Cathelicidin (LL-37) and its correlation with pro-oxidant, antioxidant balance and disease activity in systemic lupus erythematosus: a cross-sectional human study

Background Cathelicidin (LL-37), an endogenous antimicrobial peptide, has recently been involved in the pathogenesis of autoimmune diseases. To assess whether LL-37 reflects disease activity, we measured serum levels of it in systemic lupus erythematosus (SLE) patients with active and inactive disease compared to healthy controls. LL-37 was also compared between new and old cases. Moreover, the correlation of LL-37 and pro-oxidant, antioxidant balance (PAB) was measured. Methods The study population consisted of 50 SLE patients and 28 healthy controls. Of those, 39 patients had active and 11 patients had inactive disease. Serum levels of LL-37 were measured by ELISA and PAB values by a special method. Results There was no difference in levels of LL-37 between patients and healthy controls (50.920.8 vs. 67.7 +/- 43.3ng/ml, P=0.31). LL-37 did not correlate with SLEDAI and its items in total patients. LL-37 had a positive correlation with SLEDAI in active patients (P=0.01, r=0.4). In active patients (78% of patients), multivariate regression analysis showed significant negative correlation between LL-37 and C3 (P=0.01, standardized beta -0.50). No difference was found in levels of PAB between patients and controls (90.4 +/- 34.1 vs. 86.9 +/- 25.6HK, P=0.4).There was no difference in the levels of PAB between patients with active and inactive disease (93.2 +/- 34.1 vs. 80.2 +/- 33.7HK, P=0.27). No correlation was found between levels of PAB and SLEDAI items and total score. However, a positive correlation between the levels of LL-37 and PAB in SLE patients was found (r=0.3, P<0.01). Conclusion Based on this study, serum LL-37 and PAB did not increase in lupus compared with healthy individuals. LL-37 serum values rose in parallel with SLEDAI in active disease. Positive correlation between serum PAB and LL-37 could be a great achievement of this study that may suggest the role of antioxidants in controlling NETosis.