Selective anchoring in the specific plasma membrane domain: a role in epithelial cell polarity

The linearity of response was controlled by mixing 10% gelatin wl~ chromatographically pure mouse IgG (Organon Tecknika-Cappel, Malvern, PA) at final concentrations of either 1 or 10 mg/mi. Three layers of gelatin containing 0, 1, or 10 mg/ml mouse IgG were placed together in 1-mm2-section molds .and processed for frozen sections as described above. Sections containing gelatin with the three IgG concentrations were processed for immunofluorescence with affinity-purified rhodamine-coupied goat anti-mouse IgG antibody. The images from these sections were collected as described before and showed levels of fluorescence similar to those observed on MDCK cell plasma membranes labeled with specific monoclonal antibodies. After subtracting the pixel values of the background (gelatin with no IgG) the ratio between the average fluorescence on 10 and 1 mg/ml IgG gelatins was 9.65 indicating that the fluorescence intensities linearly correlate with antibody concentrations.