Recently I plan to characterize primary rat endothelial cells by immunological methods. Thus I ordered vWF antibody from Abcam (ab6994) to detect the vWF expression in endothelial cells. Before the experiment, I selected MS1, a pancreas islet endothelial cell line, and the 293, respectively as the positive and negative controls.
I used the ABC method for immunohistochemistry and the indirect fluoresent antibody method for immuofluorescence. For both of these methods, weak positive signal was detected for the MS1 endothelial cells, and no signal was detected for this cell line with only PBS added. Significantly, weak positive signal was also detected for 293 cells.
These results really bewildered me. I wonder what factor resulted in weak positive signal for the MS1 cells. In the introduction of the Abcam vWF antibody, it was used for detected of murine vWF (MS1 is a murine cell line) but the result was not consistent. 293 cells have been thought without vWF expression.
Thus I wonder if problem came from the antibody or the endothelial cells. Any advice on interpretation of these results and the correct methodology for characterization of primary endothelial cells is welcome.