Contact-dependent Stimulation and Inhibition of Dendritic Cells by Natural Killer Cells

TLDR

NK cells and dendritic cells are distinct innate immune cells, and NK cells can lyse autologous DCs in vitro. The study investigates whether contact‑dependent interactions between activated human NK cells and immature DCs act as a control switch for the immune system. Low NK‑to‑DC ratios (1:5) trigger contact‑dependent amplification of DC cytokine production and maturation via TNF‑α, whereas higher ratios (5:1) result in NK‑mediated DC killing and functional inhibition.

Abstract

Natural killer (NK) cells and dendritic cells (DCs) are two distinct cell types of innate immunity. It is known that the in vitro interaction of human NK cells with autologous DCs results in DC lysis. Here we show that contact-dependent interactions between activated human NK cells and immature DCs (iDCs) provides a "control switch" for the immune system. At low NK/DC ratios, this interaction dramatically amplifies DC responses, whereas at high ratios it completely turns off their responses. Specifically, culture of activated human NK cells with iDCs, at low NK/DC ratios (1:5), led to exponential increases in DC cytokine production, which were completely dependent on cell-to-cell contact. DC maturation was also driven by cognate interactions with NK cells and maturation was dependent on endogenously produced TNF-alpha in the culture. At slightly higher NK/DC ratios (5:1), inhibition of DC functions was the dominant feature due to potent killing by the autologous NK cells. Resting NK cells also stimulated autologous DC maturation in a TNF-alpha/contact-dependent manner, however, increasing the NK/DC ratio only led to an enhancement of this effect.