Gene expression in IFN-gamma-activated murine macrophages

Macrophages are critical for natural immunity and play a central role in specific acquired immunity. The IFN-gamma activation of macrophages derived from A/J or BALB/c mice yielded two different patterns of antiviral state in murine hepatitis virus 3 infection, which were related to a down-regulation of the main virus receptor. Using cDNA hybridization to evaluate mRNA accumulation in the cells, we were able to identify several genes that are differently up- or down-regulated by IFN-gamma in A/J (267 and 266 genes, respectively, up- and down-regulated) or BALB/c (297 and 58 genes, respectively, up- and down-regulated) mouse macrophages. Macrophages from mice with different genetic backgrounds behave differently at the molecular level and comparison of the patterns of non-activated and IFN-gamma-activated A/J or BALB/c mouse macrophages revealed, for instance, an up-regulation and a down-regulation of genes coding for biological functions such as enzymatic reactions, nucleic acid synthesis and transport, protein synthesis, transport and metabolism, cytoskeleton arrangement and extracellular matrix, phagocytosis, resistance and susceptibility to infection and tumors, inflammation, and cell differentiation or activation. The present data are reported in order to facilitate future correlation of proteomic/transcriptomic findings as well as of results obtained from a classical approach for the understanding of biological phenomena. The possible implication of the role of some of the gene products relevant to macrophage biology can now be further scrutinized. In this respect, a down-regulation of the main murine hepatitis virus 3 receptor gene was detected only in IFN-gamma-activated macrophages of resistant mice.

Reduction of the accumulation of viral mRNA and of cellular rRNA synthesis in MHV3-infected macrophages of resistant mice

1. After MHV3 infection, only macrophages from resistant A/J mice partially restricted virus growth compared to those from susceptible BALB/c mice (2 logs of difference in virus titer). 2. Cellular ribosomal ribonucleic acid (rRNA) synthesis by MHV3-infected macrophages was decreased only in A/J mouse macrophages as indicated by accumulation of the 28S rRNA fraction. 3. The accumulation of viral messenger ribonucleic acids (mRNAs) in MHV3-infected macrophages was also reduced in A/J mouse macrophages compared to BALB/c mice. 4. In pulse-chase experiments of viral protein synthesis, the appearance, glycosylation and cleavage of glycoprotein S, as well as the metabolism of nucleoprotein N were delayed in A/J mouse macrophages. 5. These data show that MHV3 infection of A/J mouse macrophages induced an imbalanced accumulation of the 28S fraction of rRNA. Furthermore the synthesis of mRNAs correlated with viral protein synthesis in both A/J and BALB/c macrophages, but was delayed in A/J mice. 6. These results suggest that the partial restriction of MHV3 replication in macrophages of resistant A/J mice may take place during or before the mRNA synthesis, although it is correlated with the appearance, glycosylation, cleavage and metabolism of viral proteins