Antigen receptor-dependent and -independent regulation of NKT patrolling and activation in liver sinusoids

Abstract Natural killer T (NKT) cells are most abundant in liver and spleen and, recognize lipid antigen presented by CD1d. Utilizing intravital fluorescence microscopy, we previously demonstrated NKT patrolling in the liver sinusoids, meaning cell migration both with and against the blood flow in surveillance of antigen. Here, we report the relationship between patrolling and activation. First, both a Sphingomonas bacteria derived weak agonist, GalA-GSL at 2 μg/g, and a synthetic strong agonist, aGalCer at 10 ng/g, induced serum IL-4, CD69 upregualtion and acute NKT arrest. Surprisingly, a low dose of aGalCer (2 ng/g) did not significantly affect NKT patrolling, although a comparable biological response was elicited. Second, IL-12 and IL-18 synergized to activate NKT cells in the absence of exogenous antigen. These cytokines activated liver NKT cells and induced serum IFN- ? but not IL-4. NKT patrolling was not significantly affected. Therefore, glycolipid antigens can induce NKT cell activation and arrest, although the requirement for arrest may be restricted to weak agonists. Importantly, IL-12 and IL-18 activate NKT cells without affecting NKT patrolling thereby allowing these primed cells to continue to survey tissue for antigen. Current studies are aimed at understanding the hierarchy of antigen receptor versus cytokine driven activation and further defining their relationship to NKT cell patrolling.