Purified OECs and Schwann cells in vitro do not express calponin. OECs and Schwann cells were immunolabeled with calponin in the presence and absence of proteinase K and no differences were found. A, B) OECs and Schwann cells were immuolabelled with p75NTR (red) and calponin (green). Greater than 99% of the cells immunolabeled with p75NTR (red) but a background level of green, punctate immunoreactivity could be seen associated with the nuclei (Ai, ii, Bi, ii, arrows). When primary antibody was omitted weaker punctate staining could just be detected (Aiii, iv, Biii, iv) Ci, ii) OEC and Schwann cell cultures containing rare fibroblast contaminants (arrows) were immunolabeled with calponin (green) and p75NTR (red). It can be seen that the calponin immunoreactivity in the fibroblasts was strongly fibrillar and distinct from the non-specific attachment of the secondary antibody detected in OECs and Schwann cells. Ciii) illustrates a higher power image of contaminating fibroblasts which although expressed fibrillar calponin immunoreactivity, also expressed the punctate nuclear background immunoreactivity seen in OECs and Schwann cells. Images for Figures A, B and Ciii were obtained using a confocal microscope and images for Figures Ci, ii were obtained using a fluorescent microscope.