CR2 and systemic lupus erythematosus: As mentioned before, we discriminated two CD19+ cell subpopulations of interest, both expressing CD11c+, and T-bet+ but segregated by their differential expression of CR2 (CD21), thus defining a CD21-/lo subset (or “classical” ABCs) and a CD21hi subset (Figure 1A) that were analyzed in three different groups: healthy individuals, patients with SLE (non-LN) and LN patients.