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The discovery and utility of clinically relevant circulating biomarkers depend on standardized methods that minimize preanalytical errors. Despite growing interest in studying extracellular vesicles (EVs) and cell-free messenger RNA (cf-mRNA) as potential biomarkers, how blood processing and freeze/thaw impacts the profiles of these analytes in plasma was not thoroughly understood. We utilized flow cytometric analysis to examine the effect of differential centrifugation and a freeze/thaw cycle on EV profiles. Utilizing flow cytometry postacquisition analysis software (FCMpass) to calibrate light scattering and fluorescence, we revealed how differential centrifugation and post-freeze/thaw processing removes and retains EV subpopulations. Additionally, cf-mRNA levels measured by RT-qPCR profiles from a panel of housekeeping, platelet, and tissue-specific genes were preferentially affected by differential centrifugation and post-freeze/thaw processing. Critically, freezing plasma containing residual platelets yielded irreversible ex vivo generation of EV subpopulations and cf-mRNA transcripts, which were not removable by additional processing after freeze/thaw. Our findings suggest the importance of minimizing confounding variation attributed to plasma processing and platelet contamination., (© 2022. The Author(s).)

Background: Current malaria diagnostic methods require blood collection, that may be associated with pain and the risk of transmitting blood-borne pathogens, and often create poor compliance when repeated sampling is needed. On the other hand, the collection of saliva is minimally invasive; but saliva has not been widely used for the diagnosis of malaria. The aim of this study was to evaluate the diagnostic performance of saliva collected and stored at room temperature using the OMNIgene ®•ORAL kit for diagnosing Plasmodium falciparum malaria. Methods: Paired blood and saliva samples were collected from 222 febrile patients in Cameroon. Saliva samples were collected using the OMNIgene ®•ORAL (OM-501) kit and stored at room temperature for up to 13 months. Thick blood film microscopy (TFM) was used to detect P. falciparum blood-stage parasites in blood. Detection of P. falciparum DNA in blood and saliva was based on amplification of the multi-copy 18 s rRNA gene using the nested-polymerase chain reaction (nPCR). Results: Prevalence of malaria detected by TFM, nPCR-saliva and nPCR-blood was 22, 29, and 35%, respectively. Using TFM as the gold standard, the sensitivity of nPCR-saliva and nPCR-blood in detecting P. falciparum was 95 and 100%, respectively; with corresponding specificities of 93 and 87%. When nPCR-blood was used as gold standard, the sensitivity of nPCR-saliva and microscopy was 82 and 68%, respectively; whereas, the specificity was 99 and 100%, respectively. Nested PCR-saliva had a very good agreement with both TFM (kappa value 0.8) and blood PCR (kappa value 0.8). At parasitaemia > 10,000 parasites/μl of blood, the sensitivity of nPCR-saliva was 100%. Nested PCR-saliva detected 16 sub-microscopic malaria infections. One year after sample collection, P. falciparum DNA was detected in 80% of saliva samples stored at room temperature. Conclusions: Saliva can potentially be used as an alternative non-invasive sample for the diagnosis of malaria and the OMNIgene ®•ORAL kit is effective at transporting and preserving malaria parasite DNA in saliva at room temperature. The technology described in this study for diagnosis of malaria in resource-limited countries adds on to the armamentarium needed for elimination of malaria. [ABSTRACT FROM AUTHOR]

Plasmodium falciparum (Pf)-specific T- and B-cell responses may be present at birth; however, when during fetal development antibodies are produced is unknown. Accordingly, cord blood samples from 232 preterm (20–37 weeks of gestation) and 450 term (≥37 weeks) babies were screened for IgM to Pf blood-stage antigens MSP1, MSP2, AMA1, EBA175 and RESA. Overall, 25% [95% CI = 22–28%] of the 682 newborns were positive for IgM to ≥1 Pf antigens with the earliest response occurring at 22 weeks. Interestingly, the odds of being positive for cord blood Pf IgM decreased with gestational age (adjusted OR [95% CI] at 20–31 weeks = 2.55 [1.14–5.85] and at 32–36 weeks = 1.97 [0.92–4.29], with ≥37 weeks as reference); however, preterm and term newborns had similar levels of Pf IgM and recognized a comparable breadth of antigens. Having cord blood Pf IgM was associated with placental malaria (adjusted OR [95% CI] = 2.37 [1.25–4.54]). To determine if in utero exposure occurred via transplacental transfer of Pf-IgG immune complexes (IC), IC containing MSP1 and MSP2 were measured in plasma of 242 mother-newborn pairs. Among newborns of IC-positive mothers (77/242), the proportion of cord samples with Pf IC increased with gestational age but was not associated with Pf IgM, suggesting that fetal B cells early in gestation had not been primed by IC. Finally, when cord mononuclear cells from 64 term newborns were cultured in vitro, only 11% (7/64) of supernatants had Pf IgM; whereas, 95% (61/64) contained secreted Pf IgG. These data suggest fetal B cells are capable of making Pf-specific IgM from early in the second trimester and undergo isotype switching to IgG towards term. [ABSTRACT FROM AUTHOR]