A long-range attraction between aggregating 3T3 cells mediated by near-infrared light scattering

At what range can a mammalian cell sense the presence of another cell and through what medium? To approach these questions, the formation of aggregates of a 3T3 cell variant (3T3x cells) grown on solid substrates was studied. Each of the aggregates consisted of cells that, at the time of their seeding, were single and located randomly. Yet somehow they seemed to detect each other within a certain range (R(a)) and move together to form aggregates. The article describes a simple assay to measure the value of R(a). When applied to 3T3x cells with altered intensities of near-infrared light scattering (I(sc)) the assay showed that (i) R(a) was much larger than one cell diameter, and (ii) R(a) was directly related to I(sc). The results suggest that near-infrared light scattering by the cells mediate a long-range attraction between them, which does not require physical contact and enables them to detect each other's presence.