Scheme 1.

Multinucleate cell origin was followed by fluorescent cell labeling. A) Macrophages were labeled green and fibroblasts were labeled red prior to co-culture. B) Cell fusion was visualized as a co-localization of two different labeled fibroblast populations (red and green) with macrophages receiving no dye (grey). Cell co-localization of red and green dyes appears yellow. C) After 24 hours, macrophage and fibroblast cultures were labeled with DAPI (blue) and macrophage-specific anti-CD14(red) to identify possible macrophage contamination within the plated fibroblast population.