CD28 and systemic sclerosis: In order to find support to this pathogenic mechanism, the frequencies of SSc patients showing impaired (suppression activity <25%) or normal (suppression activity ≥25%) CD8+ Treg function were related, by Fisher’s exact test analysis, to the existence, in the CD8+ Treg of each single patient, of an abnormal expression of CD39 and/or CD127 molecules (considering as altered expression the downregulation of CD39 and the upregulation of CD127 with respect to the relative CD8+CD28− T cell precursors, respectively).