A presentation on the review article The immunopathogenesis of seropositive rheumatoid arthritis: from triggering to targeting published in Nature Reviews, Immunology

1. Presented By:
Md. Jabed Khan
Dept. of Biomedical Science
Kyungpook National University

2. Discussion Outline
• Definitions
• Subset of Rheumatoid Arthritis (RA)
• Seropositivity in RA
• Use of genetic epidemiology in defining disease
• Triggering of RA associated immunity
• Progression to systemic immunity
• Specificity of B cell and T cell responses
• Targeting the bones and joints
• Other potential pathways towards RA
• Dissecting the molecular pathogenesis of RA
• Therapeutic implications

3. Rheumatoid arthritis
• Rheumatoid arthritis is a common autoimmune disease
that is associated with progressive disability, systemic
complications, early death, and socioeconomic costs.
• Traditionally characterized and defined by its clinical
manifestations such as
Joint inflammation
Bone destruction
Joint pain

4. Seropositive Rheumatoid Arthritis
Patients with RA can be divided into two major
subsets characterized by the presence versus
absence of –
Antibodies to citrullinated protein antigens
(ACPAs)
Rheumatoid Factor
 The antibody positive subset of disease is
known as seropositive Rheumatoid Arthritis

5. Rheumatoid Factor (RF)
• RF is an Autoantibody, that is the
antibody directed against an
organism’s own tissue
• Antibody against the Fc portion of
the IgG
• RF and IgG join to form immune
complexes that contribute to
the disease process
• Antibody against antibody

6. Anti–citrullinated protein antibody (ACPAs)
• ACPAs are autoantibodies that are
directed against peptides and
proteins that are citrullinated
• They are present in the majority
of patients with rheumatoid
arthritis
• Nowadays cyclic citrullinated
peptides (CCP) assays are
frequently used to detect these
antibodies in patient serum or
plasma

7. Citrullination
• Citrullination is the conversion of
the amino acid arginine in a
protein into the amino acid
citrulline
• Citrulline is the result of a post-
translational modification
• An enzyme called PAD catalyzes
the reaction

8. Protein-arginine deiminase (PADs)
• Protein-arginine
deiminase is an enzyme
that catalyzes a form of
post translational
modification called
arginine de-imination or
citrullination

9. Subset of Rheumatoid Arthritis

10. Seropositivity in RA
Presence of
RF
The classical immune feature associated with RA is the presence of RF
in the blood
As RF occurs in the context of many other inflammatory conditions it is
not specific for RA
Presence of
ACPAs
Identification of antibodies reactive to citrullinated autoantigens
(ACPAs) followed from a systemic analysis of RA-associated antibodies
ACPAs target post translationally modified residues
Presence of ACPAs are more specific than RF to patients with RA
Other post
translational
modifications
Antibodies specific for other post translational modifications like
Homo-citrullination and acetylation have also been associated with RA

11. Use of genetic epidemiology in defining disease
RA associated antibodies
•Presence of RA associated antibodies long
before the first sign of disease
•Development of RA associated antibodies
occur over years
Triggering of Immunity
•Emergence of RA-associated immune
responses and joint inflammation are
separated in time is where and how this
immunity is triggered
Risk Factors
•MHC class II genes are by far the greatest
genetic risk factor for seropositive RA
•Exposure to noxious airways in particular to
cigarette smoke is a major risk factor
•Gene-Environment interactions is specific for
the ACPA-positive subset of RA

12. Genetic
epidemiology
of RA
Genetic association of RA with the HLA region and with PTPN22 is
mainly confined to the ACPA-positive subset of patients
In the ACPA-negative subset, the overall heritability of disease is
much lower
The influence of HLA genes is limited and different from ACPA-
positive disease in ACPA-negative subset

13. Genetic
epidemiology
of RA
Gene–gene and gene–environment interactions are present in
ACPA-positive RA but absent in ACPA-negative disease
The figure presents the combined effects of two genetic factors
(HLA-DR-SE and PTPN22) and two environmental factors (smoking
and alcohol consumption) on the lifetime risk of RA in the two
disease subsets

14. Genetic
epidemiology
of RA
The graph illustrates such cell type-specific expression of genes
that have been associated with disease through an analysis of
single nucleotide polymorphisms (SNPs) in different cell types
The graph shows a preferential expression of genes related to T
cells in the context of SNPs related to seropositive RA
CD4+ T cells, particularly effector T cells, have been implicated in
the pathogenesis of ACPA-positive RA

15. Triggering of RA associated immunity
Lungs Major findings that substantiated the idea that RA-specific immunity
may indeed be initiated in the lungs are following:
ACPAs are enriched in the bronchoalveolar lavage of patients with early
ACPA-positive RA
Both Macroscopic and Microscopic lung changes are present in patients
with early untreated ACPA-positive RA
IgA immune responses are prominent and appear early in the
development of the immunity that precedes joint inflammation
Increased expression and activation of PADs
Accumulation and activation of several types of APCs in the lungs
Genetic mutations of COPA (Coatomer subunit-α)

16. T cell-dependent B cell activation promotes the
local production of antibodies to citrullinated
protein antigens (ACPAs) in lungs
Germinal center-like structures like iBALT are
formed in the lungs
Differentiation of B cells
PAD activation and local extracellular citrullination
Activation of dendritic cells (DCs), macrophages
and B cells by Toll-like receptor (TLR)
Stimuli from particles in cigarette smoke, silica dust
or textile dust components of an aberrant
microbial flora
Triggering of RA associated immunity, Continued

17. Triggering of RA associated immunity, Continued
Gum Periodontitis caused by
Porphyromonas gingavalis
This bacterium harbours its own
PAD and hence contains
citrullinated proteins
RA-associated ACPA response
originates from a protective
immune response against P.
gingivalis
Curr Rheumatol Rep. 2014 Mar;16(3):408

18. Triggering of RA associated immunity, Continued
Intestinal
tract
Changes in the gut microbiota
may be related to the
presence of RA
Experimental perturbations of
the gut microbiota and the gut
barrier may contribute to the
development of arthritis
[J Clin Med. 2017 Jun; 6(6): 60]

19. Progression to systemic immunity
Sera from individuals in whom no evidence was found for future development of RA had
lower titres of ACPAs and had reactivity against fewer citrullinated peptides compared with
sera from individuals who later developed RA
The induction of several other antibody types, modification of antibodies and occurrence of
other biomarkers have been observed during this phase
Different isotypes of RF, including IgA RF, may occur early during the systemic response
Simultaneous presence of RF and ACPAs in the serum is highly predictive of future RA
development
Epitope spreading of the antibody response
Increasing titres of antibody

20. Specificity of B cell and T cell responses
•The peptide-binding
capacity of HLA molecules
has pathogenic significance
•A positively charged P4
pocket is an unfavourable
binding site for arginine-
containing peptides,
whereas it easily
accommodates citrullinated
variants of the same
peptides
•An arginine to citrulline
conversion by PADs will
enhance HLA binding and
therefore the presentation
of peptides that would not
be bound in their native
form
HLA class II
alleles

21. Specificity of B cell and T cell responses, Continued
•Citrulline-reactive CD4+
T cells from patients with
RA have been validated
for several ACPA targets
•Specific T cell mediated
immune responses to
candidate autoantigens
are formed outside the
joints
•Additional factors may
further enhance the
activities of antigen
specific T cells
CD4+ T
cells

22. Specificity of B cell and T cell responses, Continued
•Citruline reactive B cells are present among patients with
RA and are relatively frequent
•Autoreactive B cells accumulate in the inflamed joints
• B cells are reactive to post-translationally modified auto
antigens and helped by HLA class II dependent T cells
•These B cells and plasma cells and their immunoglobulin
products are able to promote joint inflammation and bone
destruction
Autoreactive
B cells

23. Targeting the bones and joints
Osteoclast dependent bone loss
•Osteoclasts develop from monocyte precursors in
the presence of RANKL and M-CSF
•The physiological maturation of these precursor
cells depends on the enzymatic activity of PADs
•Osteoclasts express citrullinated antigens on their
surface, as a result these cells are prime targets for
circulating ACPAs
•Some ACPAs can bind these targets and activate
osteoclasts to secrete CXCL8, which in turn induces
further osteoclast development and maturation
•Antibodies incorporated in immune complexes, can
also bind to the Fc receptors expressed on the
surface of maturing osteoclasts to increase
osteoclast differentiation
•The activation of osteoclasts through antibodies,
finally leads to bone erosion, cortical fenestration
and loss of trabecular bone in the absence of any
sign of inflammation

24. Targeting the bones and joints, Continued
Osteoclast dependent
Arthralgia
•Arthralgia (joint pain) is a common
symptom that often precedes the
development of joint inflammation in RA
•ACPAs bound to osteoclasts trigger CXCL8
release
•CXCL8 sensitizes or activates sensory
neurons by binding to CXCR1 and CXCR2
receptors expressed on nociceptors
•ACPAs induce mechanical and thermal
hypersensitivity as well as a decrease in
spontaneous locomotor activity

25. Targeting the bones and joints, Continued
Joint inflammation
•Binding of ACPAs to osteoclasts can induce
CXCL8 secretion, which promotes neutrophil
chemoattraction
•Neutrophils can also migrate to joints in
response to non-specific inflammatory stimuli
•CXCL8 promotes neutrophils to release
neutrophil extracellular traps (NETs), which
can be further enhanced by ACPAs binding to
citrullinated histones exposed in the NETs
•Expression of citrullinated proteins in
articular cartilage might allow ACPAs to bind
the cartilage surface and initiate local
inflammation through immune complex-
mediated mechanisms
•ACPAs might also bind citrullinated proteins
directly in the synovial membrane following
minor insults

26. Targeting the bones and joints, Continued
Joint inflammation, Continued
•Immune complexes between citrullinated
proteins and ACPA-IgG can drive inflammation
by engaging both Toll-like receptor 4 (TLR4)
and Fc receptors
•Inflammation results in the production of IL-6
and tumour necrosis factor (TNF), which are a
hallmark of the synovial inflammation in
rheumatoid arthritis
•As a consequence, both ACPA- and
RF-dependent events contribute to the
initiation and propagation of chronic synovial
inflammation
•These events further synergize with T cell
activation and enhance the local production
of autoantibodies, antigen-presenting cell,
matrix metalloproteinases and T cell receptor

27. •Triggering of
Autoimmunity
•Lungs, gums and gut as
possible sites of
triggering
Triggering
•Epitope spreading
•Increased titers of
antibody
Maturation
•Bone loss
•Joint pain
•Synovitis
Targeting
•Classical symptoms of
RA
•Formation of NETosis
•Production of IL-6, TNF
and MMPs
Fulminant
disease

28. Other potential pathways towards RA
Immunity to type II collagen
and related cartilage
derived autoantigens
May also involve
citrunillation
ACPAs are cross-
reactive with
citrullinated
epitopes of type II
collagen (Many, but
not all)
Formation of immune
complexes with ubiquitously
available autoantigens, such
as GPI (Glucose Phosphate
Isomerase)
Anti-GPI reactivity is
neither specific nor
common for RA
This principle has
obvious implications for
other antigen
specificities
MHC class II-independent
mechanisms
Cytokine
dysregulation and
the activation of
synovial fibroblasts

29. Dissecting the molecular pathogenesis of RA
Future studies of
RA must take
into accounts
two concepts
Heterogenicity of the
disease
Stratify patients with RA as
well as individuals at risk
of RA
Addressing gradual
development of
disease
Which requires
longitudinal studies
beginning with individuals
at risk of disease who
have not yet developed
joint inflammation
To allow immunologists to properly study RA close collaboration will be necessary with clinicians in
charge of cohorts and with biobanks, and a means to stratify the patients will be required
Similar strategies are needed for the seronegative subset of RA, for which much less is known
Finally, we need a better understanding of when and in which contexts autoimmunity is converted to
autoimmune disease.

30. Therapeutic implications

31. For Your