PDCD1 and systemic sclerosis: However, in our study, SLE subjects seemed to exhibit increased levels of PD-1, similar to what has been just revealed in systemic sclerosis [24] and another study showing that SLE patients exhibited increased frequencies of circulating PD1+ICOS+ T follicular helper cells and PD1+ICOS+ T memory cells [25], possibly suggesting a feedback mechanism of the immune system.