Non-specific background in immunoglobulin G staining can be effectively eliminated using heating or a catalase inhibitor.

Immunoglobulin G (IgG) staining is a widely used method for assessing blood-brain barrier (BBB) integrity. However, significant non-specific binding is often observed in many studies, which can interfere with the accurate interpretation of results. In this study, the horseradish peroxidase (HRP)-based polymer method and the streptavidin-biotin complex (SABC) method were used to perform IgG staining. The effects of hydrogen peroxide, heating, and a catalase inhibitor on reducing background staining were evaluated in brain sections from untreated mice and those subjected to middle cerebral artery occlusion (MCAO). The results showed that immunohistochemistry without hydrogen peroxide pretreatment still produced minimal background in paraffin-embedded sections. However, IgG staining with hydrogen peroxide pretreatment led to substantial background in vibratome sections. Compared to the SABC method, a mixture of the catalase inhibitor 3-amino-1,2,4-triazole and hydrogen peroxide reduced background staining by 35.4 % ± 5.7 % in the cortex of untreated mouse brains and by 36.9 % ± 1.8 % in the contralateral cortex of MCAO mice when using the polymer method. Additionally, heating at 75°C was sufficient to eliminate non-specific binding in brain sections from both untreated and MCAO mice. Hydrogen peroxide pretreatment alone was ineffective in removing background staining in brain sections from either untreated or MCAO mice. In summary, this study demonstrates that hydrogen peroxide pretreatment is effective in reducing background only when combined with a catalase inhibitor but is unnecessary when the tissue is heated. Heating is a simple and effective method for removing the IgG staining background when detecting BBB leakage.