Gout is a paradigm of acute, self-limiting inflammation caused by the deposition of
monosodium urate (MSU) crystals within intra-and/or peri-articular areas, leading
to excruciating pain, joint swelling and stiffness. The infiltration of leukocytes
drives the inflammatory response and remains an attractive target for therapeutic
intervention. In this context, emerging evidence supports the view that systemic differentiation
of Th17 cells and their in situ infiltration as one of the potential mechanisms by
which these cells, and their main product IL-17, causes damage to target tissues.
To test if IL-17 was having a detrimental role in gouty onset and progression we targeted
this cytokine, using a neutralizing antibody strategy, in an experimental model of
gout. Joint inflammation was induced in CD-1 mice by the intra-articular (i.a.) administration
of MSU crystals (200 μg/20 μl). Animals from IL-17Ab-treated groups received 1, 3
and 10 μg (i.a.) in 20 μl of neutralizing antibody after MSU crystals administration.
Thereafter, joints were scored macroscopically, and knee joint oedema determined with
a caliper. Histological analysis, myeloperoxidase assay and western blots analysis
for COX-2/mPGEs-1/IL-17R pathway were conducted at 18 h (peak of inflammation) to
evaluate leukocytes infiltration and activation, followed by the analysis, in situ,
of pro/anti-inflammatory cytokines and chemokines. Flow cytometry was also used to
evaluate the modulation of infiltrated inflammatory monocytes and systemic Th17 and
Treg profile. Treatment with IL-17Ab revealed a dose-dependent reduction of joint
inflammation scores with maximal inhibition at 10 μg. The neutralizing antibody was
also able to significantly reduce leukocytes infiltration and MPO activity as well
the expression of JE, IL-1α, IL-1β, IL-16, IL-17, C5a, BLC and, with a less extent
IP-10, Rantes, KC, TIMP-1, SDF-1 and metalloproteinases in inflamed tissues. Biochemical
analysis also revealed that IL-17Ab treatment modulated COX-2/mPGEs-1 pathway (and
related PGE2 production) without interfering with IL-17R expression. Furthermore,
flow cytometry analysis highlighted a selective modulation of infiltrating inflammatory
monocytes (B220-/GR1hi-F480hi/CD115+) and circulating Th17, but not Treg, cells after
IL-17Ab treatment. Collectively the results of this study report for the first time,
that i.a. injection of MSU crystals stimulates in vivo production of Th17 cells and
Th17-related inflammatory cyto-chemokines. In addition, we have demonstrated that
the administration of a neutralizing antibody against IL-17 attenuates joint symptoms,
swelling and leukocytes infiltration to the inflamed tissue, possibly providing a
new strategy for the treatment of gouty inflammation and/or arthritis.