Contact Sensitivity to Pityrosporum ovale in Patients with Atopic Dermatitis

Abstract

The cause of atopic dermatitis (AD) is unclear, but from the clinical and histopathologic resemblance to allergic contact dermatitis, as well as the nature of the cellular-infiltrate seen in the skin lesions of AD, it is suspected that inflammatory changes based on cell-mediated immunity may be involved in the pathogenesis of the skin lesions. The morphology and distribution of the skin lesions change with age. However, seborrheic area, i.e. scalp and face, are involved in most patients. Suspecting a role played by regional microorganisms in the formation of these lesions, we studied contact sensitivity and immediate hypersensitivity to extracts from Pityrosporum ovale. In a chamber-scarification patch test, 75 (64%) of 118 patients with AD responded positively, compared with one (3%) of 35 healthy volunteers. However, no significant statistical correlations were found between contact sensitivity to P. ovale in patients with AD and any of the following factors: age, sex, distribution of skin lesions, presence of pruriginous papules, history of infantile seborrheic dermatitis, or concomitance of other atopic diseases. Lymphocyte transformation test with P. ovale antigen confirmed that those with positive patch test reactions showed significantly high stimulation indexes.

The antigenic substances divided by gel filtration high-performance liquid chromatography were found in a fraction of components with molecular weights above 60 KD. In addition, 25 (71%) of 35 patients with AD showed a positive immediate response to P. ovale extract in a prick test, whereas none of 11 healthy volunteers showed any response. Although the incidence of the positive immediate responses was similar to that in contact sensitivity, there was no clear correlation between the delayed and immediate hypersensitivity reaction. Based on these results, we think that P. ovale may play a role in the exacerbation of the skin lesions of AD.