CD44 variant isoform v10 is expressed on tumor-infiltrating lymphocytes and mediates hyaluronan-independent heterotypic cell-cell adhesion to melanoma cells

CD44 is a family of cell-surface receptors on human lymphocytes that act as co-stimulatory molecules leading to the induction of effector functions in T cells. We have analyzed primary cutaneous malignant melanomas with clinical and histologic signs of tumor regression using immunohistochemistry and observed the predominant expression of the CD44 variant isoform v10 on CD3 CD4/CD8 co-expressing tumor-infiltrating lymphocytes (TIL). We further analyzed the role of CD44v10 in adhesion of lymphocytes to human melanoma cells. In contrast to CD44- lymphatic cells, CD44v10+ lymphatic cells strongly bound to cultured human melanoma cells and to frozen tissue samples of melanomas. Antibody blocking studies revealed a hyaluronan-, integrin-, and selectin-independent pathway of adhesion. Furthermore, CD44v10+ lymphatic cells exhibited significantly higher invasiveness in three-dimensional collagen matrices as compared with CD44H+ and CD44-negative lymphocytes. These results indicate that expression of CD44v10 on TIL may mediate adhesion to melanoma cells and result in gain of novel invasive properties.     

Changes in CD44 isoform expression during inflammatory skin disease

The CD44 family of cell surface glycoproteins is widely-expressed in epithelial, mesothelial and haemopoietic tissues and is thought to function primarily as adhesion molecules. The molecule has an intracellular, a trans-membrane and an extracellular domain. The membrane proximal region of the extracellular domain is of variable structure depending on which of 10 variable exons are involved in coding for this region. Both in vitro stimulated T cells and cytokine stimulated keratinocytes are known to express certain isoforms. In this study we have investigated whether specific isoforms of the CD44 molecule are expressed on epithelial cells and lymphocytes in the course of two inflammatory skin diseases, namely lupus erythematosus and lichen planus. Monoclonal antibodies, specific to the epitopes of the CD44 molecule encoded by v3, v4/5, v6 and v8/9 variable exons and a pan CD44 marker, were used on 10 lupus and 8 lichen planus frozen skin samples and compared with normal skin from 9 different body sites. Results failed to show detectable levels of variant isoforms of CD44 on lymphocytes in either inflammatory skin disease, despite evidence of T cell activation. All CD44 variant isoforms were reduced on the keratinocytes in some sections of lupus and lichen planus. The results are discussed in the context of the current models for the role of CD44 in the immune response.     

Hyaluronan and CD44 in psoriatic skin. Intense staining for hyaluronan on dermal capillary loops and reduced expression of CD44 and hyaluronan in keratinocyte-leukocyte interfaces

The distributions of hyaluronan (HA) and its presumptive receptor, CD44, were studied in skin samples from 13 psoriasis vulgaris patients, using an HA-specific probe (HABC), and monoclonal antibodies, respectively. The general distribution of HA and CD44 in psoriatic lesional epidermis resembled that in normal epidermis. However, areas of epidermis invaded by leukocytes showed a local depletion of HA and CD44, particularly at the contact areas of keratinocytes to lymphocytes and neutrophils. Removal by cellular uptake or extracellular degradation of CD44 and HA may be required for tight adherence between a keratinocyte and a leukocyte. On the dermal side, the tips of the prolonged dermal papillae in psoriatic lesions were intensively stained with HABC. The dilated capillaries and the space below the tip basal lamina, in particular, were heavily covered with HA. Occasionally, a similar intense staining was seen around an enlarged capillary in uninvolved psoriatic skin. CD44-positive leukocytes were found around the affected capillaries. The accumulation of HA in the dermal papillae may support the growth of psoriatic lesions, since HA stimulates the growth of capillaries as well as attracting inflammatory cells.     

CD44 expression in normal and inflamed skin

CD44 is the principal cell surface receptor for hyaluronate. In non-inflamed skin, CD44 expression is limited to the cell membrane of eccrine coil cells. The distribution on these cells is assymetric, with intense staining on the dermal side and little staining on the luminal side of the coil cell. In skin containing a pathologic process, either inflammatory or neoplastic, CD44 expression can be widespread on the membranes of keratinocytes and on infiltrating lymphocytes in the vicinity of the process. Diverse roles have been proposed for CD44 and largely involve aspects of cellular adhesion in one setting or another. CD44 may identify a more mobile, proliferating keratinocyte that is responding to local injury. In eccrine coil, the stable presence of CD44 on the non-luminal surface of secretory cells indicates an undefined function for CD44 in the generation of eccrine sweat.     

CD44 and melanocytic tumors: a possible role for standard CD44 in the epidermotropic spread of melanoma

CD44 is a polymorphic family of cell membrane glycoproteins that mediate cell-matrix and cell-cell interactions involved in the mechanisms of tumor invasion and metastasis, and are subject to differential regulation during normal and malignant cell growth. We have investigated immunohistochemically the expression of CD44S and the variant isoforms CD44v3 and CD44v6 in paraffin-embedded tissue from 5 Spitz nevi, 3 compound melanocytic nevi, 2 blue nevi, 6 primary melanomas, 15 cutaneous metastases (three epidermotropic, nine dermal and three ulcerated) and 10 lymph node metastases of melanoma. Melanocytes were extensively positive for CD44S in primary melanomas and benign melanocytic proliferations. Among 15 cases of cutaneous metastases of melanoma, the three epidermotropic metastases, as well as one of the three ulcerated ones were positive for CD44S. CD44S expression was diminished or totally absent in six of the nine dermal metastases, in two of the ulcerated metastases and in seven of the ten lymph node metastases. CD44v3 and CD44v6 melanocytic expression was absent in all the lesions studied.
According to our results, selective retention of CD44S expression by melanocytes in epidermotropic metastases of melanoma seems to indicate that preservation of CD44S may contribute to the intraepidermal spread of melanoma.     

Hyaluronan,CD44 and versican in epidermal keratinocyte tumours

BACKGROUND: The high molecular weight polysaccharide hyaluronan is a major component of the extracellular matrix between the vital cells of human skin epidermis. The levels of hyaluronan, and those of the hyaluronan receptor CD44 and the hyaluronan binding proteoglycan versican, correlate with the aggressiveness of different human carcinomas of epithelial origin. OBJECTIVES: To study skin keratinocyte tumours for the expression of hyaluronan, the hyaluronan receptor CD44 and the hyaluronan binding proteoglycan versican. METHODS: Paraffin-embedded sections of 114 basal cell carcinomas (BCC), 31 in situ carcinomas (ISC) and 35 squamous cell carcinomas (SCC) were stained with a hyaluronan specific probe, biotinylated hyaluronan binding complex, and with monoclonal antibodies against CD44 and versican. RESULTS: Compared with normal epidermis, ISC and well differentiated SCCs showed an enhanced hyaluronan signal on carcinoma cells while CD44 expression level resembled that of normal skin. Less differentiated SCCs showed reduced and irregular expression of both hyaluronan and CD44 on carcinoma cells. In BCCs, hyaluronan and CD44 signals were absent or very low on the surface of carcinoma cells. However, hyaluronan was frequently present on BCC cell nuclei, a feature completely absent in ISC, SCC and normal epidermis. An accumulation of hyaluronan in the connective tissue stroma around the tumour was more frequent in SCCs than BCCs. Versican staining was positive around hair follicles and dermal blood vessels of normal skin. Peritumoral versican signal was present in a part of the BCCs but not in other tumours. CONCLUSIONS: The completely different hyaluronan and CD44 expression patterns in BCC and SCC probably reflect the different origins of the tumours, with BCC an undifferentiated keratinocyte and SCC a keratinocyte at an early stage in the differentiation pathway. The difference in hyaluronan and CD44 expression between these tumours may also contribute to the difference in their capacity to metastasize.     

A ligand of human thy-1 is localized on polymorphonuclear leukocytes and monocytes and mediates the binding to activated thy-1-positive microvascular endothelial cells and fibroblasts

Thy-1 is known to be expressed on fibroblasts, nerve cells, and blood stem cells. Previous studies have shown the induction of Thy-1 on phorbol ester stimulated human dermal microvascular endothelial cells in vitro. In situ Thy-1 expression was found on activated endothelium. In this study we were interested in the localization of a Thy-1 ligand and the characterization of the function of Thy-1 on human dermal microvascular endothelial cells and fibroblasts. Human Thy-1 purified from fibroblast extracts was labeled and used as a probe for the detection of a Thy-1 ligand. In cryostat sections of bullous pemphigoid skin a Thy-1 ligand was found on inflammatory cells, whereas the Thy-1 antigen was expressed on the endothelial cells and fibroblasts. By flow cytometry we could show the expression of a Thy-1 ligand on polymorphonuclear leukocytes and monocytes, whereas lymphocytes did not express this Thy-1 ligand. To study whether Thy-1 is involved in cell-cell adhesion we separated Thy-1-positive and Thy-1-negative cells by magnetic cell separation using the monoclonal antibody AS02. Cell adhesion assays and blocking experiments revealed a direct involvement of the Thy-1/Thy-1 ligand interaction in the binding of monocytes and polymorphonuclear leukocytes to Thy-1-positive activated endothelial cells and fibroblasts.     

Colocalization of basic fibroblast growth factor and CD44 isoforms containing the variably spliced exon v3 (CD44v3) in normal skin and in epidermal skin cancers

Previous in vitro studies have shown CD44 isoforms containing the alternatively spliced exon v3 (CD44v3) to be modified with heparan sulphate (HS) and to bind HS-binding basic fibroblast growth factor (bFGF). Here, we demonstrate that exogenously added bFGF is also bound in vivo by CD44v3-positive keratinocytes in normal skin and by tumour cells in basal cell carcinoma and squamous cell carcinoma (SCC), two skin cancers of keratinocyte origin. bFGF binding and CD44v3 expression were colocalized in cultured human normal keratinocytes (HNK) and on the SCC cell line A431. By contrast, benign or malignant tumours of melanocyte origin failed to express CD44v3 and bound no bFGF. The bFGF binding to normal or transformed keratinocytes in vivo and in vitro was dependent on HS modification, as it was completely eliminated by pretreatment with heparitinase or by blocking with free heparin, whereas chondroitinase had no effect. In addition, specific removal of CD44v3 by antibody-induced shedding also diminished bFGF binding to keratinocytes. Furthermore, bFGF stimulated the proliferation of CD44v3-positive HNK and A431 in a dose-dependent fashion. This bFGF effect was again completely abolished by heparitinase or free heparin, but not by chondroitinase. In aggregate, our results suggest that a function of HS-modified CD44 isoforms such as CD44v3 in skin is to present the HS-binding growth factor bFGF, thereby stimulating the proliferation of normal or transformed keratinocytes.     

CD44 and variants in melanocytic skin neoplasms

Expression of cell surface molecules that mediate cell-matrix and cell-cell interactions largely contributes to the ability of melanoma cells to migrate and spread beyond the primary site of the tumor. CD44, the principal cell-surface receptor for hyaluronate, and its numerous splice variants have been reported to play a crucial role in invasion and the metastatic process of different human neoplasms, including primary malignant melanoma (PMM). The aim of this study was to clarify which isoforms of CD44 (standard CD44 and CD44 variants) are distributed in PMM with a vertical tumor thickness of >1.4 mm. Staining of CD44 standard (CD44s) and splice variants was further examined for diagnostic and prognostic relevance in a panel of melanocytic skin lesions. Ten cases of PMM with Breslow >1.4 mm were analysed by immunohistochemistry using monoclonal antibodies specific for CD44s and the splice variants v3, v5, v6, v7, v7-8, and v10. In addition, using anti-CD44s, v5, and v6 antibodies, 55 meianocytic lesions, including dermal nevi (n=12), Clark nevi (dysplastic nevi) (CN; n=11), melanoma in situ (Mis; n=8), PMM (n=18), and cutaneous metastasis of malignant melanoma (cM-MM; n=6) were assessed. Staining intensities were scored visually and evaluated by means of a staining index. In ten cases of PMM with a Breslow index >1.4 mm positive staining was ascertained for CD44s, v5 and for v6 in three cases. No staining was found for v3, v7, v7-8, and v10. Examination of CD44s, v5, and v6 in 55 melanocytic skin lesions revealed a high index for CD44s in all specimens and a weak staining of v5 in Mis; dermal nevi and CN did not stain for v5. However, in PMM and cMMM we found v5 to be strongly positive. The isoform v6 showed a variable index only in PMM, but without connection to established prognostic criteria. We conclude that CD44s and splice variants can not be regarded as indicators for tumor progression in malignant melanomas. However, v5 may potentially serve as a diagnostic marker for meianocytic skin lesions.     

Lymphocyte migration into the skin: the role of lymphocyte homing receptor (CD44) and endothelial cell antigen (HECA-452).

Lymphocyte migration into the lymphoid organs and sites of inflammation is controlled by lymphocyte-endothelial cell interaction at sites where lymphocytes exit from the blood. Expression of Hermes-defined CD44 class of lymphocyte homing receptor and HECA-452 antigen specific for high-endothelium-mediating physiologic lymphocyte extravasation was studied in dermatitis herpetiformis, celiac disease, psoriasis, mycosis fungoides, lymphocytosis cutis, atopic dermatitis, and allergic contact dermatitis. Also, duodenal biopsies of patients suffering from dermatitis herpetiformis or celiac disease were studied for existence of these antigens. Infiltrating lymphocytes in the skin and in the duodenal area expressed homing receptor molecules when studied with monoclonal antibodies, Hermes-1 and Hermes-3, that recognize the CD44 class of molecules involved in lymphocyte binding to high endothelial venules in peripheral lymph nodes, mucosa-associated lymphatic tissues, and inflamed synovium. However, the HECA-452 antigen was not detected on the venules, neither in the skin nor in the duodenum. Even the venules possessing high endothelium morphologically were HECA-452 negative. These findings suggest the CD44 class of lymphocyte homing receptor(s) is also involved in lymphocyte homing to inflamed skin and the duodenal area of the gut. However, on the basis of HECA-452 staining, high endothelial venules in inflamed skin and duodenum are not antigenically identical with high endothelial venules in organized lymphoid tissues. This finding indirectly supports the idea that molecules and/or mechanisms mediating lymphocyte extravasation might be distinct in these organs.     

HMEC-1: establishment of an immortalized human microvascular endothelial cell line.

The study of human microvascular endothelial cells has been limited, because these cells are difficult to isolate in pure culture, are fastidious in their in vitro growth requirements, and have a very limited lifespan. In order to overcome these difficulties, we have transfected human dermal microvascular endothelial cells (HMEC) with a PBR-322-based plasmid containing the coding region for the simian virus 40 A gene product, large T antigen, and succeeded in immortalizing them. These cells, termed CDC/EU.HMEC-1 (HMEC-1), have been passaged 95 times to date and show no signs of senescence, whereas normal microvascular endothelial cells undergo senescence at passages 8-10. HMEC-1 exhibit typical cobblestone morphology when grown in monolayer culture, express and secrete von Willebrand's Factor, take up acteylated low-density lipoprotein, and rapidly form tubes when cultured on matrigel. HMEC-1 grow to densities three to seven times higher than microvascular endothelial cells and require much less stringent growth medium. HMEC-1 will grow in the absence of human serum, whereas microvascular endothelial cells require culture medium supplemented with 30% human serum. These cells express other cell-surface molecules typically associated with endothelial cells, including CD31 and CD36 and epitopes identified by monoclonal antibodies EN4 and PAL-E. They also express the cell adhesion molecules ICAM-1 and CD44 and following stimulation with interferon-gamma express major histocompatibility complex class II antigens. HMEC-1 specifically bind lymphocytes in cell adhesion assays. Thus HMEC-1 is the first immortalized human microvascular endothelial cell line that retains the morphologic, phenotypic, and functional characteristics of normal human microvascular endothelial cells.     

Lymphocyte adhesion to psoriatic dermal endothelium: mechanism and modulation

Psoriasis is characterized by the hyperproliferation of keratinocytes in the epidermis and the accumulation of activated CD4+ T lymphocytes in the upper dermis. We have recently tested the hypothesis that the abnormal endothelial proliferation in the dermal papillae of psoriatic lesions may be mechanistically linked to the expression of endothelial ligands capable of promoting lymphocytes binding and extravasation. The results indicated that specialized endothelial cells lining the post-capillary venules of psoriatic lesions are capable of promoting the selective adherence of human CD4+ T cells and its memory subset. In contrast, B cells, CD8+ T cells, and CD45RA+ T cells are deficient in their capacities to bind. The adhesion process is energy and calcium dependent and involves tissue-specific lymphocyte receptors, with LFA-1 molecules playing an accessory role. We concluded that transformation of the dermal endothelium into a lymphocyte-receptive phenotype by defined growth factors or cytokines may represent a positive feedback mechanism promoting lymphocyte migration into the diseased sites.     

Interaction of HSV-1 infected peripheral blood mononuclear cells with cultured dermal microvascular endothelial cells: a potential model for the pathogenesis of HSV-1 induced erythema multiforme

The effect of herpes virus infection on human dermal microvascular endothelial cells and herpes-virus-1-infected peripheral blood mononuclear cells on human dermal microvascular endothelial cells was studied as a model of herpes-associated erythema multiforme. After infection of human dermal microvascular endothelial cells with native herpes virus and overnight culture, 60%--90% of human dermal microvascular endothelial cells showed cytopathic effects. HLA class I molecules and CD31 (PECAM-1) surface expression in herpes-virus-infected endothelial cells were substantially downregulated, whereas CD54 (ICAM-1) remained unchanged. Cocultivation with herpes-virus-1-infected peripheral blood mononuclear cells left characteristic plaques on the human dermal microvascular endothelial cell monolayer; however, very few human dermal microvascular endothelial cells (1%--3%) were infected. Adhesion molecule expression of human dermal microvascular endothelial cells cocultivated with herpes-virus-infected peripheral blood mononuclear cells demonstrated a 5-fold increase in CD54 expression, a 2-fold increase in HLA class I expression, but no change of CD31 by fluorescence-activated cell sorter analysis. Incubation of human dermal microvascular endothelial cells with ultraviolet-C irradiated herpes-virus-infected peripheral blood mononuclear cells had no effect on morphology or adhesion molecule expression levels. Changes of adhesion molecule expression by direct infection or cocultivation with peripheral blood mononuclear cells (with native and ultraviolet-C inactivated herpes virus infection) were also documented at the mRNA level. Adhesion assays demonstrated an increased binding of herpes-virus-infected peripheral blood mononuclear cells versus noninfected peripheral blood mononuclear cells to noninfected human dermal microvascular endothelial cells. Our results suggest that incubation of herpes-virus-infected peripheral blood mononuclear cells with human dermal microvascular endothelial cells induces significant upregulation of CD54 and major histocompatibility complex class I molecules in the surrounding noninfected human dermal microvascular endothelial cells, which is associated with an increased binding of peripheral blood mononuclear cells. Our in vitro findings may serve as a model for herpes-associated erythema multiforme possibly explaining the dermal inflammatory reaction seen in that condition.     

The effect of in vivo interferon-gamma on the distribution of LFA-1 and ICAM-1 in normal human skin

Lymphocyte function associated antigen 1 (LFA-1) and its ligand intercellular adhesion molecule 1 (ICAM-1) are cell surface adhesion molecules important in many lymphocyte-mediated responses. Recent in vitro studies have demonstrated that the cytokine interferon-gamma (IFN-gamma) can induce ICAM-1 expression by keratinocytes, and that lymphocytes adhere to IFN-gamma treated keratinocytes. In view of the importance of keratinocyte/lymphocyte interactions in the pathogenesis of cutaneous disease, we have examined the effects of in vivo IFN-gamma on cutaneous expression of LFA-1 and ICAM-1. Fourteen volunteers received intradermal IFN-gamma (dose: 1 or 10 micrograms) daily for 3 d. Biopsy was obtained on day 6. Cryostat sections were stained by the peroxidase antiperoxidase technique employing murine monoclonal antibodies to CD11, CD18, and ICAM-1. IFN-gamma intensified ICAM-1 expression by dermal endothelial cells and induced keratinocyte expression of ICAM-1. Furthermore, after administration of 10 micrograms of IFN-gamma LFA-1 positive (LFA + ve) lymphocytes were observed along the basement membrane zone closely related to ICAM-1 + ve basal keratinocytes and also surrounding dermal endothelium. Exposure to IFN-gamma induced expression of both CD11a and CD18 antigens on epidermal Langerhans cells. These studies suggest that the distribution of adherence molecules expression within cutaneous tissue in vivo is modulated by IFN-gamma, and that these alterations may be important in interactions involving cutaneous immunocompetent cells.     

CD44 and hyaluronate expression in follicular mucinosis

BACKGROUND: CD44 is a membrane glycoprotein and the major cell-surface receptor of hyaluronate (HA). Lack of CD44 expression in mouse epidermis leads to an abnormal HA accumulation in the dermis, indicating an important role of CD44 in local HA metabolism. Decrease of epidermal CD44 expression in patients of lichen sclerosus et atrophicus is potentially responsible for dermal deposition of HA in this disease. Stromal HA accumulation is associated with decreased or lost expression of CD44 in perifollicular solitary cutaneous myxoma, myxoid dermatofibroma, and dermatofibrosarcoma protuberans. METHODS: We examined the expression of CD44 and HA in the skin biopsy specimens of 10 patients with follicular mucinosis by using CD44-specific antibodies and biotinylated HA-binding protein (HABP), respectively. RESULTS: No difference of CD44 expression was observed in the follicular keratinocytes when compared with those of unaffected interfollicular epidermis. The follicular zones of mucin deposition were strongly positive for HA. A weak interkeratinocyte staining for HA was also observed in the interfollicular epidermis. However, HABP staining revealed a stronger reactivity in the follicular keratinocytes surrounding the mucin-accumulated areas compared to the interfollicular keratinocytes. CONCLUSION: Our results suggest an active secretion of HA by follicular cells in follicular mucinosis.     

Mitigation of delayed-type hypersensitivity reactions by a CD44 variant isoform v3-specific antibody: blockade of leukocyte egress.

In allergic alterations of human skin the majority of infiltrated leukocytes express CD44v3, but no other CD44 variant isoform. Vessel endothelium, too, is brightly stained with a CD44v3-specific antibody. Being concerned about therapeutic intervention, it became of importance to define whether expression of CD44v3 on the endothelial cells or on the leukocytes or on both is of functional importance. As expression of CD44v3 in the mouse on activated endothelium and on subpopulations of activated CD4+ cells, B cells and monocytes was similar to the expression in the human, we answered the question in a mouse delayed-type hypersensitivity model. The effect of anti-CD44v3 was compared with the effect of anti-CD44s and anti-CD44v10, both known to suppress delayed-type hypersensitivity reactions. Anti-CD44v3 mitigated the delayed-type hypersensitivity reaction in dinitrofluorobenzene sensitized and challenged mice comparable with anti-CD44s and anti-CD44v10. The seemingly similar effects of CD44 isoform-specific antibodies, however, resulted from a distinct modulation of response. Anti-CD44s mainly suppressed T cell activation and interleukin-2 as well as interferon-gamma expression. Anti-CD44v10 inhibited the activation of monocytes in the draining lymph nodes and in the infiltrate, which led to a strong reduction in the proinflammatory cytokines tumor necrosis factor-alpha and interleukin-12 and in edema formation. Anti-CD44v3 had only a weak effect on cytokine expression by isolated subpopulations of leukocytes, but suppressed cytokine production by helper T cells when cocultured with antigen-presenting cells, i.e., blocked an interaction between antigen-presenting cells and helper T cells. The dominating effect of anti-CD44v3, however, relied on a blockade of leukocyte extravasation. As leukocytes transferred into dinitrofluorobenzene sensitized, anti-CD44v3-treated and lethally irradiated mice did not infiltrate the sensitized skin, anti-CD44v3 most likely prevented leukocyte extravasation by blocking CD44v3 on endothelial cells.     

Expression of CD44 isoforms in basal cell carcinomas

The expression of CD44 isoforms (CD44std, CD44v6, CD44v10) was investigated by an immuno-histochemical technique in 42 basal cell carcinomas (BCC) of the superficial and nodular variety. All BCCs studied displayed very low amounts of CD44std, a receptor for hyaluronic acid. Except for single CD44std-positive cells located preferentially in the central parts of the BCC nests, the bulk of the tumour formations were CD44std-negative. CD44v6 showed a heterogeneous distribution pattern accentuated in the peripheral palisading tumour cells. In superficial BCCs, the labelling intensity for CD44v6) increased with the size of the tumour nests. CD44v10 was not detectable in BCCs Our findings support the notion that CD44v6 is not linked to the metastatic proclivity of tumours originating from keratinocytes. We suggest that the very low expression of the receptor for hyaluronic acid (CD44std) may be one of the factors which block the formation of metastases from BCCs.     

Distribution of CD44 variant isoforms in human skin: differential expression in components of benign and malignant epithelia

Expression of cell adhesion molecules regulates epithelial cell differentiation and organization of complex tissues such as skin. The CD44 family of adhesion molecules is generated by alternative splicing of up to 10 variant exons encoding inserts into the extracellular domain. Expression of CD44 variant exons has been correlated with metastatic potential of some epithelial malignancies. We studied the distribution of total and variant CD44 isoforms containing exons v4, v6, and v9 in normal skin, basal cell carcinoma, and in control tissues using immunohistologic assays. While normal epidermis and other stratified squamous epithelia reacted strongly with antibodies specific for standard CD44 (CD44S) and CD44 isoforms containing exons v4, v6, and v9, the epithelium of eccrine glands was reactive, often in a polarized distribution, only with antibodies specific for CD44S and isoforms containing exon v9. These studies suggest that differential expression of CD44 variant exons may be important in development and organization of epithelial structures within skin. Malignant cells in basal carcinoma tissues were found to have low reactivity with antibodies specific for CD44S or variant CD44 molecules. The low expression of CD44 molecules in basal cell carcinomas may play a role in the relatively low probability of metastasis of these neoplasms.     

Increased neutrophil adherence in psoriasis: role of the human endothelial cell receptor Thy-1 (CD90)

The chronic inflammatory skin disease psoriasis is characterized by prominent skin infiltration by neutrophils and microabscess formation. The adhesion of leukocytes and subsequent transmigration through the activated endothelium is one prerequisite for the accumulation of these cells in skin. In recent studies, the human Thy-1 (CD90) was characterized as an adhesion molecule on activated endothelial cells (ECs) mediating the adhesion of neutrophils via the interaction with the beta2-integrin Mac-1. Based on these novel findings, we compared the roles of Thy-1 and ICAM-1 in the adhesion of neutrophils from patients with psoriasis to activated ECs. The adhesion of peripheral blood neutrophils of patients suffering from psoriasis to Thy-1-transfected cells as well as to activated, Thy-1-expressing human dermal microvascular ECs (HDMECs) is distinctly increased in comparison to the adhesion of neutrophils from healthy controls. In contrast, adherence of psoriatic neutrophils to ICAM-1 transfectants is, if at all, only slightly enhanced compared to healthy controls. The interaction of healthy as well as psoriatic polymorphonuclear cells to Thy-1 transfectants and HDMECs was significantly inhibited by blocking Thy-1 on ECs or its receptor Mac-1 on neutrophils, indicating the importance of this interaction for the adhesion of neutrophils to activated endothelium. In conclusion, our data indicate that the adhesion of neutrophils to activated ECs mediated by Thy-1/Mac-1 interaction is an important attachment mechanism facilitating their subsequent migration into lesional psoriatic skin.     

Mechanism of the interaction of leukocytes and dermal endothelial cells in cutaneous inflammation]

The infiltration of specific leucocyte populations into inflamed cutaneous tissue is dependent on their interactions with dermal endothelial cells. The dynamic multistep process of vasodilatation, adhesion, transendothelial migration, and penetration through the basal membrane is controlled by a considerable number of soluble mediators and cell adhesion molecules. In this process, dermal endothelium plays a critical role as a gate-keeper who regulates adhesion and penetration of neutrophils, lymphocytes, or monocytes by selection and activation of specific leucocyte subpopulations. In this review, the presently known functions of the involved cell adhesion molecules of the integrin, selectin, and immunoglobulin superfamily, as well as their interactions and their regulation by cytokines and other mediators are summarized.