Disparities in estimates of IgG bound to normal platelets

Area of Science:

• Immunology
• Hematology

Background:

• Estimates of platelet-associated IgG (PAIgG) vary significantly, ranging from hundreds to tens of thousands of molecules per platelet.
• Discrepancies arise from different methodologies, including direct binding assays and competitive binding assays using soluble IgG standards.

Purpose of the Study:

• To accurately quantify the number of IgG molecules bound to normal platelets.
• To reconcile the wide range of existing PAIgG estimates.

Main Methods:

• Utilized a kinetic-enzyme-linked immunosorbent assay (ELISA) antiglobulin assay.
• Employed both competitive binding assays with soluble IgG standards and direct measurement of bound antiglobulin.

Main Results:

• Competitive assays estimated 21,200 +/- 9,400 IgG molecules per platelet.
• Direct kinetic-ELISA measurements yielded significantly lower estimates of 259 +/- 117 IgG molecules per platelet.
• Demonstrated that soluble IgG and PAIgG have different binding affinities for anti-IgG.

Conclusions:

• Methodological differences are the primary cause of disparate PAIgG estimates.
• The most accurate estimate for normal PAIgG is likely several hundred IgG molecules or less per platelet.
• Direct measurement methods are more reliable for quantifying PAIgG.