Type III collagen or reticular connective tissue provides architectural framework for lymphatic tissue and organs such as the liver and spleen. Reticulin fibers form a honeycomb network where the cell types are deposited and/or anchored, providing structure in organs that can expand. Reticulin fibers cannot be visualized in a hematoxylin and eosin (H&E) stained slide. Reticulin fibers are argyrophilic, meaning that these tissue elements will stain black with a silver solution using the aid of a chemical reducer which brings the silver into to a visible form.
Texts that instruct on histologic techniques will provide several variations of the retuculin stain. Examples of reticulin stains using different methodologies are the Gordon & Sweets, Wilder, Gridley, Snook, Laidlaw, and Gomori. However, all methodologies have identical staining steps that prepare the reticulin fibers for staining. Procedural steps include an oxidizer, oxidizer bleach, sensitizer, silver solution, reducer, toner, removal of unreacted silver, and an optional counter stain.
The reticulin stain used to demonstrate reticulin fibers for this course is Gordon & Sweets. Reagents used in the Gordon & Sweets stain method are as follows:
- Oxidizer: Potassium permanganate
- Oxidizer bleach: Oxalic acid
- Sensitizer: Ferric ammonium sulfate
- Silver solution: Ammonia silver solution
- Reducer: 10% formalin
- Toner: Gold chloride
- Removal of unreated silver: Sodium thiosulfate
- Counterstain: Nuclear fast red (NFR)
A liver biopsy stained with Gordon & Sweets reticulin stain is shown in the image demonstrating normal reticulin architecture, at 40X magnification.