VITT antibodies are monoclonal or oligoclonal. (A-B) Eluates from PF4-heparin beads and control heparin beads were evaluated in PF4-polyanion ELISA for binding to PF4-polyvinylsulfonate complexes and for platelet activation in the PEA. Means and SD (n = 3) are shown. Control (heparin) bead studies were not performed with patients 4 and 5 because of limited sample volume. (C-G) Displayed are LC-ESI-QTOF MS light chain +11 (mass to charge [m/z]) distributions from anti-PF4 antibodies isolated from 5 patients with VITT. In the spectra, green represents the distribution of all λ-containing Ig’s, red represents the +11 m/z distribution of all κ-containing Ig’s, and blue represents the +11 m/z light chain distribution of κ and λ light chains associated with an IgG heavy chain. The number listed above the peaks indicates the +11 m/z ratio of the identified light chain. The x-axis shows m/z ratios, and the y-axis shows the relative abundance of the monoclonal or oligoclonal antibody identified.