TRIM21 and Autoimmunity: Furthermore, Co-19 seems to trigger the overexpression of the tripartite motif-containing protein 21 (E3 protein ligase TRIM21), which belongs to a tripartite motif protein family that is encoded by gene 21 and is an important autoantigen in autoimmune pathologies (Sjogren syndrome, systemic lupus erythematosus (SLE)).