Receptor-mediated binding of the acute-phase reactant mouse serum amyloid P-component (SAP) to macrophages

Cell Immunol. 1988 Dec;117(2):239-52. doi: 10.1016/0008-8749(88)90115-3.

Abstract

Serum amyloid P-component (SAP) is a major acute phase protein of mice which we have previously shown increases the bactericidal activity of elicited, inflammatory macrophages (M phi). The presence of specific receptors for mouse SAP on M phi was demonstrated and the receptor-ligand (SAP) interaction characterized. Purified 125I-labeled mouse SAP binds to elicited M phi with the characteristics of a receptor-mediated event, i.e., the binding was saturable, specific, and reversible. A single type of receptor population was detected with an affinity of 5 x 10(-8) M (KD) and the calculated number of receptor sites per cell was approximately 10(5). Binding of SAP to M phi required Ca2+ or Mg2+ and was inhibited at a pH less than or equal to 5.6. Activated M phi from mice given BCG bind less SAP than nonactivated M phi. Activation of M phi with mouse interferon-gamma (IFN-gamma) or lipopolysaccharide (LPS) also decreased their SAP binding capacity. SAP is a glycosylated protein with a high mannose content; therefore mannose and other sugars were tested for inhibition of binding. Specific binding of SAP was inhibited by less than 1 mM concentrations of mannose 6-P, mannose 1-P, and mannose; however, other monosaccharides did not inhibit the binding. Removal of the oligosaccharide from SAP with an endoglycosidase specific for N-linked carbohydrate reduced the binding of SAP to M phi. The pattern of inhibition by sugars, the divalent cation requirement, and the sensitivity to low pH indicate that the receptor binding SAP is the cation-dependent mannose 6-P receptor, or a closely related receptor. The results suggest that SAP may alter or trigger M phi functions associated with inflammation by binding to glycoprotein receptors.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Binding, Competitive
  • Carbohydrates / pharmacology
  • Cations, Divalent / physiology
  • Glucose / physiology
  • Hydrogen-Ion Concentration
  • Interferon-gamma / pharmacology
  • Lectins, C-Type*
  • Lipopolysaccharides / pharmacology
  • Macrophage Activation
  • Macrophages / metabolism*
  • Mannose / metabolism
  • Mannose-Binding Lectins*
  • Mice
  • Mice, Inbred A
  • Mice, Inbred C57BL
  • Peritoneal Cavity / cytology
  • Phosphorylation
  • Receptors, Cell Surface*
  • Receptors, Immunologic / metabolism*
  • Receptors, Peptide*
  • Serum Amyloid P-Component / isolation & purification
  • Serum Amyloid P-Component / metabolism*
  • Species Specificity

Substances

  • Carbohydrates
  • Cations, Divalent
  • Lectins, C-Type
  • Lipopolysaccharides
  • Mannose-Binding Lectins
  • Receptors, Cell Surface
  • Receptors, Immunologic
  • Receptors, Peptide
  • Serum Amyloid P-Component
  • mannose receptor
  • Interferon-gamma
  • Glucose
  • Mannose