Selectivity of antibody-mediated destruction of axons in the cat's optic nerve

The purpose of this study was to determine the selectivity with which polyspecific antibodies directed against large retinal ganglion cells destroy axons in the cat's optic nerve. Immune serum prepared against large ganglion cells isolated from ox retinas was injected into 1 eye of each of 2 cats. After more than 1 month, the cats were perfused with mixed aldehydes and the optic nerves were prepared for transmission electron microscopy. On the basis of a large sample of micrographs of transverse thin sections, we estimated that each of the nerves that issued from treated eyes contained approximately 62,500 necrotic fibers, amounting to 42-46% of the total fiber population in 1 case and 39-42% in the other. The diameters of 2900-5000 intact axons from each of 4 nerves (2 from immune-treated eyes and 2 from untreated eyes) were measured. Comparisons of histograms of axon diameter for nerves from treated and untreated eyes revealed that 90-100% of large axons with diameters above 3.5-4.0 micron were eliminated by the antibodies. Between 65 and 70% of medium-sized fibers were also eliminated. The number of small axons--those with diameters less than 1.2-1.6 micron--did not differ appreciably from normal. These results suggest that the immune serum destroyed virtually all alpha cell axons and a substantial fraction of beta cell axons but did not reduce the number of small fibers that largely stem from the gamma class of retinal ganglion cells.