Fig 1: TRIM21 deficiency causes overexpression of IRF5 due to decreased ubiquitylation. (A) Extracts from resting B cells from Trim21+/+ and Trim21-/-MRL/lpr mice, which were stimulated with anti-IgM Ab and TLR3 ligand for 72 h, were immunoprecipitated with anti-IRF5 Ab and blotted with anti-ubiquitin Ab. Ubiquitylated IRF5 protein in the total cell lysate is decreased in the total extracts from Trim21-/-MRL/lpr mice as compared with Trim21+/+MRL/lpr mice (top panel). The amount of total ubiquitylated proteins is not different in two genotypes (the second panel). The amount of unubiquitylated IRF5 protein was higher in cells from Trim21-/-MRL/lpr mice as compared with Trim21+/+MRL/lpr mice (the third panel). ß-Actin was used as a loading control (the lowest panel). (B) Western blot analysis shows that the expression level of IRF5, IRF4, and IRF8 protein in resting B cells at 72 h after stimulation with anti-IgM Ab and TLR3 ligand is higher in Trim21-/-MRL/lpr mice as compared to Trim21+/+MRL/lpr mice (n = 4 in each group). (C) mRNA expression levels of Blimp-1, Bcl6, Irf5, Irf4, and Irf8 in resting B cells at 72 h after stimulation with anti-IgM Ab and TLR3 ligand (n = 4 in each group) in qPCR. Statistically significant (*p < 0.05 and **p < 0.01) data by Student's t-test, respectively.