|C Moran-Toro, A Fifi-Mah*, R Tabassum and MJ Fritzler|
|Corresponding Author: Aurore Fifi-Mah, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada|
|Received: June 18, 2019; Accepted: July 31, 2019; Published: January 06, 2020;|
|Citation: Moran-Toro C, Fifi-Mah A, Tabassum R & Fritzler MJ. (2020) LAMP-2 a Biomarker in Vasculitis: A Case Series of Polyarteritis Nodosa. J Rheumatol Res, 2(1): 70-74.|
|Copyrights: ©2020 Moran-Toro C, Fifi-Mah A, Tabassum R & Fritzler MJ. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.|
Polyarteritis nodosa (PAN) is a systemic necrotizing vasculitis affecting medium-sized arteries with occasional involvement of small muscular arteries. Unlike small vessel vasculitides, PAN is not associated with anti-neutrophil cytoplasmic antibodies (ANCA). We report the presence of anti-LAMP-2 antibody (lysosome associated membrane protein-2) in 5 patients presenting with biopsy proven PAN. We report five cases of PAN diagnosed between January 2010 and April 2013. Laboratory tests and clinical correlations were studied retrospectively. Serum analysis included c- and p-ANCA and atypical ANCAs including anti-LAMP-2. We compared the autoantibodies titers to control groups of patients with giant cell arteritis (GCA), granulomatosis with polyangiitis (GPA), Takayasu arteritis (TAK) and other small vessel vasculitis (SVV). We observed higher titers of anti-LAMP-2 autoantibodies in the PAN patients in comparison to the other vasculidities. Our study suggests that anti-LAMP-2 autoantibodies represent a novel biomarker of PAN with high disease activity. The role of anti-LAMP-2 antibodies in the pathogenesis and associated clinical phenotype of vasculitis needs further investigation.
Polyarteritis nodosa (PAN) is an idiopathic, systemic necrotizing vasculitis primarily involving medium-sized arteries that can affect adults and children alike [1,2]. Anti-neutrophil cytoplasmic antibodies (ANCA), anti-nuclear antibodies (ANA) and other biomarkers in PAN are typically absent. Other laboratory abnormalities, such as an elevated ESR, reflect an acute phase response but are non-specific. Hence, histologic confirmation of PAN as evidenced by vasculitis in medium sized arteries of skin, muscle and/or nerves is usually required to confirm the diagnosis . If biopsies are negative, equivocal or cannot be obtained, angiography of the viscera may be helpful if multiple micro-aneurysms are observed .
In the course of our studies where various autoantibodies, particularly atypical ANCAs and other biomarkers were being re-evaluated, we observed an interesting apparent association of autoantibodies to LAMP-2 (lysosome-associated membrane protein) in a small cohort of PAN. This piqued our interest because previous studies had suggested that autoantibodies directed against LAMP-2 have been linked to a subset of primary vasculopathies  and ANCA-negative pauci-immune focal necrotizing glomerulonephritis .
This report suggests that anti-LAMP-2 autoantibodies may be a useful biomarker for PAN.
PATIENTS AND METHODS
The study was approved by the Conjoint Health Ethics Review Board and each patient provided signed informed consent. Accordingly, this study was carried out in compliance with the Helsinki Declaration of 1975 for human studies as revised in 2013. SVV included Henoch-Schonlein purpura, microscopic polyangiitis, eosinophilic granulomatosis with polyangiitis, cryoglobulinemic vasculitis and leukocytoclastic vasculitis. Due to the small numbers we included them together as one comparator group.
Each patient’s clinical reports, consultation letters, electronic medical records were retrospectively reviewed and biologic, histopathological, radiologic findings and treatments, from the time of first symptoms and during follow-up were obtained. The diagnosis of PAN was based on clinical presentation, histopathology and CT angiogram. Using retrospective data collection, each of the organ system was assessed based on rheumatologist evaluation.
Antibody profile and luminex assay
Statistical analysis was used to compare titers of the antibodies and compared across all entities of vasculitis. We used non-parametric analysis (Kruskal Wallis) to compare medians and IQR (Inter Quartile Range) between groups.
The diagnosis of vasculitides is often complex and delayed due to overlap of clinical patterns and vague or protean symptoms; requiring invasive and/or costly investigations. The use of molecular biomarker arrays has changed our diagnostic approach and understanding of ANCA associated vasculitis. It is in this setting that we commenced our studies of systemic vasculitis in search of biomarkers that might have hitherto been overlooked. A variety of other proteins can be targeted by autoantibodies to cellular components, and some of these antibodies directed to LAMP-2, elastase, GW 182, GE-1, EEA-1, GRASP 1 can produce atypical ANCA-staining patterns [9,10] and many of these are also reported to be associated with a variety of autoimmune diseases. Anti-LAMP-2 antibodies have been described to be associated with various diseases including glomerulonephritis and ANCA vasculitis [11-13].
One of our main interest is a group of atypical ANCA (aANCA) usually characterized by neutrophil cytoplasmic immunofluorescent staining but a negative anti-PR3 and anti-MPO antibody test. Our studies have been facilitated by using multiplex arrays on the Luminex platform that allows a rapid, high throughput assay that is referred to addressable laser bead immunoassay (ALBIA) .
Three distinct ANCA staining patterns have been described: cytoplasmic-ANCA (c-ANCA), perinuclear-ANCA (p-ANCA) and atypical ANCA (aANCA) [11,12]. C-ANCA is classically associated with GPA and p-ANCA with eosinophilic granulomatosis with polyangiitis (EGPA) and microscopic polyangiitis (MPA). A-ANCA is used to identify immunofluorescence staining patterns that do not conform to the typical c-ANCA or p-ANCA patterns and react with a variety of cellular targets seen in a wide variety of conditions. The specific antigen target of c-ANCA is typically proteinase 3 (PR-3) and for p-ANCA is myeloperoxidase (MPO). Together these clinical entities have been referred to as ANCA associated vasculitis (AAV) .
The 2 classical antigens of PR3 and MPO are clearly not the only ones. For example, the lysosomal membrane protein LAMP-2 which has a related protein in renal glomerular endothelial cells has been demonstrated as yet another target of ANCAs  and a link to the pathogenesis of renal disease .
In the present study, we found significantly elevated levels and a high frequency of anti-LAMP-2 antibodies in a group of PAN patients that was distinct from that observed in other vasculitides. In the PAN group with active disease, 60% of the patients had positive anti-LAMP-2 antibodies. We also noted elevated titers that were associated with high disease activity. Our results are interesting in the context of a recently published study by Li et al.  who reported that serum LAMP-2 protein levels reflected both disease activity and renal involvement of SVV and were significantly higher in PAN compared with AAV. Our observations suggest that in PAN there may be anti-LAMP-2 antibody excess and that circulating LAMP-2 immune complexes may be an important feature of PAN. Future studies should focus on this aspect of the disease. Interestingly, other studies also reported that anti-LAMP-2 autoantibodies fluctuated in concert with disease activity in a variety of vasculitides [4,13,14,16]. The association of anti-LAMP-2 autoantibodies with disease activity and their decline after initiation of immunosuppression treatment suggests that they are also involved in the pathogenesis of disease.
The role of ANCAs as causative and/or pathogenic
agents in vasculitis has been debated [16,17]. It is thought that
PAN may be triggered by viral infections, particularly hepatitis B virus, but
remains idiopathic in most cases . There has been a decreased incidence of
PAN paralleling increased protection against hepatitis B from immunization .
LAMP-2 protein which
has some sequence similarity to bacterial proteins is shedding some light
toward pathophysiology of systemic vasculitis [15,19].
Our study suggests that anti-LAMP-2 autoantibodies represent a novel biomarker of PAN with high disease activity. Studies of larger, multi-center cohorts are needed to validate this association.
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