The muramyl dipeptide analog GMTP-N-DPG preferentially induces cellular immunity to soluble antigens

Bacterial Peptidoglycan Fragments Differentially Regulate Innate Immune Signaling

The human innate immune system responds to both pathogen and commensal bacteria at the molecular level using bacterial peptidoglycan (PG) recognition elements. Traditionally, synthetic and commercially accessible PG monosaccharide units known as muramyl dipeptide (MDP) and N-glycolyl MDP (ng-MDP) have been used to probe the mechanism of innate immune activation of pattern recognition receptors, such as NOD-like receptors. However, bacterial PG is a dynamic and complex structure, with various chemical modifications and trimming mechanisms that result in the production of disaccharide-containing elements. These molecules pose as attractive targets for immunostimulatory screening; however, studies are limited because of their synthetic accessibility. Inspired by disaccharide-containing compounds produced from the gut microbe Lactobacillus acidophilus, a robust and scalable chemical synthesis of PG-based disaccharide ligands was implemented. Together with a monosaccharide PG library, compounds were screened for their ability to stimulate proinflammatory genes in bone-marrow-derived macrophages. The data reveal distinct gene induction patterns for monosaccharide and disaccharide PG units, suggesting that PG innate immune signaling is more complex than a one activator-one pathway program, as biologically relevant fragments induce transcriptional programs to different degrees. These disaccharide molecules will serve as critical immunostimulatory tools to more precisely define specialized innate immune regulatory mechanisms that distinguish between commensal and pathogenic bacteria residing in the microbiome.

Comparative immunomodulatory properties of a chitosan-MDP adjuvant combination following intranasal or intramuscular immunisation

As the precise functions of adjuvants become clearer, opportunities are presented in their complementary use for the induction of tailored immune responses to subunit vaccines. Here we comparatively investigate the immunological outcome following intranasal or intramuscular immunisation with Helicobacter pylori urease admixed to a chitosan and muramyl di-peptide (MDP) combination. MDP appeared to limit the antigenicity of rUre by either administration route. Nasal administration of the combined adjuvant formulation resulted in an up-regulation of type I recall responses in splenocytes as opposed to adjuvantisation with chitosan alone. In contrast, intramuscular immunisation appeared to limit the responsiveness to the antigen when adjuvanted with chitosan and even more so when chitosan was combined with MDP, suggesting that the mechanism of adjuvantisation and adjuvant synergy differed depending on the immunisation route. Recognising the benefit of improved delivery of MDP intranasally due to the specific physiological effects of chitosan, we discuss the impact of the newly identified pathogen associated molecular pattern (PAMP) role of MDP with respect to the adjuvanticity of proposed chemical variants of this peptide adjuvant.

Adjuvant synergy: The effects of nasal coadministration of adjuvants

Modern peptide and protein subunit vaccines suffer from poor immunogenicity and require the use of adjuvants. However, none of the currently licensed adjuvants can elicit cell-mediated immunity or are suitable for mucosal immunization. In this study we explored the immunological effect of nasal co-administration of adjuvants with distinct functions: cholera toxin subunit B, a potent mucosal adjuvant that induces strong humoral responses, muramy di-peptide (MDP), an adjuvant known to elicit cell mediated immunity but rarely used nasally, and chitosan, an adjuvant that achieves specific physiological effects on mucosal membranes that improve antigen uptake. Groups of five female BALB/c mice received on days 1 and 56 nasal instillations of the recombinant Helicobacter pylori antigen urease admixed to single or multiple adjuvant combinations. Serum IgG kinetics were followed over 24 weeks. At the conclusion of the experiment, local antibody responses were determined and antigen-specific recall responses in splenocyte cultures were assayed for proliferation and cytokine production. The combination of adjuvants was shown to further contribute to the increased antigenicity of recombinant H. pylori urease. The data presented here outline and support facilitation of increased immunomodulation by an adjuvant previously defined as an effective mucosal adjuvant (chitosan) for another adjuvant (MDP) that is not normally effective via this route.

A pyrophosphate bridge links the pyruvate-containing secondary cell wall polymer of Paenibacillus alvei CCM 2051 to muramic acid

The peptidoglycan, the secondary cell wall polymer (SCWP), and the surface layer (S-layer) glycoprotein are the major glycosylated cell wall components of Paenibacillus alvei CCM 2051. In this report, the complete structure of the SCWP, its linkage to the peptidoglycan layer, and its physicochemical properties have been investigated. From the combined evidence of chemical and structural analyses together with one- and two-dimensional nuclear magnetic resonance spectroscopy, the following structure of the SCWP-peptidoglycan complex is proposed: [(Pyr4,6)-beta-D-ManpNAc-(1-->4)-beta-D-GlcpNAc-(1-->3)]n-11-(Pyr4,6)-beta-D-ManpNAc-(1-->4)-alpha-D-GlcpNAc-(1-->O)-PO2-O-PO2-(O-->6)-MurNAc- Each disaccharide unit is substituted by 4,6-linked pyruvic acid residues. Under mild acidic conditions, up to 50% of them are lost, leaving non-substituted ManNAc residues. The anionic glycan chains constituting the SCWP are randomly linked via pyrophosphate groups to C-6 of muramic acid residues of the peptidoglycan layer. 31P NMR reveals two signals that, as a consequence of micelle formation, experience different line broadening. Therefore, their integral ratio deviates significantly from 1:1. By treatment with ethylenediaminetetraacetic acid, sodium dodecyl sulfate, and sonication immediately prior to NMR measurement, this ratio approaches unity. The reversibility of this behavior corroborates the presence of a pyrophosphate linker in this SCWP-peptidoglycan complex. In addition to the determination of the structure and linkage of the SCWP, a possible scenario for its biological function is discussed.

Improving vaccine performance with adjuvants

New vaccines are presently under development and in testing for the control of infectious diseases, including human immunodeficiency virus (HIV) and tuberculosis. Several of these vaccines are composed of synthetic, recombinant, or highly purified subunit antigens. Subunit vaccines are designed to include only the antigens required for protective immunization and to be safer than whole-inactivated or live-attenuated vaccines. However, the purity of the subunit antigens and the absence of the self-adjuvanting immunomodulatory components associated with attenuated or killed vaccines often result in weaker immunogenicity. Immunologic adjuvants are agents that enhance specific immune responses to vaccines. Formulation of vaccines with potent adjuvants is an attractive approach for improving the performance of vaccines composed of subunit antigens. Adjuvants have diverse mechanisms of action and should be selected for use on the basis of the route of administration and the type of immune response (antibody, cell-mediated, or mucosal immunity) that is desired for a particular vaccine.

Therapeutic vaccination against HSV-2: influence of vaccine formulation on immune responses and protection in mice

Therapeutic immunisation may represent a means of influencing viral infections that persist in the host by modulating the nature or level of host immunity. To assess the influence of the form of the antigenic stimulus on immunity to type-2 herpes simplex virus (HSV-2), mice pre-infected with sublethal doses of HSV-2 were immunised with various HSV-2 vaccine formulations prior to challenge infection with heterologous HSV-1. Measurements of interleukin-2 (IL-2), interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) levels in mouse spleen cell cultures restimulated in vitro with HSV-2 antigens showed that, depending on the form of HSV-2 antigen preparation used in this therapeutic context, changes in the levels of these cytokines could be effected. Measurement of HSV-specific antibody by serological tests support the contention that immunisation of HSV-2-infected mice can either enhance the existing Th1-like immune response elicited following HSV-2 infection, or modulate this response towards a more Th2-like profile, and this is dependent on the form of the antigenic stimulus. The degree of protection against subsequent lethal, heterologous HSV-1 challenge infection varied according to the nature of the infection and the immunisation history of the animals.