Mucosal surfaces act as functional barriers against the perpetual bombardment of foreign antigens and pathogens to the body. This barrier is maintained by homeostatic interactions between the microbiome and cells of the innate and adaptive immune system, interactions that mucosal vaccines can exploit to yield both mucosal and systemic amnestic responses to foreign antigen. The commensal lactic acid Lactobacillus spp. represent one constituent of this microbiome that has been utilized as both a homeostatic promoting probiotic and as a vaccine vector. The immune modulatory capacity of Lactobacillus spp. has been demonstrated in proof-of-principle studies utilizing lactobacilli-based vaccine vectors against several pathogens. Our laboratory has focused on the development of Lactobacillus gasseri and Lactobacillus acidophilus NCFM (NCFM) as mucosal vaccine vectors for human immunodeficiency virus-1 (HIV-1), a mucosal pathogen affecting more than 35 million people worldwide and for which no current licensed vaccine exists. As activation of innate immune receptors, including toll-like receptor (TLR), NOD-like receptor (NLR), and C-type lectin receptor (CLR), by lactobacilli have been shown to be species and strain specific, characterizing the innate receptors specific to our vectors is important for rationale vaccine design.
We first demonstrate that in addition to the previously characterized TLR2/6 activating capacity of lactobacilli, L. gasseri and NCFM activate intracellular NOD2 receptor. Co-culture of murine macrophages with L.gasseri, NCFM, or NCFM-derived mutants NCK2025 and NCK2031 elicited an M2b-like phenotype, a phenotype associated with TH2 skewing and immune regulatory function. For NCFM, this M2b phenotype was dependent on expression of lipoteichoic acid and S layer proteins, as demonstrated by the use of respective mutants, NCK2025 and NCK2031. Through the use of macrophage genetic knockouts, we identified TLR2, NOD2, and inflammasome associated caspase 1 as contributors to macrophage activation to varying degrees, with NOD2 cooperating with caspase 1 for inflammasome derived IL-1β in a pyroptosis-independent fashion. Finally, utilizing an NCFM-based mucosal vaccine with surface expression of HIV-1 Gag, we show that NOD2 signaling and the presence of an intact microbiome is required for HIV-specific IgG. We show that lactobacilli differentially utilize innate immune pathways and highlight NOD2 as a key mediator of macrophage function and antigen-specific humoral responses to a NCFM-based mucosal vaccine vector.
|Advisor:||Dean, Gregg A.|
|School:||North Carolina State University|
|School Location:||United States -- North Carolina|
|Source:||DAI-B 77/10(E), Dissertation Abstracts International|
|Subjects:||Microbiology, Virology, Immunology|
|Keywords:||Inflammasomes, Innate immunity, Lactobacillus, Mucosal vaccine|
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