Comparison of CD spectroscopy changes and ELISA results. Comparison of PF4 structural changes (antiparallel β-sheet content, determined by CD spectroscopy) and PF4/heparins antigenicity (OD obtained from ELISA measurements) for (A) UFH, (B) HO16, (C) HO08, (D) HO06, and (E) fondaparinux as a function of molar ratio monosaccharides/PF4. The open and filled squares represent average values of antiparallel β-sheet content and OD values, respectively. Error bars correspond to the standard deviation (calculated from the results of n = 3 experiments). (F) ELISA measurements for PF4 alone or in complex with fondaparinux, HO06, HO08, HO16, and UFH using a panel of 14 well-characterized sera containing anti-PF4/heparin antibodies. The filled squares represent average values of the maxima of the OD values. Error bars correspond to the standard deviation. Data for LMWH are given in supplemental Figure 2.