Immunohistochemical detection of tissue factor (TF) on paraffin sections of routinely fixed human tissue

Tissue factor (TF), a 47 kDa transmembrane glycoprotein, is the essential receptor and cofactor for factor VII/VIIa. Its distribution in normal tissues and in tumours has been recently investigated immunohistochemically with monoclonal and polyclonal anti-TF antibodies in frozen sections. The cardinal problem of this technique is the difficulty of determining exactly the localization of the reaction product at least in certain tissues. Here, we demonstrate a method using monoclonal anti-TF antibodies to detect TF in routinely fixed, microwaved, paraffin-embedded tissues. Generally, there were no fundamental differences in TF distribution in frozen and paraffin-embedded material. However, in most cases, the paraffin sections allow a better cellular localization of TF. For example, the staining pattern for TF in both kinds of sections is identical in kidney, brain and skin. The paraffin-embedded material, however, clearly shows that TF expression is restricted to the parietal and the visceral epithelia of Bowman's capsule of glomeruli in the kidney, and to astrocytes and their processes in the brain. TF reactivity in the skin is revealed to be cell membrane-bound; in cardiomyocytes TF shows an exclusively sarcolemmal localization. The immunohistological detection of TF in paraffin sections is a powerful tool for systematic studies on the possible role of TF in the context of physiological and pathological studies.