Elastin. Coloured transmission electron micrograph (TEM) of an elastin fibre (diagonal red band) in human connective tissue. Elastin is an elastic protein that allows body tissue to spring back into shape following deformation. This elastin fibre is in contact with a fibroblast cell (upper left, yellow/blue), which is probably synthesising the fibre. Nearby are collagen fibres (speckled green), which give tissue tensile strength. At upper right is a mast cell, a type of white blood cell often found in connective tissue. The round granules (red) inside it contain substances released during an allergic response or an inflammation. Magnification x2225 at 6x4.5cm size.