Considering that Hb is the primary target of IsdB (29), and that Hb-haptoglobin (Hb-Hp) complexes are cleared via CD163-medicated endocytosis by macrophages (30), we explored the possibility that anti-IsdB mAb–mediated infection of macrophages via CD163 receptor–mediated endocytosis is facilitated by a multimolecular complex containing Spa–anti-IsdB antibody–IsdB-Hb-Hp (Figure 5A). Here, HP is linked to infection.