Hyperactive STAT5 hijacks T cell receptor signaling and drives immature T cell acute lymphoblastic leukemia.

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive immature T cell cancer. Mutations in IL7R have been analyzed genetically, but downstream effector functions such as STAT5A and STAT5B hyperactivation are poorly understood. Here, we studied the most frequent and clinically challenging STAT5BN642H driver in T cell development and immature T cell cancer onset and compared it with STAT5A hyperactive variants in transgenic mice. Enhanced STAT5 activity caused disrupted T cell development and promoted an early T cell progenitor-ALL phenotype, with upregulation of genes involved in T cell receptor (TCR) signaling, even in absence of surface TCR. Importantly, TCR pathway genes were overexpressed in human T-ALL and mature T cell cancers and activation of TCR pathway kinases was STAT5 dependent. We confirmed STAT5 binding to these genes using ChIP-Seq analysis in human T-ALL cells, which were sensitive to pharmacologic inhibition by dual STAT3/5 degraders or ZAP70 tyrosine kinase blockers in vitro and in vivo. We provide genetic and biochemical proof that STAT5A and STAT5B hyperactivation can initiate T-ALL through TCR pathway hijacking and suggest similar mechanisms for other T cell cancers. Thus, STAT5 or TCR component blockade are targeted therapy options, particularly in patients with chemoresistant clones carrying STAT5BN642H.

External quality assessments for SARS-CoV-2 genome detection in Austria : A comparison of the first postpandemic round with results from the pandemic era.

BACKGROUND: External quality assessment (EQA) schemes provide objective feedback to participating laboratories about the performance of their analytical systems and information about overall regional analytical performance. The EQAs are particularly important during pandemics as they also assess the reliability of individual test results and show opportunities to improve test strategies. With the end of the COVID-19 pandemic, the testing frequency significantly decreased in Austria. Here, we analyzed whether this decrease had an effect on participation and/or performance in SARS-CoV­2 virus detection EQAs, as compared to the pandemic era. MATERIAL AND METHODS: Identical samples were sent to all participating laboratories, and the EQA provider evaluated the agreement of the reported results with defined targets. The EQA was operated under two schemes with identical samples and therefore we analyzed it as a single EQA round. The performance of testing was reported as true positive ratios, comparing the post-pandemic data to previous rounds. Furthermore, subgroups of participants were analyzed stratified by laboratory type (medical or nonmedical) and the test system format (fully automated or requiring manual steps). RESULTS: While the frequency of false negative results per sample did not change during the 3 years of the pandemic (5.7%, 95% confidence interval [CI] 3.1-8.4%), an average per sample false negative ratio of 4.3% was observed in the first post-pandemic EQA (0%, 1.8%, and 11% for the 3 positive samples included in the test panel, n = 109 test results per sample). In this first post-pandemic EQA medical laboratories (average 0.4% false negative across 3 samples, n = 90) and automated test systems (average 1.2% false negative, n = 261) had lower false negative ratios than nonmedical laboratories (22.8%, n = 19) and manual test systems (16.7%, n = 22). These lower average ratios were due to a low concentration sample, where nonmedical laboratories reported 36.8% and manual test systems 54.5% true positive results. CONCLUSION: Overall ratios of true positive results were below the mean of all results during the pandemic but were similar to the first round of the pandemic. A lower post-pandemic true positive ratio was associated with specific laboratory types and assay formats, particularly for samples with low concentration. The EQAs will continue to monitor the laboratory performance to ensure the same quality of epidemiological data after the pandemic, even if vigilance has decreased.

Dynamic control of gene expression by ISGF3 and IRF1 during IFNß and IFNγ signaling.

Type I interferons (IFN-I, including IFNß) and IFNγ produce overlapping, yet clearly distinct immunological activities. Recent data show that the distinctness of global transcriptional responses to the two IFN types is not apparent when comparing their immediate effects. By analyzing nascent transcripts induced by IFN-I or IFNγ over a period of 48 h, we now show that the distinctiveness of the transcriptomes emerges over time and is based on differential employment of the ISGF3 complex as well as of the second-tier transcription factor IRF1. The distinct transcriptional properties of ISGF3 and IRF1 correspond with a largely diverse nuclear protein interactome. Mechanistically, we describe the specific input of ISGF3 and IRF1 into enhancer activation and the regulation of chromatin accessibility at interferon-stimulated genes (ISG). We further report differences between the IFN types in altering RNA polymerase II pausing at ISG 5' ends. Our data provide insight how transcriptional regulators create immunological identities of IFN-I and IFNγ.

JAK-STAT signaling maintains homeostasis in T cells and macrophages.

Immune cells need to sustain a state of constant alertness over a lifetime. Yet, little is known about the regulatory processes that control the fluent and fragile balance that is called homeostasis. Here we demonstrate that JAK-STAT signaling, beyond its role in immune responses, is a major regulator of immune cell homeostasis. We investigated JAK-STAT-mediated transcription and chromatin accessibility across 12 mouse models, including knockouts of all STAT transcription factors and of the TYK2 kinase. Baseline JAK-STAT signaling was detected in CD8+ T cells and macrophages of unperturbed mice-but abrogated in the knockouts and in unstimulated immune cells deprived of their normal tissue context. We observed diverse gene-regulatory programs, including effects of STAT2 and IRF9 that were independent of STAT1. In summary, our large-scale dataset and integrative analysis of JAK-STAT mutant and wild-type mice uncovered a crucial role of JAK-STAT signaling in unstimulated immune cells, where it contributes to a poised epigenetic and transcriptional state and helps prepare these cells for rapid response to immune stimuli.

JAK-Inhibitors - A Story of Success and Adverse Events.

Rheumatoid arthritis (RA) is a systemic, chronic, immune-mediated inflammatory condition. Treatments options encompass conventional synthetic disease-modifying antirheumatic drugs (csDMARDs), biologic disease-modifying antirheumatic drugs (bDMARDs) like tumor necrosis factor (TNF) inhibitors (TNFis) and targeted synthetic disease-modifying antirheumatic drugs (tsDMARDs) including Janus Kinase inhibitors (JAKinibs). Orally administered JAKinibs have demonstrated comparable or, in specific cases, superior efficacy compared to bDMARDs in inflammatory conditions. However, the escalating clinical utilization has been accompanied by the emergence of serious adverse effects, including major adverse cardiac events (MACE), malignancies and venous thrombotic episodes (VTE), leading to regulatory restrictions imposed by health authorities in both the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA).

Performance of SARS-CoV-2 nucleic acid amplification testing in Austria as measured by external quality assessment schemes during 3 years of the COVID-19 pandemic: an observational retrospective study.

BACKGROUND: The aim of external quality assessment (EQA) schemes is to evaluate the analytical performance of laboratories and test systems in a near-to-real-life setting. This monitoring service provides feedback to participant laboratories and serves as a control measure for the epidemiological assessment of the regional incidence of a pathogen, particularly during epidemics. Using data from EQA schemes implemented as a result of the intensive effort to monitor SARS-CoV-2 infections in Austria, we aimed to identify factors that explained the variation in laboratory performance for SARS-CoV-2 detection over the course of the COVID-19 pandemic. METHODS: For this observational study, we retrospectively analysed 6308 reverse transcriptase quantitative PCR (RT-qPCR) test results reported by 191 laboratories on 71 samples during 14 rounds of three SARS-CoV-2 pathogen detection EQA schemes in Austria between May 18, 2020, and Feb 20, 2023. We calculated the overall rates of false and true-negative, false and true-positive, and inconclusive results. We then assessed laboratory performance by estimating the sensitivity by testing whether significant variation in the odds of obtaining a true-positive result could be explained by virus concentration, laboratory type, or assay format. We also assessed whether laboratory performance changed over time. FINDINGS: 4371 (93·7%) of 4663 qPCR test results were true-positive, 241 (5·2%) were false-negative, and 51 (1·1%) were inconclusive. The mean per-sample sensitivity was 99·7% in samples with high virus concentrations (1383 [99·4%] true-positive, three [0·2%] false-negative, and five [0·4%] inconclusive results for 1391 tests in which the sample cycle threshold was ≤32), whereas detection rates were lower in samples with low virus concentrations (mean per-sample sensitivity 92·5%; 2988 [91·3%] true-positive, 238 [7·3%] false-negative, and 46 [1·4%] inconclusive results for 3272 tests in which the cycle threshold was >32). Of the 1645 results expected to be negative, 1561 (94·9%) were correctly reported as negative, 10 (0·6%) were incorrectly reported as positive, and 74 (4·5%) were reported as inconclusive. Notably, the overall performance of the tests did not change significantly over time. The odds of reporting a correct result were 2·94 (95% CI 1·75-4·96) times higher for a medical laboratory than for a non-medical laboratory, and 4·60 (2·91-7·41) times greater for automated test systems than for manual test systems. Automated test systems within medical laboratories had the highest sensitivity when compared with systems requiring manual intervention in both medical and non-medical laboratories. INTERPRETATION: High rates of false-negativity in all PCR analyses evaluated in comprehensive, multiple, and repeated EQA schemes outline a clear path for improvement in the future. The performance of some laboratories (eg, non-medical laboratories or those using non-automated test systems) should receive additional scrutiny-for example, by requiring additional EQA schemes for certification or accreditation-if the aggregated data from EQA rounds suggest lower sensitivity than that recorded by others. This strategy will provide assurances that epidemiological data as a whole are reliable when testing on such a large scale. Although performance did not improve over time, we cannot exclude extenuating circumstances-such as shortages and weakened supply chains-that could have prevented laboratories from seeking alternative methods to improve performance. FUNDING: None.

Inducible overexpression of a FAM3C/ILEI transgene has pleiotropic effects with shortened life span, liver fibrosis and anemia in mice.

FAM3C/ILEI is an important factor in epithelial-to-mesenchymal transition (EMT) induction, tumor progression and metastasis. Overexpressed in many cancers, elevated ILEI levels and secretion correlate with poor patient survival. Although ILEI's causative role in invasive tumor growth and metastasis has been demonstrated in several cellular tumor models, there are no available transgenic mice to study these effects in the context of a complex organism. Here, we describe the generation and initial characterization of a Tet-ON inducible Fam3c/ILEI transgenic mouse strain. We find that ubiquitous induction of ILEI overexpression (R26-ILEIind) at weaning age leads to a shortened lifespan, reduced body weight and microcytic hypochromic anemia. The anemia was reversible at a young age within a week upon withdrawal of ILEI induction. Vav1-driven overexpression of the ILEIind transgene in all hematopoietic cells (Vav-ILEIind) did not render mice anemic or lower overall fitness, demonstrating that no intrinsic mechanisms of erythroid development were dysregulated by ILEI and that hematopoietic ILEI hyperfunction did not contribute to death. Reduced serum iron levels of R26-ILEIind mice were indicative for a malfunction in iron uptake or homeostasis. Accordingly, the liver, the main organ of iron metabolism, was severely affected in moribund ILEI overexpressing mice: increased alanine transaminase and aspartate aminotransferase levels indicated liver dysfunction, the liver was reduced in size, showed increased apoptosis, reduced cellular iron content, and had a fibrotic phenotype. These data indicate that high ILEI expression in the liver might reduce hepatoprotection and induce liver fibrosis, which leads to liver dysfunction, disturbed iron metabolism and eventually to death. Overall, we show here that the novel Tet-ON inducible Fam3c/ILEI transgenic mouse strain allows tissue specific timely controlled overexpression of ILEI and thus, will serve as a versatile tool to model the effect of elevated ILEI expression in diverse tissue entities and disease conditions, including cancer.

Design of external quality assessment schemes and definition of the roles of their providers in future epidemics.

During an epidemic, individual test results form the basis of epidemiological indicators such as case numbers or incidence. Therefore, the accuracy of measures derived from these indicators depends on the reliability of individual results. In the COVID-19 pandemic, monitoring and evaluating the performance of the unprecedented number of testing facilities in operation, and novel testing systems in use, was urgently needed. External quality assessment (EQA) schemes are unique sources of data reporting on testing performance, and their providers are recognised contacts and support for test facilities (for technical-analytical topics) and health authorities (for planning the monitoring of infection diagnostics). To identify information provided by SARS-CoV-2 genome detection EQA schemes that is relevant for public health microbiology, we reviewed the current literature published in PubMed between January, 2020, and July, 2022. We derived recommendations for EQA providers and their schemes for best practices to monitor pathogen-detection performance in future epidemics. We also showed laboratories, test facilities, and health authorities the information and benefits they can derive from EQA data, and from the non-EQA services of their providers.

Duodenal macrophages control dietary iron absorption via local degradation of transferrin.

Iron is an essential cellular metal that is important for many physiological functions including erythropoiesis and host defense. It is absorbed from the diet in the duodenum and loaded onto transferrin (Tf), the main iron transport protein. Inefficient dietary iron uptake promotes many diseases, but mechanisms regulating iron absorption remain poorly understood. By assessing mice that harbor a macrophage-specific deletion of the tuberous sclerosis complex 2 (Tsc2), a negative regulator of mechanistic target of rapamycin complex 1 (mTORC1), we found that these mice possessed various defects in iron metabolism, including defective steady-state erythropoiesis and a reduced saturation of Tf with iron. This iron deficiency phenotype was associated with an iron import block from the duodenal epithelial cells into the circulation. Activation of mTORC1 in villous duodenal CD68+ macrophages induced serine protease expression and promoted local degradation of Tf, whereas the depletion of macrophages in mice increased Tf levels. Inhibition of mTORC1 with everolimus or serine protease activity with nafamostat restored Tf levels and Tf saturation in the Tsc2-deficient mice. Physiologically, Tf levels were regulated in the duodenum during the prandial process and Citrobacter rodentium infection. These data suggest that duodenal macrophages determine iron transfer to the circulation by controlling Tf availability in the lamina propria villi.

Three rounds of a national external quality assessment reveal a link between disharmonic anti-SARS-CoV-2 antibody quantifications and the infection stage.

OBJECTIVES: The WHO's standardized measuring unit, "binding antibody units per milliliter (BAU/mL)," should allow the harmonization of quantitative results by different commercial Anti-SARS-CoV-2 immunoassays. However, multiple studies demonstrate inter-assay discrepancies. The antigenic changes of the Omicron variant affect the performance of Spike-specific immunoassays. This study evaluated the variation of quantitative Anti-SARS-CoV-2-Spike antibody measurements among 46, 50, and 44 laboratories in three rounds of a national external quality assessment (EQA) prior to and after the emergence of the Omicron variant in a diagnostic near-to-real-life setting. METHODS: We analyzed results reported by the EQA participant laboratories from single and sequential samples from SARS-CoV-2 convalescent, acutely infected, and vaccinated individuals, including samples obtained after primary and breakthrough infections with the Omicron variant. RESULTS: The three immunoassays most commonly used by the participants displayed a low intra-assay and inter-laboratory variation with excellent reproducibility using identical samples sent to the participants in duplicates. In contrast, the inter-assay variation was very high with all samples. Notably, the ratios of BAU/mL levels quantified by different immunoassays were not equal among all samples but differed between vaccination, past, and acute infection, including primary infection with the Omicron variant. The antibody kinetics measured in vaccinated individuals strongly depended on the applied immunoassay. CONCLUSIONS: Measured BAU/mL levels are only inter-changeable among different laboratories when the same assay was used for their assessment. Highly variable ratios of BAU/mL quantifications among different immunoassays and infection stages argue against the usage of universal inter-assay conversion factors.

Converting to an international unit system improves harmonization of results for SARS-CoV-2 quantification: Results from multiple external quality assessments.

BACKGROUND: The detection of SARS-CoV-2 vRNA in clinical samples has relied almost exclusively on RT-qPCR as the gold standard test. Published results from various external quality assessments ("ring trials") worldwide have shown that there is still a large variability in results reported for the same samples. As reference standards of SARS-CoV-2 RNA are available, we tested whether using standard curves to convert Ct values into copies/mL (cp/mL) improved harmonization. METHODS: Nine laboratories using 23 test systems (15 of which were unique) prepared standard dilution curves to convert Ct values of 13 SARS-CoV-2 positive samples to cp/mL (hereafter IU/mL). The samples were provided in three rounds of a virus genome detection external quality assessment (EQA) scheme. We tested the precision and accuracy of results reported in IU/mL, and attempted to identify the sources of variability. RESULTS: Reporting results as IU/mL improved the precision of the estimated concentrations of all samples compared to reporting Ct values, although some inaccuracy remained. Variance analysis showed that nearly all variability in data was explained by individual test systems within individual laboratories. When controlling for this effect, there was no significant difference between all other factors tested (test systems, EQA rounds, sample material). CONCLUSIONS: Converting results to copies/mL improved precision across laboratory test systems. However, it seems the results are still very specific to test systems within laboratories. Further efforts could be made to improve accuracy and achieve full harmonization across diagnostic laboratories.

Stress signaling boosts interferon-induced gene transcription in macrophages.

Promoters of antimicrobial genes function as logic boards, integrating signals of innate immune responses. One such set of genes is stimulated by interferon (IFN) signaling, and the expression of these genes [IFN-stimulated genes (ISGs)] can be further modulated by cell stress-induced pathways. Here, we investigated the global effect of stress-induced p38 mitogen-activated protein kinase (MAPK) signaling on the response of macrophages to IFN. In response to cell stress that coincided with IFN exposure, the p38 MAPK-activated transcription factors CREB and c-Jun, in addition to the IFN-activated STAT family of transcription factors, bound to ISGs. In addition, p38 MAPK signaling induced activating histone modifications at the loci of ISGs and stimulated nuclear translocation of the CREB coactivator CRTC3. These actions synergistically enhanced ISG expression. Disrupting this synergy with p38 MAPK inhibitors improved the viability of macrophages infected with Listeria monocytogenes. Our findings uncover a mechanism of transcriptional synergism and highlight the biological consequences of coincident stress-induced p38 MAPK and IFN-stimulated signal transduction.

Tyk2 is a tumor suppressor in colorectal cancer.

Janus kinase Tyk2 is implicated in cancer immune surveillance, but its role in solid tumors is not well defined. We used Tyk2 knockout mice (Tyk2Δ/Δ) and mice with conditional deletion of Tyk2 in hematopoietic (Tyk2ΔHem) or intestinal epithelial cells (Tyk2ΔIEC) to assess their cell type-specific functions in chemically induced colorectal cancer. All Tyk2-deficient mouse models showed a higher tumor burden after AOM-DSS treatment compared to their corresponding wild-type controls (Tyk2+/+ and Tyk2fl/fl), demonstrating tumor-suppressive functions of Tyk2 in immune cells and epithelial cancer cells. However, specific deletion of Tyk2 in hematopoietic cells or in intestinal epithelial cells was insufficient to accelerate tumor progression, while deletion in both compartments promoted carcinoma formation. RNA-seq and proteomics revealed that tumors of Tyk2Δ/Δ and Tyk2ΔIEC mice were immunoedited in different ways with downregulated and upregulated IFNγ signatures, respectively. Accordingly, the IFNγ-regulated immune checkpoint Ido1 was downregulated in Tyk2Δ/Δ and upregulated in Tyk2ΔIEC tumors, although both showed reduced CD8+ T cell infiltration. These data suggest that Tyk2Δ/Δ tumors are Ido1-independent and poorly immunoedited while Tyk2ΔIEC tumors require Ido1 for immune evasion. Our study shows that Tyk2 prevents Ido1 expression in CRC cells and promotes CRC immune surveillance in the tumor stroma. Both of these Tyk2-dependent mechanisms must work together to prevent CRC progression.

Standardizing continuous data classifications in a virtual T-maze using two-layer feedforward networks.

There continues to be difficulties when it comes to replication of studies in the field of Psychology. In part, this may be caused by insufficiently standardized analysis methods that may be subject to state dependent variations in performance. In this work, we show how to easily adapt the two-layer feedforward neural network architecture provided by Huang1 to a behavioral classification problem as well as a physiological classification problem which would not be solvable in a standardized way using classical regression or "simple rule" approaches. In addition, we provide an example for a new research paradigm along with this standardized analysis method. This paradigm as well as the analysis method can be adjusted to any necessary modification or applied to other paradigms or research questions. Hence, we wanted to show that two-layer feedforward neural networks can be used to increase standardization as well as replicability and illustrate this with examples based on a virtual T-maze paradigm2-5 including free virtual movement via joystick and advanced physiological data signal processing.

Results of a SARS-CoV-2 virus genome detection external quality assessment round focusing on sensitivity of assays and pooling of samples.

OBJECTIVES: Results of earlier external quality assessment (EQA) rounds suggested remarkable differences in the sensitivity of SARS-CoV PCR assays. Although the test systems are intended to detect SARS-CoV-2 in individual samples, screening is often applied to sample pools to increase efficiency and decrease costs. However, it is unknown to what extent these tests actually meet the manufacturer's specifications for sensitivity and how they perform when testing sample pools. METHODS: The sensitivity of assays in routine use was evaluated with a panel of positive samples in a round of a SARS-CoV-2 virus genome detection EQA scheme. The panel consisted of samples at or near the lower limit of detection ("weakly positive"). Laboratories that routinely test sample pools were asked to also analyze the pooled EQA samples according to their usual pool size and dilution method. RESULTS: All participants could detect a highly positive patient-derived sample (>106 copies/mL). Most (96%) of the test systems could detect at least 1,000 copies/mL, meeting the minimum acceptable benchmark, and many (94%) detected the vRNA in a sample with lower concentration (500 copies/mL). The false negative ratio increased to 16 and 26% for samples with 100 and 50 copies/mL, respectively. CONCLUSIONS: The performance of most assays met or exceeded their specification on sensitivity. If assays are to be used to analyze sample pools, the sensitivity of the assay and the number of pooled samples must be balanced.

Interferons reshape the 3D conformation and accessibility of macrophage chromatin.

Engagement of macrophages in innate immune responses is directed by type I and type II interferons (IFN-I and IFN-γ, respectively). IFN triggers drastic changes in cellular transcriptomes, executed by JAK-STAT signal transduction and the transcriptional control of interferon-stimulated genes (ISG) by STAT transcription factors. Here, we study the immediate-early nuclear response to IFN-I and IFN-γ in murine macrophages. We show that the mechanism of gene control by both cytokines includes a rapid increase of DNA accessibility and rearrangement of the 3D chromatin contacts particularly between open chromatin of ISG loci. IFN-stimulated gene factor 3 (ISGF3), the major transcriptional regulator of ISG, controlled homeostatic and, most notably, induced-state DNA accessibility at a subset of ISG. Increases in DNA accessibility correlated with the appearance of activating histone marks at surrounding nucleosomes. Collectively our data emphasize changes in the three-dimensional nuclear space and epigenome as an important facet of transcriptional control by the IFN-induced JAK-STAT pathway.

PTPN2 elicits cell autonomous and non-cell autonomous effects on antitumor immunity in triple-negative breast cancer.

The tumor-suppressor PTPN2 is diminished in a subset of triple-negative breast cancers (TNBCs). Paradoxically, PTPN2-deficiency in tumors or T cells in mice can facilitate T cell recruitment and/or activation to promote antitumor immunity. Here, we explored the therapeutic potential of targeting PTPN2 in tumor cells and T cells. PTPN2-deficiency in TNBC associated with T cell infiltrates and PD-L1 expression, whereas low PTPN2 associated with improved survival. PTPN2 deletion in murine mammary epithelial cells TNBC models, did not promote tumorigenicity but increased STAT-1-dependent T cell recruitment and PD-L1 expression to repress tumor growth and enhance the efficacy of anti-PD-1. Furthermore, the combined deletion of PTPN2 in tumors and T cells facilitated T cell recruitment and activation and further repressed tumor growth or ablated tumors already predominated by exhausted T cells. Thus, PTPN2-targeting in tumors and/or T cells facilitates T cell recruitment and/or alleviates inhibitory constraints on T cells to combat TNBC.

External quality assessment providers' services appear to more impact the immunohaematology performance of laboratories than national regulatory and economic conditions.

OBJECTIVES: Medical laboratories may, at their own discretion, exceed but not undercut regulatory quality requirements. Available economic resources, however, may drive or hinder eagerness to exceed minimum requirements. Depending on the respective scopes of regulatory and economic framework conditions, differing levels of quality efforts to safeguard laboratory performance can be anticipated. However, this has not yet been investigated. METHODS: Immunohaematology external quality assessment (EQA) results collected by 26 EQA providers from their participant laboratories in 73 countries from 2004 to 2019 were evaluated. Error rates were aggregated in groups according to the respective national regulatory and economic framework conditions, to whether or not expert advice was provided in case of incorrect results, and the frequency of EQA samples. RESULTS: These representative data indicate no association between national regulatory (mandatory participation in EQA, monitoring of performance of individual laboratories by authorities, financial consequences of incorrect results) and economic (level of national income, share of national health expenditure) conditions to the quality performance of medical laboratories in immunohaematology. However, EQA providers' support for laboratories in the event of incorrect results appear to be associated with lower error rates, but a high EQA sample frequency with higher error rates. CONCLUSIONS: Further research into the impact of introducing or changing services of EQA providers is needed to confirm the results found in this first of its kind study.