Endogenous pathological deposits are a subset of pigment deposits. After undergoing certain pathological changes, histiocytes form deposits with different morphological characteristics. These polymerized special proteins can be stained to reveal fibrin proteins.Fibrin is a special protein formed by the polymerization of fibrinogen molecules in the blood, also known as fibrin. Under normal physiological conditions, it is produced by the polymerization of fibrinogen molecules in the blood. This protein exists in tissues in the form of curved fibrin filaments, mostly presenting a reticular structure, and sometimes forming coarse fibrin networks. Old fibrin can aggregate into amorphous masses. When tissues are damaged, vascular endothelial cells suffer severe injury, leading to increased vascular permeability, which in turn causes massive leakage of fibrin.
Fibrin Staining Solution (Modified MSB Method) is a simple and cost-effective fibrin staining solution. After staining, fibrin appears red or blue.
Operating Procedure
1. Fix the tissue, perform routine dehydration and embedding, then conduct routine dewaxing to water.
2. Immerse the tissue in Sodium Thiosulfate Solution for 3–5 minutes, followed by a brief rinse with water.
3. Transfer to Celestine Blue Staining Solution and stain for 3–5 minutes.
4. Move to Mayer's Hematoxylin Staining Solution and stain for 3–5 minutes.
5. Differentiate with Acid Alcohol Differentiating Solution for several seconds, then rinse thoroughly under running water for 10 minutes.
6. Rinse briefly with 95% ethanol.
7. Immerse in Martius Yellow Staining Solution for 2–3 minutes, then rinse briefly with distilled water.
8. Transfer to Acid Fuchsin Staining Solution and stain for 10 minutes, followed by a brief rinse with distilled water.
9. Treat the sections with Phosphotungstic Acid Solution until the red color of collagen fibers fades to nearly colorless, then rinse briefly with distilled water. (Observe under a microscope; the treatment usually takes 5–10 minutes.)
10. Immerse in Aniline Blue Staining Solution and stain for 5–10 minutes.
11. Rinse briefly with Weak Acid Solution and blot dry with absorbent paper.
12. Rinse rapidly twice with 95% ethanol.
13. Dehydrate with anhydrous ethanol, clear with xylene, and mount with neutral balsam.
Staining Results
Fibrin: Red (old fibrin appears blue to purple-black)
Muscle fibers: Red
Cell nuclei: Blue-grayish brown
Collagen fibers: Blue
Red blood cells: Yellow
Precautions
1. The treatment with Phosphotungstic Acid Solution serves two purposes: first, it differentiates the red-stained collagen fibers to nearly colorless; second, it acts as a mordant for collagen fibers, enabling them to bind more firmly to aniline blue.
2. Better staining results can be achieved if the sections are mordanted with Bouin's solution before proceeding with the above staining procedure.
3. Aniline blue staining generally takes 5 minutes. However, observe the sections every 2 minutes to avoid over-staining, which would result in excessively deep blue coloration.
4. For your safety and health, wear a lab coat and disposable gloves during operation.
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