VDR and systemic lupus erythematosus: MRL‐LPr/LPr mice with SLE (n = 20) and normal MRL mice (n = 20) were assigned into the control group (normal mice, without feeding with 1,25(OH)2D3), the 1,25(OH)2D3 group (SLE mice, feeding with 1,25(OH)2D3), the VDR‐knock‐in + 1,25(OH)2D3 group (SLE mice, VDR‐knock‐in, feeding with 1,25(OH)2D3) and the VDR‐knockout group (normal mice, VDR‐knockout, without feeding with 1,25(OH)2D3) (n = 10 per group).