Regulation of inflammation and fibrosis by macrophages in lymphedema

Abstract

Lymphedema, a common complication of cancer treatment, is characterized by inflammation, fibrosis, and adipose deposition. We have previously shown that macrophage infiltration is increased in mouse models of lymphedema. Because macrophages are regulators of lymphangiogenesis and fibrosis, this study aimed to determine the role of these cells in lymphedema using depletion experiments. Matched biopsy specimens of normal and lymphedema tissues were obtained from patients with unilateral upper extremity breast cancer-related lymphedema, and macrophage accumulation was assessed using immunohistochemistry. In addition, we used a mouse tail model of lymphedema to quantify macrophage accumulation and analyze outcomes of conditional macrophage depletion. Histological analysis of clinical lymphedema biopsies revealed significantly increased macrophage infiltration. Similarly, in the mouse tail model, lymphatic injury increased the number of macrophages and favored M2 differentiation. Chronic macrophage depletion using lethally irradiated wild-type mice reconstituted with CD11b-diphtheria toxin receptor mouse bone marrow did not decrease swelling, adipose deposition, or overall inflammation. Macrophage depletion after lymphedema had become established significantly increased fibrosis and accumulation of CD4(+) cells and promoted Th2 differentiation while decreasing lymphatic transport capacity and VEGF-C expression. Our findings suggest that macrophages home to lymphedematous tissues and differentiate into the M2 phenotype. In addition, our findings suggest that macrophages have an antifibrotic role in lymphedema and either directly or indirectly regulate CD4(+) cell accumulation and Th2 differentiation. Finally, our findings suggest that lymphedema-associated macrophages are a major source of VEGF-C and that impaired macrophage responses after lymphatic injury result in decreased lymphatic function.

Pathophysiology of lymphedema—Is there a chance for medication treatment?

“…Here also, depletion of either CD4+ cells or macrophages inhibited lymphangiogenesis . Although macrophages appear to play a positive role in the initial development of lymphedema, Ghanta et al demonstrated that in chronic lymphedema M2 macrophages inhibit lymphedema development and improve lymphatic function . Macrophage depletion in chronic lymphedema in this study, lead to increase CD4 + infiltration and fibrosis.…”

Implications of Lymphatic Transport to Lymph Nodes in Immunity and Immunotherapy

“…The associated lymphostasis causes persistence and accumulation of antigen, foreign material, and immune complexes in the interstitium, which can cause chronic localized inflammation (107) in addition to fibrosis (4, 108, 109). This chronic inflammation also attenuates lymphatic contraction (90), hindering lymphatic flow to the lymph node and disrupting the trafficking of lymphocytes to the lymph node.…”

Diphtheria toxin–mediated ablation of lymphatic endothelial cells results in progressive lymphedema

“…To isolate hind limb macrophages, hind limb skin was digested as previously described (15,64), and CD11b + macrophages were isolated using magnetic beads (MACS, Miltenyi Biotec) according to the manufacturer's recommendations. RNA extraction was performed on these macrophages using TRIzol (Invitrogen, Life Technologies) according the manufacturer's recommendations.…”