CD4 and systemic lupus erythematosus: To investigate whether differences in the composition of the total CD4+ T cell pool with ICOS+ or ICOS− Tregs/Tresps could be responsible for the higher prevalence of SLE in women compared to men and especially for the characteristic occurrence of this disease in rather young women but older men, we determined the percentages of these Treg/Tresp subsets within the total CD4+ T cell pool in healthy controls (Group 1) and SLE patients with low disease activity (Group 2).