ICOS and systemic lupus erythematosus: The expression of ICOS on CD4+ T cells decreased after co-culture with CD57+ NK cells from HCs (23.8 ± 1.49%, n = 4 versus 15.9 ± 4.64%, n = 4), and such an inhibitory effect was not significant for NK cell subsets from SLE patients (Fig. 6E).