Imaging cells in three-dimensional collagen matrix.

The use of in vitro three-dimensional (3-D) collagen matrices to mimic an in vivo cellular environment has become increasingly popular and is broadening our understanding of cellular processes and cell-ECM interactions. To study cells in in vitro 3-D collagen matrices, both cellular proteins and the collagen matrix must be visualized. In this unit, the authors describe the protocol and provide troubleshooting for immunolabeling of cells in 3-D collagen gels to localize and visualize cellular proteins with high-resolution fluorescence confocal microscopy. The authors then describe confocal reflection microscopy as a technique for direct imaging of 3-D fibrillar collagen matrices by discussing the advantages and disadvantages of the technique. They also provide instrument settings required for simultaneous imaging of cellular proteins with fluorescence confocal imaging and 3-D collagen fibrils with confocal reflection microscopy. Additionally, the authors provide protocols for a "cell sandwiching" technique to prepare cell cultures in 3-D collagen matrices required for high-resolution confocal imaging.