[One heat-induced antigen retrieval step allows the sequential detection of two antigens on the same slide of tissue fixed and enclosed in paraffin].

The heat-induced antigen retrieval (HIAR) procedure allows the immunohistochemical detection of various antigens on paraffin-embedded sections. The re-use of slides negative for the detection of a first set of antigens may be an interesting alternative in case of a limited number of slides. After HIAR, a series of Bouin's liquid-fixed tonsil sections was stained for Epithelial Membrane Antigen (EMA) which labelled epithelial cells and plasma cells. A second immunostaining for CD20 (L26) was performed on the same slides divided in two sets. The HIAR was repeated in the first set but not in the second one. A similar staining of follicular B-cells was observed in the two sets. However background staining was enhanced by repetition of HIAR. Analogous results were obtained using anti-cytokeratin (KL1) instead of anti-EMA. This was confirmed on slides for which three or four cycles of HIAR were performed prior immunostaining. Our data suggest that the renewal of the HIAR procedure must be avoided since it was found stable for at least 1 year.