Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED; APS-1) is an autosomal recessive autoimmune disease, caused by mutations in the AIRE (autoimmune regulator) gene. Due to the proposed role of AIRE in central immune tolerance, the immune investigation of four females diagnosed with APECED, their siblings, parents and 14 age-matched controls was performed. The parameters analyzed included immunoglobulins, autoantibodies, cellular immunity and production of cytokines IFNgamma, IL-4 and IL-10, reflecting Th1xTh2 balance. Low IFNgamma levels (455 +/- 191 pg/ml) were detected in all affected girls compared to controls (910 +/- 406 pg/ml). Two girls with homozygous R257X mutations showed similarly marked elevation of IgM and increase of CD3+CD4+ lymphocytes. Positive autoantibodies against smooth muscle were found in one affected girl; another girl and her mother had antibodies against gastric parietal cells. Interestingly, all fathers had dramatically elevated levels of IgA and activated T lymphocytes. High frequency of abnormal immune results among parents is a novel finding which might suggest a subclinical immune deficit in heterozygotes with AIRE mutations.