CD4 and systemic lupus erythematosus: Because ICOS was predominantly expressed on CD45RO+ T cells in normal control individuals as well as in patients with SLE (Table 1, Figure 2 and data not shown), we gated on either CD4+CD45RO+ or CD8+CD45RO+ T cells and analyzed the expression of ICOS on these subsets (Figure 2a–f).