Post-natal paucity of regulatory T cells and control of NK cell activation in experimental biliary atresia

Abstract

Although recent studies have identified important roles for T and NK cells in the pathogenesis of biliary atresia (BA), the mechanisms by which susceptibility to bile duct injury is restricted to the neonatal period are unknown. We characterised hepatic regulatory T cells (Tregs) by flow cytometry in two groups of neonatal mice challenged with rhesus rotavirus (RRV) at day 7 (no ductal injury) or day 1 of life (resulting in BA), determined the functional interaction with effector cells in co-culture assays, and examined the effect of adoptive transfer of CD4+ cells on the BA phenotype. While day 7 RRV infection increased hepatic Tregs (Foxp3+ CD4+ CD25+) by 10-fold within 3 days, no increase in Tregs occurred at this time point following infection on day 1. In vitro, Tregs effectively suppressed NK cell activation by hepatic dendritic cells and decreased the production of pro-inflammatory cytokines, including TNFalpha and IL-15, following RRV infection. In vivo, adoptive transfer of CD4+ cells prior to RRV inoculation led to increased survival, improved weight gain, decreased population of hepatic NK cells, and persistence of donor Tregs in the liver. (1) The liver is devoid of Tregs early after perinatal RRV infection; (2) Tregs suppress DC-dependent activation of naive NK cells in vitro, and Treg-containing CD4+ cells inhibit hepatic NK cell expansion in vivo. Thus, the post-natal absence of Tregs may be a key factor that allows hepatic DCs to act unopposed in NK cell activation during the initiation of neonatal bile duct injury.