Cell-mediated immunity to the mycelial phase of Malassezia spp. in patients with pityriasis versicolor and controls

Background Malassezia is the aetiological agent of pityriasis versicolor. T he mycelial phase of the organism predominates in lesions of pityriasis ver sicolor. Objectives To evaluate the cell-mediated immune (CMI) response to the mycel ial phase of Malassezia in patients with this disease, which has not previo usly been studied. Methods The CMI status of 12 patients with pityriasis versicolor and 12 age - and sex-matched controls to mycelial antigen(s) of the organism was exami ned. The responses to the mycelial form of three strains of the organism we re assessed using lymphocyte transformation and leucocyte migration inhibit ion assays. Results The transformation responses of the lymphocytes from both patients and controls gave transformation indices less than or equal to 3, although the responses of lymphocytes from patients with pityriasis versicolor to th e mycelial form of Malassezia strains were generally higher than those of t he controls. In the leucocyte migration inhibition assay, leucocytes from p atients with pityriasis versicolor and controls responded to the mycelial a ntigens of three different Malassezia strains; however, there was no signif icant difference in leucocyte response between patients with pityriasis ver sicolor and controls. Conclusions Patients with pityriasis versicolor do not therefore have a CMI deficiency to Malassezia mycelial antigens but fail to generate a protecti ve CMI response to mycelial antigens over and above that of control individ uals during active disease.