monensin and Dermatitis--Contact

Langerhans cells (LCs) are antigen-presenting cells of the skin that trap small contact-sensitizing molecules and induce cutaneous hypersensitivity. LCs can present larger molecules but the mechanisms of processing have required investigation. A system combining in vitro culture of antigen with epidermal cells in the presence of inhibitors, followed by fixation and transfer of these antigen/drug-treated epidermal cells to naive mice, was developed to investigate the steps of antigen processing. Langerhans cells undertake similar, but not identical, pathways for the processing of simple and complex molecules. Complex molecules such as trinitrophenyl conjugated to ovalbumin (TNP-OVA) were internalized and modification required a chloroquine-sensitive proteolysis step and a cycloheximide-sensitive protein synthesis step. This modified product was actively recycled to the cell membrane as presentation was inhibited by blocking receptor translocation with either monensin or cytochalasin B. Small contact sensitizers such as trinitrophenyl did not undergo modification but required internalization and presentation was also inhibited by blocking receptor translocation.

Topics: Animals; Antigen Presentation; Chloroquine; Cycloheximide; Cytochalasin B; Dermatitis, Contact; Female; Langerhans Cells; Male; Mice; Mice, Inbred BALB C; Mice, Inbred C3H; Monensin; Ovalbumin; Skin; Trinitrobenzenes

MHC class II molecules play an important role during the sensitization phase of allergic contact dermatitis. To study the influence of contact allergens on the expression of these molecules by murine epidermal Langerhans cells (LC), we performed a flow-cytofluorometric analysis of the Ia-antigen expression after in vivo application of contact allergens. A distinct decrease in the Ia-antigen expression of the entire LC population was noticed 3 h after in vivo application of the contact allergen 2,4-dinitrofluorobenzene (DNFB). This decrease was transient and balanced 24 h after in vivo application of DNFB. A downregulation was also detectable after in vivo application of the contact allergens 1-chloro-2,4-dinitrobenzene (DNCB), oxazolone, K2Cr2O7, 2,4,6-trinitrochlorobenzene (TNCB), and toxic concentrations of the irritant compound sodium dodecyl sulfate (SDS). In vitro studies showed that freshly prepared as well as 3-d cultured LC downregulated their Ia-antigen expression in the presence of DNFB, which was used as a model compound. This decrease was not inhibited by the MHC class II molecule transport-inhibitor brefeldin A nor by the ionophore monensin. The inhibition of receptor-mediated endocytosis with hypertonic media (0.45 M sucrose) abolished the DNFB-mediated downregulation of Ia-antigen expression. An accelerated clearance of cell-surface-expressed antibody-labeled IA molecules was detectable in the presence of DNFB. Internalization studies carried out with peroxidase-labeled anti-IA-antibody complexes showed remarkable alterations in the intracellular distribution of endocytosed material under the influence of subtoxic concentrations of DNFB, DNCB, K2Cr2O7, and TNCB. The irritant substance sodium dodecyl sulfate (SDS) influenced the intracellular distribution pattern of internalized material only when used in toxic concentrations. An augmented participation of MHC class II molecules in endocytotic processes is mediated by reactive substances like contact allergens and might contribute to the processing and presentation of these compounds.

Topics: Allergens; Animals; Antibodies, Monoclonal; Brefeldin A; Cyclopentanes; Dermatitis, Contact; Endocytosis; Female; Histocompatibility Antigens Class II; Hypertonic Solutions; Langerhans Cells; Male; Mice; Mice, Inbred BALB C; Monensin