Detection of Pityrosporum orbiculare reactive T cells from skin and blood in atopic dermatitis and characterization of their cytokine profiles

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Abstract
Atopic dermatitis (AD) is associated with increased levels of serum IgE, and T-helper (Th) cells are thought to a play role in the pathogenesis. Individuals with AD often develop IgE antibodies against the yeast Pityrosporum orbiculare, a member of the normal cutaneous flora. The role of P. orbiculare in atopic dermatitis was investigated by examining the T-cell reactivity for P. orbiculare. Freshly isolated peripheral blood mononuclear cells (PBMC) were isolated from 10 AD patients with serum IgE antibodies against P. orbiculare, and from six healthy controls. The proliferative response after P. orbiculare stimulation, measured by [3H]thymidine incorporation, was examined in the PBMC and in T-cell clones (TCC) obtained from skin and blood of one patient. The cytokine profile of the TCC was determined by enzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA) and reverse transcriptase-polymerase chain reaction (RT-PCR) following challenge with either P. orbiculare extract or anti-CD3 antibodies and phytohaemagglutinin. The PBMC response to P. orbiculare was significantly higher in the AD patients than in the control group (P < 0.05). Twenty-nine out of 36 tested TCC derived from one responding patient were reactive for P. orbiculare. The clones were CD2+ and CD4+, except for one CD8+ blood clone. A majority of the TCC derived from lesional skin showed a Th2- or Th2/Th0-like cytokine profile. A co-expression of interleukin-5 (IL-5) mRNA and IL-13 mRNA was detected in five out of six P. orbiculare-reactive clones analysed for their cytokine gene expression with RT-PCR. Our data suggest that P. orbiculare can induce a T-cell response in AD patients. The Th2-like profile of P. orbiculare-reactive TCC derived from lesional skin indicates that P. orbiculare may play a role in maintaining IgE-mediated skin inflammation in AD.

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