Development and characterization of a monoclonal antibody 369.2B specific for the carboxyl-terminus of the beta A4 peptide.

The beta-amyloid deposits in Alzheimer's diseased (AD) brain are made up mainly of beta A4 peptides which show both N- and C-terminal heterogeneity. The predominant C-terminal species, identified by peptide sequencing of purified beta-amyloid, end either at position 40 or 42 of the beta A4 peptide. The distribution of these two beta A4 species in postmortem tissue as well as their generation in vitro could not be addressed previously due to the lack of specific antibodies that could differentiate them. This report describes the generation of a highly specific monoclonal antibody, MAb 369.2B which was raised against a synthetic peptide consisting of the C-terminus of the 1-42 beta A4 species. MAb 369.2B does not recognize the shorter beta A4 species 1-40 in solution or in solid phase. Furthermore, both beta A4 1-40 and 1-43 were unable to absorb out the antibody when used immunocytochemically. The regional distribution of MAb 369.2B immunoreactivity in AD and non-AD brain samples were compared to MAb 286.8A, an antibody raised against the N-terminal region of beta A4. Overall, the staining patterns were very similar. In AD cases with extreme vascular involvement, the N-terminal (MAb 286.8A) antibody was more likely to label the vascular basement membrane of affected vessels, and to label them more uniformly. In addition, preliminary quantitative analyses revealed that the C-terminal antibody labeled fewer, larger plaques than the N-terminal antibody. Qualitative analyses revealed that these smaller plaques were typically subregions of the larger plaques. The data corroborate the biochemical findings of N-terminal raggedness in beta A4 plaques. Further studies are required to explain this differential pattern of deposition.