MyD88-dependent changes in the pulmonary transcriptome after infection with Chlamydia pneumoniae Running title: MyD88 influences gene expression in Chlamydia-infected mice

MyD88-dependent changes in the pulmonary transcriptome after infection with Chlamydia pneumoniae Running title: MyD88 influences gene expression in Chlamydia-infected mice Abstract Chlamydia pneumoniae, an intracellular bacterium, causes pneumonia in humans and mice. Toll-like receptors and the key adaptor molecule MyD88 play a critical role in inducing immunity against this microorganism and are crucial for survival. To explore the influence of MyD88 on induction of immune responses in vivo on a genome wide level, WT or MyD88-/-mice were infected with C. pneumoniae upon anesthesia and the pulmonary transcriptome was analyzed three days later by microarrays. We found that the infection caused pulmonary cellular infiltration in WT but not in MyD88-/-mice. Furthermore, it induced the transcription of 360 genes and repressed 18 genes in WT mice. Of these, 221 genes were not or weakly induced in lungs of MyD88-/-mice. This cluster contains primarily genes encoding for chemokines and cytokines like MIP-1, MIP-2, MIP-1, MCP-1, TNF and KC, and other immune effector molecules like immunoresponsive gene 1 and TLR2. Arginase was highly induced after C. pneumoniae infection and was MyD88 dependent. Genes induced by interferons were abundant in a cluster of 102 genes which were only partially MyD88-dependent. Also, lcn2 (lipocalin-2) and timp1 were represented within this cluster. Interestingly, a set of 37 genes including sprr1a were induced more strongly in MyD88-/-mice and most of them are involved in the regulation of cellular replication. In summary, ex vivo analysis of the pulmonary transcriptome upon infection with C. pneumoniae demonstrated a major impact of MyD88 on inflammatory responses but not on interferon-type responses, and identified MyD88-independent genes involved in cellular replication.