Multiplexed immunoassay for detection of rheumatoid factors by FIDISTM technology

Our objective was to (i) compare FIDIS Rheuma, a new multiplexed immunoassay designed for simultaneous detection of IgM class rheumatoid factors (RF) directed against Fc determinants of IgG from humans and animals, with agglutination and ELISA (conventional methods) and (ii) evaluate the clinical sensitivity and specificity of biological markers for rheumatoid arthritis (RA). To do this, FIDIS technology was employed using the Luminex system. It consists of distinct color-coded microsphere sets, a flow cytometer, and digital signal processing hardware and software. Agglutination and ELISA tests were performed with commercial kits. The study included 134 samples from RA patients and 105 from healthy blood donors. For human specificity, we compared FIDIS with latex agglutination and ELISA. Relative sensitivities were 98.9% and 88.5% and specificities were 90.2% and 94.6%, respectively. For animal specificity, we compared FIDIS with Waaler-Rose and ELISA. The results were 84.9% and 71.9% for the sensitivities and 97.5% and 98.4% for the specificities, respectively. Detection of IgG anti-CCP by ELISA and IgG antikeratin by immunofluorescence was also determined in order to compare their clinical sensitivity and specificity with IgM-RF, according to the method used. The results were: IgG anti-CCP 72.3%, 97.2%; IgG antikeratin 36.6%, 100%; latex agglutination 66.4%, 97.2%; Waaler-Rose 55.9%, 96.3%; FIDIS human 73.9%, 92.1%; FIDIS animal 49.2%, 97.2%; ELISA human 93.2%, 95.5%; and ELISA animal 74.6%, 91.3%. The results showed the efficiency of FIDIS with analytical performance equivalent to the conventional methods, but having the advantage of giving quantitative results (IU/mL).

Filtration induces changes in activity states and leucocyte populations

The distribution of leucocyte subpopulations in platelet concentrates (PC) derived from pre-storage filtered platelet-rich plasma (PRP), the cell suspension obtained by reverse filter washing and the post-filtered PC, were monitored by immunophenotyping analysis using CD3, CD20 and CD33. Leucocyte activation analysis with the CD11b marker revealed that this molecule is up regulated in neutrophils taken from the filter. This, together with the loss of cell viability during the enrichment process, suggests that contact with the filter matrix and processing and storage of samples containing leucocytes may lead to activation and loss of leucocyte viability. These changes were found to be more pronounced in less stable myeloid cells and account for the differences reported among various authors which in some cases related to operational conditions such as the enrichment process used and the length of time between filtration and analysis of samples. Finally, statistical analysis of the results obtained by immunophenotypic studies indicate that post-filter samples (S) contain significantly higher numbers of CD33+ myeloid cells when compared to (PF) the pre-filter samples (65.03%+/-12.6 and 24.56%+/-14.73, p<0.0000), with a decrease in T cells (50.72%+/-14.80 in PF and 24.05+/-9.48 in the cell suspension (S), p<0.0007) and B cells (14.96+/-9.31 in PF and 9.9+/-5.22 in S, p<0.201). A new strategy for assessing the influence of the filtration process on residual leucocyte activation and viability is described. This has direct relevance to collection, processing, storage and quality monitoring of PC.