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Development and assessment of enzyme immunoassay for platelet-derived microparticles
Abstract:
Platelet-derived microparticles (PMPs) are released from platelets through the platelet activation by high shear stress, collagen, or calcium ionophore (A23187). PMPs are observed in patients with acute myocardial infarction, thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, heparin-induced thrombocytopenia and other thrombotic disorders, but the importance of circulating PMPs in the pathogenesis of these diseases is still debated. Numbers of PMPs are usually determined by flowcytometry (FCM), but easier and reproducible PMP assay systems are needed. To develop a better ELISA for PMPs, we used antibodies against the platelet antigens anti-GPIb (NNKY5-5), anti-GPIIb/IIIa (NNKY2-11, anti-CD41), anti-GPIX (KMP-9), and anti-CD9 (NNKY1-19). PMPs were detected with all combinations of these antibodies, but the ELISA having the highest and most specific absorbance was obtained with a combination of KMP-9 (capture antibody) and NNKY5-5 (detecting antibody). PMPs in blood samples were measured by ELISA and FCM. ELISA correlated with PMPs quantitated by FCM. By shaking ELISA plates during incubation, nonspecific binding of platelets was eliminated. The level of PMPs was not increased in diabetes mellitus, thrombotic thrombocytopenic purpura, antiphospholipid syndrome, or sepsis. The concentration of PMP was elevated in hemolytic uremic syndrome. Activated PMPs were absorbed to 0.8 microm filter, but circulating PMPs were not absorbed. These results suggest that activated PMPs are likely to adhere to leukocytes or endothelial cells at the activation site and that the circulating form of PMPs are likely to be a residue of activated PMPs. To detect only the activated form of PMPs, a new ELISA needs to be developed, and it will likely use a combination of antibodies that detect platelet activation markers such as P-selectin (CD62P) or activated GPIIb/IIIa.
Insights
A new ELISA assay accurately quantifies platelet-derived microparticles (PMPs), revealing elevated levels in hemolytic uremic syndrome but not other thrombotic disorders. This method distinguishes activated PMPs, crucial for understanding disease pathogenesis.
Area of Science:
- Hematology
- Immunology
- Biochemistry
Background:
- Platelet-derived microparticles (PMPs) are implicated in thrombotic disorders, but their role is debated.
- Current methods like flow cytometry (FCM) for PMP quantification lack ease and reproducibility.
- There is a need for improved diagnostic tools to measure PMPs in various clinical conditions.
Purpose of the Study:
- To develop and validate a more reliable enzyme-linked immunosorbent assay (ELISA) for quantifying PMPs.
- To investigate the levels of circulating PMPs in patients with specific thrombotic and non-thrombotic conditions.
- To differentiate between activated and circulating PMPs and understand their potential roles in disease.
Main Methods:
- Developed an ELISA using specific antibodies against platelet antigens (anti-GPIb, anti-GPIIb/IIIa, anti-GPIX, anti-CD9).
- Optimized ELISA by identifying the most specific antibody combination (KMP-9 capture, NNKY5-5 detection) and including plate shaking.
- Correlated ELISA results with FCM for PMP quantification in blood samples; tested PMP filtration characteristics.
Main Results:
- The optimized ELISA demonstrated high specificity and correlated well with FCM measurements.
- Elevated PMP concentrations were found in hemolytic uremic syndrome but not in diabetes mellitus, thrombotic thrombocytopenic purpura, antiphospholipid syndrome, or sepsis.
- Activated PMPs were retained by a 0.8 µm filter, while circulating PMPs were not, suggesting distinct properties and potential localization.
Conclusions:
- The developed ELISA provides a reproducible and accurate method for quantifying circulating PMPs.
- Circulating PMP levels are elevated in hemolytic uremic syndrome, supporting their role in this specific thrombotic disorder.
- Activated PMPs may adhere to cells at activation sites, with circulating PMPs representing a residue, necessitating assays for activated PMPs using markers like CD62P.