Correlating short-term Ca2+ responses with long-term protein expression after activation of single T cells

In order to elucidate the dynamics of cellular processes that are induced in context with intercellular communication, defined events along the signal transduction cascade and subsequent activation steps have to be analyzed on the level of individual cells and correlated with each other. Here we present an approach that allows the initiation of cell-cell or cell-particle interactions and the analysis of cellular reactions within various regimes while the identity of each individual cell is preserved. It utilizes dielectrophoresis (DEP) and microfluidics in a lab-on-chip system. With high spatial and temporal precision we contacted single T cells with functionalized microbeads and monitored their immediate cytosolic Ca2+ response. After this, the cells were released from the chip system and cultivated further. Expression of the activation marker molecule CD69 was analyzed the next day and correlated with the previously recorded Ca2+ signal for each individual cell. We found a significant difference in the patterns of Ca2+ traces between activated and non-activated cells, which shows that Ca2+ signals in T cells can provide early information about a later reaction of the cell. Although T cells are non-excitable cells, we also observed irregular Ca2+ transients upon exposure to the DEP field only. These Ca2+ signals depended on exposure time, electric field strength and field frequency. By minimizing their occurrence rate, we could identify experimental conditions that caused the least interference with the physiology of the cell.