Impact of storage conditions on peripheral leukocytes transcriptome

Monocyte antigen-presenting capacity to iNKT cells is influenced by the blood collection conditions

It is widely accepted that different blood collection conditions, including anticoagulants, influence leukocyte phenotype and function. Buffy Coats originated from a donated whole blood bag unit are commonly used in immunological research as a source of leukocytes. They are a residual product of healthy donor whole blood processing. The preservative solution present in the blood bag unit and consequently in the derived Buffy Coat is Citrate-Phosphate-Dextrose (CPD), in which citrate is the anticoagulant. There is a lack of information on the possible difference in the functionality of leukocytes from Buffy Coats originated from a blood bag unit vs leukocytes isolated from blood collection tubes with various anticoagulants. Herein, we aimed at studying monocyte function when the monocytes are isolated from Buffy Coats originated from a blood bag unit vs blood collection tube containing EDTA, CPD with adenine (CPDA), or sodium citrate. The function of monocytes, isolated 20 h after blood collection, to present lipid antigens to invariant Natural Killer T (iNKT) cells was investigated. iNKT cells are activated by lipids bound to CD1d, a non-polymorphic MHC-class I-like molecule, present on the surface of antigen-presenting cells. A striking result showed that monocytes isolated from EDTA blood tubes have a lower capacity to present lipid antigens to iNKT cells than monocytes isolated from Buffy Coats originated from a blood bag unit. No differences were found between monocytes isolated from sodium citrate or CPDA and the ones isolated from Buffy Coats originated from a blood bag unit. This was accompanied by a decrease in viability of the EDTA-isolated monocytes. Expression of the surface markers CD1d and CD86 was higher for monocytes isolated from EDTA than those isolated from Buffy Coats. In conclusion, EDTA-containing blood tubes are not the ideal choice of anticoagulant for monocyte antigen presentation assays. We advise that the blood collection condition and the time between biospecimen collection and analysis should be carefully considered when designing experimental procedures.

Evaluating the Effects of Storage Conditions on Multiple Cell-Free RNAs in Plasma by High-Throughput Sequencing

Background: Plasma cell-free RNAs (cfRNAs) can serve as noninvasive biomarkers for the diagnosis and monitoring of diseases. However, the delay in blood processing may lead to unreliable results. Therefore, an unbiased evaluation based on the whole transcriptome under different storage conditions is needed. Methods: Here, blood samples were collected in ethylenediaminetetraacetic acid tubes and processed immediately (0 hour), or stored at room temperature (RT) or 4°C for different time intervals (2, 6, and 24 hours) before plasma separation. High-throughput sequencing was applied to assess the effects of storage conditions on the transcript profiles and fragment characteristics of plasma cell-free mRNA, long noncoding RNA (lncRNA), and small RNAs. Results: More genes changed their expression levels with time when blood was stored at RT compared with those at 4°C. Cell-free mRNA and lncRNA were relatively stable in blood preserved at 4°C for 6 hours, while cell-free microRNA (miRNA) and piwi-interacting RNA (piRNA) remained stable at 4°C for 24 hours. After 24 hours, more contamination of the leukocyte-derived RNAs occurred at RT, possibly due to apoptosis. Meanwhile, significant changes were also observed regarding the characteristics of the RNA fragments, including fragment size, the proportion of intron, and the pyrimidine frequency of the fragmented 3' end. Fifteen tissue-enriched genes were detected in the plasma but not expressed in leukocytes. The expression level and fragment length of these genes gradually decreased during storage, suggesting the degradation of the cfRNA and the dilution of leukocyte-derived RNA with other tissue-derived cfRNA. Conclusions: Our results suggest that the contamination of leukocyte-derived RNA and the degradation of original cfRNA contribute to the changes in the cfRNA expression profiles and the fragment characteristics during short-term storage. The storage of blood at 4°C for 6 hours allows plasma cfRNA to remain relatively stable, which will be useful for further studies or clinical applications where adequate quantification or the fragment signature of cfRNA is required.

Effects of Freezing and Rewarming Methods on RNA Quality of Blood Samples

Background: RNA extracted from human blood has been widely applied to biological, medical, and clinical research of numerous diseases. Previous studies have demonstrated that high-quality RNA is indispensable to guarantee the reliability of downstream assays. In this study, we investigated the effects of freezing procedures, rewarming methods, and blood components on RNA quality of blood samples. Methods: Rabbit blood samples were divided into two groups: (1) whole blood (WB) and (2) blood cell components (BCC) with plasma removed. Samples were frozen using four representative freezing procedures (snap freezing in liquid nitrogen, snap freezing at -80°C, traditional slow freezing, and programmable controlled rate freezing) and rewarmed by placing at 4°C or by vortexing. RNA was extracted using the phenol-chloroform RNA extraction method and measured by an Agilent bioanalyzer. Then, human blood was used to verify the best protocol obtained from the rabbit blood experiment. Results: For the four freezing procedures, there were no differences in RNA integrity. For different rewarming methods, RNA integrity number (RIN) values of RNA extracted from frozen WB and BCC samples in the vortex group were above 9, while RNA obtained from WB showed worse quality compared with BCC in the 4°C group. For verification using human blood, RIN values of frozen human WB rewarmed by vortexing ranged from 8.0 to 9.1. Conclusions: Blood components and rewarming methods could affect the RNA quality of blood samples. For scenarios where WB samples have already been cryopreserved, the vortex rewarming method is optimal for high-quality RNA. Otherwise, we would recommend centrifuging fresh WB and cryopreserving it in the form of BCC, which showed a tendency to obtain high-quality RNA by either of the two rewarming methods.