Studying the effect of double-stranded RNA upon activity of mouse splenocytes using flow cytometry

Ribonucleic acids (RNA), in particular, double-stranded RNAs, due to their ability to modulate innate immune responses, are of undoubted interest in view of their usage as vaccine adjuvants. However, despite the fact that dsRNA preparations have been known for a long time, the issues of cellular interactions and orientation of immune response upon their exposure have not yet been properly studied. The aim of this work was to evaluate the in vitro response of mouse splenocytes to dsRNA exposure in cell cultures, and after drug administration in vivo. The studies were carried out in female Balb/c mice. Activation status of various splenocyte populations after treatment with yeast dsRNA and reference substance (PolyI:PolyC) was assessed by means of flow cytometry by expression of CD69 and CD86 activation markers on CD19+B lymphocytes and CD11c+ dendritic cells (DC). During in vitro studies, the splenocytes were incubated in DMEM medium containing 10% fetal calf serum for 22 hours following addition of the yeast dsRNA preparations, or PolyI:PolyC (2.5 μg/mL) preparation. Single-stranded high-polymer RNA (hpRNA), which is a component of the substance, was used as an additional control at the dose of 16 μg/mL. Our study has shown that the activating effect of dsRNA and PolyI:PolyC on expression of CD86 and CD69 markers upon the cells of the entire pool of splenocytes, B lymphocytes and DC. Highly polymeric RNA increased the total number of CD86+ cells in the population without changing the expression level of these markers upon B lymphocytes and DCs. When performing the in vivo studies, yeast dsRNA substance was administered intravenously into mice at a dose of 2.5 mg/kg, and hpRNA was used at a dose of 16 mg/kg. The number of CD69+ and CD86+ splenocytes was assessed 4 hours after drug administration. The highest stimulating effect of dsRNA was registered with CD69 expression marker: significantly increased numbers of CD69+ cells were registered for B lymphocytes and the entire cell population. The stimulation of CD86 co-receptor expression on B lymphocytes was less pronounced, but statistically significant. The ability of single-stranded and double-stranded RNAs to cause significant increase in CD86+ cell numbers was demonstrated among dendritic cell population. The results of the study made it possible to evaluate the effect of dsRNA on the immune cell function, with respect of their interaction, maturation, and migration. This approach may be useful for developing optimal strategies for selection and screening of new nucleic acid-based adjuvants.

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