Identification of Low-Abundance Urinary Biomarkers in Lupus Nephritis using Electrochemiluminescence Immunoassays.

OBJECTIVE: To identify low abundance urinary protein biomarkers in Lupus nephritis (LN), this study aims to investigate the utility of a more sensitive platform using electrochemiluminescence (ECL).

METHODS: 48 human urine samples across 2 independent cohorts (each matched for age/gender/race and containing 8 active LN (rSLEDAI>0), 8 inactive lupus (rSLEDAI=0), and 8 healthy controls) were tested using a pre-existing 40-plex ECL panel. A custom 5-plex ECL panel was then developed for further validation studies and used to test 140 urine samples.

RESULTS: 17 urinary proteins were elevated (2-tailed U-test, p<0.05) in active LN samples compared to inactive LN and healthy controls in cohort 1, while 9 were similarly elevated in cohort 2. Of these, IL-7, IL-12p40, IL-15, IP-10 and TARC were chosen for further validation. These 5 proteins were undetectable by ELISA. Hence, a custom 5-plex ECL panel was developed, and used to validate the results from the initial 40-plex screening panel. Urinary IL-7, IL-12p40, IL-15, IP-10 and TARC were again significantly elevated in active LN compared to inactive LN and healthy controls and correlated well with rSLEDAI and PGA (R>0.69, p<0.05). All 5 urine proteins were more frequently elevated in LN compared to other CKD controls, although overall group differences attained significance only for urine IL-7 and IL-15.

CONCLUSIONS: Urinary levels of IL-7, IL-12p40, IL-15, IP-10 and TARC are potentially useful diagnostic tools in LN. Utilizing ECL assays may allow detection of urinary biomarkers that are below ELISA detection limits. This article is protected by copyright. All rights reserved.