Evaluation of toxicity and adjuvant effects of peptidoglycan microspheres orally administered to mice

Peptidoglycan-based immunomodulation

Peptidoglycan (PGN) is a unique component in the cytoderm of prokaryotes which can be recognized by different pathogen-associated molecular patterns (PAMPs) in eukaryotes, followed by a cascade of immune responses via different pathways. This review outlined the basic structure of PGN, its immunologic functions. The immunomodulation pathways mediated by PGN were elaborated. PGN induces specific immunity through stimulating different cytokine release and Th1/Th2-dominated immune responses during humoral/cellular immune response. The nonspecific immunity activation by PGN involves immunomodulation by different pattern recognition receptors (PRRs) including PGN recognition proteins (PGRPs), nucleotide oligomerization domain (NOD)-like receptors (NLRs), Toll-like receptors (TLRs), and C-type lectin receptors (CLRs). The sources and classification of PGRPs were summarized. In view of the stimulating activities of PGN and its monomers, the potential application of PGN as vaccine or adjuvant was prospected. This review provides systematic information on PGN functionalities from the point of immunoregulation, which might be useful in the deep exploitation of PGN.Key points. The immunological functions of PGN were illustrated. Cellular and humoral immunomodulation by PGN were outlined. The use of PGN as vaccine or adjuvant was prospected.

Uptake, recognition and responses to peptidoglycan in the mammalian host

Microbiota, and the plethora of signalling molecules that they generate, are a major driving force that underlies a striking range of inter-individual physioanatomic and behavioural consequences for the host organism. Among the bacterial effectors, one finds peptidoglycan, the major constituent of the bacterial cell surface. In the steady-state, fragments of peptidoglycan are constitutively liberated from bacterial members of the gut microbiota, cross the gut epithelial barrier and enter the host system. The fate of these peptidoglycan fragments, and the outcome for the host, depends on the molecular nature of the peptidoglycan, as well the cellular profile of the recipient tissue, mechanism of cell entry, the expression of specific processing and recognition mechanisms by the cell, and the local immune context. At the target level, physiological processes modulated by peptidoglycan are extremely diverse, ranging from immune activation to small molecule metabolism, autophagy and apoptosis. In this review, we bring together a fragmented body of literature on the kinetics and dynamics of peptidoglycan interactions with the mammalian host, explaining how peptidoglycan functions as a signalling molecule in the host under physiological conditions, how it disseminates within the host, and the cellular responses to peptidoglycan.

The regulatory effects of L. plantarum peptidoglycan microspheres on innate and humoral immunity in mouse

OBJECTIVE

To study the effects of Lactobacillus Plantarum cell wall peptidoglycan (LPG) microspheres on mouse intestinal flora changes, peptidoglycan recognitions protein (PGRP) and cytokines expression levels.

METHOD

Plate counting was used for enumeration of the intestinal flora. Real-time PCR was used for quantification PGRP in different tissues. Cytokines content were determined by ELISA kits.

RESULT

The mouse administered orally with LPG microspheres showed significantly higher number of Lactobacillus and Bifidobacterium in caecum contents (p < 0.01). The amount of PGRP expression in different organs was highest in LPG microspheres-treated group. IL-4, 12, IFN-γ, TNF-α contents in serum from LPG microspheres-treated mouse were significantly higher than those in normal saline-treated group (p < 0.01).

CONCLUSIONS

This study shows that the LPG microspheres can regulate intestinal flora imbalance and improve systemic immunity, improve both Th1 and Th2 immune response, which provide some basis for the use of LPG as potential adjuvants.