Mechanisms of Immunomodulation By Probiotics: Influence of Lactobacilli On Innate and T Cell Immune Responses Induced By Rotavirus Infection and Vaccines

TR Number
Journal Title
Journal ISSN
Volume Title
Virginia Tech

My dissertation research focused on studying mechanisms of immunomodulation by probiotic lactobacilli on innate and T cell immune responses induced by rotavirus infection and vaccines in a gnotobiotic pig model of human rotavirus (HRV) infection and vaccination. We first studied the effects of probiotics on antigen-presenting cells (APCs) through TLR activation. We found that a mixture of Lactobacilli acidophilus strain NCFM (LA) and L. reuteri (ATCC# 23272) induced strong TLR2-expressing APC responses and virulent HRV induced a TLR3 response. Probiotics and HRV had an additive effect on TLR2- and TLR9-expressing APC responses, consistent with the adjuvant effect of lactobacilli.

Dose effects of LA on T cell immune responses were investigated. We found that low dose LA significantly enhanced frequencies of HRV-specific IFN-γ producing CD4⁺ and CD8+ T cells whereas high dose LA reduced frequencies of HRV-specific IFN-γ producing CD4+ T cells. Low dose LA reduced frequencies of induced regulatory (iTreg) cells and TGF-β expression in the iTreg cells whereas high dose LA increased frequencies of iTreg cells and IL-10 expression in the iTreg cells. The dose effects of LA were independent of HRV infection/vaccination.

In addition, we demonstrated that TCR-γδ T cells play an important role in modulating immune responses to rotavirus infections. All three γδ T cell subsets showed evidence of activation after HRV infection by increasing TLR2, TLR3, TLR9 expression and IFN-γ production during the acute phase of infection. There was an additive effect between lactobacilli and HRV in inducing total γδ T cell expansion in ileum and in recruiting the cells from blood. HRV infection induced a significant expansion of the CD2+CD8+ γδ T cell subset in the ileum. This subset mainly exerts regulatory functions as evident by expressing FoxP3, secreting TGF-β and IL-10 or increasing production of the anti-inflammatory cytokines by CD4+ and/or CD8+ αβ T cells in the co-cultures. CD2+CD8- and CD2-CD8- γδ T cell subsets have mainly pro-inflammatory and anti-viral functions as evident by secreting IFN-γ or promoting CD4+ αβ T cell proliferation and IFN-γ production.

This knowledge will facilitate the development of more effective vaccination and therapeutic strategies to protect children and young animals against rotavirus gastroenteritis.

rotaviruses, gd T cells, lactobacilli, innate and adaptive immunity, gnotobiotic pigs