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Background: Migration and maturation of epidermal dendritic cells, the Langerhans cells (LC), are central events in the initiation of the cutaneous immune response. LC migration from skin to draining lymph nodes is regarded as an indispensable step for the early phase of antigen-specific sensitization. Among the several agents which influence the ability of LC to migrate, previous studies have revealed that matrix metalloproteinases (MMPs) and protein kinase C (PKC) contribute to promoting LC migration. In this work, we studied the effect of two recently developed PKC and MMPs inhibitors of vegetable origin on the migration of in vitro activated LC. Methods: The migratory capacity of epidermal and in vitro generated LC was assessed using a reconstituted basement membrane assay (Matrigel), mimicking the prerequisite passage through the dermal-epidermal basement membrane on the way to the lymph nodes. Results: Contact with chemical allergens, Bandrowski’s base or 2,4-dinitrobenzenesulfonic acid (DNBS), triggered migration. In the presence of PKC inhibitors, D-erythro-sphingosine and OX100, or an inhibitor of MMPs, LU105, allergen-induced migration of LC was strongly decreased. The association between OX100 and LU105 was more efficient in modulating the migration of activated LC compared to each molecule tested separately. Conclusions: These results showed that PKC and MMPs inhibitors act in synergy to inhibit the migration of activated epidermal dendritic cells in vitro. They underscore the role of PKC and MMPs inhibitors and suggest they may be of relevance for therapeutically regulating epidermal dendritic cell migration in inflammatory dermatoses.

Background: GM-CSF, IL-4 and TGF-β1 can drive the differentiation of CD14+ monocytes towards the immature Langerhans (LC) dendritic cell (DC) pathway. Their in vivo epidermal LC counterparts are mainly identified by the langerin molecules which are cross-linked into Birbeck granules (BG) upon mannose residue activation. Objective: The IL-13 and IL-14 cytokines sharing similar anti-inflammatory/immune functions, we investigated whether IL-13 (plus GM-CSF/TGF-β1) can substitute for IL-4 to preferentially skew the CD14+ monocyte differentiation towards LC. Methods: CD14+ monocytes cultured in the presence of GM-CSF/TGF-β1/IL-13 (IL-13-DC) for 6 days were then compared to GM-CSF/TGF-β1/IL-4-generated LC (IL-4-DC) by studying their phenotype, ultrastructural and functional features. Results: IL-13, in synergy with GM-CSF/TGF-β1, induced CD14+ monocytes to differentiate into LC after a short TNF-α stimulation more efficiently than IL-4. IL-13-DC are more immature than IL- 4-DC, as shown by both their preserved expression of monocyte markers (CD14, CD68) and their strong capacity of FITC-dextran uptake. Conclusion: IL-13 in combination with GM-CSF/TGF-β1/TNF-α favors CD14+ monocyte differentiation into LC which display numerous BG.

Recently, sustance P receptors (SPR) have been detected in neonatal foreskin. Our purpose was to determine the expression of SPR in other localizations than neonatal foreskin. As SP has been implicated in the pathogenesis of inflammatory cutaneous lesions, we wondered whether SPR localization was modified in psoriatic lesions. In normal skin, SP binding sites were detected using biotinylated SP and abrogated by a specific NK1 antagonist (spantide) on blood vessels, sweat glands and hair follicles. In the normal epidermis, SPR were usually observed on granular layers but may also be observed on other cell layers. The SP binding processed on cultured keratinocytes demonstrated that SPR were expressed in the epidermis, except basal cell layers, confirming that keratinocytes constitutively express SPR. In skin lesions of psoriatic patients, SP binding sites were expressed on the uppermost keratinocytes which are not granular cells, and seem to be overexpressed. Our results raise the question of the role of SPR on psoriatic keratinocytes.

As retinoic acid (RA, all trans) induces irritant reactions when applied topically to skin, we wondered whether it may be involved in the activation state of keratinocytes through ICAM-1 induction. Human skin explants and cultured keratinocytes were treated by RA and /or interferon-Γ (IFNΓ) at different concentrations during 24, 48 and 72 h. ICAM-1 expression was examined and quantified by immunohistochemistry, in situ, on cutaneous frozen sections and in cultured keratinocytes by flow cytometry analysis. Expression of mRNA was checked by Northern blot hybridizations using an oligonucleo-tide probe. Our results indicate: (1) the absence of spontaneous ICAM-1 expression by normal human keratinocytes both in skin explants and in cultures; (2) an ICAM-1 -induced expression after 48 h of treatment by RA concentrations > 10-6M; this induction is dose- and time-dependent; in skin explants, ICAM-1 is occasionally observed on foci of epidermal cells; this protein induction is correlated with transcript expression in cultured keratinocytes; and (3) a synergistic effect of RA and IFNΓ (5 IU/ml) on the percentage of ICAM-1 -positive cells and the level of expression of the protein. These findings indicate that RA, in a therapeutical range of concentrations, can induce or stimulate ICAM-1 expression in normal human keratinocytes. This may in part explain the erythematous reaction observed in vivo after topical applications of RA which may be considered as a mediator of keratinocyte activation.

Immunological characterization of cells in the malignant epidermotropic lymphomas requires techniques which define the lymphocytic nature of the cells, and for the lymphocytes techniques which demonstrate subpopulations of T or B cells. The results obtained using such methods in patients with cutaneous lymphomas are reported. The predominantly thymodependent nature of the cells of epidermotropic lymphomas is confirmed and the existence of a thymodependent non-epidermotropic cutaneous lymphoma is demonstrated.

We have investigated on human skin the reactivity of a panel of 42 anti-thymus monoclonal antibodies (MCA) supplied by the Third International Workshop and Conference on Human Leucocyte Differentiation Antigens, Oxford, 1986. MCA of the first cluster of differentiation (CD1) define a group of surface molecules expressed by cortical thymocytes. Some of them (OKT6, M241 and Na1/34) have been shown to react in normal human skin with the epidermal Langerhans cells (LC). Twenty-two CD1 MCA were investigated in the present study. On normal human skin, 13 MCA reacted with LC in situ. This result suggests and confirms the heterogeneity of CD1 MCA. Recently, some of them were shown to recognize biochemically different molecules and/or epitopes of thymocytes. In addition, 20 anti-thymic epithelium MCA were tested on human skin. The MCA which only reacted with the thymic epithelial cell network (except Hassall’s corpuscles) decorated only the epidermal basal cell layer. The MCA which reacted with all the thymic epithelial cells (including Hassall’s corpuscles) decorated all the epidermal cell layers. These results confirm the heterogeneity of the thymic epithelial microenvironment and underline the antigenic similarities between the thymic epithelial structures and the different epidermal cell layers. The existence of bone-marrow-derived CD1-positive cells (thymocytes or LC) in an epithelial cell network (the thymus and the epidermis) focus the speculation around the immunological role of the epidermal basal cell layer in the T cell education and the exact lineage of the epidermal LC.

The malignant cutaneous lymphomas come into the category of hematodermias but can equally be considered as an abnormality of the immune system. Having described the methods used in the immunocytological investigation of 21 lymphomas and 3 pseudolymphomas, the authors expound their classification of malignant cutaneous lymphomas before stating the results obtained in immunocytological studies in each of the groups. They show how formal separation between epidermotropic malignant cutaneous lymphomas and non-epidermotropic malignant cutaneous lymphomas can be confirmed by immunocytological and ultrastructural facts.