Local immune response to primary infection and re-infection by Clonorchis sinensis in FVB mice.

Although Clonorchis sinensis lives in the bile duct, few studies have investigated the local immune response in the liver and bile duct. To investigate the local immune response to C. sinensis, we investigated the activation and recruitment of various immune cells and cytokine levels in the liver and bile duct lymph nodes (BLN) in FVB mice after primary infection and re-infection. Male 4-week-old FVB mice were divided into 6 experimental groups: uninfected controls, primary infection lasting 1week (PI 1w), primary infection lasting 4weeks (PI 4w), praziquantel treatment after PI 4w (Tx), re-infection lasting 1week after Tx (RI 1w), and re-infection lasting 4weeks after Tx (RI 4w). Recovery rates were 80.0% and 73.0% in PI 1w and PI 4w mice, respectively, but significantly decreased during re-infection to 26.6% in RI 1w and 13.3% in RI 4w. This result suggested that the mice were resistant to re-infection. In the liver, Kupffer cells were augmented 70-fold in PI 1w mice (P<0.001). Kupffer cells expressed Th2-related cytokines (IL-10 and IL-13) during primary infection. In addition, serum levels of C. sinensis-specific IgG1 and IgG2a strongly increased in RI 1w mice. Secretion of C. sinensis-specific IgE reached a plateau at 4weeks after primary infection, and remained elevated in all infected groups. In conclusion, during infection with C. sinensis, Kupffer cells likely act as antigen-presenting cells, stimulating the Th2 cytokine production system.