1 Overview

1.1 Purpose and Scope of Application

This protocol is used to establish a routine staining procedure for the Mallory phosphotungstic acid hematoxylin method. It is suitable for displaying striated muscle cross-striations, fibrin, and neuroglial fibers in paraffin-embedded tissue sections. It can also assist in observing tissue components such as collagen fibers, cartilage matrix, and coarse elastic fibers. This method is suitable for morphological studies of striated muscle-related tissues, inflammatory exudative tissues, and neuropathology-related tissues.

1.2 Principle

(1) The Mallory phosphotungstic acid hematoxylin method is a classic PTAH staining method. It is based on a complex staining system formed by phosphotungstic acid and hematoxylin, showing strong selective staining capacity for different tissue structures.

(2) Mallory PTAH staining solution prepared by the natural oxidation method has relatively high maturity, stable staining power, and long storage stability. It is suitable for histological observation requiring long staining time and good reproducibility.

(3) This method strongly stains striated muscle cross-striations, fibrin, nuclei, red blood cells, and neuroglial fibers, which usually appear dark blue. Collagen fibers and cartilage matrix are usually brownish red, while coarse elastic fibers may appear purple. Therefore, this method is useful for differential visualization of various tissue components.

1.3 Staining Quality Requirements

(1) Striated muscle cross-striations, fibrin, and neuroglial fibers should be clearly stained dark blue.

(2) Collagen fibers and cartilage matrix should appear brownish red, forming clear contrast with dark-blue structures.

(3) The background should be relatively clean, tissue contours should remain intact, and color layers should be distinct.

2 Materials and Reagents

2.1 Sample Types

(1) Paraffin sections of striated muscle-related tissues.

(2) Tissue sections requiring observation of fibrin deposition in inflammatory exudates.

(3) Neuropathology-related tissue sections.

(4) Routine tissue sections requiring differentiation of striated muscle cross-striations, collagen fibers, and other stromal components.

2.2 Main Reagents

(1) PTAH oxidizing agent A.

(2) PTAH oxidizing agent B.

(3) Oxalic acid solution.

(4) Mallory PTAH staining solution (natural oxidation method).

(5) 10% formalin fixative.

(6) Distilled water.

(7) Graded ethanol.

(8) Xylene or deparaffinization clearing solution.

(9) Neutral balsam.

2.3 Consumables and Equipment

(1) Glass slides and coverslips.

(2) Staining jars.

(3) Forceps and absorbent paper.

(4) Paraffin microtome.

(5) Microscope.

3 Staining Solution and Sample Preparation

3.1 Preparation of PTAH Oxidizing Agent

(1) Before use, mix equal volumes of PTAH oxidizing agent A and PTAH oxidizing agent B.

(2) The mixture is the PTAH oxidizing agent and should be prepared fresh before use.

(3) The prepared oxidizing agent should not be stored for a long time, as changes in oxidation capacity may affect staining performance.

3.2 Fixation Requirements

(1) Tissues should be fixed in 10% formalin solution.

(2) After fixation, dehydration and paraffin embedding should be completed according to routine procedures.

(3) Samples within the same batch should preferably use consistent fixation conditions to reduce staining variation.

3.3 Sectioning and Deparaffinization Requirements

(1) The recommended paraffin section thickness is 4 μm.

(2) Sections should adhere firmly to the slides to prevent detachment during long staining procedures.

(3) Paraffin sections should be routinely deparaffinized with xylene or deparaffinization clearing solution and brought to water.

(4) Before entering the staining steps, sections should be fully hydrated.

4 Experimental Procedure

4.1 Fixation and Embedding

(1) Fix tissues in 10% formalin solution.

(2) After fixation, dehydrate and embed according to routine procedures.

4.2 Sectioning and Deparaffinization

(1) Prepare paraffin sections at a thickness of 4 μm.

(2) Routinely deparaffinize with xylene or deparaffinization clearing solution and bring sections to water.

4.3 Oxidation with PTAH Oxidizing Agent

(1) Place sections in freshly prepared PTAH oxidizing agent.

(2) Oxidize for 5 min.

(3) After oxidation, rinse briefly with water to remove residual solution from the section surface.

4.4 Bleaching with Oxalic Acid Solution

(1) Place sections in oxalic acid solution for bleaching for 1–2 min.

(2) Rinse with tap water for 2 min.

(3) Wash once with distilled water.

4.5 Mallory PTAH Staining

(1) Immerse sections in Mallory PTAH staining solution.

(2) Cover during staining to reduce evaporation and contamination.

(3) Stain for 24–48 h.

(4) This is a progressive staining method. After staining for 24 h, sections may be examined microscopically first, and the staining time may then be extended if necessary.

4.6 Removal of Excess Staining Solution

(1) Remove the sections after staining.

(2) Do not rinse with water first.

(3) Directly and rapidly wash away excess dye with 95% ethanol.

(4) The 95% ethanol washing time should not be too long, to avoid fading of already stained structures.

4.7 Dehydration, Clearing, and Mounting

(1) Continue dehydration according to the routine procedure.

(2) Transfer sections into xylene or deparaffinization clearing solution for clearing.

(3) Add neutral balsam, apply the coverslip, and complete mounting.

(4) After mounting, avoid air bubbles and keep the mounting medium evenly distributed.

5 Staining Results

5.1 Dark Blue

(1) Cross-striations of striated muscle.

(2) Fibrin.

(3) Nuclei.

(4) Red blood cells.

(5) Neuroglial fibers.

5.2 Brownish Red

(1) Collagen fibers.

(2) Cartilage matrix.

5.3 Purple

(1) Coarse elastic fibers.

6 Key Points for Result Interpretation

6.1 Interpretation of Striated Muscle Cross-Striations

(1) Dark-blue striated muscle cross-striations indicate good visualization of striated structures.

(2) If clear blue cross-striated structures are visible in the cytoplasm, this may indicate striated muscle differentiation characteristics in the relevant cells.

(3) If cross-striations are unclear, first review the oxidation step, staining time, and 95% ethanol washing time.

6.2 Interpretation of Fibrin

(1) Dark-blue fibrin in inflammatory exudates is helpful for distinguishing it from surrounding connective tissue.

(2) Intravascular fibrin deposition may also appear dark blue, helping identify abnormal deposition sites.

6.3 Interpretation of Neuroglial Fibers

(1) Dark-blue neuroglial fibers facilitate observation of related structures in neuropathological samples.

(2) Interpretation should be integrated with the tissue background and distribution pattern.

6.4 Interpretation of Collagen Fibers and Cartilage Matrix

(1) Brownish-red collagen fibers and cartilage matrix can form clear contrast with dark-blue cross-striations and fibrin.

(2) If stromal components are too dark or too pale, fixation, oxidation, staining time, and other factors should be considered comprehensively.

6.5 Interpretation of Elastic Fibers

(1) Coarse elastic fibers appearing purple can serve as auxiliary identification markers in background tissue.

(2) This method is not the most specific staining method for elastic fibers, so interpretation should distinguish them from other stromal components.

7 Common Problems and Cause Analysis

7.1 Cross-Striations Show Insufficient Blue Staining or Appear Bright Red

(1) PTAH oxidation time is insufficient.

(2) The oxidizing agent is unstable or has been left standing too long after preparation.

(3) Over-oxidation may also be present. Replace the staining solution or prepare fresh oxidizing solution and repeat the test.

7.2 Target Structures Become Pale or Staining Is Washed Out

(1) Sections were rinsed with water after Mallory PTAH staining.

(2) The 95% ethanol washing time was too long.

(3) Improper dehydration caused partial loss of already stained color.

7.3 Entire Section Is Overstained

(1) Staining time is too long.

(2) Microscopic examination was not performed in time during progressive staining.

(3) Subsequent staining time was not adjusted according to staining intensity after 24 h.

7.4 Sections Appear Gray or Have Poor Transparency

(1) Dehydration is insufficient.

(2) Clearing is insufficient.

(3) Residual water remains before mounting, affecting microscopic observation.

8 Application Scope

8.1 Striated Muscle-Related Research

(1) Used to display striated muscle cross-striations.

(2) Suitable for auxiliary observation of tissues related to striated muscle differentiation.

8.2 Fibrin Visualization

(1) Used to observe fibrin in inflammatory exudates.

(2) Used to observe fibrin deposition in capillaries.

8.3 Neuropathology-Related Research

(1) Used to display neuroglial fibers.

(2) Suitable for observation of the central nervous system and related tissue structures.

8.4 Auxiliary Differentiation of Connective Tissue

(1) Used to observe collagen fibers and cartilage matrix.

(2) Can serve as a supplementary method for multi-component contrast visualization in histology.

9 Safety and Operating Requirements

9.1 Personal Protection

(1) Wear a laboratory coat and disposable gloves during the experiment.

(2) Fixatives, ethanol, xylene, and staining solutions should be handled in a well-ventilated environment.

9.2 Waste Disposal

(1) Waste liquids containing fixatives, ethanol, xylene, and residual staining solutions should be collected separately.

(2) All waste liquids and contaminated consumables should be disposed of according to laboratory chemical waste handling regulations.

10 Reagent Selection for the Mallory Phosphotungstic Acid Hematoxylin Method

For more related articles, please see below:

[1] Histological and Cytological Section Staining: Principles and Methodological Essentials for Routine Pathology Stains and Structural Special Stains