The Impact of Severe Albuminuria on the Proinflammatory Monocyte Subset CD14++CD16+ and Antigen-Specific Immune Responses.

Loss of renal function is associated with premature aging of the immune system; however, earlier studies on this topic enrolled patients with reduced GFR and did not distinguish between those with or without proteinuria. Clinical observations suggest that proteinuria alone might also impair immune defense. It is thus an open question whether patients with a urinary albumin-to-creatinine ratio > 300 mg/g (severe albuminuria) independent of their eGFR have an inflammatory risk profile and a disturbed adaptive immune response. This cross-sectional study included 25 patients with severe albuminuria (uACR > 300 mg/g; P-Group), 19 patients with an eGFR < 60 mL/min 1.73 m2 and a uACR < 300 mg/g (G-Group), and 30 patients with adequate kidney function (C-group). All three cohorts have a similar cardiovascular background with arterial hypertension and coronary artery disease. PBMCs from the patients were challenged with the superantigen Staphylococcal enterotoxin B (SEB) as well as with CMV- and SARS-CoV-2-specific antigens. Monocyte subsets and CD86 and HLA-DR expression were determined through flow cytometry. Transcripts of CD28 and IFN-α and -γ were measured by qPCR. Compared to those in the C-group, patients in the G-group showed a higher polyclonal SEB response and had significantly elevated circulating numbers of inflammatory monocytes (subset CD14++CD16+). CD28 transcripts were decreased in the P-group and G-group compared to the C-group, reaching significance for the G-Group. The CMV- and SARS-CoV-2-specific immune response, as measured by the frequency of CD4+69+137+ T and CD8+69+137+ T cells, was comparable in all three groups. Severe albuminuria per se does not alter the antigen-specific immune response; however, patients with reduced GFR, but not those with proteinuria, show inflammatory and polyclonal immune activation.