TNF and diabetic retinopathy: Previous findings demonstrate the involvement of the proNGF/p75NTR system in optic nerve axotomy, diabetic retinopathy and glaucoma, diseases primarily affecting the retinal ganglion cell neurons.19, 20 We studied whether this mechanism is functional in a disease primarily affecting photoreceptor neurons, by quantifying the expression of p75NTR and proNGF as well as the downstream effectors TNFα and α2M, and the glial activation during the neurodegenerative process associated with RP.