The whole blood is composed of different types of white cells with distinct roles which express different kinds of transcripts . It is thus likely that a modification in blood cell composition may influence the gene expression level without having cells actually express transcripts differently. As blood cell composition was found to vary over time after LPS injection, we used the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\frac {\text {Lymphocyte}}{\text {Granulocyte}}$\end{document}LymphocyteGranulocyte (L/G) ratio as a covariate in our analyses.