Urinary immunoglobulin M as a novel biomarker for disease activity of lupus nephritis

Abstract

This study is carried out to assess the role of the urinary IgM as a marker of lupus nephritis & the correlation between urinary IgM excretion and systemic lupus activity and its relation to SLICC end organ damage. This study was conducted on thirty SLE patients fulfilling at least four of the updated ACR revised criteria for the classification of SLE (Hochberg, 1997), thirty SLE patients with renal biopsy -Proven lupus nephritis and thirty apparently healthy volunteers matched for age and sex with the SLE patients included as a control group. All patients (90% Of them were females and 10% were males ) were subjected to full history taking, complete clinical examination and laboratory investigation. urinary levels of IGM in all patients and control were determined by the ELISA technique. Activity of SLE disease was measured according to SDI damage score, SLEDAI index and the activity of renal disease was measured according to rSLEDAI,SDI renal domain. A kidney biopsy was obtained from each patient on the same day of blood sampling under computed tomography "CT" guidance using a true cut needle biopsy. Specimens were stained with hematoxylin and eosin (H&E) and classified according to the World Health Organization (WHO) criteria for grading of lupus nephritis (LN). , in Comparison between all studied groups, regarding the renal parameters :Creatinine , BUN, Proteinuria(P < 0.05) ( Table 2), global SLEDAI-2K and global SDI showed highly statistical significant difference (P < 0.05) ( Table 4 ) ,all of them were with most high Mean + SD in those with nephritis(LN group) than those without nephritis (SLE group) who were again with higher Mean + SD than the controls .Regarding GFR , it was most low Mean + SD in those with nephritis and most high Mean + SD in controls . When we further preformed post hoc test ,in a comparison between LN patients group and SLE patients group without nephritis, highly statistical significant difference was found regarding anti-dsDNA titres(p<0.001) ( Table 3), Proteinuria(p<0.001) ( Table 2) and urinary IgM(p<0.001) ( Table 5) . Regarding the mean urinary IGM levels, it was of statistical significant difference in comparison between all studied groups, and of statistical significant difference between controls and both two patients groups and also between control and SLE patients group. Also, between controls and LN patients group .It reflects that this was specific to renal insults that occurred in progressive deterioration in SLE patients. In a correlation between urinary IgM versus different variables among SLE group , urinary IgM inversely correlated versus GFR( r = - 0.13 , p=0.22), and renal domain SLEDI( r = 0.10 , p=0.23 (Table 12). In a correlation between urinary IgM versus different variables among LN group , urinary IgM was in weak correlation with global SLEDI( r = - 0.22 , p=0.18). Also,urinary IgM highly strong inversely correlated with GFR( r = - 0.33 , p=0.02) and highly strong correlated with renal domain SLEDI( r = - 0.36 , p=0.01) . No correlation was found with the extrarenal SLEDAI ( r = 0.06 , p=0.70) (Table 11). It reflects that these correlations were due to renal damage in LN patients and was specific for the renal insult . In turn ,it strongly suggesting that urinary IgM levels could potentially serve as a biomarker of renal disease activity.