Advances in Bioscience and Biotechnology, 2013, 4, 937-940 ABB Published Online October 2013 (
Multifaceted role of TNF-α during the pathogenesis of
rheumatoid arthritis
Ramanjaneya V. R. Mula, Rangaiah Shashidharamurthy*
Department of Pharmaceutical Sciences, Philadelphia College of Osteopathic Medicine, School of Pharmacy, Suwanee, USA
Email: *
Received 9 July 2013; revised 9 August 2013; accepted 10 September 2013
Copyright © 2013 Ramanjaneya V. R. Mula, Rangaiah Shashidharamurthy. This is an open access article distributed under the Crea-
tive Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the
original work is properly cited.
Tumor necrosis factor alpha (TNF-α) a cytokine has
been shown to be the key player during the patho-
genesis of several autoimmune inflammatory disor-
ders (presumably sterile inflammation) including rheu-
matoid arthritis (RA). Several studies have shown
that TNF-α is mainly involved in the proinflamma-
tory responses. However recent studies have reported
multifunctional role of TNF-α during the develop-
ment of RA. Therefore, in this article we have high-
lighted the distinct functions of TNF-α during patho-
genesis of RA.
Keywords: Cytokines; Tumor Necrosis Factor-α;
Rheumatoid Arthritis; Inflammation
The organization of infiltrated cells in the arthritic mi-
croenvironment resembles the secondary lymphoid organ
including the presence of CD4+ T cells [1]. Typically, in
secondary lymphoid organs the presence of chemokine
gradient is necessary for the localization of T cells, espe-
cially to interact maximally with antigen presenting cells
[2]. The cytokine TNF-α plays a crucial role during the
pathogenesis of RA [3]. The focal immunological func-
tion of TNF-α is thought to be the induction of several
proinflammatory cytokines and stimulate the effector im-
mune cells through interaction with TNF-α receptors. In
addition TNF-α is also known to act as chemoattractant
for various cells including T cells [4,5]. However, the
additional role of TNF-α in early phase of T cell migra-
tion to arthritic microenvironment, especially adhesion
and transmigration through endothelium is not clear.
Therefore, Rossol et al. [6] observed that the interactions
of TNF-α and TNFRI are necessary for T-cell migration
into synovium using in vitro and ex vivo experiments.
The results of Rossol et al. [6] study show that the in-
teraction of TNF-α with receptor type1 (TNFR1) is in-
deed a migratory stimulus for CD4+ T cells in RA pa-
tients which is a TNF-α gradient dependent”.
In this article, the authors used horizontally oscillating
microtome for synovial sections and confocal as well as
fluorescent microscopic methods to follow the T lym-
phocyte migration. They also collected the migrated T
lymphocytes for phenotyping. The in vitro transwell ex-
periment was performed to ascertain that TNF-α is in-
deed required for T cell migration. In support of this,
they also carried out the ex vivo T cell migration assay
using synovial tissue section from RA patients by co-
incubating with autologous peripheral CD4+ T cells. The
migrated CD4+ T cells in the tissue sections were visu-
alized by Fluorescent microscopy. The results showed
that only the CD4+ T cells form RA patients migrated
into synovial tissue but not from the healthy controls. In
continuation with this observation, they found that the
expression of TNFR1 and ICAM-1 is necessary for acti-
vated CD4+ T cells to migrate into synovium. Subse-
quent flow cytometry results of cells isolated from syno-
vial tissue show that expression of TNFR1 is specific in
transmigrated activated CD4+ T cells but not in control
healthy volunteer CD4+ T cells. Taken together, these
results suggest that the TNF-α is necessary for CD4+ T
cell migration in arthritic joints. At the conclusive point
the goal of the investigation on the role of TNF-α in
synovium which was proven concretely as a potential
chemoattractnat may possibly pave way to develop ther-
apy of TNF-α inhibitors as well as new approaches that
can be more focused towards targeting T-cells that ex-
press TNFR1 in excess.
*Corresponding author.
R. V. R. Mula, R. Shashidharamurthy / Advances in Bioscience and Biotechnology 4 (2013) 937-940
A step-by-step manifestation of synovial inflammation in
RA quietly transforms into chronic inflammation through
elevated levels of many inflammatory mediators [7] of
which TNF-α plays a key role during synovial inflamma-
tion. Both macrophages and fibroblast-like synovial cells
(FLS) are most prominent among multiple cell types for
prolonged synovial inflammation [8,9] in RA. In addition,
TNF-α secreted at the arthritic microenvironment is
known to influence these two cells differently. Activa-
tion of macrophages through TNF-α is transient, while
the FLS are responsible for prolonged synovial inflam-
mation [10]. The distinct role of TNF-α in activating the
macrophages and FLS is not clearly understood. How-
ever, it can be postulated that the main function of ma-
crophages is to promote the inflammation and later
dampen the inflammation by triggering the tissue repair
mechanism as protective role to avoid the local and sys-
temic toxicity caused by high levels of inflammatory
mediators [11]. Therefore, they may transiently respond
to the TNF-α to initiate the inflammation in the early
phase. Whereas, since FLS normal function is to create a
mechanical platform of synovium [12] and usually never
exposes to foreign antigens, therefore they may lack the
haemostatic mechanism to control their activation during
RA. However, the molecular mechanism of FLS activa-
tion leading to prolonged synovial inflammation is not
clearly understood. An attempt to investigate the possible
mechanism was carried out by Lee et al. [13] have
shown that TNF-α induced FLS activation leads to un-
controlled NF-κB signaling in FLS resulting in secretion
of cytokines, chemokines and metalloproteinases for
longer period of time leading to persistent synovial in-
TNF-α induces prolonged canonical NF-κB signaling
resulting in uncontrolled production of inflammatory
mediators contributing to the persistent synovial inflam-
mation during RA through FLS but not macrophages. In
other words FLS may be the contributing cell type for
chronic inflammation during RA”.
The authors studied the distinct functional role of
TNF-α using macrophages and FLS. The signaling me-
chanisms of NF-κB were elucidated by western blot
analyses and the protein involvement in transcriptional
regulation was analyzed by histone acetylation, chroma-
tin accessibility, and NF-κB, p65 and RNA polymerase II
(Pol II) occupancy at the interleukin-6 (IL-6) promoter
using chromatin immunoprecipitation and restriction
enzyme accessibility assays. Lee et al. have shown ma-
crophage and FLS stimulation by TNF-α is transient and
sustained respectively during the inflammatory RA con-
dition. The feedback inhibition of inflammatory re-
sponses mediated by ABIN-3, IRAK-M, SOCS-3, ATF-3
and STAT-3 are expressed at high level in macrophages
while at a low level in FLS. This may be a contributing
factor for persistence of synovial inflammation in RA
through FLS. Further, TNF-α facilitated histone modifi-
cation and increased accessibility for RNA polymerase II
at IL-6 promoter site resulting in secretion of proin-
flammatory cytokine IL-6 in FLS. Taken together this
investigation has shown that sustained inflammatory
response by FLS through TNF-α mediated inflammatory
gene transcriptions and protein expressions prolong the
synovial inflammation. This may pave a way to make
FLS as an additional target in countering the unresolved
TNF-α, a proinflammatory cytokine initiates the inflam-
matory response leading to edematic joint and subse-
quent bone destruction during the development of rheu-
matoid arthritis [3]. The bone destruction is mainly me-
diated by osteoclast, a cell of myeloid origin (OC). OC
differentiation, maturation and activation are primarily
mediated by RANKL and its receptor RANK. Recent
studies have shown that TNF-α can magnify the process
of osteoclastogenesis in the presence of RANKL [14-16]
as an additional role apart from its proinflammatory re-
sponse. It has been shown that monoclonal antibody
therapy (infliximab, etanercept and adalimumab) against
TNF-α, though inhibited/reduced the bone erosion after
the treatment, the clinical symptoms of inflammation
were not affected [17]. Nonetheless, the mechanism of
the biphasic effect of biological TNF-α inhibitors was
not yet fully understood. Therefore, Binder et al. [18]
investigated the fundamental mechanism of TNF-α dur-
ing RA by in vitro studies and human TNF-α (hTNF)
transgenic destructive arthritis mouse model. Binder et al.
have shown the differential effects of TNF-α on osteo-
clastogenesis and bone erosion activity using above men-
tioned mouse model of experimental arthritis.
High level of TNF-α is required for osteoclastogene-
sis than to initiate the inflammation at the synovial joints.
Hence, low doses of TNF-α inhibitor used in present in-
vestigation lead to expression of low levels of TNF-α,
which impede osteoclastogenesis but do not inhibit syno-
vial inflammation. Therefore, high levels of TNF-α in-
hibitors are required to inhibit both inflammation and
bone resorption”.
The authors have chosen monocytes derived from
spleen cells and tested the osteoclastogenesis in vitro us-
Copyright © 2013 SciRes. OPEN ACCESS
R. V. R. Mula, R. Shashidharamurthy / Advances in Bioscience and Biotechnology 4 (2013) 937-940 939
ing different concentrations of TNF-α inhibitor adalimu-
mab and activator RANKL. An hTNF-transgenic de-
structive arthritis mouse model was employed for in vivo
studies of inhibition of osteoclast precursors by the ther-
apeutic. The dose dependent differential effect of TNF-α
on osteoclastogenesis though countered with low doses
of immunotherapeutic inhibitor adalimumab even in the
absence of RANKL, the inflammation of synovium was
not affected. These data suggested that TNF-α alone can
activate the osteoclasts. The mRNA levels of proinflam-
matory mediators such as IL-1, matrix metalloproteinase
(MMP) 3, and MMP13 are significantly upregulated in
untreated hTNF-transgenic mice compared to hTNF-
transgenic mice treated with high concentration (10
mg/kg body weight) of adalimumab. Whereas low dose
(0.1 mg/kg) did not have any affect. Osteoclast associ-
ated genes such as NF-ATc1, cathepsin K, c-Fms, and
M-CSF were also upregulated at higher dose but, inter-
estingly not at lower dose. These data suggest that anti-
resorptive activity of TNF-α was not affected at lower
concentration but not synovial inflammation. Taken to-
gether Binder et al. [18] exemplified the need of control-
ling both cartilage destruction as well as inflammation
mediated by TNF-α during the treatment of rheumatoid
This work was supported by American Heart Association award
(11SDG5710004) to R.S. The authors declare no competing financial
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