TRIM21 and infection: At the same time, TRIM21 sends a signal to the cell nucleus to activate certain genes that protect the cell from subsequent infection.41 Recently, it was reported that intracellular antibody signaling is regulated by phosphorylation of TRIM21, and the activation of TRIM21 is independent of all known pattern recognition receptors (PRRs).42 Activation of TRIMK21 catalyzes K63-ubiquitin chain formation, thereby stimulating transcription factor pathways involving NF-κB, AP-1 and IRF3, IRF5, IRF7.