Electron Microscopy of Myofibroblasts

In inflammatory conditions, myofibroblasts are derived from fibroblasts in response to cytokines. Ultrastructurally, myofibroblasts are characterized by prominent rough endoplasmic reticulum (RER), bundles of myofilaments with focal subplasmalemmal densities, and extracellular fibronexus junctions with surrounding matrix. The myofibroblast produces collagen matrix, and the actin filaments in the cytoplasm along with the contiguous fibronexus junctions produce the contraction involved in wound healing [1].

Note: These ultrastructural features, although characteristic of myofibroblasts, may also be found in other types of cells; e.g. neoplastic squamous cells [1].

Figure 1: This low-power view of a myofibroblast from an IMT shows RER and one subplasmalemmal density at the upper left. Fine actin myofilaments radiate from it. Compare the thickness of these fine fibrils to the extracellular collagen fibers. The nucleus lies to the right.

collagenmyofilnucleusrer

Find a cluster of cytoplasmic myofilaments.

Find a group of collagen fibers, extracellularly.

Find the nucleus.

Find some rough endoplasmic reticulum.

 

Figure 2: At higher magnification, a cluster of fine actin myofilaments is in the cytoplasm near focal subplasmalemmal densities. The fibronexus junction lies over the densities. The nucleus lies at the bottom. Note: The plasma membrane to the left of the junction is not well defined.

nucleus1myofil1myofil2densitydensityjunction

Find the nucleus.

Find a cluster of myofilaments.

Find subplasmalemmal focal densities.

Find an extracellular fibronexus junction.

Reference

1. Eyden B, Banerjee S. Spindle-cell squamous carcinoma exhibiting myofibroblastic differentiation. A study of two cases showing fibronexus junctions. Virchows Arch 2002; 440:36-44. Abstract

Return to immunoperoxidase stain for actin.

Return to Unknown 9

TOP----Rad/Path Home Page

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Myofilaments

Return

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Collagen fibers

Return

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Nucleus

Return

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Myofilaments

Return

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Subplasmalemmal density

Return

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fibronexus junction

Return

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Nucleus

Return

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Rough endoplasmic reticulum

Return