Regulation of IgE-dependent zinc release from human mast cells

Zinc (Zn) affects many aspects of immune function, including thymic development and the activities of immune cells. Zn is also involved in many steps of high-affinity IgE receptor (FcεRI)-induced mast cell (MC) activation, which is required for degranulation and cytokine production. Intracellular Zn levels increase in mouse MCs after FcεRI stimulation. We previously reported that Zn distribution in a human MC line, LAD2, changed dramatically following FcεRI aggregation with synchrotron radiation microbeams. However, the kinetics of Zn distribution and the underlying mechanisms following FcεRI cross-linking remain unknown.

We used cord-blood-derived MCs and LAD2 cells. Degranulation was assessed by β-hexosaminidase (β-hex) release. Extracellular Zn levels were determined by inductively coupled plasma atomic emission spectrometry or based on the fluorescence intensity of a Zn indicator. We also used RNAi to knockdown ZnT1 expression. mRNA expression levels were determined by real-time RT-PCR.

Zn was rapidly released from human MCs after FcεRI aggregation. The kinetics and optimal conditions for FcεRI cross-linking for Zn release were different from those for degranulation. Treating LAD2 cells with an intracellular Ca(2+) chelator significantly inhibited IgE-mediated β-hex release but not Zn release. We investigated IgE-mediated β-hex and Zn release with specific inhibitors of signaling pathways. Zn and β-hex release were partly correlated with but also partly independent of IgE. Knockdown of the Zn efflux transporter, ZnT1, significantly inhibited Zn release from human MCs.

Our results indicate that IgE-dependent Zn release from human MCs involves signaling cascades that are distinct from those of degranulation. Thus, Zn may have a unique function as a mediator of allergic inflammation.