MyD88-dependent influx of monocytes and neutrophils impairs lymph node B cell responses to chikungunya virus infection via Irf5, Nos2 and Nox2

McCarthy, Mary K.; Reynoso, Glennys V.; Winkler, Emma S.; Mack, Matthias; Diamond, Michael S.; Hickman, Heather D.; Morrison, Thomas E.

The upregulation of iNOS in monocytes in the dLN, but not in circulation, and the requirement for IFNAR1 and IRF5 in this induction suggested the presence of an IRF5-dependent type I IFN pathway acting locally in the dLN. To investigate this idea, we infected WT, Irf3 -/-Irf7 -/-, and Irf3 -/-Irf5 -/-Irf7 -/mice with pathogenic CHIKV. At 24 hpi, we measured the induction of interferon stimulated genes (ISGs) including Ccl2, Cxcl10, Ifng, Il6, Ifit1, and Rsad2 mRNA [44, 45] in the inoculated foot and in the dLN by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Each of these ISGs was upregulated in both the foot and dLN of CHIKV-infected WT mice at this timepoint (Fig 8A-8F) . However, upregulation was differentially dependent on IRF3/IRF7 or IRF5 in each tissue. In the inoculated foot, upregulation of all ISGs analyzed was dependent on IRF3/IRF7 (Fig 8A-8F) . However, in the dLN, the induction of Ccl2, Cxc10, Ifng, and Il6 mRNA was similar between WT and Irf3 -/-Irf7 -/mice (Fig 8A-D) , whereas Ifit1 and Rsad2 upregulation in the dLN were only partially dependent on the presence of IRF3/IRF7 (Fig 8E and 8F) . Instead, for each ISG, the combined deficiency of IRF3, IRF5, and IRF7 resulted in reduced upregulation in the dLN compared with WT or Irf3 -/-Irf7 -/mice (Fig 8A-8F) . Together, these data demonstrate that induction of multiple ISGs at the site of inoculation is dependent on IRF3/IRF7, whereas an IRF5-dependent ISG induction pathway is activated in the dLN.