T Cells Activated by Zwitterionic Molecules Prevent Abscesses Induced by Pathogenic Bacteria

Abstract

Immunologic paradigms classify bacterial polysaccharides as T cell-independent antigens. However, these models fail to explain how zwitterionic polysaccharides (Zps) confer protection against intraabdominal abscess formation in a T cell-dependent manner. Here, we demonstrate that Zps elicit a potent CD4؉ T cell response in vitro that requires available major histocompatibility complex class II molecules on antigen-presenting cells. Specific chemical modifications to Zps show that: 1) the activity is specific for carbohydrate structure, and 2) the proliferative response depends upon free amino and carboxyl groups on the repeating units of these polysaccharides. Peptides synthesized to mimic the zwitterionic charge motif associated with Zps also exhibited these biologic properties. Lysine-aspartic acid (KD) peptides with more than 15 repeating units stimulated CD4؉ T cells in vitro and conferred protection against abscesses induced by bacteria such as Bacteroides fragilis and Staphylococcus aureus. Evidence for the biologic importance of T cell activation by these zwitterionic polymers was provided when human CD4؉ T cells stimulated with these molecules in vitro and adoptively transferred to rats in vivo conferred protection against intraabdominal abscesses induced by viable bacterial challenge. These studies demonstrate that bacterial polysaccharides with a distinct charge motif activate T cells and that this activity confers immunity to a distinct pathologic response to bacterial infection.The study of T cell recognition of foreign antigens has been directed primarily toward an understanding of the host's immune system response to proteins or peptides. The recent demonstration that non-peptide-containing mycobacterial lipid and glycolipid antigens activate T cells in conjunction with CD1 molecules on the surface of antigen-presenting cells (APCs)

Introduction of Zwitterionic Motifs into Bacterial Polysaccharides Generates TLR2 Agonists Able to Activate APCs

“…It was shown previously that conversion of a primary amine to a tertiary amine on PSA was associated with a loss of T cell stimulatory activity (6). The chemically derived ZPS2 forms shown in this study all contain tertiary amines and are able both to activate APCs and to induce T cell proliferation.…”

“…1) were treated with 37% formaldehyde (H 2 CO; Carlo Erba) in the presence of sodium cyanoborohydride to convert the generated free amino group to a tertiary dimethylamine such that it retained a positive charge (6).…”

Microbial carbohydrate depolymerization by antigen-presenting cells: Deamination prior to presentation by the MHCII pathway

“…In addition, after the N-acetylation, a change in the chemical shift of C-6 of the AATp residue of PSA-NO (as in PSA) proved that N-acetylation took place on the C-4 of AATp. Our structural characterization of the deamination product PSA-NO showed that PSA-NO shares the same chain structure with PSA-with most AATp residues staying intact-a requirement for sustaining this molecule's zwitterionic nature and antigenicity (17).…”

Bacteroides fragilis polysaccharide A is necessary and sufficient for acute activation of intestinal sensory neurons

“…Then PSA was purified from the aqueous phase as previously described 28,53 . PSA structure and purity were assessed by NMR spectroscopy.…”