The invention includes compositions, kits and methods comprising a
monoclonal antibody which shares key functional properties with the
polyclonal antibodies which participate in the pathogenesis of heparin
induced thrombocytopenia/thrombosis (HIT/HITT) in a mammal. The
monoclonal antibody of the invention preferentially binds with a
PF4/heparin complex relative to the binding of the antibody with PF4 or
heparin alone. The monoclonal antibody of the invention also binds
specifically with PF4 in a complex with other glycosaminoglycans besides
heparin, and also activates platelets. The monoclonal antibody of the
invention is useful in methods for diagnosing and treating HIT/HITT in a
mammal. A humanized version of the monoclonal antibody of the invention
is also included, along with a process for humanizing the monoclonal
antibody of the invention.