Dysregulation of the immune system in chronic kidney disease and the impact on disease manifestations and co-morbidity

Abstract

Background: Chronic kidney disease (CKD) is associated with an increased risk of cardiovascular disease and infections. Both conditions share the same underlying cause comprising of changes in innate and adaptive immunity.

Aim: The objective of this thesis was to contribute to an increased understanding of the dysregulation in the immune system in CKD and to evaluate if selected markers can add prognostic information about the presence of vascular changes and infection outcomes in CKD.

Methods: In study I, we phenotyped subsets of monocytes, B and T cells in patients with IgA nephropathy (IgAN) using flow cytometry. We included a disease control group (patients with autosomal dominant polycystic kidney disease (ADPKD)) and healthy controls (HC). Cytokines were analyzed using ELISA. In study II, we measured levels of IgE anti double-stranded DNA (dsDNA) in patients with active lupus nephritis (LN), patients with a history of LN, SLE patients with no kidney involvement and population-based controls. Levels of IgE anti-dsDNA were measured using fluorescence enzyme immunoassay. In a subgroup of patients with active LN and healthy controls, we evaluated the effect of active LN serum on healthy donor granulocytes compared to control sera. Granulocytes were stained for markers involved in cell migration, adhesion and immune modulation and were analyzed by flow cytometry. In study III, affinity proteomics was used to detect potential biomarkers for early vascular changes in patients with CKD stages 2-3. Three proteins of interest, potentially involved in vascular lesions, were identified and further analyzed with Luminex. Vascular status was evaluated using ankle-brachial index (ABI) and carotid media-intima thickness (CIMT). In study IV, we evaluated monocyte related markers in relation to kidney function and mortality in hospitalized patients with COVID-19 infection. As controls we included healthy individuals and patients with CKD without infection.

Results: In study I, we demonstrated that patients with IgAN, compared to HC, had an altered balance in B cell subsets, changed balance between B and T cells and an increased proportion of CD19- long-lived plasma cells. Compared to both control groups, patients with IgAN had an increased proportion of non-classical monocytes. We showed an association between sCD40L and MCP-1 levels and urine albumin/creatinine ratio in IgAN. In study II, we found higher levels of IgE antidsDNA in active LN compared to controls. Other lupus groups did not differ from controls. We also showed that SLE patients with low complement component 3 (C3) levels, as compared to SLE patients with normal C3, had higher levels of IgE anti-dsDNA. We were also able to demonstrate that sera from active LN had a different impact on the phenotype profile of human basophils, neutrophils and eosinophils. In study III, comparing the two CKD groups at baseline with healthy controls, higher levels of sCD14, ANG and OPG were observed in both CKD groups. After 5 years, of followup, sCD14 and ANG remained higher in CKD stages 2-3 compared to healthy controls. Also, at 5th year of follow-up, a positive correlation was seen between levels of OPG and ABI and between sCD14 and ABI. In study IV, we showed that COVID-19 patient who died during hospital stay, as compared to those who survived, were more often in CKD stages 3-5 and had higher levels of IL-6 and MIP-1α. In addition, we demonstrated that levels of MCP-1 and MIP-1α provided additional prognostic information about hospital survival in patients with COVID-19, with either normal or impaired kidney function.

Conclusions: In IgAN, an altered immunological B cell phenotype appears to be mediated by a changed balance between B and T cell subsets, rather than cytokines levels affecting B cell survival, implying the importance of T cell dependent B cell maturation. Determining B cell subsets might be of importance, particularly in terms of number of long-lived B cells, which cannot be targeted through anti-CD20 treatment.

Elevated levels of IgE anti-dsDNA in active LN, but not in other lupus groups, reflect a broader autoreactive mechanism extending the immunological disturbances in LN to also engage IgEdependent pathways. Serological factors in serum from active LN can moderate granulocyte phenotype implying immunological disturbances in innate immunity during LN flares.

Elevated levels of sCD14 and OPG in patients with CKD stages 2-3 are associated with ABI, as a non-invasive measure of arterial stiffness. This implies the use of sCD14 and OPG as possible biomarkers of vascular lesions even at early stages of CKD. If they can be used as prognostic, or as a possible target for future therapeutic approach warrants further studies.

Patients with COVID-19 who died in the hospital, as compared to patients who survived, were more often in CKD stages 3-5 and had higher levels of MIP-1α and IL-6. Levels of MCP-1 and MIP1α provide additional prognostic information in hospitalized patients with COVID-19, and this is valid both for patients with normal and impaired kidney function.