Functional blockade of tyrosine kinase A in the rat basal forebrain by a novel antagonistic anti-receptor monoclonal antibody

We have exploited a new monoclonal antibody against the tyrosine kinase A ( TrkA) nerve growth factor (NGF) receptor to block the NGF-TrkA interaction in the rat basal forebrain. The monoclonal antibody MNAC13 is a potent anta gonist that prevents the binding of NGF to TrkA in a variety of systems. Th is antibody was used to study the maintenance of the cholinergic phenotype in the rat basal forebrain in vivo, by the implant of antibody-secreting ce lls. Basal forebrain cholinergic neurons (BFCNs) are greatly affected by th e antibody treatment, both in terms of cell number and of cell soma size. W hen antibody-secreting cells are implanted at postnatal day 2 (P2), the eff ects observed at P8 are as severe as those obtained with anti-NGF antibodie s and, interestingly, are observed also if anti-TrkA cells are implanted at P8, when anti-NGF antibodies, delivered by the same route, are no longer e ffective (Molnar et al., 1998). The effects induced by anti-TrkA, as those induced by anti-NGF, are reversible, but the time required for recovery and the critical period in the sensitivity of BFCNs to the functional inactiva tion of TrkA is twice as long than that observed when NGF is intercepted. T hese results demonstrate that BFCNs are more sensitive to the block of TrkA activation than they are to the block of NGF. The cloning of MNAC13 variab le regions and their assembly into a functional polypeptide of reduced size (single chain Fv fragment) will allow its use in gene transfer application s.