Investigation of MCMV-induced suppression of TNF production in vitro and in vivo

Abstract

The murine cytomegalovirus (MCMV) immediate early 1 (IE1) protein has been described as a trans-activator of viral and host gene expression. However, the precise role that IE1 plays in the viral life cycle, and in particular its effect on the host immune response is not known. This thesis investigates the functional relationship of the IE1 protein and the immune response induced after infection. By using an ie1-deletion mutant MCMV (MCMVdie1) it was demonstrated that, early after infection, tumor necrosis factor (tnf ) gene activation and protein production was significantly induced in infected-primary macrophages (M ) to a much greater extent than its wild type counterpart. In addition, preliminary studies on the signalling pathways activated upon infection were carried out in order to gain information about the pathways that might be involved in MCMVinduced modulation of tnf activation. Initial observations on the MAPK family members Erk1/2, p38 and JNK did not revealed any differential activation in the absence of IE1. However, due to a number of limitations, it was not possible to draw any firm conclusions from this study. Investigation of the role of IE1 in the in vivo production of TNF were also performed in both susceptible (BALB/c) and resistant (C57Bl/6) mice. These experiments confirmed the attenuated phenotype of MCMVdie1 in vivo, whereby the mutant strain grew to much lower titers than wild type. When cytokine production was assessed in relation to PFU levels a significant production of TNF after infection is observed in different organs of both mice strains. This raises the question whether IE1 contributes to MCMV modulation of TNF production in the natural host. Although, because it is still unclear whether the phenotype of MCMVdie1 in vivo is due to a defect in the virus or the result of a immune response, it was not possible to conclude unequivocally that IE1 is responsible for dampening this cytokine response. This thesis also tested whether the attenuated replication of MCMVdie1 in vivo was due to the increased TNF production induced after infection. An initial investigation in tnf depleted mice revealed that the MCMVdie1 growth phenotype is not due to TNF response. Overall, this study has provided insight into a potential immune modulatory function by MCMV associated with IE1 protein and the regulation of TNF in vivo and in vitro.