Heterogeneity of epidermal Thy-1-positive cells defined by lectin-binding sites

A new cell type that expresses Thy-1 antigen (dendritic epidermal Thy-1-positive cells, d-Thy-1+ EC) was discovered in the murine epidermis in 1983. It is not clear, however, whether all d-Thy-1+EC represent a unitary population. We investigated the cell surface glycoconjugate pattern of d-Thy-1+EC using 6 lectins: concanavalin A (Con-A), Dolichos biflorus agglutinin (DBA), Ricinus communis agglutinin 1 (RCA-1), wheat germ agglutinin (WGA), Ulex europaeus agglutinin (UEA-1), and peanut agglutinin (PNA). These lectins could be divided into 3 groups: lectins binding to most d-Thy-1+EC (Con-A and RCA-1); lectins virtually unreactive with d-Thy-1+EC (DBA and UEA-1); and lectins binding to subpopulation of d-Thy-1+EC (WGA and PNA). For lectins of group 1 and group 2, no difference was observed from strain to strain of mice (C3H/He, BALB/c, and C57B1/6), or from site to site of the body (back, ear, and tail). However, striking difference of percentage of lectin-binding d-Thy-1+EC was observed in group 3 lectins in the tail region compared with the back or the ear, although no strain difference was noted: back or ear, 83.6-95.5% with PNA, 13.6-29.6% with WGA in C3H; tail, 4.0-19.4% with PNA, 30.0-59.1% with WGA in C3H. These results indicate that d-Thy-1+EC are a heterogeneous population and that their distribution is different from site to site in the body.     

Differing lectin-binding patterns of malignant melanoma and nevocellular and Spitz nevi

Summary The lectin-binding patterns of primary malignant melanoma, nevocellular nevus, and Spitz nevus were studied on formalin-fixed, paraffin-embedded sections using a series of biotinylated lectins —concanavalin A (ConA), Ricinus communis agglutinin-1 (RCA1), dolichos biflorus agglutinin (DBA), soybean agglutinin (SBA), maclura pomifera agglutinin (MPA), peanut agglutinin (PNA), wheat germ agglutinin (WGA), and Ulex europeus agglutinin-1 (UEA1)- and employing the avidin-biotin-peroxidase complex method. In nevocellular and Spitz nevi, all of the nevus cells were positively stained with ConA and RCA1. No positive staining was observed, however, with the other lectins and no change in binding patterns occurred following neuraminidase pretreatment. In malignant melanoma, all of the melanoma cells were positively stained with ConA and RCA1, and some were also stained with MPA, PNA, and WGA. Inaddition, DBA, SBA, MPA, PNA, and WGA labeled all of the melanoma cells after neuraminidase pretreatment. No positive staining was observed with UEA1 despite neuraminidase pretreatment. The present results showed that malignant melanoma and nevocellular and Spitz nevi have different lectin-binding patterns and different responses to neuraminidase pretreatment. We, therefore, belive that the lectin staining on paraffinembedded sections can be a useful probe for the differentiation of these diseases.     

Lectin-binding sites in eccrine sweat gland tumours

Lectin-binding sites in sections of formalin-fixed, paraffin-embedded eccrine sweat gland tumours were investigated using fluorescein isothiocyanate (FITC) conjugated peanut agglutinin (PNA), FITC conjugated Ricinus communis 1 agglutinin (RCA-1) and FITC conjugated wheat germ agglutinin (WGA). In 22 benign eccrine sweat gland tumours, lectin-binding sites were noted primarily on the cell surface, and in the secretions. In five malignant sweat gland tumours, all showed cytoplasmic lectin-binding sites in variable proportions of malignant cells in addition to cell surface staining. These results indicate that cytoplasmic lectin-binding sites may be a useful marker of neoplastic transformation of eccrine sweat gland tumours.     

Ultrastructural localization of lectin binding sites in human melanocytes

Summary The ultrastructural localization of carbohydrate residues in human melanocytes of normal epidermis and of one compound naevus was studied. The following lectins were used in a post-embedding technique: 1. peanut agglutinin (PNA), which reacts specifically with N-acetyl-galactosamine; 2. Concanavalia ensiformis (Con A) indicating -d-glucose and -d-mannose binding sites; 3. Ulex europaeus agglutinin (UEA I) specific for -l-fucose; 4. Wheat germ agglutinin (WGA), reacting specifically with N-acetyl-glucosamine and neuraminic acid (sialic acid); and 5. Limax flavus agglutinin (LFA), also specific for sialic acid (Neu5Ac--2,3-Gal and Neu5Ac--2,6-Gal). When incubated with WGA, Con A and LFA strong labelling was seen within the cytoplasm and in the plasma membrane of melanocytes, whereas incubations with PNA and UEA I revealed an occasional gold particle only. The determination of the distribution of carbohydrate residues in normal melanocytes is a prerequisite for future studies of abnormal melanocytes.     

Lectin-binding sites in clear cell acanthoma

Lectin-binding sites in clear cell acanthoma (CCA) were studied using an avidin-biotin complex (ABC) with 9 lectins. Formaldehyde-fixed, paraffin-embedded sections of 7 CCA lesions were employed. Positive stainings, similar to those seen in normal epidermis, were observed on the cell surface in CCA with Ricinus communis agglutinin I (RCA-I), Ricinus communis agglutinin II (RCA-II), and wheat germ agglutinin (WGA). Reduced reactivities were observed with Concanavalin A (ConA) and peanut agglutinin (PNA) in CCA. In some areas of CCA lesions, faint stainings were seen with Ulex europaeus agglutinin I (UEA-I). Capability of staining with soybean agglutinin (SBA) was completely lost in the lesions. With Bandeiraea simplicifolia agglutinin II (BSA-II), cytoplasmic stain was seen in a part of upper and spinous layers in CCA lesions. Dolichos biflorus agglutinin (DBA) did not bind to either CCA or normal epidermis. These results indicate that the lectin-binding sites of proliferating cells of CCA resemble those of epidermal keratinocytes and suggest that CCA is a tumor of epidermal origin.     

Lectin-binding sites in Paget''s disease

The presence and distribution of lectin-binding sites on neoplastic cells of Paget's disease was studied using fluorescein isothiocyanate (FITC)-conjugated peanut agglutinin (PNA), and FITC-conjugated wheatgerm agglutinin (WGA), and compared with such lectin-binding sites on keratinocytes, and cells of eccrine glands, apocrine glands, and mammary glands. Neoplastic cells of both mammary and extramammary Paget's disease showed cytoplasmic staining with both lectins. There were however fewer stained cells in mammary Paget's disease than in extramammary Paget's disease. The cytoplasmic staining of lectin-binding sites in cells of apocrine glands was in sharp contrast to the cell-surface staining seen on keratinocytes, or cells of eccrine glands or mammary glands. These results indicate that the lectin-binding sites of neoplastic cells of Paget's disease more closely resemble those of cells of apocrine glands than of keratinocytes, cells of eccrine glands or cells of mammary glands.     

Murine epidermal Langerhans cells and keratinocytes express functional P2X7 receptors

Please cite this paper as: Murine epidermal Langerhans cells and keratinocytes express functional P2X₇ receptors. Experimental Dermatology 2010; 19 : e151–e157. Abstract: Extracellular ATP via the activation of purinergic P2 receptors has an emerging role in cutaneous biology; however, the distribution of these receptors in mouse skin is poorly defined. This study investigated whether murine epidermal cell subpopulations express functional purinergic P2X₇ receptors. P2X₇ expression was examined by immunoblotting and immunofluorescence staining of epidermal cells from C57Bl/6 mice. P2X₇ function was evaluated by nucleotide‐induced ethidium⁺ uptake measurements in epidermal cells from C57Bl/6 mice, and from P2X₇ deficient mice and wild‐type littermate controls. P2X₇ was detected in whole epidermal cell preparations, and specifically on Langerhans cells (LCs) and keratinocytes (KCs). ATP induced ethidium⁺ uptake into LCs and KCs, with EC₅₀ values of 503 and 482 μm, respectively. BzATP, and to a lesser extent ATPγS and ADP, also induced ethidium⁺ uptake; while UTP, αβ‐meth‐ATP and NAD were ineffective. ATP‐induced ethidium⁺ uptake was impaired by Na⁺ and Mg²⁺, and the P2X₇ antagonist, A‐438079 and was absent in LCs and KCs from P2X₇ deficient mice. These results demonstrate that murine LCs and KCs express functional P2X₇, and support a role for this receptor in cutaneous biology.     

Effect of genetically determined immunodeficiency on epidermal dendritic cell populations in C57BL/6J mice

Summary Mice homozygous for three different recessive mutations known to cause pleiotropic defects in the immune system and in the skin were used to evaluate the relationship between the classical immune system and dendritic epidermal cell populations. Numbers of Langerhans cells (LCs) and Thy-1⁺ dendritic cells (Thy-1⁺DEC) were determined using indirect immunofluorescence microscopy of epidermal whole mounts taken from viable motheaten (me ^v ), nude (nu), and rhino (rh ^hr ) mice. All mutants were maintained on the C57BL/6J strain background and were compared with their respective littermate normal controls. Viable motheaten mice had normal numbers of LCs at 1 month of age. However, by 8 weeks of age, LC density had decreased threefold. Nude and rhino mice had normal numbers of LCs at all ages tested. There was no significant effect of the viable motheaten mutation on numbers of Thy-1⁺DEC. Although nude mice showed normal numbers of Thy-1⁺ DEC at 1 month of age, these athymic mice had a threefold decrease in numbers of such cells by 6 months. In contrast to the reduced numbers of Thy-1⁺DEC seen in nude mice, rhino mice showed a four- to fivefold increase in the numbers of these epidermal cells at all ages tested. These findings suggest new mouse models for investigating the development, regulation, and biological properties of epidermal dendritic cell populations.This work was supported in part by grants from the US-Israel Binational Foundation for Science, the United States-Israel Bi-national Agricultural Research and Development Fund (BARD), the Foundation for the Study of Cell Biology and Molecular Virology, Phoenix, Arizona and United States Public Health Service grant CA-20408. E. S. is a fellow of the Foulkes Foundation, London, UK     

IL-10-producing Langerhans cells and regulatory T cells are responsible for depressed contact hypersensitivity in grafted skin

Although skin grafting is a common surgical technique, the immunological state of grafted skin remains unelucidated. An experimental model has shown that the development of murine contact hypersensitivity (CHS) is depressed when mice are sensitized with a hapten through full-thickness grafted skin. We explored the immunological mechanisms underlying this hyposensitization, focusing on the fate of Langerhans cells (LCs). When FITC was applied to grafted skin, FITC-bearing LCs were capable of migrating to the draining lymph nodes. Epidermal cell suspensions isolated from the grafted skin produced a high amount of IL-10 as assessed by real-time PCR. Adoptive transfer of immune lymph node cells from the sensitized mice suppressed the CHS response of recipients in an antigen-specific manner. CD4(+)CD25(+) but not CD4(+)CD25(-) T cells purified from lymph node cells were responsible for this suppression. Finally, we detected high expression of receptor activators of nuclear factor kappa-B ligand (RANKL) in the grafted skin, and found that recombinant RANKL stimulated LCs to produce IL-10. These findings suggest that the hyposensitization of CHS through the grafted skin is not attributable merely to the reduction of LC number but that IL-10-producing LCs exert a downmodulatory effect by inducing regulatory T cells.     

Induction of tolerance by administration of hapten-immunoglobulin conjugates is associated with decreased IL-2 and IL-4 production

Intravenous administration of trinitrophenyl-modified isologous immunoglobulin-induced nonresponsiveness to subsequent epicutaneous painting of sensitizing doses of trinitrochlorobenzene. Isologous immunoglobulin with various degrees of trinitro-phenyl substitution (11.2, 14.3, 27 and 47.3) prevented sensitization. The suppression of contact hypersensitivity was dependent on the dose of tolerogen and was hapten specific. Tolerance was inducible in mice of the strains CBA (H-2^k), C57BL/6 (H-2^b), and DBA/2 (H-2^d) but not in Balb/C (H-2^d) mice, suggesting that this trait maps outside the murine major histocompatibility complex. Tolerance induced by trinitro-phenyl-modified immunoglobulin was associated with decreased hapten-induced proliferation of draining lymph-node cells. Unlike in other models of tolerance in which a decreased interleukin-2 to interleukin-4 ratio can be observed, administration of tolerizing trinitrophenylated immunoglobulin was associated with deficient hapten-induced release of both interleukin-2 and interleukin-4.     

Effect of gamma-interferon on lectin-binding glycoproteins in cultured human keratinocytes

Summary We report the effect of exposure of human keratinocyte cultures to human recombinant gamma-interferon (g-IFN) on the expression of glycoproteins. Concanavalia ensiformis agglutinin (Con-A), and Arachis hypogaea agglutinin (PNA) were used to investigate expression of glycoproteins. NP-40 extracts from cultures grown with or without 100 U/ml g-IFN were analyzed by incubation of SDS-polyacrylamide gels with ¹²⁵I-labeled lectins. Comparison of Con-A binding glycoprotein profiles showed both qualitative and quantitative changes related to the effect of g-IFN. Differences were also apparent after labeling of the gels with PNA. A limited number of components were labeled, with most of the reactivity falling within a couple of diffuse bands with high molecular weight (300 to 360 kDa). These components were strongly labeled in extracts from cells grown in the presence of g-IFN, but weakly reactive in control cultures. Neuraminidase treatment unmasked a 205 kDa PNA binding molecule only when cells were cultured in the absence of g-IFN. These changes are interpreted in terms of increased keratinocyte differentiation induced by g-IFN and demonstrate that glycoproteins bearing carbohydrate residues available to lectins Con-A and PNA have to be taken into account to better understand the complex action of this lymphokine. In inflammatory lesions, such changes in the glycoproteins of keratinocytes expressing HLA-DR antigens remain to be explored.This work was presented at the 10th International Lectin Meeting, 3–8 July 1988, Prague, Czechoslovakia, and at the Congrès Annuel de Recherche Dermatologique, 15–16 September 1988, Grenoble, France     

Alterations in lectin binding to the epidermis following treatment with 8-methoxypsoralen plus long-wave ultraviolet radiation

The alterations in lectin fluorescence stainings to the epidermis were examined in guinea pig skin treated with topical application of a 1% 8-methoxypsoralen (8-MOP) solution plus long-wave ultraviolet (UVA) radiation (1.5-3.5 J/cm2) (PUVA). Serial biopsy specimens taken up to 21 days postirradiation were stained with 8 commercially available lectins labeled with either fluorescein isothiocyanate (FITC) or biotin (followed by avidin D-FITC): Bandeiraea simplicifolia agglutinin I (BSA), concanavalin A (Con-A), Dolichos biflorus agglutinin (DBA), peanut agglutinin (PNA), Ricinus communis agglutinin I (RCA), soybean agglutinin (SBA), Ulex europeus agglutinin I (UEA), and wheat germ agglutinin (WGA). In normal guinea pig skin UEA staining was absent. Following PUVA treatment, UEA and DBA stainings became apparent or stronger in intensity after days 7-14 (UEA) and days 4-7 (DBA), respectively, and returned to negative or weak by days 14-21. Stainings with Con-A, SBA, and WGA gave remarkable decreases in intensity after days 2-4 and recovered to the baseline by days 7-14. Intensity of BSA, PNA, and RCA stainings was decreased to a lesser degree than the other lectins. Such changes were not produced by application of 8-MOP, UVA radiation (less than 10 J/cm2), UVB radiation (900-2700 mJ/cm2), or tape stripping. These results suggest that PUVA treatment perturbs the composition or organization of epidermal cell surface glycoconjugates to induce alterations in lectin stainings.     

Turnover and kinetics of epidermal langerhans cells and their dendritic precursor cells in experimental contact dermatitis

The numerical density of epidermal Langerhans cells (LCs) in contact sensitivity and toxic contact dermatitis is still a matter of controvery, mainly due to changes in the phenotypic markers of this antigen-presenting cell during the skin reactions. Since the electron microscopic detection of Birbeck granules is the most reliable marker for the identification of normal and pathologically altered LCs, we performed an ultrastructural-morphometric time-course analysis to evaluate their epidermal turnover in the earskin of BALB/c mice after painting the ears with the hapten 2,4-dinitrofluorobenzene and the irritant croton oil. The counts revealed degeneration and depletion of epidermal LCs in both allergic and toxic dermatitis. In contrast, a slightly increased number of activated epidermal LCs was found during contact sensitization. All experimental procedures resulted in an enhanced immigration of so-called indeterminate dendritic cells which also became ultrastructurally activated and often showed Birbeck granule-like formations at their cell membrane. Immunohistochemistry with the monoclonal antibody 4F7, a new marker for dendritic precursor cells of LCs, demonstrated a significant increase in these accessory cells in the epidermis. Our results indicate that contact sensitivity and toxic skin reactions are characterized by complex but distinct changes in the turnover, kinetics and cellular properties of epidermal LCs and their dendritic precursor cells. Received: 16 March 1995     

Subsets of epidermal Langerhans cells as defined by lectin binding profiles

In this study we characterize the cell surface glycoconjugate moieties of strain 2 guinea pig epidermal Langerhans cells (LC) in single cell suspension by using a battery of 17 fluorescent lectins. All LC displayed binding sites for concanavalin A, succinylated concanavalin A, Lens culinaris agglutinin, Pisum sativum agglutinin, wheat germ agglutinin, succinylated wheat germ agglutinin, Griffonia simplicifolia agglutinin I, Ricinus communis agglutinin I, Phaseolus vulgaris E agglutinin, and Phaseolus vulgaris L agglutinin, but failed to bind Sophora japonica agglutinin (SJA), Dolichos biflorus agglutinin (DBA), and Ulex europaeus agglutinin I (UEA I). Neuraminidase pretreatment rendered LC reactive for SJA, but not for DBA and UEA I. The binding profiles of certain lectins point to the existence of LC subpopulations in that Griffonia simplicifolia I-B4 isolectin, peanut agglutinin (PNA), Helix pomatia agglutinin, and soybean agglutinin bound to only 80% (range 70-90%) of Ia-positive epidermal cells; binding sites for these lectins on primarily unreactive Ia-positive cells were unmasked when epidermal cells were treated with neuraminidase prior to lectin labeling. Ultrastructural PNA labeling studies revealed that the vast majority of Birbeck granule-containing LC displayed PNA binding sites, whereas indeterminate cells were consistently PNA-negative. Identification of carbohydrate configurations expressed on LC surfaces by lectin binding may provide a clue for the elucidation of the mechanisms of established LC functions and possibly the discovery of as yet unknown properties of this cell type.     

Down-regulation of Langerhans cell protein kinase C-β isoenzyme expression in inflammatory and hyperplastic dermatoses

The family of protein kinase C (PKC) isoenzymes plays a fundamental part in signal transduction, and thereby regulates important cellular functions, including growth, differentiation, cytokine production and adhesion molecule expression. In lesional psoriatic skin. Ca²⁺-dependent PKC activity, PKC-β protein and epidermal Langerhans cell (LC) PKC-β immunostaining are significantly decreased, indicating activation and subsequent down-regulation of PKC. Whether these changes occur in other inflammatory/hyperplastic dermatoses is, however, unknown. We examined PKC-α and PKC-β expression in normal skin, psoriasis, cutaneous T-cell lymphoma (CTCL), lamellar ichthyosis, non-bullous ichthyosiform erythroderma, atopic dermatitis, urushiol-induced allergic contact dermatitis, and sodium lauryl sulphate (SLS)-induced irritant contact dermatitis. Cryostat sections were stained for PKC-α and PKC-β, and the LC marker CDla, using an immunoperoxidase technique and specific monoclonal antibodies. Double-labelling studies, in normal skin, revealed co-expression of PKC-β and CDla by epidermal LCs. Analysis of the number of PKC-^β+ and CDl^a+ epidermal LCs, in diseased compared with normal skin, revealed three categories: (i) in psoriasis and CTCL. the PKC-^β+ epidermal LC number was significantly reduced, whereas the CDl^a+ epidermal LC number was unchanged; (ii) in allergic and irritant contact dermatitis, both PKC-β+ and CDla⁺ epidermal LCs were significantly reduced in number; and (iii) in atopic dermatitis, the PKC-β⁺ epidermal LC number was normal, and CDla⁺ epidermal LCs were significantly increased in number. Moreover, the ratio of epidermal LC PKC⁺/CDla⁺ was reduced in all the dermatoses studied, suggesting activation of PKC-β, with subsequent down-regulation. Within the dermis, increased PKC-β staining of infiltrating cells was observed in all the conditions studied except lamellar ichthyosis and non-bullous ichthyosiform erythroderma. These data indicate that: (i) down-regulation of LC FKC-β occurs in a variety of inflammatory and hyperplastic skin disorders, and is not unique to psoriasis, and (iii the pattern of epidermal LC PKC-β and CDla expression varies among the diseases studied. In mice, PKC activation induces LC migration. Thus, down-regulation of epidermal LC PKC-β associated with reduced CDla⁺ epidermal LCs in allergic and irritant contact dermatitis suggests that PK.C-β may transduce the signal for migration of LCs from human epidermis.     

Autoradiographic studies of cell dynamics in immunogenic granulomas transplanted into the skin of athymic nude mice

Summary Schistosome egg granulomas in the livers of thymus-intact (nu/+) mice are large and contain eosinophils and mast cells, while those in nude athymic (nu/nu) mice are small and devoid of eosinophils or mast cells. To investigate the cell sources and cell kinetics of hepatic granulomas of nu/+ mice isolated and grafted into the skin of nu/nu mice, biopsies taken after grafting were examined by light and electron microscopy and autoradiography after ³H-thymidine (TdR) injection of either the donor or recipient mice. At 1 week, the grafted granulomas appeared to be amorphous and were surrounded by leukocytes, and the ³H-TdR-labeled donor cells had disappeared. After 2 weeks, repopulation with macrophages began and by 3–5 weeks, the granulomas morphologically resembled hepatic lesions of nu/+ mice. Injection of recipients with ³H-TdR before grafting, showed that labeled macrophages, eosinophils, and mast cells repopulated in granulomas. No granulomas were seen when nu/nu mice were grafted with schistosome eggs alone, and organ culture of nu/+ granulomas before grafting reduced the number of repopulated granulomas. These findings indicate that nu/+cells in grafted granulomas are replaced by nu/nu cells. Granulomatous reaction of the grafted sites in nu/ nu mice is influenced by a substance in nu/+ granulomas, and cells of nunu mice locally acquire a nu/+ type response.     

Role of Langerhans cells in epidermotropism of T cells

Summary Certain T lymphocytes display a specific affinity for the epidermis (epidermotropism). Recent studies have suggested that Ia⁺ Langerhans cells (LCs) are possible targets for the epidermotropism. A variety of self-Ia-reactive cloned T cells were tested for their ability to migrate into the epidermis following intradermal inoculation into the footpads of syngeneic mice. Clone BB5 was chosen as representative of the epidermotropic T cells. We investigated whether the depletion of Ia⁺ LCs from the epidermis by tape-stripping could alter the migration of BB5 cells into the epidermis. The epidermal invasion of BB5 cells was markedly impaired in those mice whose LCs were depleted by 95% after repetitive tape-stripping. Because production of epidermal-derived thymocyte activating factor (ETAF) by the epidermal cells was augmented after repetitive tape-stripping, the diminished migration of BB5 cells into tape-stripped epidermis did not result from a decrease in ETAF production which is thought to attract T cells chemotactically. These results suggest that Ia⁺ LCs may play an inductive role in the preferential migration of T cells into the epidermis.     

Low ICAM-1 expression in the epidermis of depigmenting C57BL/6J-mivit/mivit mice: A possible cause of muted contact sensitization

Abstract The depigmenting C57BL/6J-mi^vit/mi^vit) (mi^vit/mi^vit) mouse, a congenic mutant of the C57BL/6 strain, exhibits an isolated, single immune deficiency. It is unable to mount a normal immune/inflammatory response upon epicutaneous application of DNFB or TNCB, although it does respond normally to oxazalone. The present investigtions have been carried out to further study this deficiency. In vivo, C57BL/6 mice could be sensitized by the epicutaneous application of the hapten TNCB, the subcutaneous injection of haplen(TNBS)-conjugated C57BL/6, and hapten conjugated mi^vit/mi^vit epidermal cells. In the mi^vit/mi^vit mice, however, only subcutaneous injection of haptcnizcd C57BL/6 epidermal cells caused an immune response. The response of these mi^vit/mi^vit mice could be documented only by adoptive transfer of splenic lymphocytes into naive C57BL/6 animals which then reacted to challenge doses of TNCB. These observations suggest that mi^vit/mi^vit epidermal cells can process and present and mi^vit/mi^vit T lymphocytes can react to the antigen. We postulated the presence of a deficient in vivo interaction between epidermal cells and T lymphocytes in the mi^vit/mi^vit mice. ICAM-I is an important adhesion signal regulating epidermal cell/T-lymphocyte interaction. Us expression in mi^vit/mi^vit mice was studied using YN1/1 antibody against MALA-2, the murine counterpart of human ICAM-1. In contrast to C57BL/6 animals, the mi^vit/mi^vit epidermis essentially did not stain with the antibody after hapten challenge. In vitro after stimulation with TPA or IFN-γ, the mi^vit/mi^vit epidermal cells expressed significantly lesser amounts of ICAM-1 than the C57BL/6 epidermal cells. Lower expression of ICAM-1 by mi^vit mi^vit/mi^vitsol;mi^vit epidermal cells has also been demonstrated both by direct staining and by flow cytomelry. The binding of lymphocytes to mi^vit/mi^vit epidermal monolayers, which were stimulated to express ICAM-1 by IFN-y, was decreased compared to that of C57BL/6 epidermal cells. We conclude that the muted contact sensiliza-tion response detected in vivo in the mi^vit/mi^vit mice at least partly results from lower expression of ICAM-1 and thus defective epidermal ccll/T-lymphocyte interaction.