Retrieved endogenous biotin: a novel marker and a potential pitfall in diagnostic immunohistochemistry

Aim: Antigen retrieval (AR) procedures are based on the effect of heating (by either microwave or pressure cooling treatments) on routinely fixed and paraffin embedded tissues. We observed that AR procedures restore the reactivity of endogenous biotin (EB) and report on the distribution of EB following AR in a series of routinely fixed and embedded tissues, Methods and results: Following pressure cooling or microwave treatments, a simple streptavidin-peroxidase staining revealed retrieved endogenous biotin (REB) in normal tissues (such as liver, kidney and adrenal cortex), in oxyphylic cells and in some tumours, especially in carcinomas of the kidney and of the adrenal cortex, In formalin-fixed (but not: in alcohol-fixed) tissue sections, the heating procedures caused an intense and finely granular cytoplasmic reaction, following a routine streptavidin-conjugated peroxidase treatment, The staining was prevented bg blocking of EB by a sequential avidin-biotin treatment, Conclusions: Retrieval of EB reactivity can cause pitfalls in diagnostic immunohistochemistry but, alternatively, it might also constitute a useful and novel diagnostic marker.