Au antigen discovery. An Australian aborigine (top) and the precipitin line formed between the aboriginal serum and that of a multiply transfused patient with hemophilia (bottom). The precipitin failed to stain for lipid, but stained red with the azocarmine counterstain for protein. Reprinted with permission of Nature Publishing Group from Alter HJ and Houghton M, Hepatitis C virus and eliminating posttransfusion hepatitis (Nat Med. 2000;6:1082-1086).