[The influence of heat-induced epitope retrieval on endogenous avidin-binding activity (EABA) and blocking of EABA in immunohistochemistry]

Abstract

Objective: To study the influence of heat-induced epitope retrieval (HIER) on endogenous avidin-binding activity (EABA) and to establish an effective way to block EABA in immunohistochemistry.

Methods: Systematically screening EABA in 164 (679 samples) formalin-fixed and paraffin-embedded human tissues including 76 (102 samples) normal tissues and 88 (577 samples) tumor tissues as well as 4 (80 samples) formalin-fixed and paraffin-embedded rat normal tissues using tissue array (tissue chip), HIER, immunohistochemistry and egg white solution blocking. In addition, EABA was also examined in 9 (15 samples) human frozen tissues.

Results: (1) EABA was detected in frozen tissues. (2) No staining for EABA was seen in formalin-fixed and paraffin-embedded tissues. (3) EABA was revealed after the tissues treated with microwave HIER. (4) The density of signal for EABA was variable from tissue to tissue and cell to cell. (5) The signals of EABA expressed in scatter or diffuse in tissues and in granular form in cytoplasm. (6) EABA was found in a wide range of epithelial tissues, especially in gland epithelia of normal and tumor tissues. These included kidney, adrenal cortex, liver, C cells of thyroid gland, oxyphil cells of parathyroid, fundal gland of stomach, sebaceous gland of skin, duct of salivary; oncocytoma and papillary adenocarcinoma of kidney and thyroid gland, adenolymphoma of parotid, carcinoma of liver cell, adenocarcinoma of stomach, colon, prostate, gall bladder and endometrium, and so on. (7) EABA was easier revealed by higher pH value buffer (EGTA pH 9.0) than that with lower pH value (EDTA pH 8.0 and citrate pH 6.0). (8) The revealed EABA could be effectively blocked using 20% egg white solution.

Conclusions: HIER could unmask EABA in formalin-fixed and paraffin-embedded tissues. The unmasked EABA present in a wide range of human normal and tumor tissues as well as in rat normal tissues. The EABA could influence routine immunohistochemistry staining when using (strept)avidin-horseradish peroxidase detective system. The egg white solution could effectively block EABA and eliminate the influence of EABA on immunohistochemistry.