fetching data ... 
Background: Kidney involvement in Sjögren’s Syndrome (SJS), most commonly in the form of a tubulointerstitial nephritis (TIN) causes significant morbidity including chronic kidney failure. Whilst reduced kidney function, proteinuria and leukocyturia are clinically accepted markers for kidney involvement, they are neither sensitive nor specific for SJS-TIN. Leukocyturia, measured by dipstick test or urinary sediment is semiquantitative at best and cannot differentiate leukocyte subtypes nor distinguish between different causes of leukocyturia. There are currently no good biomarkers for SJS-TIN. Invasive kidney biopsy is thus routinely required to establish the diagnosis. Furthermore, no validated biomarkers exist, which correlate with response to treatment, so repeat renal biopsies are often needed to guide SJS-TIN therapy. Better markers for diagnosis and therapeutic monitoring are needed. In this respect, detailed analysis of urinary leukocytes by flow cytometry (FC) might be of use.
Objectives: First, we wanted to find out whether detailed analysis of leukocyturia by FC is technically possible in SJS-TIN patients. Secondly, we wanted to test whether analysis of leukocyturia might provide useful biomarkers for the diagnosis of SJS-TIN. In addition, we wanted to assess whether leukocyturia might correlate with the degree of interstitial kidney inflammation in general and particularly with tubulitis, which are hallmarks of TIN. Finally, we wanted to explore whether detailed analyses of leukocyturia might uncover markers, which correlate with the clinical course of disease and help to direct therapy.
Methods: We developed a FC panel to characterize and quantify urinary leukocytes. Nine different cell types (neutrophils, eosinophils, classical macrophages, alternative macrophages, B-cells, natural killer cells, total T-cells, CD8 + cytotoxic T cells and CD4 + T-Helper cells (T H )) could be differentiated. We prospectively enrolled 13 patients with SJS and suspected TIN in whom a kidney biopsy was performed. Patients were followed up longitudinally for a median of 325 days. In addition to urinary FC, routine clinical tests, as well as detailed analyses of kidney biopsies were performed. Histological TIN-activity, including the degree of tubulitis, was quantified in a blinded manner by a nephropathologist. Patients with urinary tract infections (UTI, n=9) as well as healthy volunteers (HC, n=10) acted as additional controls. Patients with SJS-TIN were treated with a range of drugs (Prednisolone, Azathioprine, Rituximab) as per discretion of the treating clinician.
Results: Kidney biopsy revealed TIN in a total of 8 SJS-patients with the other 5 patients having only signs of chronic kidney disease (CKD). Analyses of urinary leukocytes identified that among the nine characterized populations, T H cells correlated best with the presence of SJS-TIN. SJS-TIN patients had markedly and significantly higher percentages of urinary T H cells, as compared to HC, SJS-CKD and UTI patients. Absolute T H cell numbers were also increased, as compared to SJS-CKD and HC. In all SJS-TIN patients, urinary T H cells made up >3% of total leukocytes, whereas in all the SJS-CKD and other controls (19 in total) they made up <1.5%. Total T-cells, as well as CD8 + cytotoxic T-cells were also significantly increased in SJS-TIN, but not as markedly as T H cells. The other leukocyte subtypes could not differentiate between the groups. Furthermore, there was a significant and strong correlation between relative urinary T H cells and histological TIN-severity, including interstitial inflammation (Spearmans r = 0.61) as well as tubulitis (Spearmans r = 0.85). In contrast, none of the clinical parameters, including the renal part of the ESSDAI, proteinuria, serum creatinine or estimated glomerular filtration rate, correlated with histology, highlighting the usefulness of urinary T H cells as a biomarker. Importantly, upon treatment of SJS-TIN with immunosuppression, we observed an early (median follow up: 37 days) and significant reduction in both relative (82%) and absolute (93%) urinary T H cells. This reduction was maintained at the last follow up (median 325 days) in both relative (80%) and absolute (89%) terms. In line, Proteinuria also relevantly improved with treatment. Finally, repeat biopsies, which were available in two of the patients showed an improvement in TIN, which correlated with a simultaneous and strong reduction in urinary T H cells.
Conclusion: Our prospective proof-of-principle study shows that quantification and differentiation of urinary leukocytes is possible and can be used for clinical routine. Among urinary leukocytes, particularly T H cells correlate with presence and severity of SJS-TIN at diagnosis and reflect response to therapy. Thus, urinary T H cells might represent the first reported non-invasive biomarker for SJS-TIN. Replication in a larger cohort is needed for validation of our findings.
REFERENCES: NIL.
Acknowledgements: NIL.
Disclosure of Interests: Viona Laas: None declared. Frederic Christian Feindt: None declared. Tom Zimmermann: None declared. Pascal Böse: None declared. Laura Ehnold: None declared. Pavels Klimicevs: None declared. Julia Hagenstein: None declared. Matthias Warkotsch: None declared. Thorsten Wiech Alexion, internal training, Eleva GmbH, speaker WCN, Eleva GmbH, Novartis, Tobias B Huber Alexion, AstraZeneca, Bayer, Beren Therapeutics, Boehringer-Ingelheim, DaVita, Euroimmun, Fresenius Med-ical Care, Nipoka, Novartis, Pfizer, Renovate, Retrophin-Travere, Sanofi, Vera Therapeutics, Vifor, Vivoryon, Amicus Therapeutics, Fresenius Medical Care, Euroimmun, Oliver M. Steinmetz: None declared. Simon Melderis: None declared.
© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license (