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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.
INTRODUCTION
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 [3]. If biopsies are negative, equivocal or cannot be
obtained, angiography of the viscera may be helpful if multiple micro-aneurysms
are observed [1].
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 [4] and ANCA-negative
pauci-immune focal necrotizing glomerulonephritis [5].
This report
suggests that anti-LAMP-2 autoantibodies may be a useful biomarker for PAN.
PATIENTS AND METHODS
Patient population
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.
Data collection
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
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.
RESULTS
DISCUSSION
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) [8].
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) [13].
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 [14] and a link to
the pathogenesis of renal disease [4].
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. [15] 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 [2]. There has been a decreased incidence of
PAN paralleling increased protection against hepatitis B from immunization [18].
LAMP-2 protein which
has some sequence similarity to bacterial proteins is shedding some light
toward pathophysiology of systemic vasculitis [15,19].
CONCLUSION
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.
ACKNOWLEDGEMENT
1. Hernandez-Rodriguez
J, Alba MA, Prieto-Gonzalez S, Cid MC (2014) Diagnosis and classification of
polyarteritis nodosa. J Autoimmun 48-49: 84-89.
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T (2012) A review of pediatric vasculitis with a focus on juvenile
polyarteritis nodosa. Am J Clin Dermatol 13: 389-398.
3. Strunk
DA, Schmidt-Pogoda C, Beuker LS, Milles C, Korsukewitz SG, et al. (2019)
Biomarkers in vasculitides of the nervous system. Front Neurol 10: 591.
4. Bosch
X, Mirapeix E (2009) Vasculitis syndromes: LAMP-2 illuminates pathogenesis of
ANCA glomerulonephritis. Nat Rev Nephrol 5: 247-249.
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A, Basu N, Benharkou A, Brandes R, Brown M, et al. (2014) Autoantibodies to
hLAMP-2 in ANCA-negative pauci-immune focal necrotizing GN. J Am Soc Nephrol
25: 455-463.
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GG, Arend WP, Bloch DA, Calabrese LH, Fauci AS, et al. (1990) The American
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A, Choi MY, Tarnopolsky M, Brady L, Clarke AE, et al. (2019) Anti-NT5c1A
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S, Woodman RC, Fritzler MJ (2000) Autoantibodies to early endosome antigen
(EEA1) produces a staining pattern resembling cytoplasmic anti-neutrophil
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LM, Eystathioy T, Selak S, Chan EKL, Fritzler MJ (2004) Autoantibodies to
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AS (2010) Autoantibodies in ANCA-associated vasculitis. Rheum Dis Clin North Am
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FC, Specks U (2013) Vasculitis: Refining phenotypes in ANCA-associated
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13. Kain
R, Matsui K, Exner M, Binder S, Schaffner G, et al. (1995) A novel class of
auto-antigens of anti-neutrophil cytoplasmic antibodies in necrotizing and
crescentic glomerulonephritis: The lysosomal membrane glycoprotein h-LAMP-2 in
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