Differential impacts of toll-like receptor 9 agonism on human natural killer cell cytotoxic functions

Abstract

The innate immune system is the front line of the body’s defenses. Innate effector cells, including natural killer (NK) cells, represent some of the first immune cells to respond to malignities or infections. There are two mechanisms by which NK cells recognize and kill their targets: (i) direct killing and (ii) antibody dependent cellular cytotoxicity (ADCC). NK cells are typically activated for performing effector functions by exposure to key cytokines which are not necessarily produced by the NK cells themselves. Cells that produce these activating cytokines often trigger signaling cascades. Our research focuses on such a cascade elicited by treating human peripheral blood cells with a toll-like receptor 9 (TLR9) agonist. Then the human NK cells are magnetically enriched and incorporated into our novel Natural Killer cell Simultaneous ADCC and Direct Killing Assay (NK-SADKA). This assay was designed to control for human-to-human variation by ensuring that human NK cells from the same donors are tested for both their ability to mediate direct killing as well as ADCC. Using this approach, we identified differential impacts of TLR9 agonism between human NK cell’s ability to mediate direct killing versus ADCC ex vivo. Specifically, we found that NK cells from the treatment group showed an increase in their ability to mediate direct killing while simultaneously experiencing a decreased ability to mediate ADCC. Experiments to identify the mechanism of this paradoxical effect are ongoing