Aβ immunostainings of Sw2 patient’s frontal and temporal cortex and mass spectra of Aβ peptides in Sw2 patient’s temporal cortex. a: Confocal micrograph from Sw2 patient’s temporal cortex shows the targetoid pattern of the plaque: the corona contains Aβx-42 and the centre Aβ1-5 species. b: The central accentuation of abAβarc (specific for the Arctic mutation) immunopositivity suggests that much of the mutated Aβ has preserved N-termini (Sw2, frontal cortex; see Figure 2g and h). c and d: Pyroglutamate specific abAβ3pE and abAβ11pE antibodies demonstrate that much of the Aβ is truncated and glutamates 3 and 11 are cyclised into pyroglutamate and this modification occurs in parallel at both sites. Note the strong positivity in pial arteries (Sw2, temporal cortex, consecutive sections). e: Average mass spectra of Aβ peptides extracted from Sw2 patient’s temporal cortex with formic acid and immunoprecipitated with abAβ17–24 and abAβArc (conformation specific epitope 17-24arc), which precipitate both wild type Aβ and Arctic Aβ (see inserted cartoon). Three peaks corresponding to arcAβ species (with the Arctic mutation) and recognized by AβpE specific antibodies (values observed in two independent MALDI-TOF experiments m/z=3061.5 and m/z=3062.8 Da → Aβ11pE-40arc; m/z=3246.2 and m/z=3246.0 Da → Aβ11pE-42arc; m/z=4057.0 Da → Aβ3pE-40arc) as well as two peaks corresponding to arcAβ with full length N-termini (m/z=4258.7 and m/z= 4259.1 Da → 1-40arc; m/z=4443.5 and m/z=4443.0 Da → 1-42arc) are labelled. Additional values with relative intensities of the peaks, see Additional file 5: Table S1. (bar in a 50 μm; bar in b 200 μm for b-d).