I am working on human oligodendrocytes precursor cells, studying their differentiation into oligodendrocytes. I have a problem recently in staining O4, I do live staining 30 min incubation with primary antibody at 37 degrees, then fix using 4% PFA for 15 min, wash 3 times with PBST then block with 5 % goat serum for an hour and secondary antibody incubation for 1 hr, then wash again with PBST 3 times. I get positive staining which are bright and visible fluorescent oligodendrocytes but not all cells in my fields are stained not even a weak stain they are totally missing though I can see them as moderate to highly branched oligodendrocytes in the phase contrast images. If you have any feedback, I just what to know what is the technical issue behind this problem.