[Show abstract][Hide abstract] ABSTRACT: Activation of Natural Killer-like T cells (NKT) with the CD1d ligand α-GC leads to enhanced production of anthrax toxin protective Ag (PA)-neutralizing Abs, yet the underlying mechanism for this adjuvant effect is not known. In the current study we examined the role of Th1 and Th2 type responses in NKT-mediated enhancement of antibody responses to PA. First, the contribution of IL-4 and IFNγ to the production of PA-specific toxin-neutralizing Abs was examined. By immunizing C57Bl/6 controls IL-4(-/-) mice and IFNγ(-/-) mice and performing passive serum transfer experiments, it was observed that sera containing PA-specific IgG1, IgG2b and IgG2c neutralized toxin in vitro and conferred protection in vivo. Sera containing IgG2b and IgG2c neutralized toxin in vitro but were not sufficient for protection in vivo. Sera containing IgG1 and IgG2b neutralized toxin in vitro and conferred protection in vivo. IgG1 therefore emerged as a good correlate of protection. Next, C57Bl/6 mice were immunized with PA alone or PA plus a Th2-skewing α-GC derivative known as OCH. Neutralizing PA-specific IgG1 responses were modestly enhanced by OCH in C57Bl/6 mice. Conversely, IgG2b and IgG2c were considerably enhanced in PA/OCH-immunized IL-4(-/-) mice but did not confer protection. Finally, bone marrow chimeras were generated such that NKT cells were unable to express IL-4 or IFNγ. NKT-derived IL-4 was required for OCH-enhanced primary IgG1 responses but not recall responses. NKT-derived IL-4 and IFNγ also influenced primary and recall IgG2b and IgG2c titers. These data suggest targeted skewing of the Th2 response by α-GC derivatives can be exploited to optimize anthrax vaccination.
[Show abstract][Hide abstract] ABSTRACT: The current Bacillus anthracis vaccine consists largely of protective antigen (PA), the protein of anthrax toxin that mediates entry of edema factor (EF)
or lethal factor (LF) into cells. PA induces protective antibody (Ab)-mediated immunity against Bacillus anthracis but has limited efficacy and duration. We previously demonstrated that activation of CD1d-restricted natural killer-like
T cells (NKT) with a CD1d-binding glycolipid led to enhanced Ab titers specific for foreign antigen (Ag). We therefore tested
the hypothesis that activation of NKT cells with the CD1d ligand (α-galactosylceramide [α-GC]) at the time of immunization
improves PA-specific Ab responses. We observed that α-GC enhanced PA-specific Ab titers in C57BL/6 mice. In CD1d−/− mice deficient in type I and type II NKT cells the anti-PA Ab response was diminished. In Jα281−/− mice expressing CD1d but lacking type I α-GC-reactive NKT cells, α-GC did not enhance the Ab response. In vitro neutralization assays were performed and showed that the Ab titers correlated with protection of macrophages against anthrax
lethal toxin (LT). The neutralization capacity of the Ab was further tested in lethal challenge studies, which revealed that
NKT activation leads to enhanced in vivo protection against LT. Anti-PA Ab titers, neutralization, and protection were then measured over a period of several months,
and this revealed that NKT activation leads to a sustained protective Ab response. These results suggest that NKT-activating
CD1d ligands could be exploited for the development of improved vaccines for Bacillus anthracis that increase not only neutralizing Ab titers but also the duration of the protection afforded by Ab.
Full-text · Article · Apr 2010 · Infection and immunity
[Show abstract][Hide abstract] ABSTRACT: Exogenous CD1d-binding glycolipid (alpha-Galactosylceramide, alpha-GC) stimulates TCR signaling and activation of type-1 natural killer-like T (NKT) cells. Activated NKT cells play a central role in the regulation of adaptive and protective immune responses against pathogens and tumors. In the present study, we tested the effect of Bacillus anthracis lethal toxin (LT) on NKT cells both in vivo and in vitro. LT is a binary toxin known to suppress host immune responses during anthrax disease and intoxicates cells by protective antigen (PA)-mediated intracellular delivery of lethal factor (LF), a potent metalloprotease. We observed that NKT cells expressed anthrax toxin receptors (CMG-2 and TEM-8) and bound more PA than other immune cell types. A sub-lethal dose of LT administered in vivo in C57BL/6 mice decreased expression of the activation receptor NKG2D by NKT cells but not by NK cells. The in vivo administration of LT led to decreased TCR-induced cytokine secretion but did not affect TCR expression. Further analysis revealed LT-dependent inhibition of TCR-stimulated MAP kinase signaling in NKT cells attributable to LT cleavage of the MAP kinase kinase MEK-2. We propose that Bacillus anthracis-derived LT causes a novel form of functional anergy in NKT cells and therefore has potential for contributing to immune evasion by the pathogen.