Scientific background

Macrophages are white blood cells that "scavenge" a broad range of cellular components and play a central role in orchestrating the immune defense in autoimmune diseases and infections. They migrate from the blood (as monocytes) into tissues where they mature into macrophages to be ready to respond on tissue destruction or infection.

The haemoglobin receptor CD163 was identified by Cytoguide Scientists

(Nature 2001; 409: 198 - 201)

Monocytes/macrophages express on their surface in abundant measure the CD163 protein, which is the established receptor for scavenging hemoglobin. The receptor acts in concert with haptoglobin that binds to hemoglobin prior to recognition of the complex by CD163. Binding of the haptoglobin-hemoglobin complex leads to degradation of the ligand whereas the receptor recycles .

CHO cells expressing CD163 bind and internalize fluorescent antibody conjugate.

Control cells not expressing  CD163 do not  bind and internalize the conjugated antibody

The heme moiety of hemoglobin is transformed to the yellow pigment bilirubilin, which is released from the macrophage. The entire pathway haptoglobin, CD163 and the enzyme of heme metabolization are upregulated by IL-6, a main mediator of the acute phase response on infection. CD163 is constitutively internalized thus indicating that it in principle will transport any substance bound to it.