TLR-9-/- mice are more susceptible to viral exacerbation of fibrosis. (A) Balb/c and TLR-9-/- mice were treated with either saline or bleomycin intratracheally on day 0. They were then given either sham infection or infection with 5 × 104 PFU of γHV68 on day 14 by intranasal infection. On day 21, lungs were harvested and Sircol assay was performed. TLR-9-/- mice were more susceptible than wild-type mice to viral exacerbation of existing fibrosis (705.4 ± 52.79 versus 468.6 ± 42 mg collagen/ml; n = 5; P < 0.01). There were no significant differences in collagen levels between Balb/c and TLR-9-/- saline-treated mice (255 ± 9.06 versus 227.3 ± 14.95 mg/ml) or between both groups after bleomycin challenge alone (317.0 ± 43.0 versus 362.5 ± 78.8 mg/ml.) This was true in three experiments, and the relative increase in collagen production in bleomycin-treated mice over saline controls was also not different. (B) Lungs from WT or TLR-9-/- mice treated with bleomcyin on day 0 and infected with γHV68 on day 14. Lungs were harvested for histologic analysis on day 21 and stained with hematoxylin and eosin. Sections are representative of three mice examined.