CD4 and systemic lupus erythematosus: Although, SmD1p-specific CD4+ T cells according to CD154 expression were detectable above background in CW F1 mice upon in vitro re-stimulation (mean 0.09% vs 0.02%, p=0.002, SmD1p vs control peptide; Figure 3A) their frequency was more than 2-fold lower compared to the responses observed in Treg depleted NZB/W F1 lupus-prone mice (p=0.002; CW F1 vs NZB/W mice; Figure 3A).