As a result of hemolysis, hemoglobin is found to accumulate in the kidney and is secreted in the urine. Haptoglobin captures, and combines with free plasma hemoglobin to allow hepatic recycling of heme iron and to prevent kidney damage. Haptoglobin also acts as an antioxidant, has antibacterial activity and plays a role in modulating many aspects of the acute phase response. Hemoglobin/haptoglobin complexes are rapidly cleared by the macrophage CD163 scavenger receptor expressed on the surface of liver Kupfer cells through an endocytic lysosomal degradation pathway (By similarity). Tetramer of two alpha and two beta chains; disulfide-linked (By similarity). The hemoglobin/haptoglobin complex is composed of a haptoglobin dimer bound to two hemoglobin alpha-beta dimers (By similarity). Interacts with CD163 (By similarity). Interacts with ERGIC3 (By similarity). The beta chain mediates most of the interactions with both subunits of hemoglobin, while the alpha chain forms the homodimeric interface. Belongs to the peptidase S1 family. Although homologous to serine proteases, it has lost all essential catalytic residues and has no enzymatic activity.