Macrophage Polarization Is Impaired in Hemophilia

Macrophages are master regulators of inflammation and wound healing. As such they play an important role in hemophilia, which is commonly associated with delayed tissue regeneration and bleeding-induced joint inflammation. The objective of this study is to determine if macrophage function is deregulated in hemophilia and whether this affects the physiological balance of tissue regeneration and inflammation.

For this study, we analyzed monocytes and plasma from a cohort of 26 adult patients with hemophilia A or B that visited our clinic for their annual routine check-up. Patients with acute bleeding events were excluded. The majority of patients had severe forms of hemophilia with factor VIII or IX activity < 1% and, therefore, received prophylactic factor replacement therapy (recombinant or plasmatic) but we also included patients with moderate to mild hemophilia, which were only treated in case of bleeding. Corresponding control samples stemmed from healthy male individuals that we recruited randomly from our blood donor center.

To assess macrophage differentiation, we isolated monocytes from the peripheral blood of hemophilia patients as well as healthy controls and began treatment with M-CSF or GM-CSF for 7 days. Macrophage differentiation was confirmed by phase contrast and fluorescence microscopy, which revealed a spread and elongated cell phenotype in donor monocytes in the presence of M-CSF and, to a lesser extent, GM-CSF. Hemophilia monocytes, on the other hand, failed to spread properly in response to either of the cytokines suggesting that macrophage polarization is diminished in patients with reduced activity of coagulation factor VIII or IX.

As hemophilia macrophages failed to spread in response to M-CSF, they also failed to express TNFα and CD163, which are macrophage differentiation markers typically induced by M-CSF. In contrast, GM-CSF-induced differentiation was only mildly suppressed suggesting that hemophilia macrophages specifically resist the differentiating stimulus of M-CSF. Consequently, we experienced a significant impairment in M-CSF-induced regenerative macrophage functions such as clot infiltration and red blood cell phagocytosis in hemophilia. Intriguingly, while monocyte invasion was impaired, protein expression in response to M-CSF was regained with respect to CD163 and CD206 after embedding hemophilia monocytes in clotted plasma from healthy blood donors suggesting that a functioning coagulation system has positive effects on regenerative macrophage functions.

The inability of hemophilia macrophages to promote M-CSF-mediated signals correlates with a marked down regulation of the M-CSF receptor CSF-1R on hemophilia monocytes as determined in citrated whole blood by flow cytometry. Alongside with a modest reduction of GM-CSF-R, we also detected a substantial reduction of CD163 and Tie2, which are specifically expressed on regenerative monocytes/macrophages, suggesting that clotting deficiencies impair the immune function either directly or indirectly. To further analyze the immune status of hemophilia patients, we performed a cytokine array on plasma samples from hemophiliacs versus healthy blood donors, which revealed the down regulation of a large spectrum of anti-inflammatory and regenerative cytokines in the blood of hemophilia patients.

Among the few cytokines upregulated in the blood of hemophiliacs, the adipokine leptin was the most prominent (6-fold, hemophiliac vs. donor). Since leptin has been shown to cause deregulation of the innate immunity, we treated the human monocyte cell line THP1 with recombinant leptin and found a significant inhibitory effect of M-CSF-induced spreading and clot invasion. Therefore, these data suggest that high leptin levels in the blood can reiterate the changes in monocyte function we observed in hemophilia. Together, we conclude that macrophage differentiation is deregulated in hemophilia as a result of resistance towards the cytokine M-CSF. Consequently, hemophilia macrophages are unable to properly perform regenerative functions such as clot invasion and red blood cell phagocytosis. The hemophilic monocyte/macrophage phenotype we describe can be induced by high levels of leptin and mitigated by correcting the clotting dysfunction suggesting a two prone approach to prevent delayed wound healing and persistent inflammation in hemophilia.