Background Malassezia is the aetiological agent of pityriasis versicolor. The mycelial phase of the organism predominates in lesions of pityriasis versicolor.
Objectives To evaluate the cell-mediated immune (CMI) response to the mycelial phase of Malassezia in patients with this disease, which has not previously 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 examined. The responses to the mycelial form of three strains of the organism were assessed using lymphocyte transformation and leucocyte migration inhibition assays.
Results The transformation responses of the lymphocytes from both patients and controls gave transformation indices ≤ 3, although the responses of lymphocytes from patients with pityriasis versicolor to the mycelial form of Malassezia strains were generally higher than those of the controls. In the leucocyte migration inhibition assay, leucocytes from patients with pityriasis versicolor and controls responded to the mycelial antigens of three different Malassezia strains; however, there was no significant difference in leucocyte response between patients with pityriasis versicolor and controls.
Conclusions Patients with pityriasis versicolor do not therefore have a CMI deficiency to Malassezia mycelial antigens but fail to generate a protective CMI response to mycelial antigens over and above that of control individuals during active disease.