Altered IL-1β and IL-2 mRNA Expression in Murine Splenic Cells After Concomitant Stimulation by Semliki Forest Virus and Lipopolysaccharide

Co-infection with virus and bacteria happens frequently and often results in an exacerbated clinical course of the disease, possibly due to mechanisms including altered cytokine production. In the present study, the authors investigated the combined effects of avirulent Semliki Forest virus (SFV-A7) and bacterial lipopolysaccharide (LPS) on the interleukin-1β (IL-1β) and IL-2 gene expression in murine splenic cells. The authors found that 10 ng/ml of LPS in the culture medium induced expression of IL-1β but not IL-2, while infection with SFV-A7 did not induce either of these two cytokines. However, when SFV-A7 and LPS were applied together, a synergistic increase of both IL-1β and IL-2 was observed. Further experiments showed that addition of SFV-A7 3 h before LPS enhanced, whereas addition of the virus 3 h after the LPS inhibited, IL-1β gene expression. These results indicate that an interaction of virus and Gram-negative bacteria can result in an altered cytokine gene expression.