Background/Purpose:

NGAL (lipocalin-2), a member of the lipocalin superfamily, is expressed by a variety of cells including neutrophils, hepatocytes, alveolar epithelial cells and renal resident cells. NGAL is a sensitive marker for tissue injury, and is upregulated following ischemia, inflammatory conditions, metabolic diseases and neoplastic disorders. Furthermore, several studies have demonstrated the use of NGAL as a biomarker in lupus nephritis. Previously, NGAL was reported to be involved in innate immune responses during bacterial infection, and was found to worsen renal disease in nephrotoxic serum nephritis. However, the role of NGAL in adaptive immunity is still largely unknown. 

Methods:

To investigate a possible role for NGAL in adaptive immune responses in an experimental lupus model, we injected pristane (tetramethyl-pentadecane) (0.5 ml/mouse intraperitoneally) into wild type B6 (n=10) and NGAL-deficient (LCN2-/-) (n=10) mice. Wild type (WT) B6 and LCN-/- mice receiving PBS injections served as controls. Serum autoantibodies were analyzed by ELISA, Hep-2 immunostaining, and immunoprecipitation. Autoantibody producing cells were quantitated by ELISPOT. Expression of mRNA in spleen was performed by real-time qPCR.

Results:

Analyzing the levels of serum autoantibodies 4 months post pristane injection, we found that pristane challenged LCN2-/- mice had significant increases in IgG_2b anti-single and anti-double stranded DNA as well as IgG anti-histone antibodies as compared to pristane injected B6 mice. Furthermore, elevated levels of serum anti-ribonucleoprotein antibodies were observed in pristane injected LCN2-/- mice by immunoprecipitation. Confirming these results, analysis of serum anti-nuclear antibodies (ANA) on Hep-2 cells revealed significantly increased homogenous and speckled staining in pristane challenged LCN2-/- mice as compared to WT B6 mice, while ELISPOT revealed increased numbers of autoantibody producing cells to DNA, histone and RNP in the spleen. Moreover, we found significant upregulation of interferon regulatory factor-5 (IRF5), IP-10, CXCL13, CXCR5, CXCR3, and activation induced cytidine deaminase (AID) in spleens of LCN2-/- mice compared to B6 mice post pristane challenge. Pristane promoted NGAL secretion by splenocytes in vitro, while pristane challenge in vivo induced significant upregulation of NGAL expression in the spleen and serum of B6 mice.

Conclusion:

NGAL/LCN2 deficiency accelerates the onset of anti-nuclear antibodies in pristane induced lupus, via increased levels of inflammatory mediators and autoantibody producing cells.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/neutrophil-gelatinase-associated-lipocalin-ngallipocalin-2-regulates-the-onset-of-serum-autoantibodies-in-pristane-induced-lupus/