Background: Rapid diagnosis of the causative organism of invasive infections is critical to the improved care of patients. A new platform, FilmArray (BioFire Diagnostics, LLC, Salt Lake City, UT) allows for rapid PCR to be performed in less than two hours on positive blood cultures Objective: The aim was to perform a retrospective diagnostic accuracy study in a paediatric tertiary referral hospital comparing results from culture, our gold standard, against those obtained when the samples were tested directly using the FilmArray Blood Culture Identification (BCID) Panel (BioFire Diagnostics, LLC, Salt Lake City, UT). Method: Samples from sterile site infections were tested using traditional culture based methods as well as PCR testing, and these results were then compared to testing which was done directly on the FilmArray BC-ID panel. Results: Ninety-four samples were tested in total and concordant results were observed in 71 samples (76%). Correlation between detection of pathogens such as Staphylococcus aureus and Streptococcus pyogenes by PCR and culture result was high (94% and 88% respectively). Discordant results could be explained by the cultured organism not having a target on the panel (n=8) or PCR detection of potentially non-viable bacteria in the sample (n=8); the remaining samples (n=9) were negative by PCR despite culturing an organism with a target present on the panel for that organism. We have demonstrated an overall correlation of 76% and that in some instances the PCR detected non-viable yet clinically significant bacteria. Conclusion: Use of the FilmArray BCID panel directly for samples from sterile sites should be considered when there is a high index of suspicion of a single-organism infection at that site prior to sampling.
Autoimmunity in rheumatoid arthritis (RA) is characterized by autoantibodies to citrullinated proteins/peptides (ACPA)1. These antibodies, present in 60-70% of patients, antedate clinical onset and associate with an erosive disease course, suggesting a direct pathogenic involvement in disease initiation and progression2.
Objectives
With this study, we aimed to develop an efficient method for the purification of human ACPA, and to characterize their frequency and fine-specificity pattern in synovial fluid (SF) and plasma of RA patients.
Methods
SF and plasma samples were collected with informed consent and ethical approval from patients (fulfilling the ACR criteria for RA) with high anti-CCP antibody levels. SF samples (n=36) were first treated with hyaluronidase to decrease viscosity, then proteins were precipitated with ammonium sulfate, dissolved and further dialysed against phosphate buffered saline (PBS), before the IgG fractions were purified on ProteinG columns (GE Healthcare, Uppsala, Sweden). Plasma samples (n=10) were diluted in PBS before applied to the ProteinG column. ACPAs were further purified using CCP2 affinity columns, kindly provided by Euro-Diagnostica. Recovery and purity of total IgG and anti-CCP IgG were analysed using SDS-PAGE, Nanodrop (Thermo Scientific, Wilmington, DE, USA) and the CCP2-ELISA kit. Fine-specificity of the purified ACPAs were investigated using in-house ELISAs, with peptides from citrullinated α-enolase (CEP-1), -vimentin (Cit-vim), -fibrinogen (Cit-fib) and -collagen type II (Cit-C1).
Results
Anti-CCP IgG could efficiently be purified from SF and plasma, using ProteinG-, followed by CCP2-, columns. No CCP IgG response could be detected in the flow-through fractions. Higher concentrations of total IgG were found in plasma (13,6 mg/ml) compared to SF (4,2 mg/ml), while a higher percentage of CCP-specific IgG was detected in SF (3%), compared to plasma (2%). The purified anti-CCP IgG fractions cross-reacted with CEP-1, Cit-vim, Cit-fib and Cit-C1, while no reactivity to these citrullinated antigens were detected in the IgG flow-through fractions. Anti-CCP IgG dilution curves (starting at 10 μg/ml of purified antibodies) demonstrated differences in affinity between patients, which may correspond to the different ACPA-fine specificity patterns seen in patients.
Conclusions
The described methodology efficiently purifies ACPAs with multiple specificities, which will allow for their use in in vivo and in vitro studies, to further elucidate their arthritogenic and pathogenic capacity. In addition, the ACPAs will be tools for future immunoprecipitation-, immunoblotting- and immunohistochemistry experiments.
References
Schellekens, G. A. et al., The diagnostic properties of rheumatoid arthritis antibodies recognizing a cyclic citrullinated peptide. Arthritis Rheum 43(1), 155 (2000). van der Helm-van Mil AH, Verpoort KN, Breedveld FC, Toes RE, Huizinga TW, Antibodies to citrullinated proteins and differences in clinical progression of rheumatoid arthritis. Arthritis Res Ther 7(5), R949 (2005).
Autoimmunity in rheumatoid arthritis (RA) is characterised by autoantibodies to citrullinated proteins/peptides (ACPA). These antibodies, present in 60–70% of patients, antedate clinical onset and associate with an erosive disease course, suggesting a direct pathogenic involvement in disease initiation and progression. With this study, the authors aimed to develop an efficient method for the purification of human ACPA, and to characterise their frequency and fine-specificity pattern in synovial fluid (SF) and plasma of RA patients.
Materials and methods
SF and plasma samples were collected with informed consent and ethical approval from patients (fulfilling the American college of rheumatology criteria for RA) with high anti-CCP antibody levels. SF samples (n=36) were first treated with hyaluronidase to decrease viscosity, then proteins were precipitated with ammonium sulphate, dissolved and further dialysed against PBS, before the IgG fractions were purified on Protein G columns (GE Healthcare, Uppsala, Sweden).Plasma samples (n=10) were diluted in PBS before applied to the Protein G column. ACPAs were further purified using CCP2 affinity columns, kindly provided by Euro-Diagnostica. Recovery and purity of total IgG and anti-CCP immunoglobulin G (IgG) were analysed using SDS-PAGE, Nanodrop (Thermo Scientific, Wilmington, DE, USA) and the CCP2-ELISA kit. Fine-specificity of the purified ACPAs were investigated using inhouse ELISAs, with peptides from citrullinated α-enolase (CEP-1), -vimentin (Cit-vim), -fibrinogen (Cit-fib) and -collagen type II (Cit-C1).
Results
Anti-CCP IgG could efficiently be purified from SF and plasma, using ProteinG-, followed by CCP2-, columns. No CCP IgG response could be detected in the flow-through fractions. Higher concentrations of total IgG were found in plasma (13.6 mg/ml) compared to SF (4.2 mg/ml), while a higher percentage of CCP-specific IgG was detected in SF (3%), compared to plasma (2%). The purified anti-CCP IgG fractions cross-reacted with CEP-1, Cit-vim, Cit-fib and Cit-C1, while no reactivity to these citrullinated antigens were detected in the IgG flow-through fractions. Anti-CCP IgG dilution curves (starting at 10 µg/ml of purified antibodies), demonstrated differences in affinity between patients, which may correspond to the different ACPA-fine specificity patterns seen in patients.
Conclusions
The described methodology efficiently purifies ACPAs with multiple specificities, which will allow for their use in in vivo and in vitro studies, to further elucidate their arthritogenic and pathogenic capacity. In addition, the ACPAs will be tools for future immunoprecipitation-, immunoblotting- and immunohistochemistry experiments.
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