Abstract Our laboratory has recently developed the monoclonal antibody 4F7 which recognizes a molecule on dendritic cells in the dermis of mice that is upregu- lated after application of contact allergens in vivo. Furthermore, this antibody detects an antigen on den- dritic cells in spleen, lymph nodes and colon. In order to study the influence of contact allergens on the sur- face expression of the 4F7 molecules on dendritic cells, FACScan analysis of splenic dendritic cells was car- ried out after in vitro application of contact allergens. Freshly isolated splenic dendritic cells were found to be positive for 4F7, 33D1, N418 (CD11c) and MHC class II. After overnight culture the expression of the dendritic cell-specific molecules 4F7 and 33D1 was de- creased. This downregulation was not inhibited by the addition of the cytokines TNF-α or GM-CSF during in vitro culture. However, in vitro treatment of freshly isolated dendritic cells with the contact allergen 2,4- dinitrofluorobenzene prevented this downregulation of the 4F7 surface molecules. The same effect was ob- served after treatment with other contact allergens (1-chloro-2,4-dinitrobenzene or potassium dichromate). Treatment with the irritant substance sodium dodecyl sulphate, the lectins concanavalin and lipopolysaccha- ride or the phorbol ester PMA did not prevent the downregulation of 4F7 and 33D1. Moreover, the influ- ence of contact allergens on the expression of the mole- cules 4F7 and 33D1 was not inhibited by the protein synthesis inhibitor cycloheximide. No effects of contact sensitizers were detectable on the expression of MHC class II molecules or the costimulatory molecules B7 and heat-stable antigen. Our results show a specific stabilizing effect of contact allergens on the dendritic cell-specific molecules 4F7 and 33D1 independent of de novo protein synthesis. Key words 4F7 · Dendritic cells · Contact allergens · Langerhans cells Introduction The central importance of dendritic cells (DC) in antigen presentation and T-cell activation is well established [1]. DC are critically involved in initiating primary immune responses such as the sensitization of MHC-restricted T cells and the formation of T cell-dependent antibodies [2–4]. These cells represent a subpopulation of bone marrow-derived leucocytes that are widely distributed throughout the body as interdigitating cells in lymphoid organs, veiled cells present in afferent lymph, circulating blood DC, dermal DC and Langerhans cells as the general antigen-presenting cells in the epidermis [1, 5]. DC are also found in nonlymphoid organs such as the heart, lung, gut and synovium [1]. Although there is considerable interest in DC, working with these cells has proved difficult because in all tissues that have been studied to date, DC comprise only a small fraction of the total cells and only a few antibodies are known that specifically react with them. In our laboratory a mAb (4F7) has been generated by immunizing rats with Langerhans cell-enriched epidermal cells obtained from mouse earskin after epicutaneous ap- plication of the contact allergen 2,4-dinitrofluorobenzene (DNFB) [6]. In normal mouse skin the antibody 4F7 de- tects the few dermal cells showing morphological, pheno- typical, and functional properties of DC, but lacking Bir- beck granules. After epicutaneous DNFB application, the number of 4F7 + DC in the dermis is increased and, in ad- dition, some labelled Langerhans cells occur in the epi- dermis in situ [6]. Furthermore, 4F7 reacts specifically with a molecule on DC in spleen, lymph nodes, and colon [6, 7]. Characterization of 4F7 + spleen DC with mAbs has revealed the expression of MHC class I and class II, Helmut Jonuleit · Sabine Lohmann · Gabriele Müller · Uwe Lempertz · Alexander Enk · Jürgen Knop Specific stabilization of the 4F7 molecule on dendritic cells by contact allergens Arch Dermatol Res (1996) 288 : 745–752 © Springer-Verlag 1996 Received: 16 October 1995 ORIGINAL PAPER Helmut Jonuleit () · Sabine Lohmann · Gabriele Müller · Uwe Lempertz · Alexander Enk · Jürgen Knop Clinical Research Unit, Department of Dermatology, University of Mainz, Langenbeckstrasse 1, D-55131 Mainz, Germany Tel. 49-6131-173541; Fax 49-6131-176614