Immunohistochemical detection of fibronectin using different fixatives in paraffin embedded sections

Different fixatives and immunohistochemical methods were tested for detection of fibronectin in various paraffin embedded tissues: rat kidney, spleen, gastro-intestinal tract, muscle, normal and fibrotic liver and human skin. Using cryostat sections, localisation with immunofluorescence and peroxidase technics comparable to those obtained in unfixed tissue sections, could be obtained with the following fixatives: 10% formalin in PBS containing 4% sucrose; 96% ethanol; 96% ethanol + 1% acetic acid; a series of ethanol solutions of increasing strength: 70-80-96%. These fixatives also proved to be the best for paraffin embedding. Without enzyme digestion, however, satisfactory results could not be obtained with either indirect peroxidase or immunofluorescence methods in paraffin embedded tissues. Following digestions with the enzymes at the concentrations described in the literature, the alteration of tissues made the morphological localization of fibronectin difficult. The self-sandwich peroxidase method following a gentle pepsin digestion gave results closest to those of unfixed cryostat sections; however a slight increase in background staining was observed but without interfering with the evaluation of results.