Measurement of Heparin Dependent Antibodies with Immunoassays

Immunoassays for heparin dependent antibodies have been introduced since the discovery of PF4 as the major target antigen in presence of heparin. Different immunoassay presentations are available, and interestingly heparin can   be   replaced   by   polyanions complexes and its native structure is then altered as shown on figure 3.

This alteration exposes PF4 epitopes, characteristic of the molecule involvement in heparin complexes, which can bind heparin dependent antibodies. Enzyme Linked Immuno-Sorbent Assays (Elisa) for heparin dependent antibodies, use stoichiometric such as Polyvinyl-Sulfonate (PVS), providing evidence that the location of the reactive epitopes of heparin dependent antibodies are on the PF4 molecule. PF4, in presence of heparin (UFH or LMWH) at stoichiometric concentrations, forms ultra-large, multimolecular HPF4 complexes, or complexes of PF4 with PVS for coating the Elisa microwell, which then captures antibodies, when present.

An Anti- IgG linked with peroxidase, or another label, is then introduced for characterizing immobilized IgG antibodies. A more dynamic assay has been introduced in the form of plates coated with a limited amount of protamine sulfate.