Download In Focus Autoantibodies in anti-neutrophil cytoplasm antibody

Nephrol Dial Transplant (2014) 29: 1105–1107
doi: 10.1093/ndt/gft526
Advance Access publication 23 January 2014
In Focus
Autoantibodies in anti-neutrophil cytoplasm
antibody-associated vasculitis
Alan D. Salama and Andrew J. Rees
UCL Centre for Nephrology, Royal Free Hospital, London, UK and Clinical Department of Pathology, Medical University of Vienna,
Vienna, Austria
Correspondence and offprint requests to: Alan D. Salama; E-mail: [email protected]
The discovery of autoantibodies to neutrophil cytoplasm antigens (ANCA) just over 30 years ago and their association with
focal necrotizing glomerulonephritis (FNGN) and small vessel
vasculitis created a paradigm shift: within a few years these diseases had changed from archetypal ‘immune complex diseases’
into the autoantibody mediated diseases they are considered
today, justifying the term ANCA-associated vasculitis (AAV).
Although most extensively studied, ANCA are not the only
autoantibodies found in AAV and Suzuki et al. describe a novel
autoantibody that may also contribute to pathogenesis [1].
ANCA were originally described in a small group of individuals presenting with systemic illness and FNGN whose renal biopsies were ‘indistinguishable from microscopic polyarteritis
nodosa’ (now known as microscopic polyangiitis—MPA) [2].
Shortly afterwards, ANCA were described independently in two
larger cohorts of patients with Wegener’s granulomatosis (now
called granulomatosis with polyangiitis—GPA) firmly establishing their association with systemic vasculitis [3] and ultimately
leading to the term ANCA-associated vasculitis [4]. Indirect
immunofluorescence identified two distinct ANCA staining
patterns: perinuclear (pANCA) usually indicative of autoantibodies to myeloperoxidase (MPO); and cytoplasmic (cANCA)
that reflect autoantibodies to proteinase 3 (PR3). These in turn
are strongly (but not exclusively) associated with clinical diagnoses of MPA and GPA, respectively. Other ANCA targets have
been identified (including elastase, lactoferrin and bacterial permeability increasing protein), but these are not associated with
vasculitic syndromes.
ANCA specific for either MPO or PR3 (but rarely both)
can be detected in 85–90% of patients presenting with pauciimmune FNGN and positive assays for them have a diagnostic
sensitivity and specificity of around 90%. This strongly suggests
their involvement in pathogenesis and there is a wealth of clinical,
© The Author 2014. Published by Oxford University Press on
behalf of ERA-EDTA. All rights reserved.
experimental and genetic evidence to support this. Antibodies to
MPO and PR3 both activate primed human neutrophils and
enhance neutrophil mediated endothelial injury in vitro (reviewed
in [5] and [6]); and passive immunization with antibodies to
MPO and possibly PR3 induces FNGN in mice although injury is
mild unless an additional stimulus such as bacterial lipopolysaccharide is administered [7, 8]. Finally, a recent genome-wide association study identified single-nucleotide polymorphisms in
genes encoding PR3 and its inhibitor a1-anti-trypsin, which
both increase susceptibility to develop autoantibodies to PR3
and clinical diagnosis of GPA but not to MPA or autoantibodies to MPO [9].
Despite the strength of this evidence, new data that have
emerged over the past 5 years which challenge the assumption
that injury in pauci-immune FNGN is uniquely caused by
autoantibodies to MPO or PR3 and suggest the need for a
more nuanced approach. First, results from certain randomized prospective controlled trials [10] and from meta-analyses [11] show that neither the presence, or the titre, of
autoantibodies to MPO or PR3 consistently correlates with
disease activity or clinical response to treatment, and does not
predict clinical relapses [12]. This is in contrast to earlier
cohort studies demonstrating that significant increases in
ANCA can predict relapses and may be used as a basis for alteration in immune therapies [13, 14]. Second, the renal
morphology of ANCA-negative patients presenting with
pauci-immune FNGN is indistinguishable from ANCA-positive patients [15], raising the question of what causes injury in
the absence of detectable antibodies to MPO and PR3.
However, even this does not preclude an exclusive role for
autoantibodies to MPO and PR3 in pathogenesis as there is
evidence that antibodies specific for particular MPO [16] or
PR3 [17, 18] epitopes better reflect disease activity, and
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IN FOCUS
autoantibodies to MPO may be masked by fragments of the
acute phase reactant ceruloplasmin in ANCA-negative patients [16]. Nevertheless, it seems highly likely that additional
factors other than the classical ANCA are required for the full
expression of AAV and this coincides with the need for a critical analysis of the role of more recently described autoantibodies, such as those specific for LAMP-2 [19], plasminogen
[20, 21] and now moesin [1].
Autoantibodies to LAMP-2 have been described in 80–90%
of patients presenting with pauci-immune FNGN [19, 22] although a lower frequency has been reported by others [23].
They become rapidly undetectable after the start of immunosuppressive treatment, are rare in patients during remission, but
recur in those with clinical relapses. Antibodies to LAMP-2
cause FNGN in rodent models [19, 24] and can also be detected
in ANCA-negative patients with FNGN and the autoantibodies
from these patients bind glomerular endothelium [25]. Antiplasminogen antibodies are found in approximately a quarter of
patients with AAV (both MPO- and PR3-ANCA) and interfere
with fibrinolysis. They are associated with more severe glomerular pathology and with a higher incidence of thromboembolic
disease [20, 26] that is increased in AAV, during both active
disease and remission [21, 27]. The limited longitudinal data
available show a variable response of the autoantibodies to treatment [26] but have identified a single example of fluctuations in
anti-plasminogen antibody mirroring clinical thromboembolic
events [20]. Clearly, much needs to be learnt about both these
autoantibodies and their interactions with those specific for
MPO and PR3, and the same is true for the autoantibodies to
moesin described by Suzuki et al.
Moesin is a member of the ezrin family of proteins that
links actin to the plasma membrane. The Suzuki group
originally described anti-moesin antibodies in serum from
SCG/Kj mice that spontaneously develop vasculitis, FNGN
with immune complexes and a range of autoantibodies including anti-MPO [28]. In a cross-sectional study of 60 patients [1],
they now describe anti-moesin antibodies in the serum from
around half of the Japanese patients with MPO-associated AAV.
The autoantibodies bound to moesin in neutrophils and
monocytes both on the cell surface and intracellularly
resulting in a cytoplasmic ANCA pattern on indirect immunofluorescence. The anti-moesin antibodies were detected in
both active disease and remission but were associated with
more renal damage (as assessed by measures of BUN, serum
creatinine and proteinuria) regardless of the titre of MPOANCA, and with higher concentrations of selected circulating
pro-inflammatory cytokines. IgG containing anti-moesin
antibodies bound to neutrophils and monocytes in vitro and
stimulated them to release cytokines, including IL-17, IL-8,
IL-6, TNF-α, MCP-1 and IFN-γ. This raises the possibility
that anti-moesin autoantibodies contribute to inflammation
and organ damage in some patients with AAV, although more
work is needed to determine their clinical significance. In particular, the studies need to be extended to non-Japanese
populations and to patients with PR3 related disease. Additionally, there is a critical need for longitudinal studies to correlate their presence with disease activity and susceptibility
for relapse.
1106
Interestingly, these findings raise the possibility that antibodies to moesin might underlie some of the apparently paradoxical observations in AAV. For example, could they explain
the infrequent finding of an immunofluorescent cytoplasmic
ANCA pattern, in association with an anti-MPO antibody? Or
why disease activity and ANCA titre can dissociate—as it
appears that anti-moesin antibodies can persist during remission at similar titres to those in acute disease.
There is a gathering consensus that patients with AAV
should be stratified according to whether they have antibodies
to MPO or PR3 [9, 12], but should prospective studies also
take account of other autoantibodies, such as those specific for
moesin, LAMP-2 or plasminogen to better understand what
clinical phenotypes these autoantibodies may impart? For the
time being at least, these antibodies need to be validated in
other AAV cohorts, which include patients with PR3-ANCA,
and those who are ANCA negative. The collaboration with
European and North American investigators could rapidly
allow the validation of this antibody using serum from clinical
trial banks that would allow not only cross-sectional verification but also longitudinal analysis following standardized induction therapy.
Clearly, Suzuki et al. have identified another autoantibody
that could influence disease initiation or progression in Japanese
AAV patients. Their observations emphasize the wider issue of
the urgent need for sufficiently powered international collaborative studies to define the relations between the canonical ANCA,
newly identified autoantibodies and other potential pathogenic
factors. This would require gathering a global sample collection
from well-phenotyped patients that would allow all of the associated autoantibodies that have been identified to be validated
and allow us to better define clinical subsets.
AC K N O W L E D G E M E N T S
A.J.R. received funding from the European Union Seventh
Framework Programme (FP7/2007–2013) under grant agreement no. 261382 (INTRICATE).
C O N F L I C T O F I N T E R E S T S TAT E M E N T
The results presented in this paper have not been published
previously in whole or part, except in abstract format.
(See related article by Suzuki et al. A novel autoantibody against
moesin in the serum of patients with MPO-ANCA-associated
vasculitis. Nephrol Dial Transplant 2014; 29: 1168–1177.)
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