Can probiotics enhance vaccine-specific immunity in children and adults?

The growing use of probiotics by the general public has heightened the interest in understanding the role of probiotics in promoting health and preventing disease. General practitioners and specialists often receive inquiries from their patients regarding probiotic products and their use to ward off systemic infection or intestinal maladies. Enhanced immune function is among the touted health benefits conferred by probiotics but has not yet been fully established. Results from recent clinical trials in adults suggest a potential role for probiotics in enhancing vaccine-specific immunity. Although almost all vaccinations are given during infancy and childhood, the numbers of and results from studies using probiotics in pediatric subjects are limited. This review evaluates recent clinical trials of probiotics used to enhance vaccine-specific immune responses in adults and infants. We highlight meaningful results and the implications of these findings for designing translational and clinical studies that will evaluate the potential clinical role for probiotics. We conclude that the touted health claims of probiotics for use in children to augment immunity warrant further investigation. In order to achieve this goal, a consensus should be reached on common study designs that apply similar treatment timelines, compare well-characterised probiotic strains and monitor effective responses against different classes of vaccines.

Gastrointestinal Microbiome Dysbiosis in Infant Mice Alters Peripheral CD8+ T Cell Receptor Signaling

We recently reported that maternal antibiotic treatment (MAT) of mice in the last days of pregnancy and during lactation dramatically alters the density and composition of the gastrointestinal microbiota of their infants. MAT infants also exhibited enhanced susceptibility to a systemic viral infection and altered adaptive immune cell activation phenotype and function. CD8⁺ effector T cells from MAT infants consistently demonstrate an inability to sustain interferon gamma (IFN-γ) production in vivo following vaccinia virus infection and in vitro upon T cell receptor (TCR) stimulation. We hypothesize that T cells developing in infant mice with gastrointestinal microbiota dysbiosis and insufficient toll-like receptor (TLR) exposure alters immune responsiveness associated with intrinsic T cell defects in the TCR signaling pathway and compromised T cell effector function. To evaluate this, splenic T cells from day of life 15 MAT infant mice were stimulated in vitro with anti-CD3 and anti-CD28 antibodies prior to examining the expression of ZAP-70, phosphorylated ZAP-70, phospho-Erk-1/2, c-Rel, total protein tyrosine phosphorylation, and IFN-γ production. We determine that MAT infant CD8⁺ T cells fail to sustain total protein tyrosine phosphorylation and Erk1/2 activation. Lipopolysaccharide treatment in vitro and in vivo, partially restored IFN-γ production in MAT effector CD8⁺ T cells and reduced mortality typically observed in MAT mice following systemic viral infection. Our results demonstrate a surprising dependence on the gastrointestinal microbiome and TLR ligand stimulation toward shaping optimal CD8⁺ T cell function during infancy.

Maternal Antibiotic Treatment Impacts Development of the Neonatal Intestinal Microbiome and Antiviral Immunity

Microbial colonization of the infant gastrointestinal tract (GIT) begins at birth, is shaped by the maternal microbiota, and is profoundly altered by antibiotic treatment. Antibiotic treatment of mothers during pregnancy influences colonization of the GIT microbiota of their infants. The role of the GIT microbiota in regulating adaptive immune function against systemic viral infections during infancy remains undefined. We used a mouse model of perinatal antibiotic exposure to examine the effect of GIT microbial dysbiosis on infant CD8(+) T cell-mediated antiviral immunity. Maternal antibiotic treatment/treated (MAT) during pregnancy and lactation resulted in profound alterations in the composition of the GIT microbiota in mothers and infants. Streptococcus spp. dominated the GIT microbiota of MAT mothers, whereas Enterococcus faecalis predominated within the MAT infant GIT. MAT infant mice subsequently exhibited increased and accelerated mortality following vaccinia virus infection. Ag-specific IFN-γ-producing CD8(+) T cells were reduced in sublethally infected MAT infant mice. MAT CD8(+) T cells from uninfected infant mice also demonstrated a reduced capacity to sustain IFN-γ production following in vitro activation. We additionally determined that control infant mice became more susceptible to infection if they were born in an animal facility using stricter standards of hygiene. These data indicate that undisturbed colonization and progression of the GIT microbiota during infancy are necessary to promote robust adaptive antiviral immune responses.

Polymerase chain reaction test for Clostridium difficile toxin B gene reveals similar prevalence rates in children with and without inflammatory bowel disease

OBJECTIVE

Clinicians often evaluate for Clostridium difficile infection (CDI) in patients with inflammatory bowel disease (IBD) presenting with exacerbations. A highly sensitive polymerase chain reaction (PCR) test for the toxin B gene of C difficile is increasingly used to diagnose CDI. The aim of this study was to determine the prevalence of positive C difficile PCR results in children and young adults with and without active IBD compared with patients with non-IBD gastrointestinal disease.

METHODS

Fecal samples were obtained from patients with ulcerative colitis (UC, n = 76) or Crohn disease (CD, n = 69) and 51 controls followed in our gastroenterology program. Samples were analyzed for C difficile using a PCR test for the C difficile toxin B gene (BD GeneOhm Cdiff assay). Proportions of positive tests in each group were compared using the Pearson χ2 test.

RESULTS

The prevalence of positive PCR results was 11.6% in patients with CD, 18.4% in patients with UC, and 11.8% in controls (P = 0.25). There were no significant differences in the prevalence of positive C difficile results among patients with IBD with and without active disease or among patients with and without diarrhea.

CONCLUSIONS

Positive C difficile PCR results occur with similar frequency in patients with IBD with and without active disease and in patients with other gastrointestinal diseases. A positive result in a highly sensitive PCR assay that detects low copy numbers of a toxin gene in C difficile may reflect colonization in a subset of patients with IBD, confounding clinical decision making in managing disease exacerbations.

Eosinophils in the gastrointestinal tract

Although we know that eosinophils reside in the normal gastrointestinal tract and increase during inflammatory states, their exact role in gut homeostasis and in the pathogenesis of inflammatory processes is not certain. An increasing number of clinical reports suggest that eosinophils participate in the pathogenesis of mucosal inflammation, and emerging literature is beginning to define these mechanisms. For example, homing of eosinophils to the gastrointestinal tract is better understood with respect to the roles of specific eosinophilic attractants, such as the eotaxins and interleukin-5. As mechanisms of eosinophil recruitment, activation, and functional responses are further elucidated, novel targets for treatment strategies in specific diseases will likely follow. We review recent developments in eosinophil immunobiology as they relate to gastrointestinal inflammation and provide an update on clinical aspects of eosinophilic esophagitis as they relate to eosoinophilic diseases of the gastrointestinal tract.