Characterizing the KKO binding site on hPF4/heparin.
(A) Binding of KKO to single amino acid hPF4 mutants complexed to heparin was measured by ELISA. Results are the mean ± 1 SD of 3 separate experiments, each performed in duplicate. (B) Competition studies of KKO binding to hPF4/heparin using HIT plasma at increasing concentrations with the results expressed as percentage of A405 seen when no HIT plasma was included. The competition studies shown in black represent 4 different patients with HIT “insensitive” to 3rd-domain mutations of hPF4 (Table 1), whereas the competition studies shown in gray represent patients with HIT “sensitive” to 3rd-domain mutations of hPF4 (Table 1). The 50% level of reduction in A405 is indicated as a dashed line.
