TRIM21 and systemic lupus erythematosus: Further analysis of the small subset of SLE sera positive for anti-Ro52‘classic’ antibodies, but negative for antibodies to Ro52Ex4 (n = 9), revealed that these sera target the N-terminal sequence (i.e., anti-Ro52Nt) shared by Ro52α, -β, and -γ (Figure 5F).