NGFR and neuroblastoma: Formulation of this hypothesis followed our observation that p75NTR and CRABP1 protein levels vary coordinately with one another in neuroblastoid and epithelioid human neuroblastoma cell lines; the neuroblastoid line that has low p75NTR protein levels (SH-SY5Y) has undetectable levels of CRABP1 protein while epithelioid lines with higher p75NTR protein levels (SK-N-AS, SH-EP1) have higher levels of CRABP1 protein.