In response to C5a in fact, C5aR1 interacts with TLR2 in osteoblasts, promoting the upregulation of CXCL10 (Kwak et al., 2008; Mödinger et al., 2018), a chemokine that is critical for bone cancer cells recruitment, to support osteoclast differentiation and to promote the formation of osteolytic bone metastases (Lee et al., 2012). Here, C5 is linked to bone cancer.