The Effects of IL10 and NK Cells on the Susceptibility to Mouse Cytomegalovirus in BALB/c Mice despite the Compensation of IFNγ

Docosahexaenoic acid supplementation represses the early immune response against murine cytomegalovirus but enhances NK cell effector function

BACKGROUND

Docosahexaenoic acid (DHA) supplementation is beneficial for several chronic diseases; however, its effect on immune regulation is still debated. Given the prevalence of cytomegalovirus (CMV) infection and because natural killer (NK) cells are a component of innate immunity critical for controlling CMV infection, the current study explored the effect of a DHA-enriched diet on susceptibility to murine (M) CMV infection and the NK cell effector response to MCMV infection.

RESULTS

Male C57BL/6 mice fed a control or DHA-enriched diet for 3 weeks were infected with MCMV and sacrificed at the indicated time points postinfection. Compared with control mice, DHA-fed mice had higher liver and spleen viral loads at day 7 postinfection, but final MCMV clearance was not affected. The total numbers of NK cells and their terminal mature cell subset (KLRG1⁺ and Ly49H⁺ NK cells) were reduced compared with those in control mice at day 7 postinfection but not day 21. DHA feeding resulted in higher IFN-γ and granzyme B expression in splenic NK cells at day 7 postinfection. A mechanistic analysis showed that the splenic NK cells of DHA-fed mice had enhanced glucose uptake, increased CD71 and CD98 expression, and higher mitochondrial mass than control mice. In addition, DHA-fed mice showed reductions in the total numbers and activation levels of CD4⁺ and CD8⁺ T cells.

CONCLUSIONS

These results suggest that DHA supplementation represses the early response to CMV infection but preserves NK cell effector functions by improving mitochondrial activity, which may play critical roles in subsequent MCMV clearance.

Short-lived AIM2 Inflammasome Activation Relates to Chronic MCMV Infection in BALB/c Mice

Absent in melanoma 2 (AIM2) inflammasome is a crucial link bridging the innate host defense and the subsequent adaptive immunity when activated by exogenous double stranded DNA (dsDNA). Through establishing models of disseminated murine cytomegalovirus (MCMV) infection in BALB/c and C57BL/6 mice, we evaluated dynamic expression of AIM2 inflammasome components and its relationship with pathological damage and viral replication, trying to figure out whether AIM2 inflammasome is related to the chronic mechanism of MCMV. BALB/c and C57BL/6 mice were sacrificed on day 0, 1, 3, 7, 14 and 28 post infection. Expression levels of AIM2, pro-caspase-1, caspase-1 p20, pro-IL1β and mature IL1β in primary peritoneal macrophages (PMs) and spleens were detected by Western blotting. Contents of IL18 in the serum were detected by ELISA. Pathological examinations of livers were performed, and mRNA levels of MCMV glycoprotein B (gB) in salivary glands also assessed. Results showed that expression levels of AIM2 in PMs and spleens of C57BL/6 mice increased on day 3, even continued to day 28; caspase-1 p20 and mature IL1β increased on day 7, 14 and 28; the persistently high expression of IL18 in the serum started on day 1, showing a double peak curve. As for BALB/c mice, expression of AIM2 in PMs increased on day 1 and day 7, while contents of AIM2 in spleens increased on day 1 and day 3; caspase-1 p20 and mature IL1β merely increased 7 days fter infection. Thereafter, expression levels of AIM2, caspase-1 p20, mature IL1β and IL18 were limited; the duration of AIM2 inflammasome activation in BALB/c mice was much shorter than that in C57BL/6 mice. The severer pathological damage and more viral replications in BALB/c mice further proved the deficient antiviral immunity to MCMV. In conclusion, the activation of AIM2 inflammasome in BALB/c mice was short-lived, which is quite possibly related to the chronicity of MCMV infection.