Abstract
Abstract: :
Purpose: C57BL/6 (B6) mice are genetically resistant to HSV-1 infection while 129S6 and related strains (DBA/2J, BALB/c, etc) are susceptible. To facilitate identification of the Herpes Resistance Locus (Hrl) that we recently localized on distal chromosome 6, we sought to determine whether resistance to HSV-1 is transferable by bone marrow transplantation (BMT). Methods: Mice on the C57BL/6 (B6) background genetically engineered to lack B, T and NK cell subsets (‘B6-empty’ mice, IL-7R-/-, Kitw41/w41) were used as recipients for bone marrow from resistant B6 or susceptible 129S6 mice. BMT recipients were non-irradiated or lethally irradiated to ablate endogenous innate immune cells prior to infusion of B6 or 129 donor bone marrow by iv injection into the tail vein. Blood collected by retro-orbital bleeding 6 weeks after BMT was analyzed by flow cytometry for B and T cells to verify marrow engraftment. At ~10 weeks after BMT, groups of 5-7 mice were inoculated on the right cornea with 3200 PFU of HSV-1 strain 17+, which corresponds to a 10xLD50 dose for 129S6 mice, and mortality, virus shedding and necropsy titers were monitored. Additionally, MRI was done on live HSV infected B6 and 129S6 mice on day 6 PI. Results: All mice transplanted with B6 bone marrow survived. In contrast, recipients of 129 bm began dying on day 9 PI with maximal mortality of 42% being attained by day 15 PI. Remarkably, all control (no BMT) mice were alive on day 15 PI, and eventually all but one died by day 35 PI, the end of the experiment. Irradiation of recipients had no effect on outcome for B6 BMT mice, although a marginal increase in time to death was evident for 129 BMT mice. Shedding of HSV into the tear film on days 3 through 13 did not vary significantly among the mouse groups. MRI of live HSV-1 infected mice on day 6 PI revealed a discrete inflammatory lesion localized to the trigeminal nerve entry root zone on the infected side of the brainstem in susceptible 129, but not resistant B6 mice. Conclusions: Resistance or susceptibility to HSV can be transferred by BMT using B6 or 129S6 bone marrow, respectively. Mortality in 129 BMT mice was accelerated relative to control non-BMT mice, which suggests an immunopathological process is involved. This conclusion is supported by results from MRI studies of HSV-1 infected B6 and 129 mice. It is anticipated that results from ongoing MRI studies of live HSV infected B6-empty mice transplanted with B6 or 129 bone marrow will confirm that immune responses to HSV-1 in 129 mice result in immunopathology.
Keywords: herpes simplex virus • inflammation • animal model