Sex-specific differences in ICOS + T helper cell differentiation in systemic lupus erythematosus patients with low disease activity

Systemic lupus erythematosus (SLE) is a sex biased chronic autoimmune disease affecting predominantly females during reproductive ages. Changes in the ratio of inducible costimulatory molecule (ICOS) + regulatory (Treg) and non-regulatory responder (Tresp) CD4 + T cells proved to be crucial for the occurrence of high disease activity. Here, we investigated how the differentiation of ICOS + CD45RA + CD31 + recent thymic emigrant (RTE) Tresps into CD45RA − CD31 − memory Tresps affects the percentages of ICOS + Tresps within total CD4 + T cells. Three different pathways (pathway 1 via CD45RA − CD31 + memory Tresps, pathway 2 via direct proliferation and pathway 3 via resting mature naïve CD45RA + CD31 − (MN) cells) were examined in healthy controls and SLE remission patients separated by sex. In female SLE remission patients, immunosuppressive therapy inhibited the ICOS + RTE differentiation via CD45RA − CD31 + memory Tresps and direct proliferation, leaving an age-independently increased differentiation into CD45RA − CD31 − memory Tresps by conversion of resting MN Tresps compared with healthy controls. Due to exhaustion of this pathway with age, no age-dependent change in the percentages of ICOS + Tresps within total CD4 + T cells could be found. In contrast, no age-independently increased differentiation could be detected in men due to sufficient immunosuppression of all three pathways. This allowed an age-dependent differentiation of ICOS + RTE Tresps into CD45RA − CD31 − memory Tresps by conversion of resting MN Tresps, resulting in age-dependently increasing percentages of ICOS + Tresps within total CD4 + T cells. We hypothesize that the sex-specific differential effect of immunosuppression on the differentiation of ICOS + Tresps may explain the sex- and age-dependent occurrence of high disease activity.