HLA-DR EXPRESSION IS INDUCED ON KERATINOCYTES IN DELAYED-HYPERSENSITIVITY BUT NOT IN ALLERGEN-INDUCED LATE-PHASE REACTIONS

In view of increasing evidence suggesting an active immunoregulatory r ole of the skin keratinocytes and the observation that the differentia tion of allergen specific T lymphocytes is critical in the development of allergy, we evaluated epidermal expression of HLA-DR antigen in sk in reactions induced with an atopen (house dust mite) and with an non- atopic antigen (Hemocyanin). Two groups of patients with house dust mi te (Dermatophagoides pteronyssinus [Der p]) allergy were compared, one group was skin tested with Der p, the other group was immunized and s ubsequently skin tested with Helix pomatia Hemocyanin (HPH). Biopsy sp ecimens taken at 48 h after the HPH (n = 11) and Der p (n = 11) tests were analysed immunohistologically. Reactions in both groups were comp arable in size. Immunohistological analysis showed domination by CD4lymphocytes. Expression of HLA-DR antigen by epidermal keratinocytes w as observed in six out of 11 of the HPH induced reactions, but in none of the Der p induced reactions. Eosinophils were spotted only through out the Der p induced reactions, showing a good correlation with the n umber of CD4 positive lymphocytes. The lack of HLA-DR expression by ke ratinocytes during the allergen-induced reaction, compared with the He mocyanin induced reaction can be the result of a difference in cytokin e profile of the lymphocytes dominating the dermal in filtrate. On the other hand evidence exists that defective HLA-DR expression by kerati nocytes enhances antigen induced lymphocyte activation, and may thus c ontribute to the development of allergen-specific T-lymphocytes.