An estimated 5.7 million or more bats died in North America between 2006 and 2012 due to infection with the fungus Pseudogymnoascus destructans (Pd) that causes white-nose syndrome (WNS) during hibernation. The behavioral and physiological changes associated with hibernation leave bats vulnerable to WNS, but the persistence of bats within the contaminated regions of North America suggests that survival might vary predictably among individuals or in relation to environmental conditions. To investigate variables influencing WNS mortality, we conducted a captive study of 147 little brown myotis (Myotis lucifugus) inoculated with 0, 500, 5 000, 50 000, or 500 000 Pd conidia and hibernated for five months at either 4 or 10°C. We found that female bats were significantly more likely to survive hibernation, as were bats hibernated at 4°C, and bats with greater body condition at the start of hibernation. Although all bats inoculated with Pd exhibited shorter torpor bouts compared to controls, a characteristic of WNS, only bats inoculated with 500 conidia had significantly lower survival odds compared to controls. These data show that host and environmental characteristics are significant predictors of WNS mortality, and that exposure to up to 500 conidia is sufficient to cause a fatal infection. These results also illustrate a need to quantify dynamics of Pd exposure in free-ranging bats, as dynamics of WNS produced in captive studies inoculating bats with several hundred thousand conidia may differ from those in the wild.

White-nose syndrome (WNS) is a fungal disease caused by Pseudogymnoascus destructans (Pd) that affects bats during hibernation. Although millions of bats have died from WNS in North America, mass mortality has not been observed among European bats infected by the fungus, leading to the suggestion that bats in Europe are immune. We tested the hypothesis that an antibody-mediated immune response can provide protection against WNS by quantifying antibodies reactive to Pd in blood samples from seven species of free-ranging bats in North America and two free-ranging species in Europe. We also quantified antibodies in blood samples from little brown myotis (Myotis lucifugus) that were part of a captive colony that we injected with live Pd spores mixed with adjuvant, as well as individuals surviving a captive Pd infection trial. Seroprevalence of antibodies against Pd, as well as antibody titers, was greater among little brown myotis than among four other species of cave-hibernating bats in North America, including species with markedly lower WNS mortality rates. Among little brown myotis, the greatest titers occurred in populations occupying regions with longer histories of WNS, where bats lacked secondary symptoms of WNS. We detected antibodies cross-reactive with Pd among little brown myotis naïve to the fungus. We observed high titers among captive little brown myotis injected with Pd. We did not detect antibodies against Pd in Pd-infected European bats during winter, and titers during the active season were lower than among little brown myotis. These results show that antibody-mediated immunity cannot explain survival of European bats infected with Pd and that little brown myotis respond differently to Pd than species with higher WNS survival rates. Although it appears that some species of bats in North America may be developing resistance to WNS, an antibody-mediated immune response does not provide an explanation for these remnant populations.

Farnesyltransferase inhibitors (FTIs) have been shown to modulate alloreactive immune responses in mouse models of transplantation (A.E. Gaylo, et al., Transplant Immunology 20 (2009) 163-170) and graft versus host disease (A.-K. Hechinger, et al. Haematoligica 98 (2013) 31-40). FTIs can block cytokine secretion from T cells and this activity may explain the drug’s immunomodulatory mechanism. FTIs could modulate immune responses by blocking T cell cytokine secretion thereby affecting the differentiation of stimulated CD4+ T cells into Th1, Th2, or other effector subtypes. To test this hypothesis, we have examined the ability of FTIs to affect cytokine secreation from various T cell subsets and T cell polarization in mice during an allorejection response. Using qPCR we quantified cytokine gene expression in graft-draining lymph nodes (GDLNs) isolated from mice during the rejection of an MHC class II-mismatched skin allograft (bm12 donors to B6 recipients). Using ELISpot assays, we also measured the number of alloreactive Th1 (IFN-γ producing) and Th2 (IL-4-producing) cells in GDLNs. In vitro T cell polarization of polyclonally-stimulated CD4+ T cells isolated from spleen was measured using IFN-γ, IL-4, IL-17, and FoxP3 intracellular staining. We found that FTI treatment differentially affects cytokine secretion from the CD4+ T cell subsets studied. These effects lead to differences in Th1/Th2 cell polarization that could explain the immunomodulatory activity of FTIs.