Eleven (16.4%) SSc patients had DLco ≤60% of predicted, and median serum IgG3 levels were significantly higher in SSc patients with reduced DLco than SSc patients with normal DLco [0.68 g/l (IQR 0.56–1.22 g/l) vs. 0.55 g/l (IQR 0.39–0.77 g/l), p < 0.05]; moreover, a slightly significant negative linear correlation exists between DLco and IgG3 (r = −0.382, p < 0.001). Here, IGHG3 is linked to systemic sclerosis.