PDCD1 and systemic sclerosis: On the other hand, when the functional effects of cTfh cells in the blood of patients with SSc were compared, the positive correlation with plasma cell differentiation and the increase of IgG levels in co-cultures with B cells were mainly observed with PD-1+CXCR5+, but less with PD-1+CXCR5−CD4+ T cells.