Western immunoblot of sequential serum samples from a child with enteropathic HUS (lanes 6 to 10), the stained PVDF membrane (lane 1), and human control sera (lanes 2 to 5) using Stx2 as antigen. Lane 1, strip from the PVDF membrane after blotting and staining with Coomassie blue, showing the A subunit with the A1 fragment and the B subunit; lanes 2 to 5, human control sera. Two negative human control sera (lanes 2 and 5, nonreactive) and two positive human control sera (lane 3, reactive against the Stx2 B subunit; lane 4, reactive against the A subunit and the A1 fragment of Stx2) are shown. Western immunoblot strips of five sequential sera of a patient with enteropathic HUS are shown as follows: lanes 6 and 7, nonreactive 5 and 8 days, respectively, after the onset of diarrhea; lanes 8, 9, and 10, reactive 12, 17, and 38 days, respectively, after the onset of diarrhea, all showing an antibody response against the A subunit and the A1 fragment of Stx2.