MALDI-MS spectra of immunoprecipitated Aβ peptides from rat CSF. Aβ peptides were immunoprecipitated from rat CSF with the W0-2 antibody and further subjected to MALDI-MS analysis. Peaks correspond to signals for Aβ38, Aβ39, Aβ40 and Aβ42 with theoretical monoisotopic masses of 4130.0 Da, 4229.0 Da, 4328.2 Da and 4512.3 Da respectively. Note that the differences in measured versus theoretical masses are predominantly due to the linear detection method used. Signals observed in the non-transgenic animals and the PBS control result from either protein-G sepharose, the antibody or other non-specific binding components of the CSF.