Free light chains of immunoglobulins as a biomarker of glomerulopathies

Introduction. Light chains of immunoglobulins are not only structural elements of immunoglobulins of all classes, but can become independent units of immuno-mediated inflammatory reactions. Serum polyclonal free light chains (pFLC) are also found in a certain amount in practically healthy people. It has been shown that an increase in their serum levels can be considered as biomarkers of the activity of the underlying disease and a possible target for new treatment methods. There has been no extensive study of the role of pFLC in the pathogenesis of diseases unrelated to plasma cell diseases. The aim of our study was to determine the level of pFLC in various proliferative and non-proliferative glomerulopathies. Patients and methods. 97 patients with chronic kidney disease (CKD) were examined, among them 51 men and 46 women, average age 47.5±14.6 years. The diagnosis of glomerulopathy was confirmed morphologically in all the subjects. The serum level of pFLC was determined by the “Freelite” method (“Binding Site Ltd”, UK). The glomerular filtration rate (eGFR) was calculated using the “2021 CKD-EPI Creatinine” formula. Results. Proliferative glomerulopathies were detected in 46 patients, non-proliferative - in 51. The level of pFLC-kappa in the blood serum in the first group was 38.8 (18.7-61.0) mg/l, in the second - 21.7 (13.6-33.1) mg/l, p=0.003. The level of pFLC-lambda in the blood serum in the first group was 34.68 (23.1-56.4) mg/l, in the second - 25.4 (19.5-31.9) mg/l, p=0.005. In general, the reference values for pFLC-kappa (19.4 mg/L) and pFLC-lambda (26.3 mg/L) were exceeded in 65% (n=63) and 54% (n=52) patients, respectively. Regardless of the form of glomerulopathy, the presence of significant relationships between pFLC and the detection of signs of systemic inflammation (ESR, C-reactive protein) was not revealed. Also, no statistically significant relationship was found between serum pFLC and the proportion of completely sclerotic glomeruli. For eGFR, the statistical relationship became significant only when the eGFR was less than 60 ml/min/1.73 m2. Conclusion. The level of pFLC in the blood serum mainly reflects the activity of local tissue immune inflammation, which is supported by the activation of B-lymphocytes. In CKD C3 and more severe stages, eGFR should be taken into account when assessing the significance of an increase in serum levels of pFLC-kappa and lambda.