Fibroblast cells. Immunofluorescent light micrograph of fibroblast connective tissue cells taken from human foetal skin. Cell nuclei stain blue; actin stress fibres are green; cell cytoplasm stains red for fibronectin. Fibroblasts form connective tissue that provides metabolic and structural support for tissues & organs throughout the body. These cells secrete matrix material such as collagen and fibronectin. They also play a role in forming bone and cartilage. Immunofluorescence is a staining technique which uses antibodies to attach fluorescent dyes to cells and tissues. Magnification: x125 at 5x7cm size.