Pityrosporum orbiculare-reactive T-cell lines in atopic dermatitis patients and healthy individuals.

The yeast Pityrosporum orbiculare is one of the factors that may contribute to atopic dermatitis (AD). In the present study we compared the T-cell response to P. orbiculare in 12 AD patients with specific immunoglobulin (Ig)E antibodies (Ab) in serum against P. orbiculare with that of six non-atopic healthy controls. Freshly isolated peripheral blood mononuclear cells (PBMC) were cultured for 3 days in the presence of P. orbiculare extract. The proliferative response as measured by [3H]-thymidine incorporation was significantly higher in the AD patients than in the healthy controls (P < 0.05). Furthermore, significantly higher levels of interleukin (IL)-5 (P < 0.05), as analyzed by ELISA, were produced by PBMC from the AD patients compared to the healthy controls. Pityrosporum orbiculare-reactive T-cell lines (TCL) established by P. orbiculare stimulation of PBMC for 11 days produced significantly higher levels of IL-4 and IL-5 after stimulation with anti-CD3 Ab and showed a higher IL-4/interferon (IFN)-gamma ratio (P < 0.05) in the AD patients compared to the healthy controls. The higher proliferative PBMC response to P. orbiculare and the Th2-like cytokine production by P. orbiculare-stimulated TCL from AD patients indicate that P. orbiculare may play a role in maintaining skin inflammation in AD.