Detection of a mediator derived from endotoxin-stimulated macrohpages that induces the acute phase serum amyloid A response in mice.

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Abstract
The mechanism by which [Escherichia coli] LPS [lipopolysaccharide] stimulates an acute phase serum amyloid A (SAA) response in C3H mice was studied. A factor (SAA inducer) appears in the blood of C3H/HeN (lipopolysaccharide [LPS]-sensitive) mice .apprx. 1 h after administration of LPS which when passively administered, can induce C3H/HeJ mice to produce SAA although they are resistant to the LPS itself. SAA inducer was detected in the culture medium of LPS treated C3H/HeN macrophages but not spleen cells. Two stages in the induction of the acute phase SAA response are now recognized: a latent period of 2-3 h during which the SAA concentration remains at baseline values and in which SAA inducer appears; and the period of synthesis of SAA which lasts for .apprx. 24 h past induction. A macrophage response to LPS may be responsible for production of the serum mediator which induces SAA synthesis.