The plasma of the LN group also had a lower level of C1q than the SLE without the LN group (p < 0.05; Additional file 5: Supplementary Figure S3A), but these groups had no significant difference in the level of C4 (p > 0.05; Additional file 5: Supplementary Figure S3B). Here, C4A is linked to systemic lupus erythematosus.