In their earlier studies, they described how dendritic cells unfurl hidden veils - membranes that are so thin they can barely be imaged - and use these veils to move in on and capture their target. In the presence of E. coli, this occurs so rapidly and with such vigor that in accelerated time-lapse video, the cells appear more like a pack of wild animals feeding on a carcass.
But two things baffled the researchers. Dendritic cells extended their veils even before making physical contact with E. coli, yet macrophages, cells not normally picky about the antigens they engulf, were completely unresponsive to the bacteria. In order to understand how dendritic cells first sense the presence of an antigen and why the reaction is cell-specific, the authors decided to look at calcium flux, a well-recognized early measure of stimulation in numerous cell types. The use of a fluorescent dye, which allows direct measurement of calcium levels, would determine if calcium flux occurs before dendritic cells unfurl their veils.
With a microinjection tip, they squirted a mixture of E. coli fragments into a culture dish, and, indeed, one to two minutes before the appearance of the thin membranes, there were bursts of color indicative of calcium flux. Given their earlier results, the researchers anticipated that by repeating the experiment with macrophages there'd be no response. But as luck would have it, the microscopic bacteria sample somehow got clogged inside the tip, and before Dr. Watkins realized the need to pull away from the cell, he had already given it a jab.
"On the screen it looked like flash bulbs going off in a dark concert arena," Dr. Salter recalled of that moment, when to both their great surprise the researchers witnessed how that little mishap had caused the m
Source:University of Pittsburgh Medical Center