ApoE dimer is not artificially formed during sample homogenisation and processing. Freshly prepared rabbit and frozen human brain tissue (AD apoE3/3, AD 5) was homogenised in a detergent-rich lysis buffer either with or without the thiol-trapping agent iodoacetamide (Iodo) used at a final concentration of 100 mM. The effect of Iodo on the presence of apoE dimers was assessed under non-reduced (NR) and reduced (R) conditions by western blot, using goat anti-apoE polyclonal antibody (A). The extent of thiol-trapping by Iodo was determined by measuring the total thiol present, using DTNB assay (B). Data in B are means of triplicate readings with S.E. represented by error bars. *** P < 0.0001. The human brain sample (AD n = 1) is identified according to the Case # code given in Table 1.