Swine TRIM21 restricts FMDV infection via an intracellular neutralization mechanism.

The tripartite motif protein 21 (TRIM21) is a ubiquitously expressed E3 ubiquitin ligase and an intracellular antibody receptor. TRIM21 mediates antibody-dependent intracellular neutralization (ADIN) in cytosol and provides an intracellular immune response to protect host defense against pathogen infection. In this study, swine TRIM21 (sTRIM21) was cloned and its role in ADIN was investigated. The expression of sTRIM21 is induced by type I interferon in PK-15 cells. sTRIM21 restricts FMDV infection in the presence of FMDV specific antibodies. Furthermore, sTRIM21 interacts with Fc fragment of swine immunoglobulin G (sFc) fused VP1 of FMDV and thereby causing its degradation. Both the RING and SPRY domains are essential for sTRIM21 to degrade sFc-fused VP1. These results suggest that the intracellular neutralization features of FMDV contribute to the antiviral activity of sTRIM21. sTRIM21 provide another intracellular mechanism to inhibit FMDV infection in infected cells.