Microwave-antigen retrieval: the importance of pH of the retrieval solution for MIB-1 staining

Using microwaves for microscopy almost invariably implies working at elevated temperatures. In microwave studies it became evident that high temperatures do not inevitably damage the tissues. On the contrary very high temperatures can even be beneficial. The most striking example is the 'heat shock' of formalin-fixed paraffin sections in the microwave oven with temperatures higher than 100 degrees C, revealing otherwise hidden epitopes. These microwave applications have triggered a breakthrough in pathology. The pH of the microwave-retrieval solution is decisive for the staining results, particularly for MiB-1. There is no staining of proliferating cells between pH 3.5 and 5.0. Between pH 5.0 and 6.5 we observed an increase in the number of MiB-1-positive stained nuclei. Our findings indicate that in quantitative work it is of extreme importance to standardise the pH of the retrieval solution and to choose pH 6.5 for optimal results.