Pneumococcal Capsular Polysaccharide Is Immunogenic When Present on the Surface of Macrophages and Dendritic Cells: TLR4 Signaling Induced by a Conjugate Vaccine or by Lipopolysaccharide Is Conducive

Abstract

Previously, we reported that a peptide, p458, from the sequence of the mammalian 60-kDa heat shock protein (hsp60) molecule can serve as a carrier in conjugate vaccines with capsular polysaccharide (CPS) molecules of various bacteria. These conjugate vaccines were effective injected in PBS without added adjuvants. We now report that p458 conjugated to pneumococcal CPS type 4 (PS4) manifests innate adjuvant effects: it stimulated mouse macrophages to secrete IL-12 and induced the late appearance of PS4 on the macrophage surface in a TLR4-dependent manner; PS4 alone or conjugated to other carriers did not stimulate macrophages in vitro. The injection of macrophages manifesting PS4 on the surface into mice induced long-term resistance to lethal Streptococcus pneumoniae challenge. The TLR4 ligand LPS could also induce the late appearance on the surface of unconjugated PS4 and resistance to challenge in injected mice. Resistance was not induced by macrophages containing only internalized PS4 or by pulsed macrophages that had been lysed. Glutaraldehyde-fixed macrophages pulsed with PS4 did induce resistance to lethal challenge. Moreover, bone marrow-derived dendritic cells activated by LPS and pulsed with unconjugated CPS were also effective in inducing resistance to lethal challenge. Resistance induced by the PS4-pulsed bone marrow-derived dendritic cell was specific for pneumococcal CPS serotypes (type 3 or type 4) and was associated with the induction of CPS-specific IgG and IgM Abs.

The HSP60 immune system network

“…models, and others have applied HSP60 peptides to inhibit experimental arthritis [60][61][62][63][64]. The role of HSP60 peptide p458 as a potential activator of TLR4 signaling in macrophages and DCs [27] has been exploited in the development of anti-microbial vaccines. Defined multi-component vaccines conjugated to peptide p458 were found to induce IgG antibodies to otherwise poorly immunogenic capsular polysaccharide antigens of salmonella [94], pneumococci [27,95], and meningococci [96]; these vaccines were found to be effective even without added adjuvants.…”

“…It is now clear, however, that HSP60 on its own can activate innate immune receptors [23]. In macrophages and DCs, TLR4 signaling is activated in response to at least four sources of HSP60: (i) bacterial HSP60 [24], (ii) bacterial or self-HSP60 molecules that bear LPS or other bacterial ligands bound to them [25,26], (iii) self-HSP60 molecules produced by infected, transformed, damaged or stressed cells [13,14,26] and (iv) peptides of HSP60 [27]. Monocytes undergo activation and maturation in response to HSP60, resulting in the production of pro-inflammatory molecules and factors such as TNFa, IL-12, IL-15, IL-6, IL-1b and NO (reviewed in [13-15]).…”

“…At least one peptide fragment of mammalian HSP60 appears to participate in the activation of innate immune cells: a 17 amino acid peptide from the 458-474 sequence of human HSP60 (p458) can activate mouse macrophages via TLR4, provided that the HSP60 peptide is conjugated to another molecule to create a polyvalent ligand [27].…”

A Novel Exopolysaccharide from the Biofilm of Thermus aquaticus YT-1 Induces the Immune Response through Toll-like Receptor 2

“…Because TLR4 has been reported to mediate cytokine expression by macrophages in response to several kinds of polysaccharides, such as polysaccharides from Ganoderma lucidum and Streptococcus pneumoniae (2,22), we tested whether TLR4 takes part in the TA-1-induced immunoregulatory effects. In our assays, the murine macrophage cell lines HeNC2 (with functional TLR4; Fig.…”

Biomarker vaccines

“…24 These conjugate vaccines are effective because the p458 component of the conjugate provides T-cell help and the p458-CPS conjugate also activates innate TLR4 signaling in antigen presenting cells. 25 The basic idea is to provide the immune system with a conjugation of information about the pathogenthe target antigen-with a host biomarker-the HSP component. The host biomarker moiety flags the antigen and so induces the host response into an effectively protective mode (Fig.…”