We have demonstrated in vitro and in vivo the specific binding of a monoclonal antibody to the rat nerve growth factor (NGF) receptor. Previous work had shown that this antibody, designated 192-IgG, does not compete with NGF for binding to the NGF receptor of PC12 cells, but instead interacts with the receptor to increase NGF binding to PC12 cells (Chandler, C. E., L. M. Parsons, M. Hosang, and E. M. Shooter, 1984, J. Biol. Chem., 259:6882-6889). In the present study, a solid-phase separation assay verified the specific formation of a ternary complex of 192-IgG, the NGF receptor, and NGF: 125I-labeled 192-IgG precipitated from solution only when incubated with both solubilized NGF receptor and NGF covalently linked to a solid phase (Sepharose 4B). Filtration assays using plasma membrane preparations of various tissues showed strict correlation of 125I-192-IgG and 125I-labeled NGF binding; only membranes obtained from superior cervical ganglion bound significant amounts of the monoclonal antibody and NGF. Injection of 125I-192-IgG into the rat anterior eye chamber led to accumulation of intact antibody molecules in the ipsilateral superior cervical ganglion, indicating retrograde axonal transport of 125I-192-IgG from the neuronal termini, located at the iris, to the cell bodies situated in the ganglion. The time course and saturation characteristics of 125I-192-IgG retrograde transport were very similar to those previously reported for 125I-NGF transport, indicating that 192-IgG can be internalized and transported by the same mechanisms as is NGF. Consistent with results of the in vitro binding assays, 192-IgG and NGF failed to compete for retrograde transport and were actually co-transported. Retrograde axonal transport of 192-IgG appears to be species specific, since 125I-192-IgG was transported in the rat, but not in mice, gerbils, hamsters, or guinea pigs. These results establish monoclonal antibody 192-IgG as a specific probe for the rat NGF receptor in vitro and in vivo.

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