Complement activation as a biomarker for platelet-activating antibodies in heparin-induced thrombocytopenia
Sooho S. Myoung 1), Samuel J. Francis 2), Jonah Chen 2), Grace Lee 2), Lubica Rauova 3), Mortimer Poncz 3), Douglas B. Cines 4), Maragatha Kuchibhatla 2), Sanjay Khandelwal 2), Gowthami M. Arepally 2).
1) Medical Scientist Training Program, The Ohio State University College of Medicine, Columbus, Ohio, USA
2) Division of Hematology, Duke University Medical Center, Durham, North Carolina, USA
3) Division of Hematology, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
4) Department of Pathology and Laboratory Medicine, Perelman-University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA
Abstract
Background
Immunoglobulin G antibodies (Abs) to platelet factor 4 (PF4) complexed to heparin (PF4/H) commonly occur after H exposure but cause life-threatening complications of H-induced thrombocytopenia (HIT) in only a few patients. Presently, only platelet activation assays reliably distinguish anti-PF4/H Abs that cause disease (HIT Abs) from those likely to be asymptomatic (AAbs).
Objectives
Recent studies indicate that complement activation is an important serologic property of HIT Abs and is essential for IgG Fc receptor IIA-mediated cellular activation. As platelet activation by HIT Abs also relies on IgG Fc receptor IIA activation, we correlated the complement- and platelet-activating properties of anti-PF4/H Abs in a clinically annotated patient cohort.
Methods
Clinical and laboratory features of patients with HIT (n = 8) and AAbs+ (n = 14) were correlated with properties of complement, platelet, and monocyte/neutrophil activation.
Results
Expected clinical and laboratory differences were seen between HIT and AAb+ patients, with HIT patients having lower mean platelet counts, greater percentage drop in platelet counts, higher 4T and HIT expert probability scores, higher anti-PF4 polyclonal and immunoglobulin G Ab levels, and serotonin release assay positivity. Ex vivo assays revealed significant differences in complement activation by HIT vs AAb+ patients, with the extent of complement activation closely correlated with percent serotonin release by anti-PF4/H Abs and matrix metalloproteinase-9 and interleukin-8 release in whole blood.
Conclusion
These findings suggest that complement activation strongly correlates with cellular activation endpoints, including platelet and monocyte/neutrophil activation, and if confirmed in a larger prospective study, may serve as a “functional” biomarker for pathogenic HIT Abs.