Comparison of peroxidase and ferritin labelling of cell surface antigens

Abstract

In a comparative study of peroxidase and ferritin used as labels for cell surface antigens, the following observations were made: 1. 1. Peroxidase labelled more antigenic sites than did ferritin. The cell surface label was shown to be nearly continuous with peroxidase, whereas there were large discontinuities with ferritin. 2. 2. Highly diluted peroxidase conjugate showed discontinuous labelling of the cell surface similar to undiluted ferritin conjugate. 3. 3. When ferritin labelled conjugate is used in concentrations much higher than is usual, it labels the cell surface continuously as much as does a peroxidase-labelled conjugate. 4. 4. Partial removal of the cell surface coat with hyaluronidase narrowed the distance between the ferritin conjugate and the unit membrane component of the cell surface, resulting in more extensive but still discontinuous labeling. As a result of these observations, it was concluded that: 1. (A) The heavier labelling obtained with peroxidase conjugate than with ferritin conjugate was specific and not the result of diffusion. 2. (B) The patchy ferritin labelling and the uneven labelling with diluted peroxidase suggests a variability in the distribution of cell surface antigens, but does not support the concept that antigens reside in widely separated circumscribed segments of the cell surface. 3. (C)Peroxidase conjugate has the advantage over ferritin conjugate in being a much smaller molecule.