Downregulation of the Hemoglobin Scavenger Receptor in Individuals With Diabetes and the Hp 2-2 Genotype: Implications for the Response to Intraplaque Hemorrhage and Plaque Vulnerability

In individuals with diabetes mellitus (DM), the haptoglobin (Hp) genotype is a major determinant of susceptibility to myocardial infarction. We have proposed that this is because of DM and Hp genotype-dependent differences in the response to intraplaque hemorrhage. The macrophage hemoglobin scavenging receptor CD163 plays an essential role in the clearance of hemoglobin released from lysed red blood cells after intraplaque hemorrhage. We sought to test the hypothesis that expression of CD163 is DM and Hp genotype-dependent. CD163 was quantified in plaques by immunohistochemistry, on peripheral blood monocytes (PBMs) by FACS, and as soluble CD163 (sCD163) in plasma by ELISA. In DM plaques, despite an increase in macrophage infiltration, CD163 immunoreactivity was lower, resulting in a dramatic reduction in the percentage of macrophages expressing CD163 (27±2% versus 70±2%, P=0.0001). In individuals with DM as compared with individuals without DM, the percentage of PBMs expressing CD163 was reduced (3.7±0.6% versus 7.1±0.9%, P