Epidermal dendritic cells in psoriasis possess a phenotype associated with antigen presentation: in situ expression of beta 2-integrins.

Background: Epidermal dendritic cells (DCs) isolated from psoriasis possess greatly enhanced T lymphocyte-activating properties compared with DCs from normal skin, suggesting that DCs in psoriasis express surface antigens crucial for antigen presentation. These include beta 2-integrins and intercellular adhesion molecule (ICAM)-1.
Objective: Our purpose was to determine DC phenotype in psoriatic compared with normal epidermis with respect to these molecules.
Methods: Tissue sections were single labeled with a peroxidase antiperoxidase (PAP) immunohistochemical technique and double labeled where necessary with a combination of a PAP and an alkaline phosphatase-anti-alkaline phosphatase technique.
Results: In psoriatic compared with normal skin, decreased numbers of DCs expressed CD1a (p less than 0.05), whereas increased numbers of DCs expressed class II major histocompatibility antigens (p less than 0.05). In normal skin positive staining for CD18 was not observed, whereas in psoriasis both CD1a+ and CD1a- DCs expressed beta 2-integrins, LFA-1 (CD11a/CD18), and gp 150/95 (CD11c/CD18). DCs in atopic dermatitis and lichen planus were also found to express beta 2-integrins. Neither MAC 1 (CD11b/CD18) nor ICAM-1 was observed on DCs.
Conclusion: These data are consistent with either migration of dendritic antigen-presenting cells into the epidermis or in situ cytokine modulation of Langerhans cell phenotype in inflamed skin. Furthermore, they indicate that epidermal DCs in psoriasis and other cutaneous inflammatory diseases express molecules that are known to be crucial for Langerhans cell-driven T-cell activation in vitro.