Abstract
BACKGROUND: Lymphedema is an intractable disease that can be caused by injury to lymphatic vessels, such as by surgical treatments for cancer. It can lead to impaired joint mobility in the extremities and reduced quality of life. Chronic inflammation due to infiltration of various immune cells in an area of lymphedema is thought to lead to local fibrosis, but the molecular pathogenesis of lymphedema remains unclear. Development of effective therapies requires elucidation of the immunological mechanisms involved in the progression of lymphedema. The complement system is part of the innate immune system which has a central role in the elimination of invading microbes and acts as a scavenger of altered host cells, such as apoptotic and necrotic cells and cellular debris. Complement-targeted therapies have recently been clinically applied to various diseases caused by complement overactivation. In this context, we aimed to determine whether complement activation is involved in the development of lymphedema. RESULTS: Our mouse tail lymphedema models showed increased expression of C3, and that the classical or lectin pathway was locally activated. Complement activation was suggested to be involved in the progression of lymphedema. In comparison of the C3 knockout (KO) mouse lymphedema model and wild-type mice, there was no difference in the degree of edema at three weeks postoperatively, but the C3 KO mice had a significant increase of TUNEL(+) necrotic cells and CD4(+) T cells. Infiltration of macrophages and granulocytes was not significantly elevated in C3 KO or C5 KO mice compared with in wild-type mice. Impaired opsonization and decreased migration of macrophages and granulocytes due to C3 deficiency should therefore induce the accumulation of dead cells and may lead to increased infiltration of CD4(+) T cells. CONCLUSIONS: Vigilance for exacerbation of lymphedema is necessary when surgical treatments have the potential to injure lymphatic vessels in patients undergoing complement-targeted therapies or with complement deficiency. Future studies should aim to elucidate the molecular mechanism of CD4(+) T cell infiltration by accumulated dead cells.