclusion, elevated midtrimester amniotic fluid levels of ITAC and ADAM-8 could predict occult infections/inflammations, possibly resulting in preterm birth.

Investigation of midtrimester amniotic fluid factors as potential predictors of term and preterm deliveries

Aims. Our aim is to investigate, in 13 cases (delivering preterm) and 21 matched (for age, parity, and gestational age) controls (delivering at term), whether midtrimester amniotic fluid concentrations of elastase, secretory leukocyte proteinase inhibitor (SLPI), soluble intercellular adhesion molecule-1, and soluble vascular cell adhesion molecule predict asymptomatic intra-amniotic inflammation/infection and preterm labor. Results. Concentrations of all substances were not statistically different among mothers, delivering preterm or at term. SLPI concentrations significantly increased in women, going into labor without ruptured membranes, irrespective of pre- or term delivery (P < .007, P < .001, resp) and correlated with elastase (r = 0.508, P < .002). Conclusions. Midtrimester amniotic fluid SLPI concentrations significantly decrease when membrane rupture precedes pre- or full-term labor. However, none of the investigated substances predict preterm delivery.

c7E3 Fab inhibits human tumor angiogenesis in a SCID mouse human skin xenograft model

The alphavbeta3 integrin plays an important role in tumor growth and angiogenesis. Inhibition of this receptor by intact bivalent antibodies has been shown to inhibit angiogenesis and tumor growth. In this study we tested the chimeric Fab of 7E3 (c7E3 Fab), an antibody reactive with human platelet GPIIb/IIIa and alphavbeta3 to determine if it would inhibit in vivo angiogenesis and tumor growth in a SCID mouse/human skin tumor growth and angiogenesis model. c7E3 Fab inhibited human tumor angiogenesis and tumor growth. These data suggest monovalent antibody fragments devoid of antibody effector function can have efficacy in preclinical models of angiogenesis.

CCR5 usage by CCL5 induces a selective leukocyte recruitment in human skin xenografts in vivo

CCR5 is one of the major inflammatory chemokine receptors with potential therapeutical applications in humans. However, the redundancy of chemokines and their receptors, and the species specificity of chemokine receptor antagonists pose challenges to understanding of the role they play in pharmacological situations. To address this question, we used a humanized severe combined immunodeficient mouse model grafted with human skin and autologous leukocytes, and evaluated the effect of a blocking antibody against human CCR5, on CCL5-induced cutaneous leukocyte recruitment in vivo. At baseline, CCL5 induced a significant recruitment of T cells mainly of the memory phenotype, of monocytes/macrophages, eosinophils, and IFN-gamma(+) but not IL-4(+) and IL-5(+) cells. In vivo, anti-CCR5 antibody was able to almost completely inhibit the recruitment of monocytes/macrophages and T-helper (Th)1-type cells to inhibit partially the attraction of memory T cells, but had no effect on eosinophil infiltration, although all these cell types express other CCL5 binding chemokine receptors than CCR5. These results indicate that the in vivo environment regulates target cell specificity of CCL5 leading to differential cell recruitment, suggesting that antagonizing CCR5 receptor may be of therapeutic value in diseases such as acquired immuno deficiency syndrome, where CCL5/CCR5, monocytes, and Th1-type cells play a predominant role.

Differential regulation of a fibroblast growth factor-binding protein during skin carcinogenesis and wound healing

The initiation of premalignant lesions is associated with subtle cellular and gene expression changes. Here we describe a severe combined immunodeficiency mouse xenograft model with human adult skin and compare chemical carcinogenesis and wound healing. We focus on a secreted binding protein for fibroblast growth factors (FGF-BP) that enhances the activity of locally stored FGFs and is expressed at high levels in human epithelial cancers. Carcinogen treatment of murine skin induced papilloma within 6 weeks, whereas the human skin grafts displayed no obvious macroscopic alterations. Microscopic studies of the human skin, however, showed p53-positive keratinocytes in the epidermis, increased angiogenesis in the dermis of the treated skin, enhanced proliferation of keratinocytes in the basal layer, and an increase of FGF-BP protein and mRNA expression. In contrast, after surgical wounding of human skin grafts or of mouse skin, FGF-BP expression was upregulated within a few hours and returned to control levels after 2 days with wound closure. Enhanced motility of cultured keratinocytes and dermal fibroblasts by FGF-BP supports a role in wound healing. We conclude that adult human skin xenografts can be used to identify early molecular events during malignant transformation as well as transient changes during wound healing.

Techniques: species' finest blend--humanized mouse models in inflammatory skin disease research

Differences between humans and mice often hamper the transfer of promising results from the bench to the clinic. For ethical reasons, research that involves patients is limited, and so there is an urgent need for models that mimic the human situation as closely as possible. In recent years, there has been considerable progress in generating humanized mouse models, and their application to drug discovery has proved fruitful. So, how can mice be humanized, and how can humanized mice be employed in immunology research and drug discovery? In this article, we answer these questions, focusing on T-cell-mediated skin diseases as an example.

Breaking the species barrier: use of SCID mouse-human chimeras for the study of human infectious diseases

Mouse-human chimeras have become a novel way to model the interactions between microbial pathogens and human cells, tissues or organs. Diseases studied with human xenografts in severe combined immunodeficient (SCID) mice include Pseudomonas aeruginosa infection in cystic fibrosis, group A streptococci and impetigo, bacillary and amoebic dysentery, and AIDS. In many cases, disease in the human xenograft appears to accurately reproduce the disease in humans, providing a powerful model for identifying virulence factors, host responses to infection and the effects of specific interventions on disease. In this review, we summarize recent studies that have used mouse-human chimeras to understand the pathophysiology of specific bacterial and protozoan infections.

Science review: Cell membrane expression (connectivity) regulates neutrophil delivery, function and clearance

As the principal cellular component of the inflammatory host defense and contributor to host injury after severe physiologic insult, the neutrophil is inherently coupled to patient outcome in both health and disease. Extensive research has focused on the mechanisms that regulate neutrophil delivery, function, and clearance from the inflammatory microenvironment. The neutrophil cell membrane mediates the interaction of the neutrophil with the extracellular environment; it expresses a complex array of adhesion molecules and receptors for various ligands, including mediators, cytokines, immunoglobulins, and membrane molecules on other cells. This article presents a review and analysis of the evidence that the neutrophil membrane plays a central role in regulating neutrophil delivery (production, rolling, adhesion, diapedesis, and chemotaxis), function (priming and activation, microbicidal activity, and neutrophil-mediated host injury), and clearance (apoptosis and necrosis). In addition, we review how change in neutrophil membrane expression is synonymous with change in neutrophil function in vivo. Employing a complementary analysis of the neutrophil as a complex system, neutrophil membrane expression may be regarded as a measure of neutrophil connectivity, with altered patterns of connectivity representing functionally distinct neutrophil states. Thus, not only does the neutrophil membrane mediate the processes that characterize the neutrophil lifecycle, but characterization of neutrophil membrane expression represents a technology with which to evaluate neutrophil function.

T cells of atopic asthmatics preferentially infiltrate into human bronchial xenografts in SCID mice

T cells play an important role in the pathogenesis of bronchial asthma. However, it is not completely known how circulating lymphocytes infiltrate into the airways of asthmatic patients. Because SCID mice are unable to reject xenogenic transplants, many xenotransplant models using various human tissues have been developed. Therefore, to examine the interaction between bronchi and T lymphocytes of asthma, it may be possible to use the human bronchial xenograft and PBMC xenograft in SCID mice. We transplanted human bronchi into the subcutaneum of SCID mice and i.p. injected PBMCs that were obtained from patients with atopic asthma, atopic dermatitis and rheumatoid arthritis, and normal subjects (asthmatic, dermatitis, rheumatic, and normal huPBMC-SCID mice). There was no difference in the percentage of CD3-, CD4-, CD8-, CD25-, CD45RO-, CD103-, and cutaneous lymphocyte Ag-positive cells in PBMCs among the patients with asthma, dermatitis, rheumatoid arthritis, and normal subjects, and CD3-positive cells in peripheral blood of asthmatic, dermatitis, rheumatic, and normal huPBMC-SCID mice. The number of CD3-, CD4-, and CD8-positive cells in the xenografts of asthmatic huPBMC-SCID mice was higher than those of dermatitis, rheumatic, and normal huPBMC-SCID mice. IL-4 mRNA and IL-5 mRNA were significantly higher in the xenografts of asthmatic huPBMC-SCID mice than those in the xenografts of normal huPBMC-SCID mice, but there were no significant differences in the expressions of IL-2 mRNA or IFN-gamma mRNA between them. These findings suggest that T cells, especially Th2-type T cells, of asthmatics preferentially infiltrate into the human bronchi.

Stroma formation and angiogenesis by overexpression of growth factors, cytokines, and proteolytic enzymes in human skin grafted to SCID mice

Reorganization of skin during wound healing, inflammatory disorders, or cancer growth is the result of expression changes of multiple genes associated with tissue morphogenesis. We wanted to identify proteins involved in skin remodeling and select those that may be targeted for agonistic or antagonist therapeutic approaches in various disease processes. Full-thickness human skin was grafted to severe combined immunodeficient mice and injected intradermally with 38 different adenoviral vectors inserted with 37 different genes coding for growth factors, cytokines, proteolytic enzymes and their inhibitors, adhesion receptors, oncogenes, and tumor suppressor genes. Responses were characterized for infiltration of inflammatory cells, vascular density, matrix formation, fibroblast-like cell proliferation, and epidermal hyperplasia. Of the 17 growth factor vectors, 16 induced histological changes in human skin. Members of the VEGF and angiopoietin families induced neovascularization. PDGFs and TGF-betas stimulated connective tissue formation, and the chemokines IL-8 and MCP-1 attracted inflammatory neutrophils and monocytes, respectively. The serine protease uPA induced a vascular response similar to that of VEGF. Vectors with adhesion receptors, oncogenes and tumor suppressor genes had, with few exceptions, little effects on skin architecture. The overall results suggest that adenoviral vectors can effectively remodel the architecture of human skin for studies in morphogenesis, inflammatory skin disorders, wound healing, and cancer development.

CCR3-blocking antibody inhibits allergen-induced eosinophil recruitment in human skin xenografts from allergic patients

Eosinophil, basophil, and T helper 2 (TH2) cell recruitment into tissues is a characteristic feature of allergic diseases. These cells have in common the expression of the chemokine receptor CCR3, which may represent a specific pathway for their accumulation in vivo. Although animal models of allergic reactions are available, findings cannot always be extrapolated to man. To overcome these limitations, we have developed a humanized mouse model of allergic cutaneous reaction using severe combined immunodeficiency mice engrafted with skin and autologous peripheral blood mononuclear cells from allergic donors. Intradermal injection of the relevant allergen into human skin xenografts from allergic individuals induced a significant recruitment of human CD4(+) T cells, basophils, and TH2-type cytokine mRNA-expressing cells, as well as murine eosinophils. Human skin xenografts, atopic status, and autologous peripheral blood mononuclear cell reconstitution were all mandatory to induce the allergic reaction. Next, we addressed the role of CCR3 in the endogenous mechanisms involved in the inflammatory cell recruitment in this experimental model of allergic cutaneous reaction. In vivo administration of an anti-human CCR3-blocking antibody selectively reduced accumulation of eosinophils but not that of CD4(+) cells, basophils, or cells expressing mRNA for TH2-type cytokines. These findings establish a new in vivo model of humanized allergic reaction and suggest that eosinophil migration is mediated mainly through CCR3. Finally, these results suggest that this model might be useful to test human-specific antiallergic modulators.

Biologic effects of bacterial superantigens in a xenogeneic transplantation model for psoriasis

Both clinical as well as experimental data support the concept of psoriasis being a T-cell-mediated immune disease possibly triggered by bacterial superantigens. Further analysis of its pathogenesis was facilitated by the generation of a xenogeneic transplantation model in which skin from psoriatic patients is grafted onto SCID mice lacking functional B and T cells. Applying this model it was demonstrated that psoriasis can be triggered by bacterial superantigens; this process depends on the presence of immunocytes. Mutated variants of the respective superantigens exhibiting no measurable affinity to HLA class II molecules can function as competitive inhibitors in vivo.

Persistence of human vascular endothelium in experimental human prostate cancer bone tumors

Using the SCID-human model, we recently found that human circulating prostate cancer cells formed tumors in human bone but not mouse bone (Nemeth et al. Cancer Res 1999; 59: 1987-93). It is possible that this tissue preference was mediated by interaction between human tumor cells and human endothelial cells within the implanted bone tissue. We sought to determine the relative amounts of human and mouse vasculature within human bone implants and resulting prostate cancer bone tumors in the SCID-human model. Paraffin sections of plain bone implants or PC3 or LNCaP human bone tumors were double stained for factor VIII (all vessels) and human CD31 (human vessels) followed by fluorescent secondary reagents. At 4 weeks post implantation (when cancer cells are typically introduced), the vasculature within human bone fragments remained primarily human (84.5%), and this pattern persisted to at least 10 weeks (91.6% human). Injection of PC3 cells into the bone resulted in an increase in mouse-derived vessels, however the majority (58%) of the vessels remained human even after the formation of large bone tumors. LNCaP bone tumors were highly angiogenic, and there was a sharp decline in the proportion of vessels which were antigenically human (36.8%), suggesting recruitment of mouse endothelial cells during the angiogenic process. Nonetheless, the persistence of human vasculature suggests the SCID-human model can be used to study the interaction between bone-seeking tumor cells, such as prostate cancer, and human bone endothelium in vivo, and to test potential therapeutic strategies which may depend on the presence of human vessels.

Amebic infection in the human colon induces cyclooxygenase-2

We sought to determine if infection of the colon with Entamoeba histolytica induces the expression of cyclooxygenase-2 and, if it does, to determine the contribution of prostaglandins produced through cyclooxygenase-2 to the host response to amebic infection. Human fetal intestinal xenografts were implanted subcutaneously in mice with severe combined immunodeficiency and allowed to grow; the xenografts were then infected with E. histolytica trophozoites. Infection with E. histolytica resulted in the expression of cyclooxygenase-2 in epithelial cells and lamina propria macrophages. Infection with E. histolytica increased prostaglandin E(2) (PGE2) levels 10-fold in the xenografts and resulted in neutrophil infiltration, as manifested by an 18-fold increase in myeloperoxidase activity. Amebic infection also induced an 18-fold increase in interleukin 8 (IL-8) production and a >100-fold increase in epithelial permeability. Treatment of the host mouse with indomethacin, an inhibitor of cyclooxygenase-1 and cyclooxygenase-2, or with NS-398, a selective inhibitor of cyclooxygenase-2, resulted in (i) decreased PGE(2) levels, (ii) a decrease in neutrophil infiltration, (iii) a decrease in IL-8 production, and (iv) a decrease in the enhanced epithelial permeability seen with amebic infection. These results indicate that amebic infection in the colon induces the expression of cyclooxygenase-2 in epithelial cells and macrophages. Moreover, prostaglandins produced through cyclooxygenase-2 participate in the mediation of the neutrophil response to infection and enhance epithelial permeability.

Chemokine-induced cutaneous inflammatory cell infiltration in a model of Hu-PBMC-SCID mice grafted with human skin

Recently, certain chemokines and chemokine receptors have been preferentially associated with the selective recruitment in vitro of type 1 T cells, such as IP-10 and its receptor CXCR3, or type 2 T cells such as monocyte-derived chemokine (MDC) and eotaxin and their receptors CCR4 and CCR3. Very few models have provided confirmation of these findings in vivo. Taking advantage of the humanized SCID mouse model grafted with autologous human skin, the ability of the chemokines IP-10, MDC, eotaxin, and RANTES to stimulate cell recruitment was investigated. Intradermal IP-10 injection resulted in an influx of CD4+ T lymphocytes but also surprisingly in the recruitment of dendritic cells. MDC recruited mainly CD8+ T lymphocytes, and had little effect on eosinophils. As predicted, eotaxin was a potent inducer of eosinophil and basophil migration, also recruiting CD4+ T cells. RANTES, a ubiquitous chemokine associated with both type 1 and type 2 profiles, was able to recruit all cell types. CXCR3-positive cells were preferentially recruited by IP-10, whereas CCR3- and CCR4-positive cells were predominantly found after injection of eotaxin and MDC. Thus, in a human environment in vivo, some chemokines have the ability to recruit cells expressing chemokine receptors preferentially expressed on type 1 or type 2 cells. Further investigations revealed that MDC and eotaxin induced the recruitment of type 2, but not type 1, cytokine-producing cells. RANTES, on the other hand, induced the migration of both type 1 and type 2 cytokine-secreting cells, whereas IP-10 did not induce the recruitment of either subtype. These studies provide detailed information on the properties of MDC, eotaxin, IP-10, and RANTES as chemotactic molecules in skin in vivo. The use of the humanized SCID mouse model grafted with human skin is validated as a useful model for the evaluation of chemokine function in the inflammatory reaction, and suggests that therapeutic targeting of certain chemokines might be of interest in diseases associated preferentially with a type 1 or type 2 profile.

Intercellular adhesion molecule-1 suppression in skin by topical delivery of anti-sense oligonucleotides

We topically applied 20 nucleotide phosphorothioate intercellular adhesion molecule-1 anti-sense oligodeoxynucleotide in a cream formulation. It effectively inhibited tumor necrosis factor-alpha-induced expression of intercellular adhesion molecule-1 in human skin transplanted on severe compromised immunodeficient mice. The effects were concentration dependent, sequence specific, and resulted from reduction of intercellular adhesion molecule-1 mRNA levels in the skin. Intravenous administration of the drug did not show pharmacologic effects, probably due to insufficient drug concentrations in skin. Topical delivery, however, produced a rapid and a significantly higher accumulation of oligodeoxynucleotide in the epidermis and dermis. The results strongly suggest that topically applied anti-sense oligonucleotides can be delivered to target sites in the skin and may be of considerable value in the treatment of psoriasis and other inflammatory skin disorders.

Diminished interleukin 6 (IL-6) production during scarless human fetal wound repair

Fetal wound healing is characterized by minimal inflammation and scarless repair. IL-6 stimulates inflammation in postnatal wound healing. We hypothesized that fetal skin has a diminished IL-6 response and that exogenous IL-6 will result in scar formation. Human adult or fetal skin was placed subcutaneously in SCID mice and incisionally wounded. Wounds were excised after 4, 12, 24 or 72 h for IL-6 mRNA quantification by RT-PCR. In other grafts, 5 microgram of IL-6 was injected at wounding and then harvested at 7 days for analysis of scar formation. IL-6 production was examined in primary cultures of human fetal or adult dermal fibroblasts incubated for 8 h with 0, 0.1, 1 or 10 ng/ml of PDGF-BB. IL-6 mRNA was detected 4 h after wounding in fetal and adult wounds, but by 12 h there was no IL-6 mRNA in the fetal wounds. Adult wounds had IL-6 mRNA persisting to 72 h. IL-6 administration to fetal wounds resulted in scar formation. Fetal fibroblasts produced less IL-6 protein and mRNA at all points examined (P<0.01 vs adult). Diminished production of inflammatory cytokines such as IL-6 may be responsible for the lack of inflammation seen during fetal wound healing. Diminished inflammation may provide a permissive environment for scarless wound healing.

The pathogenesis of Shigella flexneri infection: lessons from in vitro and in vivo studies

Shigella flexneri is a Gram-negative facultatively intracellular pathogen responsible for bacillary dysentery in humans. More than one million deaths occur yearly due to infections with Shigella spp. and the victims are mostly children of the developing world. The pathogenesis of Shigella centres on the ability of this organism to invade the colonic epithelium where it induces severe mucosal inflammation. Much information that we have gained concerning the pathogenesis of Shigella has been derived from the study of in vitro models of infection. Using these techniques, a number of the molecular mechanisms by which Shigella invades epithelial cells and macrophages have been identified. In vivo models of shigellosis have been hampered since humans are the only natural hosts of Shigella. However, experimental infection of macaques as well as the murine lung and rabbit ligated ileal loop models have been important in defining some of the immune and inflammatory components of the disease. In particular, the murine lung model has shed light on the development of systemic and local immune protection against Shigella infection. It would be naive to believe that any one model of Shigella infection could adequately represent the complexity of the disease in humans, and more sophisticated in vivo models are now necessary. These models require the use of human cells and tissue, but at present such models remain in the developmental stage. Ultimately, however, it is with such studies that novel treatments and vaccine candidates for the treatment and prevention of shigellosis will be designed.

Intercellular adhesion molecule-1 (ICAM-1) expression and cell signaling cascades

The collective interaction between cells is, in part, mediated by different families of adhesion molecules. Intercellular adhesion molecules (ICAMs) are structurally related members of the immunoglobulin supergene family and are ligands for the beta2 integrin molecules present on leukocytes. Of the five ICAMs identified, ICAM-1 is the most extensively studied. Although ICAM-1 is expressed constitutively at low levels on endothelial cells and on some lymphocytes and monocytes, its expression can be significantly increased in the presence of cytokines (TNFalpha, IL-1, IFNgamma) and reactive oxygen species. Depending upon cell type, ICAM-1 participates in trafficking of inflammatory cells, in cell:cell interactions during antigen presentation, in microbial pathogenesis, and in signal transduction through outside-in signaling events. Again, depending upon cell type examined, ICAM-1 engagement has been documented to activate specific kinases through phosphorylation, resulting in transcription factor activation and increased cytokine production, increased cell membrane protein expression, reactive oxygen species production, and cell proliferation.

Human bronchial intraepithelial T lymphocytes as a distinct T-cell subset: their long-term survival in SCID-Hu chimeras

Intestinal intraepithelial T lymphocytes (i-IELs) show features different from those of conventional T cells and play specific roles in the mucosal immunity. To investigate whether human bronchial intraepithelial T lymphocytes (IELs) are a distinct entity, we examined T cells in human bronchial xenografts transplanted on mice with severe combined immune deficiency (SCID). We transplanted human bronchi subcutaneously into mice with SCID, resected the xenografts after various incubation periods (7-174 d), and examined them for CD3(+), CD4(+), CD8(+), and CD45(+) cells by immunohistochemistry. The number of CD3(+) cells in the lamina propria decreased significantly in the first month (from 308.7 +/- 60.2 to 70.9 +/- 49. 4/mm(2); P < 0.05), and xenografts more than 5 mo of age had scant T cells in the lamina propria (5.2 +/- 2.0/mm(2)). However, there was no significant difference between the number of CD3(+) IELs in freshly isolated bronchi and in xenografts maintained for more than 5 mo. In freshly isolated bronchi, the number of CD4(+) IELs was significantly lower than that of CD8(+) cells (2.35 +/- 0.62 versus 4.56 +/- 1.32/mm basement membrane; P < 0.01). After transplantation, the mean CD4-to-CD8 ratio of all xenografts was significantly higher than that of freshly isolated bronchi (5.2 +/- 0.9 versus 0.6 +/- 0.2; P < 0.005). The IELs were positive for CD45, which is specific for human leukocytes, and they were eliminated by irradiation before the transplantation. Almost all IELs (99.5%) in the xenografts expressed alphabeta T-cell receptor, and 35.8% of IELs expressed alpha(e)beta7 integrin. Bronchial epithelial cells in the xenografts expressed interleukin (IL)-7, stem cell factor, intercellular adhesion molecule (ICAM)-1, and human leukocyte antigen-DR (HLA-DR). We conclude that in the SCID-Hu chimera model, human bronchial IELs survive for more than 5 mo, unlike the T cells in the lamina propria, and we suggest that human bronchial IELs may be stimulated by bronchial epithelial cells expressing IL-7, stem cell factor, ICAM-1, and HLA-DR.

Adenoviral-mediated gene transfer in wound healing: acute inflammatory response in human skin in the SCID mouse model

The use of an adenoviral vector as a means of therapeutic protein delivery for the treatment of impaired wound healing is a potentially effective application of current gene transfer techniques. This study was designed to investigate the ability of adenovirus to mediate gene transfer in healing wounds in human skin in vivo. The human skin/severe combined immunodeficient mouse chimera model was used to study both the response of human tissue to adenoviral infection and the nature of the acute inflammatory response. The effects of adenoviral infection and transgene expression on the rate and quality of human wound healing were then investigated. Cell- and species-specific monoclonal antibodies were used to characterize the resident skin cell types participating in wound repair, the inflammatory response, and the proliferative potential of adenovirus-treated compared to control skin. Our studies show that, following wounding, normal skin architecture is restored in the presence of adenoviral infection equivalent to noninfected controls. Despite an increased acute inflammatory response after adenovirus injection, no difference in the healing capabilities of wounded skin was observed, suggesting that adenovirus-mediated gene transfer for growth factor-mediated acceleration of wound healing may be feasible.

Antibodies against the first Ig-like domain of human platelet endothelial cell adhesion molecule-1 (PECAM-1) that inhibit PECAM-1-dependent homophilic adhesion block in vivo neutrophil recruitment

Platelet endothelial cell adhesion molecule (PECAM-1), a member of the Ig superfamily, is found on endothelial cells and neutrophils and has been shown to be involved in the migration of leukocytes across the endothelium. Adhesion is mediated, at least in part, through binding interactions involving its first N-terminal Ig-like domain, but it is still unclear which sequences in this domain are required for in vivo function. Therefore, to identify functionally important regions of the first Ig-like domain of PECAM-1 that are required for the participation of PECAM-1 in in vivo neutrophil recruitment, a panel of mAbs against this region of PECAM-1 was generated and characterized in in vitro adhesion assays and in an in vivo model of cutaneous inflammation. It was observed that mAbs that disrupted PECAM-1-dependent homophilic adhesion in an L cell aggregation assay also blocked TNF-alpha-induced intradermal accumulation of neutrophils in a transmigration model using human skin transplanted onto SCID mice. Localization of the epitopes of these Abs indicated that these function-blocking Abs mapped to specific regions on either face of domain 1. This suggests that these regions of the first Ig-like domain may contain or be close to binding sites involved in PECAM-1-dependent homophilic adhesion, and thus may represent potential targets for the development of antiinflammatory reagents.

Basic fibroblast growth factor induces a transformed phenotype in normal human melanocytes

Basic fibroblast growth factor (bFGF or FGF-2) is produced by nearly all melanomas in vitro and in vivo but not by normal melanocytes, which require exogenous bFGF for growth. In this study, we transduced normal human melanocytes to overexpress two forms of bFGF: (bFGF-Long and bFGF-Short) using replication-deficient adenovirus 5 vectors. bFGF-Long induced the 17.8, 22.5, 23.1 and 24.2 kDa forms of bFGF, whereas bFGF-Short induced only the 17.8 kDa mature form. Growth of cultured melanocytes transduced with either vector was similar to that of nevus and melanoma cells and was independent of exogenous bFGF and of insulin/insulin-like growth factor 1, and cyclic AMP enhancers, requiring only phorbol ester as an exogenous mitogen. Like primary melanoma cells, transduced normal melanocytes grew anchorage independently in soft agar. When injected into the dermis of human skin grafted to mice, bFGF-transduced melanocytes proliferated for at least 20 days, whereas cells from control cultures showed poor survival and no proliferation. These results demonstrate that bFGF upregulation is a critical component in melanoma progression.

Accessible xenografts of human synovium in the subcutaneous tissues of the ears of SCID mice

This work was undertaken to examine whether human synovium could be engrafted into subcutaneous pouches in the ears of severe combined immunodeficient (SCID) mice. Synovium was transplanted into surgically constructed ear pouches. The grafts were examined by histological and immunohistochemical methods after varying periods after engraftment, or after percutaneous injection of TNF-alpha. Normal, osteo-arthritic and rheumatoid synovium was engrafted successfully in subcutaneous ear pouches. The general morphology and cellular compositions of xenografts were retained including human endothelial cells. In rheumatoid xenografts, macrophages, fibroblasts and lymphocytes persisted for at least 4 weeks. Vascular expression of intercellular adhesion molecule-1 (ICAM-1) was maintained but expression of vascular adhesion molecule-1 (VCAM-1), E-selectin and MHC class II diminished with time. Percutaneous injection of TNF-alpha induced up-regulation of VCAM-1. Human synovium can be engrafted into subcutaneous ear pouches in SCID mice. The xenografts are accessible and respond to injection of a pro-inflammatory cytokine.

Dermal Endothelial Cells and Keratinocytes Produce IL-7 In Vivo After Human Schistosoma mansoni Percutaneous Infection

The parasite Schistosoma mansoni infects its definitive mammalian host through an obligatory cutaneous penetration. In this work, we studied early immune response following migration of larvae through human skin, the first immunocompetent organ encountered by the parasite. For this purpose we used an experimental model of severe combined immunodeficient mice engrafted with human skin and injected with autologous PBL. Six days after percutaneous infection, we observed an infiltration of lymphocytes within the human skin, predominantly composed of CD4+ T cells. Moreover, among the cytokines potentially present in the infected skin, immunohistochemistry analysis revealed an in vivo expression of IL-7 in the epidermal layers and strikingly at the level of vascular endothelium. Using an in vitro coculture system, we showed that the S. mansoni larvae directly trigger IL-7 production by human dermal microvascular endothelial cells but not by keratinocytes. Finally, measurements of IL-7 concentrations in plasma of 187 S. mansoni-infected individuals showed that the youngest, which are also the most infected, displayed the highest IL-7 levels. Together, these findings describe dermal endothelial cells as a novel source of IL-7, a cytokine particularly important in schistosomiasis.

Primary Th1 Cell Immunization Against HIVgp160 in SCID-hu Mice Coengrafted with Peripheral Blood Lymphocytes and Skin

SCID-hu mouse models are of interest in the pathologic investigation of HIV infection, but obtaining a T cell response in SCID-hu-PBL mice is still controversial. We have developed a SCID model by engrafting human skin and autologous PBLs from HIV-seronegative individuals. The study describes the ability of this human-mouse chimera to generate in vivo a primary T lymphocyte response against HIV Ag. The injection of human autologous PBLs was performed 4 to 5 wk after the skin engraftment. Two weeks after injection of PBLs, chimeric mice were immunized with recombinant canary pox virus expressing HIV-1 LAIgp160 (vCP-LAIgp160) and supplemented or not with rIL-2. Intradermal vCP-LAIgp160 injection induced an intradermal perivascular human lymphocytic infiltrate and an epidermic network of CD1a+, CD80+, and CD86+ cells. We derived CD4+ T cell lines (STLs) from the human skin graft of immunized mice, showing that STLs mediated an MHC class II-restricted cytolytic activity directed against HIV-LAIgp160 Ags. Cytokine gene expression in both human skin cells and in STLs showed a predominance of IL-2, IFN-γ, and IL-12 transcripts. Finally, the T cell repertoire analysis using the immunoscope technique showed a very limited CDR3 length polymorphism in the skin infiltrating lymphocytes suggesting an Ag-specific repertoire. The ability to induce a primary Th1 cell response in vivo affords a useful preclinical model for testing vaccine strategies.

Tuberculin-induced delayed-type hypersensitivity reaction in a model of hu-PBMC-SCID mice grafted with autologous skin

We have developed an animal model to study human delayed-type hypersensitivity reactions. Previous studies in humans have shown after tuberculin injection the presence of a mononuclear cell infiltration, with almost no eosinophils, associated with a preferential Th-1-type cytokine profile. Human skin graft obtained from tuberculin-reactive donors was grafted onto the back of severe combined immunodeficient mice. After healing, mice were reconstituted intraperitoneally with peripheral mononuclear cells. Tuberculin and diluent were injected intradermally, and skin biopsies were performed 72 hours later. Skin grafts were divided into two parts, one for immunohistochemistry and one for in situ hybridization studies. Immunohistochemistry was performed on cryostat sections using the alkaline phosphatase anti-alkaline phosphatase technique. In the tuberculin-injected sites as compared with the diluent-injected sites, there were significant increases in the number of CD45+ pan leukocytes and CD4+, CD8+, CD45RO+ T cells but not in CD68+ monocytes/macrophages and EG2 or MBP+ eosinophils. The activation markers CD25 and HLA-DR were up-regulated in the tuberculin-injected sites. In situ hybridization was performed using 35S-labeled riboprobes for interleukin (IL)-2, interferon (IFN)-gamma, IL-4, and IL-5. After tuberculin injection, a preferential Th-1-type cytokine profile was observed with significant increases in the numbers of IL-2 and IFN-gamma mRNA-expressing cells. These results are similar to those reported after tuberculin-induced delayed-type hypersensitivity in humans, suggesting that this model might be useful to study cutaneous inflammatory reaction.

Diminished interleukin-8 (IL-8) production in the fetal wound healing response

BACKGROUND

Fetal skin wound healing results in scarless repair with minimal cellular inflammatory response. Interleukin-8 (IL-8) stimulates inflammation in postnatal wound healing but little is known about its role in fetal wounds. We hypothesized that fetal tissues have diminished IL-8 during wound repair and in response to platelet-derived growth factor (PDGF), a growth factor central to wound healing.

MATERIALS AND METHODS

To examine the IL-8 response of fibroblasts to PDGF, cultures of human fetal (17-18 weeks) and adult dermal fibroblasts were incubated 8 h with PDGF (0, 0.1, 1, or 10 ng/mL) and supernatants and cells were collected for IL-8 ELISA and IL-8 RT-PCR. To evaluate the IL-8 response to wounding, human adult and fetal skin was placed subcutaneously in the SCID mouse, wounded, and the wound cleft excised after 4, 12, 24, or 72 h for IL-8 RT-PCR.

RESULTS

Fetal fibroblasts produced less IL-8 protein at baseline (50 +/- 6 pg/mL versus 450 +/- 115 pg/mL, P < 0.001) and in response to all concentrations of PDGF examined (P < 0.001). IL-8 mRNA was detected in unstimulated adult fibroblasts but not in fetal fibroblasts. Much less IL-8 mRNA was detected in stimulated fetal fibroblasts than in adult fibroblasts. IL-8 mRNA was detected 4 h after wounding in fetal and adult wounds. By 12 h no IL-8 mRNA was detected in fetal wounds, whereas adult wounds had IL-8 mRNA persisting to 72 h.

CONCLUSIONS

Diminished inflammatory cytokine response by fetal tissues may be responsible for the lack of cellular recruitment and inflammation seen in fetal wound healing and may contribute to scarless wound repair.

UVB induces atypical melanocytic lesions and melanoma in human skin

A direct causal relationship between ultraviolet (UV) light in the B range and melanoma development has not been demonstrated in humans; this study aims to establish causality. A total of 158 RAG-1 mice, grafted with human newborn foreskin, were separated into four groups and observed for a median of 10 months: 1) no treatment, 2) a single treatment with 7,12-dimethyl(a)benzanthracene (DMBA), 3) UVB irradiation at 500 J/m2 alone, three times weekly, and 4) a combination of DMBA and UVB. Twenty-three percent of 40 normal human skin grafts treated with UVB only and 38% of 48 grafts treated with the combination of DMBA and UVB developed solar lentigines within 5 to 10 months of treatment. Melanocytic hyperplasia was found in 73% of all UVB-treated xenografts. Histological melanocytic changes resembling lentigo and lentigo maligna were seen in several skin grafts treated with both DMBA and UVB. In one graft of an animal treated with a combination of DMBA and UVB, a human malignant melanoma, nodular type, developed. This experimental system demonstrates that chronic UVB irradiation with or without an initiating carcinogen can induce human melanocytic lesions, including melanoma.

Characterization of unmyelinated axons uniting epidermal and dermal immune cells in primate and murine skin

The present study was undertaken to characterize further the structure and function of cutaneous nerves which we have previously shown to associate with skin immune cells (Hosoi et al., Nature 1993: 363:159). Ultrastructurally, axons were prominent within the superficial dermis and epidermis in neonatal murine skin, but they were inconspicuous in adult murine and primate skin. Immunohistochemical and immunoultrastuctural evaluation of normal adult human and simian skin for neural cell adhesion molecule (N-CAM), however, defined a plexus of axons surrounding superficial dermal mast cells and extending as delicate, vertical branches into the overlying epidermal layer. Antibodies to neuropeptides substance P, calcitonin gene-related peptide, and to nerve cell-specific clathrin (LCb subunit) also reacted with this neural plexus. Double labeling disclosed intimate associations of N-CAM-positive axons with dermal chymase-positive mast cells as well as with epidermal CD1a-positive Langerhans' cells by confocal scanning laser microscopy. Functionally, capsaicin applied to forearm skin revealed by 6 h discharge of mast cell chymase and induction of E-selectin in adjacent microvascular endothelium, events consistent with release of substance P from axons and subsequent stimulation of cytokine-mediated mast cell-endothelial interaction. Identical application of capsaicin to human skin xenografted to immunodeficient mice, and thus experimentally lacking in unmyelinated axons, failed to show similar findings. These results provide additional support to the concept that an elaborate network of cutaneous axons may play a functional role in regulation of skin inflammation and immunity.

Transformed and nontransformed human T lymphocytes migrate to skin in a chimeric human skin/SCID mouse model

To study human T cell migration to human skin in vivo, we grafted severe combined immunodeficient mice with 500-microm thick human skin. Two weeks after grafting, epidermal and dermal structures in the grafts were of human origin. When we intraperitoneally injected grafted mice with clones of the human HUT-78 T cell line derived from a patient with cutaneous T cell lymphoma and Sézary syndrome, we detected in the grafts the rare Vbeta23-Jbeta1.2 T cell receptor transcripts characteristic for the HUT-78 clones. These signals were found 2-6 d after cell injection in about 40% of the grafted and HUT-78 cell injected mice but not in grafts from mice that received no exogenous T cells. In contrast to HUT-78 cells, which only accumulate in low number, grafts topically challenged with nickel sufate in vaseline from mice that were injected with autologous nickel-reactive T cell lines led to massive accumulation of T cells within 3 d. Only scattered T cells accumulated in the skin when grafted mice received vaseline plus T cells, nickel sulfate alone, T cells alone, or nickel sulfate plus an allogeneic nickel-nonreactive T cell clone. When the T cell lines were labeled with the fluorochrome PKH-26 before cell injection, spots of fluorescent label in the size and shape of cells were found in the grafts challenged with nickel. Together, these results clearly demonstrate that human T cells can migrate to human skin in this chimeric human/mouse model.

UVB induction of epithelial tumors in human skin using a RAG-1 mouse xenograft model

To examine the effects of chronic ultraviolet light on human epidermal cells, we grafted white human skin onto recombinase activating gene-1 knockout mice. We found previously that the maximal concentration of ultraviolet B radiation (290-320 nm) tolerated by human skin xenografts was 500 J per m2 when given three times weekly. One hundred and fifty-eight grafted mice were randomized and observed for a median of 10 mo in four groups: (i) no treatment; (ii) one treatment with the chemical carcinogen dimethyl-(a)benzanthracene; (iii) ultraviolet B three times weekly; and (iv) a combination of dimethyl-(a)benzanthracene and ultraviolet B. Approximately half of the skin specimens treated with ultraviolet B developed superficial milia and epidermal cysts. Grafts contained up to seven milia lesions between 4 and 8 mo after initiation of treatment, whereas the number of larger epidermal cysts was rarely more than two. Milia and cysts developed in the skin regardless of pigmentation or tanning. Actinic keratoses arose in 9% of grafts treated with ultraviolet B alone and in 19% of grafts treated with the combination of dimethyl-(a)benzanthracene and ultraviolet B. Invasive squamous cell carcinomas developed in 10% of grafts after combined dimethyl-(a)benzanthracene and ultraviolet B treatment and lesions were restricted to skin grafts that did not tan. These findings demonstrate that (i) development of ultraviolet-induced lesions can be experimentally accelerated in human skin, (ii) xenografted recombinase activating gene-1 deficient mice are superior to severe combined immunodeficiency disease mice for chronic ultraviolet B studies, and (iii) benign cystic tumors and squamous cell carcinomas are caused by ultraviolet B.

Xenogeneic (bovine) peripheral blood leukocytes engrafted into severe combined immunodeficient mice retain primary immune function

The immune responsiveness of xenogeneic PBL engrafted into SCID mice was investigated using the bovine PBL-reconstituted SCID mouse model system (PBL-SCID-bo). Bovine PBL-reconstitution and B-cell activity were monitored by bovine serum Ig production. Bovine T-cell function was demonstrated by an antigen-specific immune response to bovine transplantation antigens provided by bovine skin allografts. Bovine allograft rejection was clearly evident in > 65% PBL-SCID-bo that received a bovine PBL inoculum either 30 days after bovine skin grafting, or 7-52 days before bovine skin grafting. Bovine allograft rejection was confirmed via histological examination and was characterized primarily by a band of infiltrating bovine lymphocytes at the periphery of the graft and tissue necrosis. A secondary immune response could be elicited if bovine cells in the PBL inoculum were presensitized to Ag from the bovine skin allograft donor. This study is the first to show that bovine cells engrafted in SCID mice after i.p. injection of bovine PBL retain some aspects of immune competency. These results confirm the value of the xenogeneic PBL-reconstituted SCID mouse model in the study of primary immunity.

Expression and function of endothelial cell alpha v integrin receptors in wound-induced human angiogenesis in human skin/SCID mice chimeras

Accumulating evidence indicates that endothelial cell integrins that bind to the matrix proteins associated with inflammation and wound healing are involved in the process of angiogenesis. The integrins containing the alpha v subunit appear to be particularly important. To study the involvement of these receptors in human angiogenesis, a model of wound-associated human angiogenesis was established in human skin transplanted onto severe combined immunodeficient (SCID) mice. Using this model, we studied the expression of several alpha v integrins and tested the hypothesis that blockage of the alpha v beta 3 integrin would inhibit human angiogenesis during human wound healing. These studies revealed that the alpha v beta 3, alpha v beta 5, and alpha v beta 6 integrins are up-regulated briefly during wound angiogenesis with different patterns of expression and that inhibition of the alpha v beta 3 integrin blocked new vessel formation during human wound healing.