Binding of alpha-2-macroglobulin trypsin complex to human monocytes in culture

Abstract

¹²⁵I-labelled α₂-macroglobulin-trypsin (α₂MT) complex bound specifically to freshly isolated human blood monocytes at 4 °C but not to B or T lymphocytes, polymorphonuclear leucocytes, erythrocytes or thrombocytes. Binding of 12 pmol/l labelled α₂MT to freshly isolated monocytes was low. However, when monocytes were cultured in vitro, binding increased, reaching 10- to 20-fold higher specific binding by 2–4 weeks. Non-specific binding was absent. Considerable variations were observed in binding to monocytes from different cultures (individuals). The half-time of ¹²⁵I-labelled α₂MT complex association to 14-days-old monocyte cultures was about 6 h at 4 °C. Dissociation of labelled complex after the addition of a saturing concentration of unlabelled complex was biphasic. About half of the labelled complex dissociated with a half-time of about 1 h, whereas the other half dissociated extremely slowly. At near steady state, half of the receptors were occupied at a complex concentration of about 200 pmol/l and Scatchard analysis showed that the data were adequately described by assuming one class of receptors. It is concluded that human monocytes express a marked increase in binding of α₂M complex when developing to macrophage-like cells in tissue cultures.

Key words:

• α₂-macroglobulin proteinase complex receptors
• α₂-macroglobulin-trypsin complex
• human monocytes