- During chronic kidney disease (CKD), bone mineral metabolism is disturbed owing in part to the endogenous hormone fibroblast growth factor 23 (FGF23). Elevated FGF23 levels are seen in CKD patients. Current research has demonstrated that FGF23 directly modulates the immune response and host defense to bacterial infections. FGF23 also impairs the activation and recruitment of neutrophils, which are the main immune effector cells required for host defense against bacterial infections. In addition, while FGF23 levels reduce leukocyte recruitment and functions, inflammatory conditions may also-in a reverse fashion-contribute to elevated FGF23 levels in the circulation. In this context, altered hypoxia inducible factor 1α signaling and iron metabolism may contribute to intact FGF23 (iFGF23) production. This review examines evidence on the role of FGF23 in inflammation, immune cell function and recruitment as well as the regulation of FGF23 during inflammation and the clinical implications of this process for the immune system in individuals with CKD. Clinical observations and laboratory investigations indicate an important role of FGF23 in directly modulating leukocyte activation and recruitment behavior with consequences on host defense against bacterial infections. This novel observation may in part explain the increased infectious risk among patients with CKD. However, studies of FGF23 neutralization also revealed increased mortality after sustained administration over several weeks in rats. Thus, therapeutic interventions targeting FGF23 must be carefully evaluated.Published by Oxford University Press on behalf of ERA-EDTA 2016. This work is written by (a) US Government employee(s) and is in the public domain in the US.