Epitopes of components of the plasminogen activation system are re-exposed in formalin-fixed paraffin sections by different retrieval techniques.

We present a systematic analysis of the sensitivity and specificity of immunohistochemical stainings for components of the plasminogen activation system, i.e., uPA, tPA, PAI-1, PAI-2, and uPAR, on routinely processed (formalin-fixed, paraffin-embedded) tissues. Five to nine antibodies per component were tested and the influence of different antigen retrieval regimens on immunoreactivity was investigated. We studied six different microwave-mediated pretreatments and two pretreatments by proteolytic digestion. First, positive and negative control tissues were stained. Then, frozen and paraffin sections from the same cancer lesions were stained after specific modes of pretreatment and with selected antibodies. For each component, one or a few of the tested Abs gave optimal staining on paraffin sections when combined with a particular tissue pretreatment. For PAI-1, and to a lesser degree also for tPA, an underrepresentation of stromal cell staining in paraffin material was found, whereas tumor cells showed good staining. For uPA, PAI-2, and uPAR, consistent staining results were obtained on paraffin sections.