Recent evidence indicates that alterations to epigenetic DNA methylation patterns contribute to many autoimmune diseases. Biliary atresia (BA) is a virus-induced autoimmune disease characterized by impaired T cells, which may be due to aberrant DNA methylation. CD11a, a subunit of the beta 2-integrin LFA-1 (CD11a/CD18) with costimulatory functions, is overexpressed due to hypomethylation of its promoter regulatory elements in CD4+ T cells from patients with many autoimmune diseases. However, it is unknown whether aberrant expression and methylation of CD11a occur in T cells from infants with BA. We aimed to compare the CD11a expression level and the methylation status of the CD11a promoter region in CD4+ T cells from BA infants and healthy controls (HC). We used real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) to examine CD11a mRNA levels in CD4+ T cells from BA and HC infants. Bisulfite sequencing was used to determine the methylation status of the CD11a promoter and flanking regions in CD4+ T cells from BA and HC infants, and in CD4+ T cells with DNA methylation inhibitors. We found that CD11a expression is significantly decreased in BA CD4+ T cells (P = 0.007). This was associated with hypermethylation of the CD11a promoter region in CD4+ T cells from infants with BA. Treatment with a DNA methylation inhibitor decreased CD11a promoter methylation and increased CD11a mRNA. Therefore, DNA hypermethylation at the CD11a locus contributes to the lowered expression of CD11 a in BA CD4+ T cells. (C) 2011 Elsevier Inc. All rights reserved.