Latent cytomegalovirus infection predisposes immune competent hosts to pro-inflammatory pulmonary immune responses
Varun Dwivedi, The Ohio State University; Joanne Trgovcich, The Ohio State University; Sara Mansfield, The Ohio State University; Sara Byrd, The Ohio State University; Charles Cook, The Ohio State University, Harvard University
Cytomegalovirus (CMV) is a ubiquitous virus infecting most human and developing persistent latent infections. CMV is an accepted life threating pathogen in immune suppressed patients that is increasingly being recognized as a potential pathogen in critically ill immune competent patients. We have observed the occurrence of CMV reactivation in the lungs of ~33% of immune competent patients during critical illness, associated with roughly doubled durations of mechanical ventilation.Hypothesis:
We previously have shown that bacterial sepsis can cause CMV reactivation in immuno-competent hosts. We hypothesized that latent CMV infection alters the cellular composition and immune function of cells in the lungs in a manner that worsens lung injury during sepsis.
BALB/c mice were infected with 1×106 PFU of Smith strain murine CMV and isolated lung mononuclear cells (LMNC) were characterized by flow cytometry, and also stimulated in-vitro with LPS to model their in-vivo septic response. In a separate experiment, naïve and latent CMV mice underwent cecal ligation and puncture (CLP) to induce sepsis in-vivo. Mice were evaluated by flow cytometry at 24, 48 and 72 hrs post CLP for immune cell composition.Results:
We found that unstimulated LMNC from CMV latent mice excrete more TNF-α and IL-6 than naïve mice, and latent LMNC also respond more vigorously to LPS and Con-A than naïve LMNC. This was associated with significant increases in the LMNC frequency of CD4+,CD8+ T cells and Gr1+ cells compared to naïve mice. Cells resembling myeloid derived suppressor cells (MDSC, Gr1+ CD11b+) were unchanged during acute infection, but were significantly increased during latency. Intracellular flow cytometry showed that Gr1+ cells were major TNF-α producers. Further,using our murine sepsis model we found that CMV latent mice had higher cellular accumulation of CD14+ and CD11b+cells in lungs compared to naïve mice at 24 hrs post CLP. However, at later time points 48, 72 hrs post CLP, both naïve and latent mice showed similar cellular infiltration in lungs.Conclusions:
Our findings suggest that CMV infection dramatically alters the lung immune environment. During latency there is a persistent pro-inflammatory lung immune environment as evident by elevated TNF-α and IL-6 levels. In-vitro this TNF-α responsiveness is associated with GR1+ cells. In-vivo, CMV latent mice show an early more aggressive recruitment of CD14+ and CD11b+ cells during bacterial sepsis that may contribute to immune-mediated pathology.