Structures and components of DIT in the proximal portion of the RCA in adults. a, b – DIT was demonstrated as a uniformly thickened inner layer (van Gieson). c – immunostain for alpha smooth muscle actin. Almost all cells in DIT were smooth muscle cells. d – immunostain for macrophage marker HAM56 at the same site as in c. Only a few intimal and several adventitial cells were positive (arrowheads). I – intima, M – media, A – adventitia. These microscopic images represent a normal right adult coronary artery in two intersecting planes. From: Nakashima Y, Chen YX, Kinukawa N, et al: Distributions of diffuse intimal thickening in human arteries: preferential expression in atherosclerosis-prone arteries from an early age. Virchows Arch 2002, 441:279–288. Used with permission from the publisher and authors. Copyright © 2002, Springer.