There are now many studies indicating that Pityrosporum ovale (Malassezia) plays an important role in seborrheic dermatitis (2). Many treatment studies describe the effectiveness of antimycotics, which reduces the number of P. ovale; recolonization leads to a recurrence of seborrheic dermatitis. The increased incidence of seborrheic dermatitis in patients with immunosuppressive disorders suggests that the relationship between P. ovale and the immune system is of importance.
P. ovale can activate complement by both the classic and alternative pathway (3). The humoral immune response to P. ovale in patients with seborrheic dermatitis and pityriasis versicolor has been studied using different antigen preparations and different techniques (3,4). Elevated titers in patients compared to controls as well as no difference in titers have been reported (3,4). In patients with seborrheic dermatitis, a reduced lymphocyte transformation response compared to healthy controls has been reported in two studies (5,6). However, in another study an enhanced lymphocyte stimulation response compared to healthy controls was found (7). In two recently published studies, no difference in lymphocyte stimulation response was found between patients with seborrheic dermatitis and healthy controls (8,9). In an immunological screening of patients with seborrheic dermatitis, we have found low (<0.7) responses in lymphocyte transformation tests to PHA and ConA in 13 of 30 patients (10). However, a recent study was not able to confirm that (8). Ashbee et al. found a normal PHA stimulation response in patients with seborrheic dermatitis compared to controls (7). In an earlier study we found a normal, but in the lower range (<1) CD4:CD8 ratio in 26 out of 30 patients with seborrheic dermatitis (10). Ashbee et al. found a normal CD4 : CD8 ratio in patients compared to controls (7). Kieffer et al. found a low CD4:CD8 ratio in 13 of 19 patients with seborrheic dermatitis (11).
In a study by Neuber et al., IL-2 and IFN-y production by lymphocytes from patients with seborrheic dermatitis was markedly depressed and IL-10 synthesis was increased after stimulation with P. ovale extract (5). In another paper by Kesevan et al., the Pityrosporum yeast suppressed the production of the proinflammatory cytokines IL-1 p, IL-6, and TNF-a (12).
In an immunohistochemical study in patients with seborrheic dermatitis deposits of complement C3c and IgG were found in the stratum corneum below
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