We are using human plasma and we just started with western blot for apo E in different samples. We do not want to waste time and money on too many trials.
I would recommend an antibody database available at labome.com. For Apo E antibodies suitable for WB you can check the following link: https://www.labome.com/review/gene/human/ApoE-antibody.html. In particular, Abcam ApoE antibody (Abcam, ab1906) can be used for WB on human samples at 1:1000 (Sreckovic I et al., Biochim Biophys Acta. 2014). In addition, another Abcam ApoE antibody (Abcam, ab1907) was used in WB on human samples at 1:500 (ref.: Jammart et al., J Virol 2013). Also, Santa Cruz Biotechnology has a mouse monoclonal (A1.4) ApoE antibody (Santa Cruz, sc-13521) suitable for WB on human samples at 1:8000 (Kumar et al., Brain 2016). Besides, BioLegend has an ApoE antibody (Covance, 6E10) used in WB on human samples at 1:1500 (Xu et al., Acta Neuropathol Commun. 2015). You can see the references for these and other abs following the links provided at https://www.labome.com/review/gene/human/ApoE-antibody.html.