OC 36.2 - Platelet rich plasma modulates macrophages polarization in the context of Chronic Hemophilic Synovitis

Background: The presence of hemosiderin laden-macrophages is one of the main contributors in the maintenance and promotion of M1 profile in chronic hemophilic synovitis (CHS), caused by hemophilia-associated hemarthrosis.

Aims: To evaluate macrophages polarization in the presence of synovial fluid (SF) of CHS patients and the modulatory effect of platelet rich plasma (PRP) on these cells.

Methods: SF from CHS patients were obtained before and after PRP treatment, cellularity was evaluated by optical microscopy after Giemsa staining and expression of polarized markers by flow cytometry. For in vitro assays, monocytes and PRP were obtained from healthy donors. Monocytes were differentiated to macrophages during 7 days in the presence of SF alone or plus PRP and compared with non-polarized (M0), polarized M1 (IFNy plus LPS), M2a (IL4), or M2c (dexamethasone) and evaluated by flow cytometry and qPCR.

Results: Before PRP treatment, macrophages from SF of CHS patients, showed cytoplasmic deposits of hemosiderin and a high percentage of cells expressing CD64 (78.5±4.2%) and lower levels of CD206 (22.74±8.4%) and CD163 (26.33±15.4%), indicating an M1 profile signature. In vitro monocyte-derived macrophages differentiated with SF also skewed to an M1 pattern with an specific inflammatory gene program. PRP addition significantly modulate the relative expression of CD64 and CD206 (*p < 0.05) with a particular gene induction that results in an M2-type profile. Finally, SF samples of CHS patients after PRP treatment, showed a recompositing of the normal cellular content and a reduction of CD64 and CD206 expression in 3 follow up patients, in concordance with the in vitro results.

Conclusion(s): Ex vivo macrophages as those differentiated in vitro with SF, showed an M1 signature. The modulatory effect of PRP to a pro resolving-tissue phenotype was evidenced in patients as in monocyte-derived macrophages differentiated with SF, underlying the potential therapeutic action of PRP in CHS.