MHC CLASS-II ANTIGEN EXPRESSION IS INCREASED IN DIFFERENT FORMS OF URTICARIA

Urticarial reactions encompass a variety of inflammatory and immunolog ical reactions. In order to clarify specific aspects of these processe s, we analyzed the distribution and sequential expression of major his tocompatibility complex II (MHC class II) molecules in tissue sections from different types of whealing reactions. Using immunohistochemical techniques and monoclonal antibodies, expression of HLA-DR, HLA-DP, a nd HLA-DQ was examined on resident and infiltrating cells in different skin cell compartments, comparing early with longer-lasting wheals an d lesional with uninvolved skin. Sequential biopsies were studied in c old urticaria (CU). No increase of MHC class II molecule expression wa s found in early prick test wheals to common inhalant allergens. In CU , however, sequential biopsies demonstrated an up-regulation of MHC cl ass II molecules within 30 min after elicitation. This was more pronou nced in longer-lasting urticaria lesions of acute, chronic recurrent a nd delayed pressure urticaria, with HLA-DR and, to a lesser degree, HL A-DP and HLA-DQ being noted on cell infiltrates, on vascular endotheli a and around nerves and sweat glands. Nonlesional skin in these types of urticaria also showed increased MHC class II expression. Longer-las ting urticarial wheals are thus associated with up-regulation of MHC c lass II molecules on resident and infiltrating cells, suggesting an in volvement of these molecules in the pathomechanisms of these types of urticarial lesions.