Human serum amyloid P component binds to peripheral blood monocytes

Area of Science:

• Immunology
• Biochemistry
• Cell Biology

Background:

• Human serum amyloid P component (SAP) is a pentameric protein found in circulation.
• The interaction of SAP with various blood cell types is not fully understood.
• Understanding SAP binding is crucial for elucidating its physiological roles.

Purpose of the Study:

• To investigate the binding of SAP to human blood cells, including monocytes and monocyte-derived dendritic cells.
• To characterize the nature of the SAP-monocyte interaction.
• To assess the functional consequences of SAP binding on immune cells.

Main Methods:

• Flow cytometry was employed to quantify SAP binding to different cell populations.
• Biotinylated SAP was used to measure binding avidity, dose-dependence, and saturation.
• Calcium-dependency and inhibition by C1q were assessed for the SAP-monocyte interaction.

Main Results:

• Monocytes exhibited dose-dependent and saturable binding of SAP.
• Weak binding of SAP was observed on monocyte-derived dendritic cells.
• No significant binding of SAP was detected on erythrocytes, NK cells, T lymphocytes, or B lymphocytes.
• The SAP-monocyte interaction was calcium-independent and inhibited by C1q.
• SAP did not affect lymphocyte proliferation induced by mitogenic lectins.

Conclusions:

• Monocytes are a primary target for SAP binding among human blood cells.
• The SAP-monocyte interaction is specific and modulated by calcium and C1q.
• SAP binding to monocytes may play a role in regulating complement at extravascular sites.