Chemokine synergy-inducing molecules are emerging as regulating factors in cell migration. The
alarmin HMGB1, in its reduced form, can complex with CXCL12 enhancing its activity on monocytes via the
chemokine receptor CXCR4, while the form containing a
disulfide bond, by binding to TLR2 or TLR4, initiates a cascade of events leading to production of
cytokines and
chemokines. So far, the possibility that the CXCL12/
HMGB1 heterocomplex could be maintained in chronic
inflammation was debated, due to the release of
reactive oxygen species. Therefore, we have assessed if the heterocomplex could remain active in
Rheumatoid Arthritis (RA) and its relevance in the disease assessment. Monocytes from RA patients with active disease require a low concentration of
HMGB1 to enhance CXCL12-induced migration, in comparison to monocytes from patients in clinical remission or healthy donors. The activity of the heterocomplex depends on disease activity, on the COX2 and JAK/STAT pathways, and is determined by the redox potential of the microenvironment. In RA, the presence of an active
thioredoxin system correlates with the enhanced cell migration, and with the presence of the heterocomplex in the synovial fluid. The present study highlights how, in an unbalanced microenvironment, the activity of the
thioredoxin system plays a crucial role in sustaining
inflammation.
Prostaglandin E2 stimulation of monocytes from healthy donors is sufficient to recapitulate the response observed in patients with active RA. The activation of mechanisms counteracting the oxidative stress in the extracellular compartment preserves
HMGB1 in its reduced form, and contributes to fuel the influx of inflammatory cells. Targeting the heterocomplex formation and its activity could thus be an additional tool for dampening the
inflammation sustained by cell recruitment, for those patients with chronic inflammatory conditions who poorly respond to current
therapies.