Transplantation of Psoriatic Skin onto Nude Mice

Le psoriasis : évolution et révolution

Psoriasis is a model disease in dermatology. It is a common disease that affects at least 2 to 3 % of the population. It is an illness characterized by an excessive reaction of the skin, in term of proinflammatory cytokines release, to no specific attacks: these attacks can be immunological, mechanical, metabolic, drug-induced or psychological. This excessive reaction is characterized by epidermal proliferation combined with incomplete terminal differentiation, as well as an inflammatory response responsible for the chronic nature of the lesions. The way to understand psoriasis is therefore to reach a better appreciation of the messages that enable the skin cells to initiate an inflammatory response, and by better understanding the way in which the inflammatory cells responsible for innate and acquired immune responses are capable of bringing about proliferation and abnormal epidermal differentiation. Taking an interest in psoriasis is therefore taking an interest in all facets of skin physiology and in all the ways the skin reacts to attacks from the environment. Every year for more than thirty years, more than 300 publications have endeavoured to explore one aspect or another of psoriasis from a clinical, epidemiological, physiopathological or therapeutic point of view. There is no new technique for observing the skin that has not been immediately applied to the study of psoriasis - which is privileged to enjoy the reflected progress made in dermatology. Nor has psoriasis remained untouched by whims of fashion, all manner of scenarios having been suggested to explain it, right from a scarring disease to an autoimmune illness through a genetic or psychosomatic disorder. Psoriasis is at the origin of a medical revolution mounted to supplement and enhance the effectiveness of evidence-based medicine ; it is the "patient-centred medicine". Psoriasis only exceptionally jeopardizes life. Conversely, it is a disease that does affect quality of life. The patient alone must be the judge of his or her quality of life, and it is therefore up to the patient, not the doctor, to gauge the severity of psoriasis and hence decide on reasonable therapeutic indications. Psoriasis, then, cannot be treated without placing the patient, not the illness, at the centre of therapeutic negotiations. The 20th century has seen the disease targeted by boundless efforts ; the 21st century will see the development of medical techniques that allow the patient, in all its complexity, to be positioned at the centre of therapeutic efforts. This revolution began in dermatology, centring around psoriasis, and is spreading progressively to all chronic disorders and all disciplines. New quite interesting therapeutic weapons are available from a few months making possible to better adjust the therapeutic strategies of psoriasis to the patients needs but they are expensive opening again the debates on the limit of the social solidarity.

Activation of dendritic antigen-presenting cells expressing common heat shock protein receptor CD91 during induction of psoriasis

BACKGROUND

Psoriasis is a common and chronic relapsing inflammatory skin disorder. Although a role for T cells in mediating the induction and maintenance of psoriatic lesions is well established, mechanisms responsible for activation of T cells by antigen-presenting cells (APCs) during disease relapse are poorly understood.

OBJECTIVES

(i) To determine whether expression of the common heat shock protein (HSP) receptor CD91 correlated with development of psoriasis in a mouse model of psoriasis, (ii) to characterize the lesional cells on which CD91 was expressed, and (iii) to investigate whether CD91+ cells in psoriasis showed signs of activation.

METHODS

Two systems were used in order to study the above-mentioned objectives: (i) skin biopsies taken directly from patients with psoriasis (either psoriatic plaques or symptomless prepsoriatic skin) or from healthy donors, respectively, or (ii) (human) skin biopsies collected during development of psoriasis using a novel xenograft mouse model of psoriasis. The skin samples were then either processed for analysis by light microscopy, or labelled with fluorochrome-conjugated antibodies and analysed by confocal laser scanning microscopy.

RESULTS

We observed a markedly increased number of CD91+ cells which paralleled development of new psoriatic lesions in the psoriasis mouse model and in established psoriatic plaques compared with symptomless prepsoriatic or healthy skin. Morphology as well as cell-specific markers showed that CD91 was predominantly expressed by dermal dendritic APCs characterized by activation of nuclear factor-kappaB signalling and the presence of tumour necrosis factor-alpha, an important proinflammatory cytokine in the immunopathogenesis of psoriasis. In addition, HSP70, a ligand for CD91, was increased in keratinocytes in close vicinity to CD91-bearing APCs in psoriatic lesions.

CONCLUSIONS

These findings indicate massive presence of CD91+ dendritic cells juxtaposed to lesional keratinocytes expressing HSP70, and suggest a novel pathophysiological pathway and therapeutic target for this chronic inflammatory skin disease.

Cellular and molecular composition of human skin in long-term xenografts on SCID mice

We report on the immunophenotypical characterization of adult human skin transplanted onto severe combined immunodeficient (SCID) mice. Thirty animals were followed for up to 12 months after receiving split-thickness xenografts, of which 28 were tolerated for the whole test period. Antigen mapping revealed an almost complete preservation of human cellular and extracellular tissue components in long-term transplants including skin immune cells (Langerhans-cells, macrophages, lymphocytes) and also parts of the engrafted endothelium. Hence, xenografts on SCID mice offer a versatile experimental tool for the in vivo study of both human skin immune cell function and endothelial cell-mediated interactions in an environment completely devoid of interferences by adoptive host immune response.

Is epidermal cell proliferation in psoriatic skin grafts on nude mice driven by T-cell derived cytokines?

Plasminogen activity and DNA synthesis by epidermal cells have been reported to be doubled in psoriatic skin grafts compared with grafts of normal skin 6 weeks after transplantation to nude mice. In our study human lymphocytes disappeared from such grafts within 48 h whilst some DR-positive human dendritic cells were retained in the grafts for up to 4 weeks. However, the grafts were infiltrated by Thy 1.2+ mouse lymphocytes within 6 days and this infiltration persisted at a moderate level throughout the observation period. It consisted of perivascular aggregates, scattered dermal and papillary T cells, and some mouse T cells were also found in the epidermal compartment. Grafts of psoriatic and non-psoriatic control skin were infiltrated to a similar extent, suggesting a low-grade rejection response against the human xenografts. These findings raise the possibility that psoriatic keratinocytes are responding abnormally to inflammatory cytokines released by mouse lymphocytes reacting against the skin grafts.

Failure of passive transfer of serum from patients with alopecia areata and alopecia universalis to inhibit hair growth in transplants of human scalp skin grafted on to nude mice

We have previously demonstrated regrowth of hair in scalp skin grafts taken from patients with alopecia areata (AA) and alopecia universalis (AU) following engraftment on to nude mice. This present study was to determine whether serum from patients with AA and AU, has a role in the process of hair loss and the role of antibodies and complement. Forty mice were grafted with transplants obtained from seven patients. One group of the grafted mice was given patients' serum and another group normal serum. The mice were treated topically with cyclosporin (CyA), or olive oil. Hair growth was noted in most grafts and intravenous injections of serum did not prevent or inhibit this process. Immunofluorescence studies before grafting showed deposition of immunoglobulins and complement in hair follicles in both normal and affected scalp skin, but a more striking deposition was noted in the affected skin. Deposition of immunoreactants after grafting was observed only after the injection of serum from the patients but not with normal serum. Thus the sera from patients with AA or AU, when injected into nude mice with hair transplants from the scalp skin of patients with these disorders, does not alter the hair growth despite deposition of immunoreactants around the hair follicles.

Plasminogen binding sites in normal human skin

Plasminogen is detected in the basal cell layer of the epidermis, keratinocytes can generate plasminogen activators and it is suggested that the generation of plasmin may facilitate keratinocyte division, migration and differentiation. In this study we have investigated the characteristics of plasminogen binding sites in normal human epidermis. It was found that 6-aminohexanoic acid and benzamidine displaced endogenous epidermal plasminogen from the basal layer suggesting that endogenous plasminogen binds initially via the kringle 5 aminohexyl (AH) site. Plasminogen binding sites in epidermis were further investigated by displacing endogenous plasminogen and incubating sections with exogenously added glu-plasminogen, lys-plasminogen and plasmin or the isolated plasminogen fragments kringles 1-3, kringle 4 and kringle 5L. The results suggest that the uptake of plasminogen involves primary interaction with the kringle 5AH site and a secondary interaction with lysine binding sites of kringles 1-3. Cell binding is not dependent upon additional reactions of the plasmin active centre.

The pathogenesis of lichen planus

The histological features of lichen planus (LP) are characterized by typical epidermal changes with dermal lymphocytes that are mostly Ia positive T cells. In order to find out whether the primary event of LP is damage to basal keratinocytes or a delayed hypersensitivity reaction in which an as yet unidentified antigen activates T lymphocytes that destroy keratinocytes, we transplanted skin obtained from six patients with LP. Two millimetre punch and split thickness of grafts were obtained from involved and uninvolved areas from each patient and grafted onto nude mice. Biopsies were taken from the grafts at 14 and 21 days after transplantation for histological and immunofluorescence studies and after 6 weeks for Dopa incubation for melanocyte populations. A complete disappearance of the pathological changes of LP was found 21 days following grafting. An increased number of melanocytes was noted. This indicates that the pathogenesis of LP may not be due to an inherent change in the epidermal cells, but rather to the migration of cellular elements of the immune system.

Plasminogen activator in psoriatic scales is of the tissue-type PA as identified by monoclonal antibodies

Extracts of scale from four patients with psoriasis all contained plasminogen activator. All plasminogen activator activity was of the tissue-type (t-PA) as judged from the following criteria: all enzyme activity was inhibited by a monoclonal antibody against human t-PA, while there was no measurable inhibition by a monoclonal antibody against human urokinase-type plasminogen activator (u-PA); as determined by zymography the extracts contained one type of plasminogen activator which had an electrophoretic mobility identical to that of purified t-PA; this plasminogen activator was removed by passage through a Sepharose column coupled with a monoclonal antibody against t-PA, but not by passage through a column coupled with a monoclonal antibody against u-PA. On a molar basis the detection limit for u-PA was 10% of that of t-PA present.

Psoriasis: a defect in the regulation of epidermal proteases, as shown by serial biopsies after cantharidin application

The possible role of epidermal serine proteases in the genesis of psoriatic lesions was investigated by sequential biopsies of the epidermal damage induced by topical cantharidin. In the skin of normal subjects, epidermal damage was followed by the transient appearance of proteolytic activity in the upper epidermis accompanied by temporary hyperacanthosis and perivascular inflammatory cells in the superficial dermis. In the uninvolved skin of five patients with psoriasis this proteolysis persisted longer, for more than 7 days. Thereafter, in three of the patients, the proteolysis abated, and this was followed by disappearance of the hyperacanthosis and the dermal infiltrate; in the other two psoriatics the proteolysis and hyperacanthosis increased, and a typical Koebner phenomenon ensued. Migration of neutrophils into the epidermis occurred as a later event. Thus the abnormal persistence of proteolytic activity in the upper epidermis after cantharidin application distinguishes the normal from the psoriatic skin injury response and might initiate the psoriatic lesion.