Mice lacking serum amyloid P component do not necessarily develop severe autoimmune disease

Serum amyloid P component (SAP) is a major acute-phase reactant in mice. Recently, it was reported that SAP-deficient mice spontaneously developed anti-nuclear antibodies and severe glomerulonephritis. Because the SAP-deficient mice we generated display no obvious phenotypic abnormalities, we investigated whether our SAP-deficient mice would also spontaneously develop autoimmune responses. In accordance with the report, our mice produced high titers of anti-nuclear antibody but did not develop severe glomerulonephritis. On the other hand, it was recently reported that SAP bound to gram-negative bacteria via lipopolysaccharide (LPS) prevented LPS-mediated activation of a classical complement pathway. Thus, we asked if SAP-deficient mice would show altered responses to an intraperitoneal injection of LPS from Salmonella typhimirium. SAP-deficiency did afford resistance to lethality induced by high-dose LPS. Our experiments clearly showed that contrary to documented data, SAP-deficient mice do not develop serious autoimmune disease and we suggest that SAP has a critical role in LPS toxicity.