PSMD1 and chronic kidney disease: The anti-S1-RBD IgG level was ninefold lower (P < 0.001) in KTR (117 [IQR 0–769] BAU/mL) as compared to the patients with CKD without immunosuppressive medication (1046 [IQR 470–2735] BAU/mL) (Fig. 2a).