Technical noteDistinguishing septic from normal donors by detection of sPLA2-IIA from human plasma using a microsieve-based immunoassay

Bloodstream infections that progress to septic shock are responsible for hundreds of thousands of deaths each year, and are associated with significant healthcare costs. Recent studies have shown that a member of the secreted phospholipase protein family, termed sPLA2-IIA, may play a role during the innate immune response to bacterial infections, and is elevated in the plasma of septic patients. In this report, the feasibility of a simple microsieve-based sPLA2-IIA detection immunoassay was explored. Microsieves containing 5 μm pores were covalently coupled with a sPLA2-IIA-specific monoclonal antibody at 0.1, 1.0, and 10 μg/mL and then assayed with plasma-based positive and negative controls to determine the optimal coating concentration. Recombinant sPLA2-IIA was then serially diluted to a final concentration of 200, 100, 50, 25, 12.5, and 6.25 ng/mL and tested alongside a non-spiked sample to estimate the detection limit of the prototype assay. Recombinant sPLA2-IIA was also spiked into serum, EDTA-plasma, and Lithium-Heparin plasma, in an effort to evaluate assay performance when analyzing these sample matrices. The preliminary limit of detection studies suggests that the microsieve assay is able to distinguish approximately 6-12 ng/mL of sPLA2-IIA from a non-spiked sample. When compared to an immunoassay diluent, the microsieve assay also yielded acceptable percent recoveries for each of the three sample matrices spiked with clinically significant levels of sPLA2-IIA. The sPLA2-IIA microsieve assay prototype also clearly distinguished five samples from septic patients from five normal donor samples, and the results were in good agreement with a comparator ELISA test system (R2 = 0.9347).