P1‐100: Quantitation of plasma Abeta40 and Abeta42 levels using rabbit monoclonal antibodies

Previously we quantitated plasma Abeta40 and Abeta42 levels using a combination of mouse monoclonal antibody 6E10 as a capture antibody and rabbit polyclonal antibodies specific to Abeta as detection antibodies. Recently, we have produced rabbit monoclonal antibodies (Rabmab) to Abeta40 and Abeta42. Currently there is a great interest in the measurement of plasma Abeta levels at intervals in AD and elderly non-demented controls. Reports showed conflicting data and the reason is not known. We hypothesize that differences in antibody epitopes and affinity may have contributed to the variable findings. We examined 40 AD or control plasma samples using 1) a combination of Rabmab to Abeta as capture antibodies and 4G8 mouse monoclonal antibody as detecting antibody; and 2) mouse monoclonal antibody 6E10 as a capture antibody and Rabmab to Abeta as detecting antibodies in sandwich ELISA. There was a significant relation between Abeta40 levels of Rabmab to Abeta40 and rabbit polyclonal antibody to Abeta40 using 4G8 as detecting antibody (r = .67; p < 0.001), and Rabmab to Abeta42 and rabbit polyclonal antibody to Abeta42 using 4G8 as detecting antibody (r = .97; p < 0.001). Similarly there was a relation between Abeta levels using mouse monoclonal antibody 6E10 as capture antibody and Rabmab or polyclonal antibody as detecting antibodies. When the relationship between the levels using 4G8 and 6E10 were compared, there was a significant relation in Abeta40 levels (r = .63; p < .001) but not in Abeta42 levels (r = .19; p < .24). The data show that differences in capture or detecting antibodies may contribute to different findings among published studies.