Identification of different cell types in the center of the injury (position 3) 1 week after injury in MMP-3^+/+(upper panel) or MMP-3^−/− (lower panel) mice. Immunostaining is performed with antiserum against α-actin (panels a and d), against CD45 (panels b and e), or against Mac-3 (panels c and f). The arrows and arrowheads indicate the internal and external elastical lamina respectively (original magnification ×200).