Blood-Induced Inflammation in Hemophilia

We previously showed that the acute-phase reactants IL-6, CRP and LBP are elevated in the blood of hemophilia patients in response to acute and recent bleeding. The systemic elevation of acute-phase markers in hemophilia patients was associated with increased activation of monocytes, which exhibit deficits of M2 markers such as CSF1-R, CD163 and Tie2. These deficits correlate with impaired differentiation of monocytes into macrophages thus resulting in the diminished ability of hemophilia macrophages to invade clot and phagocytose red blood cells. As macrophages are central to wound healing and tissue regeneration, we hypothesize that the diminished phagocytic activity of hemophilia macrophages contributes to blood-induced inflammation and joint degeneration in hemophiliacs with hemarthrosis.

To assess the effect of joint bleeding on inflammation, we induced a needle-puncture injury of the knee in transgenic mice with hemophilia A. While this process produced only a minor injury in coagulation competent control mice, we observed an extensive hematoma on d1 and d7 in the knees of hemophilia mice as shown by gross and histological examination. By day 28, the hematoma was completely absorbed. The degenerative changes of the knee joints that followed the bleeds included synovia hyperplasia, fibrosis and decline in bone density.

Joint bleeding reached a plateau on day 1-7 in hemophilia mice. Immunohistochemistry for myeloperoxidase revealed during this time a massive influx of neutrophil granulocytes into punctured joints that subsided at day 28 when the hematoma was replaced by arthrofibrosis. In addition, acute bleeding-induced inflammation was reflected by a steep increase of interleukin 6 in the blood circulation of knee-punctured hemophilia mice that reached a maximum at day 7 and then fell towards baseline levels at day 28. CD68-positive wound macrophages, on the other hand, were first observed in punctured knees on day 7 and persisted until the end of the observation period on day 28, when most of the macrophages were loaded up with hemosiderin. None of these complications occurred in punctured wildtype mice with normal clotting activity.

The deposition of hemosiderin-loaded macrophages in the punctured joints of hemophilia mice suggests that failure to remove red blood cells from the wound area leads to inflammation and subsequent joint degeneration. This failure to clear red blood cells and their proinflammatory components appeared to be specific to hemophilia mice, as we observed rapid absorption of sizable hematomas after injection of anticoagulated blood into the knee joint of coagulation-competent wildtype mice, which in contrast to punctured hemophilia mice showed no signs of inflammation or joint destruction 7 days after blood injection.

Together, these data show that hemarthrosis in hemophilia represents a relevant inflammatory stimulus that correlates strongly with joint degeneration. Moreover, the data indicate that inflammation in hemophilia is caused by impaired removal of red blood cells from injured joints, which may lead to the release of pro-inflammatory hemoglobin degradation products and subsequent arthrofibrosis.

No relevant conflicts of interest to declare.