Relationships between immune gene expression and circulating cytokine levels in wild house mice

Abstract

Quantitative PCR (qPCR) has been commonly used to measure gene expression ina number of research contexts, but the measured RNA concentrations do not al-ways represent the concentrations of active proteins which they encode. This canbe due to transcriptional regulation or post-translational modifications, or localiza-tion of immune environments, as can occur during infection. However, in studiesusing free-living non-model species, such as in ecoimmunological research, qPCRmay be the only available option to measure a parameter of interest, and so under-standing the quantitative link between gene expression and associated effectorprotein levels is vital. Here, we use qPCR to measure concentrations of RNA from mesenteric lymphnode (MLN) and spleen tissue, and multiplex ELISA of blood serum to measurecirculating cytokine concentrations in a wild population of a model species, Musmusculus domesticus. Few significant correlations were found between gene expression levels and cir-culating cytokines of the same immune genes or proteins, or related functionalgroups. Where significant correlations were observed, these were most fre-quently within the measured tissue (i.e., the expression levels of genes measuredfrom spleen tissue were more likely to correlate with each other rather than withgenes measured from MLN tissue, or with cytokine concentrations measuredfrom blood). Potential reasons for discrepancies between measures including differences indecay rates and transcriptional regulation networks are discussed. We highlightthe relative usefulness of different measures under different research questionsand consider what might be inferred from immune assays.