Serum amyloid A is a retinol binding protein that transports retinol during bacterial infection.
Bottom Line: Serum amyloid A (SAA) proteins are strongly induced in the liver by systemic infection and in the intestine by bacterial colonization, but their exact functions remain unclear.Mouse and human SAAs bound retinol with nanomolar affinity, were associated with retinol in vivo, and limited the bacterial burden in tissues after acute infection.Our results thus identify SAAs as a family of microbe-inducible retinol binding proteins, reveal a unique protein architecture involved in retinol binding, and suggest how retinol is circulated during infection.
Affiliation: Department of Immunology, University of Texas Southwestern Medical Center, Dallas, United States.Show MeSH
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Mentions: Although the precise tissue targets of circulating retinol-bound SAAs remain under investigation, several observations support the idea that SAAs promote immunity to infection. First, Saa1/2−/− mice exhibit increased susceptibility to chemically-induced colitis in mice (Eckhardt et al., 2010), suggesting that SAAs contribute to intestinal immunity. Second, studies in zebrafish show that commensal microbiota stimulate neutrophil migration through induction of SAA (Kanther et al., 2013). Third, we found that intraperitoneal infection of Saa1/2−/− mice with S. typhimurium resulted in higher bacterial loads in liver and spleen as compared to wild-type mice (Figure 7A,B), suggesting that SAAs also contribute to systemic immunity.10.7554/eLife.03206.019Figure 7.Saa1/2−/− mice have higher bacterial burdens following S. typhimurium infection.
Affiliation: Department of Immunology, University of Texas Southwestern Medical Center, Dallas, United States.