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Acute phase reactants of mice. I. Isolation of serum amyloid P-component (SAP) and its induction by a monokine
Abstract:
The acute phase reactant of mice, serum amyloid P-component (SAP), was purified and separated from C-reactive protein (CRP). The purified SAP is composed of identical M, 31 Kd polypeptide subunits, determined by SDS-PAGE. SAP levels increased five-fold by 24 hr after challenge with lipopolysaccharide (LPS) or thioglycollate. This response closely correlated with blood monocytosis and required new macromolecule (protein + RNA) synthesis and secretion by the liver. The induction of the SAP response was adoptively transferred by a serum factor produced in optimal concentrations only 90 min after an inflammatory stimulus, which preceded a detectable increase in SAP. A potent SAP inducer was identified in culture supernatants of LPS-activated macrophages. The rapid induction of SAP synthesis in LPS-unresponsive C3H/HeJ mice was dependent on the amount of lymphocyte-activating factor, LAF(IL 1), present in the macrophage culture supernatants. Partially purified human IL 1 also induced a rapid increase in SAP. Thus the induction of SAP in mice appears to be mediated by a product of macrophages, a cell population that is also expanded as part of the systemic inflammatory response.
Insights
Serum amyloid P-component (SAP) levels in mice increase significantly during inflammation. This acute phase response is induced by macrophage-derived factors, including Interleukin-1 (IL-1).
Area of Science:
- Immunology
- Biochemistry
- Molecular Biology
Background:
- Serum amyloid P-component (SAP) is an acute phase reactant in mice.
- SAP is structurally distinct from C-reactive protein (CRP).
Purpose of the Study:
- To investigate the regulation and induction of SAP during the acute phase response.
- To identify the cellular and molecular mediators of SAP synthesis.
Main Methods:
- Purification and characterization of mouse SAP using SDS-PAGE.
- Induction of SAP response by lipopolysaccharide (LPS) or thioglycollate.
- Adoptive transfer experiments using serum factors.
- Analysis of macrophage culture supernatants and IL-1.
- Assessment of SAP induction in LPS-unresponsive mice.
Main Results:
- Purified SAP consists of identical 31 Kd polypeptide subunits.
- SAP levels increased five-fold 24 hours post-challenge, correlating with monocytosis.
- SAP induction requires new macromolecule synthesis and liver secretion.
- A serum factor, produced 90 minutes after inflammatory stimulus, transferred SAP induction.
- LPS-activated macrophages produced a potent SAP inducer.
- SAP induction in C3H/HeJ mice depended on lymphocyte-activating factor (LAF/IL-1) levels.
- Partially purified human IL-1 also induced rapid SAP increase.
Conclusions:
- SAP induction in mice is mediated by macrophage-derived products.
- Lymphocyte-activating factor (IL-1) plays a crucial role in mediating SAP synthesis.
- Macrophages, expanded during systemic inflammation, are key regulators of SAP.