title: Positive atopy patch test reactions to Pityrosporum orbiculare in atopic dermatitis patients.
abstract: BACKGROUND
  Pityrosporum orbiculare, although a part of our normal cutaneous microflora, can cause skin infections and induce specific immunoglobulin (Ig) E antibodies in atopic dermatitis patients. P. orbiculare is therefore considered to be one of the trigger factors for atopic dermatitis.
  
  
  OBJECTIVE
  To investigate if P. orbiculare can induce an eczematous reaction in atopic dermatitis patients, seborrhoeic dermatitis patients and healthy controls.
  
  
  METHODS
  Fifteen atopic dermatitis patients, eight seborrhoeic dermatitis patients and eight healthy controls were patch tested with extract of P. orbiculare on non-lesional, tape-stripped skin of the back. NaCl was used as a negative control. The patch tests were evaluated after 24, 48 and 72 h. Skin biopsies were taken from P. orbiculare patch test sites at 24 h and 72 h, from NaCl patch test sites at 72 h, from non-lesional skin and, in the atopic dermatitis patients, also from lesional skin. The skin biopsies were investigated with immunohistochemical techniques. P. orbiculare-specific IgE in serum was analysed with RAST.
  
  
  RESULTS
  Specific IgE to P. orbiculare was found in serum from 13/15 atopic dermatitis patients and in eight of them a positive patch test reaction to P. orbiculare was observed, with a maximal reaction at 48 h. Significantly higher serum levels of P. orbiculare-specific IgE were detected in patch test-positive compared with patch test-negative atopic dermatitis patients (P < 0. 01). The seborrhoeic dermatitis patients and healthy controls were RAST and patch test-negative for P. orbiculare. In the patch test-positive atopic dermatitis patients an infiltration of CD4+ T cells and eosinophils was observed at the P. orbiculare patch test sites together with an upregulation of ICAM-1 and HLA-DR expression.
  
  
  CONCLUSIONS
  P. orbiculare can induce an eczematous reaction in sensitized atopic dermatitis patients and may be an important trigger factor in these patients. The P. orbiculare patch test can be of diagnostic value in this subgroup of atopic dermatitis patients.
authors.affiliation: Department of Laboratory Medicine, Karolinska Institute and Hospital, Stockholm, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Tengvall Linder
authors.forename: C
authors.initials: C
authors.lastname: Johansson
authors.forename: A
authors.initials: A
authors.lastname: Scheynius
authors.forename: C
authors.initials: C
authors.lastname: Wahlgren
mesh_terms: D000293:Adolescent; D000328:Adult; D000918:Antibody Specificity; D002465:Cell Movement / Q000276:immunology; D003876:Dermatitis, Atopic / Q000276:immunology* / Q000382:microbiology* / Q000473:pathology; D012628:Dermatitis, Seborrheic / Q000276:immunology / Q000382:microbiology / Q000473:pathology; D003881:Dermatomycoses / Q000276:immunology* / Q000382:microbiology / Q000473:pathology; D004804:Eosinophils / Q000276:immunology / Q000473:pathology; D005260:Female; D006801:Humans; D007073:Immunoglobulin E / Q000097:blood; D007074:Immunoglobulin G / Q000097:blood; D007150:Immunohistochemistry; D007963:Leukocytes, Mononuclear / Q000276:immunology / Q000473:pathology; D008213:Lymphocyte Activation; D008290:Malassezia / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D010328:Patch Tests; D013601:T-Lymphocytes / Q000276:immunology / Q000473:pathology
chemical_list: D007074:Immunoglobulin G; D007073:Immunoglobulin E