Abstract: Objective To investigate the expression and the role of costimulatory molecules B7:CD28/CTLA-4 in erythema nodusum of patients with Behcet disease. Methods Erythema nodusum from 5 patients with progressing Behcet disease and normal skin from 2 healthy individuals were analyzed by immunohistochemical examination for expression of CD4, CD8, CD19, CD68, HLA-DR, B7-1, B7-2, CD28 and CTLA-4 molecules. Labelled cells were visualised using either single or double staining techniques. Results Approximately 90% of epithelial cells in erythema nodusum expressed B7-1 and B7-2 molecules, but no expression of CD28 and CTLA-4. CD4⁺Tcells, CD8⁺T cells, CD19⁺cells, CD68⁺cells, HLA-DR⁺cells, B7-1⁺cells, B7-2⁺cells, CD28⁺cells and CTLA-4⁺cells were increased significantly in the dermis and subcutaneous tissue. Double staining showed that CD28 molecules were expressed on 100% of CD4⁺T cells, CTLA-4 molecules were expressed on 47.9% of CD4⁺T cells, respectively. All CD68⁺ cells expressed B7-1 and B7-2 molecules. B7-1 and B7-2 molecules were expressed on 74.5% and 60.8% of HLA-DR⁺cells, respectively. Conclusion CD28 and CTLA-4 molecules are mainly expressed on CD4~+T cells, B7-1 and B7-2 are mainly expressed on macrophages, antigen-presenting cells and keratinocytes. B7:CD28/CTLA-4 costimulatory pathway can induce the function and activation of macrophages and T lymphocytes, and play an important role for the incidence, diffusion and consistence of inflammation in erythema nodusum.

Key words: Behcet disease, erythema nodusum, costimulatory molecules