Reduction of T-Helper Cell Responses to Recall Antigen Mediated by Codelivery with Peptidoglycan via the Intestinal Nanomineral–Antigen Pathway

Rachel E Hewitt,Jonathan J Powell,Jack Robertson,Carolin T Haas,Laetitia C Pele

doi:10.3389/fimmu.2017.00284

Abstract

Naturally occurring intestinal nanomineral particles constituently form in the mammalian gut and trap luminal protein and microbial components. These cargo loaded nanominerals are actively scavenged by M cells of intestinal immune follicles, such as Peyer’s patches and are passed to antigen-presenting cells. Using peripheral blood mononuclear cell populations as an in vitro model of nanomineral uptake and antigen presentation, we show that monocytes avidly phagocytose nanomineral particles bearing antigen and peptidoglycan (PGN), and that the presence of PGN within particles downregulates their cell surface MHC class II and upregulates programmed death receptor ligand 1. Nanomineral delivery of antigen suppresses antigen-specific CD4+ T cell responses, an effect that is enhanced in the presence of PGN. Blocking the interleukin-10 receptor restores CD4+ T cell responses to antigen codelivered with PGN in nanomineral form. Using human intestinal specimens, we have shown that the in vivo nanomineral pathway operates in an interleukin-10 rich environment. Consequently, the delivery of a dual antigen–PGN cargo by endogenous nanomineral in vivo is likely to be important in the establishment of intestinal tolerance, while their synthetic mimetics present a potential delivery system for therapeutic applications targeting the modulation of Peyer’s patch T cell responses.

Highlights

A purposeful role for endogenously formed nanomineral particles of the intestine, serving as natural transfection agents, was proposed over a decade ago, arising from studies on the influence of particulates in intestinal disease [1]
Overall, synthetic mimetics of endogenous AMCP particles (sAMCP) bearing protein purified derivative (PPD) or PPD together with PGN combined within the same particles demonstrated a similar size range to the naturally occurring endogenous nanomineral [2] (i.e., 75–150 nm) with a small proportion reaching larger agglomerates of ~350 nm, as recently detailed for sAMCP with ovalbumin incorporation [20]
Using an in vitro peripheral blood mononuclear cells (PBMC)-based framework we have examined the influence of an intestinal nanomineral mimetic in a manner that will inform future in vivo studies

Summary

Introduction

A purposeful role for endogenously formed nanomineral particles of the intestine, serving as natural transfection agents, was proposed over a decade ago, arising from studies on the influence of particulates in intestinal disease [1]. Forming intestinal nanominerals have recently been characterized as nano-sized amorphous magnesium-substituted calcium phosphate (AMCP) species, constituently formed through self-assembly in the milieu of the intestinal lumen [2]. These particles comprise a blend of nanomineral, protein, and microbial components such as peptidoglycan. In situ studies of intestinal lymphoid tissue have revealed that the immuno-inhibitory receptor, programmed death receptor ligand 1 (PD-L1), is heavily upregulated on cells that have received nanomineral-mediated delivery of PGN, suggesting that these nanomineral particles may have a role in the maintenance of intestinal tolerance toward gut derived antigen and microbiota in the healthy gut [2]

Methods

Results

Conclusion