Globosides but not isoglobosides can impact the development of invariant NKT cells and their interaction with dendritic cells

Recognition of endogenous lipid Ag(s) on CD1d is required for the development of invariant NKT (iNKT) cells. Isoglobotrihexosylceramide (iGb3) has been implicated as this endogenous selecting ligand and recently suggested to control overstimulation and deletion of iNKT cells in α-galactosidase A-deficient (αGalA(-/-)) mice (human Fabry disease), which accumulate isoglobosides and globosides. However, the presence and function of iGb3 in murine thymus remained controversial. In this study, we generate a globotrihexosylceramide (Gb3)-synthase-deficient (Gb3S(-/-)) mouse and show that in thymi of αGalA(-/-)/Gb3S(-/-) double-knockout mice, which store isoglobosides but no globosides, minute amounts of iGb3 can be detected by HPLC. Furthermore, we demonstrate that iGb3 deficiency does not only fail to impact selection of iNKT cells, in terms of frequency and absolute numbers, but also does not alter the distribution of the TCR CDR 3 of iNKT cells. Analyzing multiple gene-targeted mouse strains, we demonstrate that globoside, rather than iGb3, storage is the major cause for reduced iNKT cell frequencies and defective Ag presentation in αGalA(-/-) mice. Finally, we show that correction of globoside storage in αGalA(-/-) mice by crossing them with Gb3S(-/-) normalizes iNKT cell frequencies and dendritic cell (DC) function. We conclude that, although detectable in murine thymus in αGalA(-/-)/Gb3S(-/-) mice, iGb3 does not influence either the development of iNKT cells or their interaction with peripheral DCs. Moreover, in αGalA(-/-) mice, it is the Gb3 storage that is responsible for the decreased iNKT cell numbers and impeded Ag presentation on DCs.     

Cloning of Gb3 synthase, the key enzyme in globo-series glycosphingolipid synthesis, predicts a family of alpha 1, 4-glycosyltransferases conserved in plants, insects, and mammals

We have cloned Gb(3) synthase, the key alpha1, 4-galactosyltransferase in globo-series glycosphingolipid (GSL) synthesis, via a phenotypic screen, which previously yielded iGb(3) synthase, the alpha1,3-galactosyltransferase required in isoglobo-series GSL (Keusch, J. J., Manzella, S. M., Nyame, K. A., Cummings, R. D., and Baenziger, J. U. (2000) J. Biol. Chem. 33). Both transferases act on lactosylceramide, Galbeta1,4Glcbeta1Cer (LacCer), to produce Gb(3) (Galalpha1,4LacCer) or iGb(3) (Galalpha1, 3LacCer), respectively. GalNAc can be added sequentially to either Gb(3) or iGb(3) yielding globoside and Forssman from Gb(3), and isogloboside and isoForssman from iGb(3). Gb(3) synthase is not homologous to iGb(3) synthase but shows 43% identity to a human alpha1,4GlcNAc transferase that transfers a UDP-sugar in an alpha1, 4-linkage to a beta-linked Gal found in mucin. Extensive homology (35% identity) is also present between Gb(3) synthase and genes in Drosophila melanogaster and Arabidopsis thaliana, supporting conserved expression of an alpha1,4-glycosyltransferase, possibly Gb(3) synthase, throughout evolution. The isolated Gb(3) synthase cDNA encodes a type II transmembrane glycosyltransferase of 360 amino acids. The highest tissue expression of Gb(3) synthase RNA is found in the kidney, mesenteric lymph node, spleen, and brain. Gb(3) glycolipid, also called P(k) antigen or CD77, is a known receptor for verotoxins. CHO cells that do not express Gb(3) and are resistant to verotoxin become susceptible to the toxin following transfection with Gb(3) synthase cDNA.     

Sensitive detection of isoglobo and globo series tetraglycosylceramides in human thymus by ion trap mass spectrometry

Glycosphingolipids serve as ligands for receptors involved in signal transduction and immune recognition, as exemplified by isoglobotrihexosylceramide, an antigenic ligand for T cell receptors. Mechanistic studies on the regulation of isoglobotrihexosylceramide require biochemical measurement of its lysosomal precursor, isoglobotetraglycosylceramide. It remains a challenge to distinguish between complex tetraglycosylceramide glycosphingolipid isomers with the same sugar components but diverse internal linkages. Here we established a simple and sensitive method to separate globo- and isoglobotetraglycosylceramide by MS5 ion trap mass spectrometry, and report the identification of isoglobotetraglycosylceramide in a CHO cell line transfected by iGb3 synthase, as well as in human thymus.     

Humans lack iGb3 due to the absence of functional iGb3-synthase: implications for NKT cell development and transplantation

The glycosphingolipid isoglobotrihexosylceramide, or isogloboside 3 (iGb3), is believed to be critical for natural killer T (NKT) cell development and self-recognition in mice and humans. Furthermore, iGb3 may represent an important obstacle in xenotransplantation, in which this lipid represents the only other form of the major xenoepitope Galalpha(1,3)Gal. The role of iGb3 in NKT cell development is controversial, particularly with one study that suggested that NKT cell development is normal in mice that were rendered deficient for the enzyme iGb3 synthase (iGb3S). We demonstrate that spliced iGb3S mRNA was not detected after extensive analysis of human tissues, and furthermore, the iGb3S gene contains several mutations that render this product nonfunctional. We directly tested the potential functional activity of human iGb3S by expressing chimeric molecules containing the catalytic domain of human iGb3S. These hybrid molecules were unable to synthesize iGb3, due to at least one amino acid substitution. We also demonstrate that purified normal human anti-Gal immunoglobulin G can bind iGb3 lipid and mediate complement lysis of transfected human cells expressing iGb3. Collectively, our data suggest that iGb3S is not expressed in humans, and even if it were expressed, this enzyme would be inactive. Consequently, iGb3 is unlikely to represent a primary natural ligand for NKT cells in humans. Furthermore, the absence of iGb3 in humans implies that it is another source of foreign Galalpha(1,3)Gal xenoantigen, with obvious significance in the field of xenotransplantation.     

Enzymatic synthesis of Gb3 and iGb3 ceramides

Gb3 and iGb3 are physiologically important trihexosylceramides with a terminal α-d-Galp-(1→4)-β-d-Galp- and α-d-Galp-(1→3)-β-d-Galp sequence, respectively. In particular iGb3 is attracting considerable attention as it is believed to serve as a ligand for natural killer T cells. Whether or not iGb3 is present in humans and which enzyme might be responsible for its synthesis is at present a matter of lively debate. In the current investigation we evaluated human blood group B galactosyltransferase (GTB) for its ability to catalyze the formation of iGb3 from lactosylceramide and UDP-Galp. GTB is a retaining glycosyltransferase that in vivo catalyzes the transfer of galactose from UDP-Galp donors to OH-3 of Galp on the H-antigen (α-l-Fucp-(1→2)-β-d-Galp) acceptor forming the blood group B antigen. GTB tolerates modifications in donor and acceptor substrates and its ability to accept lactosides as acceptors makes it a possible candidate for iGb3 production in humans. For comparison iGb3 and Gb3 were also synthesized from the same acceptor using an α-(1→3)- and α-(1→4)-specific galactosyltransferase, respectively. All the enzymes tested catalyzed the desired reactions. Product characterization by NMR analysis clearly differentiated between the α-Galp-(1→3)-Galp and α-Galp-(1→4)-Galp product, with the GTB product being identical to that of the α-(1→3)-GalT-catalyzed reaction. The rate of transfer by GTB however was very low, only 0.001% of the rate obtained with a good substrate, H antigen disaccharide (octyl α-l-Fucp-(1→2)-β-d-Galp). This is too low to account for the possible formation of the iGb3 structure in humans in vivo.     

Isogloboside biosynthesis in metastatic R3230AC cells results from a decreased GM3 synthase activity

We have determined that the production of a metastasis-associated neutral glycosphingolipid, isogloboside (iGb(4)Cer, GalNAcbeta1-3Galalpha1-3Galbeta1-4Glcbeta1-O-ceramide) is associated with the loss of G(M3) synthase activity. Assays for neutral glycosphingolipid-forming glycosyltransferases in cells producing various levels of iGb(4)Cer revealed no consistent differences that could account for the difference in iGb(4)Cer biosynthesis. However, comparison of the activity of G(M3) synthase in homogenates of these two cell types revealed that cells that did not synthesize iGb(4)Cer had activity significantly greater than that of cells possessing this antigen. Furthermore, somatic cell hybrids generated using clones of the iGb(4)Cer -producing and nonproducing cell lines lacked iGb(4)Cer while possessing high levels of G(M3) synthase activity. When iGb(4)Cer-producing cells were transfected with a G(M3) synthase expression vector, all of the resultant clones were negative for iGb(4)Cer production. The results of these studies clearly show that the presence of G(M3) synthase prevents the formation of iGb(4)Cer in these cells.     

The molecular basis for galalpha(1,3)gal expression in animals with a deletion of the alpha1,3galactosyltransferase gene

The production of homozygous pigs with a disruption in the GGTA1 gene, which encodes alpha1,3galactosyltransferase (alpha1,3GT), represented a critical step toward the clinical reality of xenotransplantation. Unexpectedly, the predicted complete elimination of the immunogenic Galalpha(1,3)Gal carbohydrate epitope was not observed as Galalpha(1,3)Gal staining was still present in tissues from GGTA1(-/-) animals. This shows that, contrary to previous dogma, alpha1,3GT is not the only enzyme able to synthesize Galalpha(1,3)Gal. As iGb3 synthase (iGb3S) is a candidate glycosyltransferase, we cloned iGb3S cDNA from GGTA1(-/-) mouse thymus and confirmed mRNA expression in both mouse and pig tissues. The mouse iGb3S gene exhibits alternative splicing of exons that results in a markedly different cytoplasmic tail compared with the rat gene. Transfection of iGb3S cDNA resulted in high levels of cell surface Galalpha(1,3)Gal synthesized via the isoglobo series pathway, thus demonstrating that mouse iGb3S is an additional enzyme capable of synthesizing the xenoreactive Galalpha(1,3)Gal epitope. Galalpha(1,3)Gal synthesized by iGb3S, in contrast to alpha1,3GT, was resistant to down-regulation by competition with alpha1,2fucosyltransferase. Moreover, Galalpha(1,3)Gal synthesized by iGb3S was immunogenic and elicited Abs in GGTA1 (-/-) mice. Galalpha(1,3)Gal synthesized by iGb3S may affect survival of pig transplants in humans, and deletion of this gene, or modification of its product, warrants consideration.     

Crystal structures of mouse CD1d-iGb3 complex and its cognate Valpha14 T cell receptor suggest a model for dual recognition of foreign and self glycolipids

The semi-invariant Vα14Jα18 T cell receptor (TCR) is expressed by regulatory NKT cells and has the unique ability to recognize chemically diverse ligands presented by CD1d. The crystal structure of CD1d complexed to a natural, endogenous ligand, isoglobotrihexosylceramide (iGb3), illustrates the extent of this diversity when compared to the binding of potent, exogenous ligands, such as α-galactosylceramide (α-GalCer). A single mode of recognition for these two classes of ligands would then appear problematic for a single T cell receptor. However, the Vα14 TCR adopts two different conformations in the crystal where, in one configuration, the presence of a larger cavity between the two CDR3 regions could accommodate iGb3 and, in the other, a smaller cavity fits α-GalCer more snugly. Alternatively, the extended iGb3 headgroup could be “squashed” upon docking of the TCR and accommodated between the CD1 and TCR surfaces. Thus, the same TCR may adopt alternative modes of recognition for these foreign and self-ligands for NKT cell activation.     

Enhanced activation of a T cell line specific for acetylcholine receptor (AChR) by using anti-AChR monoclonal antibodies plus receptors

Immune complex-mediated regulation of the immune response has been studied by using T cell lines and monoclonal antibodies (MAb), both specific for the acetylcholine receptor (AChR). Rat T lymphocytes bearing the W3/25 phenotype and specific for AChR from Torpedo californica have been propagated in vitro for nearly 1 yr. These T cells proliferate in response to optimal concentrations of AChR presented by irradiated syngeneic thymus cells. At suboptimal concentrations of antigen there is little activation of the T cell line. We report here that the addition of small amounts of anti-AChR MAb produces dramatic stimulation of the T cell lines at suboptimal doses of AChR. Enhanced activation depends on the isotype and not the fine specificity of the MAb that are used. The observed phenomenon is antigen specific, and in fact, the immune complexes may actually suppress the proliferative response of irrelevant T cells to some extent. The MAb plus antigen are rapidly bound to the surface of the antigen-presenting cell, which we have shown is the dendritic cell.     

Identification of glycosphingolipid receptors for pierisin-1, a guanine-specific ADP-ribosylating toxin from the cabbage butterfly

Pierisin-1, a cytotoxic protein found naturally in the cabbage butterfly, induces apoptosis of mammalian cells. Our recent studies suggest that pierisin-1 consists of an N-terminal ADP-ribosyltransferase domain, and a C-terminal region that binds to receptors on the surfaces of target cells and incorporates the protein into cells. The present study was undertaken to identify receptors for pierisin-1. The cross-linking and cloning experiments suggested that the proteins on cell membrane had no binding ability to pierisin-1. Inhibitory assays of fractionated lipids from human cervical carcinoma HeLa cells, which are highly sensitive to pierisin-1, indicated neutral glycosphingolipids on the cell surface to show receptor activity. Inhibitory assays and TLC immunostaining using anti-pierisin-1 antibodies demonstrated two neutral glycosphingolipids as active components. Analysis of their structures with glycosphingolipid-specific antibodies and negative secondary ion mass spectrometry identified them as globotriaosylceramide (Gb3) and globotetraosylceramide (Gb4). The receptor activities of Gb3 and Gb4 for pierisin-1 were also confirmed with these authentic compounds. Pierisin-1-insensitive mouse melanoma MEB4 cells were found to lack pierisin-1 receptors, including Gb3 and Gb4, but pretreatment of the cells with glycosphingolipid Gb3 or Gb4 enhanced their sensitivity to pierisin-1. Thus, Gb3 and Gb4 were proven to serve as pierisin-1 receptors. The C-terminal region of pierisin-1 consists of possible lectin domains of a ricin B-chain, containing QXW sequences, which are essential for its structural organization. Alteration of QXW by site-directed mutagenesis caused marked reduction of pierisin-1 cytotoxicity. Thus, our results suggest that pierisin-1 binds to Gb3 and Gb4 receptors at the C-terminal region, in a manner similar to ricin, and then exhibits cytotoxicity after incorporation into the cell.     

Binding and cross-linking properties of galectins

The galectins are a family of animal lectins that possess similar carbohydrate binding specificities and conserved consensus sequences. The biological properties of mammalian galectins include the regulation of inflammation, cell adhesion, cell proliferation and cell death. Evidence suggests that the biological activities of the galectins are related to their multivalent binding properties since most galectins possess two carbohydrate recognition domains and are therefore bivalent. For example, galectin-1, which is dimeric, binds and cross-links specific glycoprotein counter-receptors on the surface of human T-cells leading to apoptosis [J. Immunol. 163 (1999) 3801]. Different galectin-1 counter-receptors associated with specific phosphatase or kinase activities formed separate clusters on the surface of the cells as a result of the lectin binding to the carbohydrate chains of the respective glycoproteins. Importantly, monovalent galectin-1 is inactive in this system. This indicates that the separation and organization of signaling molecules that result from galectin-1 binding is involved in the apoptotic signal. The separation of specific glycoprotein receptors induced by galectin-1 binding was modeled on the basis of molecular and structural studies of the binding of lectins to multivalent carbohydrates resulting in the formation of specific two- and three-dimensional cross-linked lattices [Biochemistry 36 (1997) 15073]. In this article, the binding and cross-linking properties of galectin-1 and other lectins are reviewed as a model for the biological signal transduction properties of the galectin family of animal lectins.     

Synthesis of alpha-gal epitopes (Galalpha1-3Galbeta1-4GlcNAc-R) on human tumor cells by recombinant alpha1,3galactosyltransferase produced in Pichia pastoris.

This study describes the processing of human tumor cells or cell membranes to express alpha-gal epitopes (Galalpha1-3Gal-beta1-4GlcNAc-R) by the use of New World monkey (marmoset) recombinant alpha1,3galactosyltransferase (ralpha1,3GT), produced in the yeast Pichia pastoris. Such tumor cells and membranes may serve, in cancer patients, as autologous tumor vaccines that are targeted in vivo to antigen-presenting cells by the anti-Gal antibody. This ralpha1,3GT lacks transmembrane and cytoplasmic domains, ensuring its solubility without detergent. It is effectively produced in P. pastoris under constitutive expression of the P(GAP) promoter and is secreted into the culture medium in a soluble, truncated form fused to a (His)(6) tag. This tag enables the simple affinity purification of ralpha1,3GT on a nickel-Sepharose column and elution with imidazole. The purified enzyme appears in SDS-PAGE as two bands with the size of 40 and 41 kDa and displays the same acceptor specificity as the mammalian native enzyme. ralpha1,3GT is very effective in synthesizing alpha-gal epitopes on membrane-bound carbohydrate chains and displays a specific activity of 1.2 nM membrane bound alpha-gal epitopes/min/mg. Incubation of very large amounts of human acute myeloid leukemia cells (1 x 10(9 )cells) with neuraminidase, ralpha1,3GT, and UDP-Gal resulted in the synthesis of approximately 6 x 10(6 )alpha-gal epitopes per cell. Effective synthesis of alpha-gal epitopes could be achieved also with as much as 2 g cell membranes prepared from the tumor of a patient with ovarian carcinoma. These data imply that ralpha1,3GT produced in P. pastoris is suitable for the synthesis of alpha-gal epitopes on bulk amounts of tumor cells or cell membranes required for the preparation of autologous tumor vaccines.     

Cell receptors for the mammalian reovirus: reovirus-specific T-cell hybridomas can become persistently infected and undergo autoimmune stimulation.

We have previously described the development of virus-specific helper T cell hybridomas which recognize structural determinants shared by type 1 and type 3 reoviruses that have been exposed to UV radiation. We have found that T-cell hybridomas become persistently infected with live type 3 reovirus used for the immunization. Persistently infected T-hybridoma cells were found to spontaneously produce interleukin 2 (IL-2). To analyze the mechanism of induction of IL-2 secretion of persistently infected T-cell hybridomas, we exposed T-cell hybridomas specific for UV-treated virus to replicating type 3 reovirus. The T-cell hybridomas became infected but did not produce IL-2 unless simultaneously exposed to syngeneic I-A+ antigen-presenting cells. In this situation, the persistently infected T-cell hybridomas produced IL-2 without being reexposed to virus. This process was not a consequence of nonspecific IL-2 gene activation, which occurs in cells persistently infected with reovirus, because reovirus infection did not activate IL-2 secretion in T-cell hybridomas with other antigenic specificities. Reovirus exposure also resulted in persistent infection of certain antigen-presenting B-cell tumor lines. The persistently infected B-cell tumor lines could stimulate reovirus-specific helper T cells but not T-cell hybridomas of other specificities. The data support the thesis that persistent infection of reovirus-specific T cells creates a mechanism in which the virus released from these cells is processed and then reexpressed by I-A+ antigen-presenting cells. The IA antigen and reovirus structures on the antigen-presenting cells then restimulate the T cells through their specific receptors, resulting in IL-2 synthesis and release. These observations may be relevant to mechanisms of autoimmunity induced by virus.     

Spontaneous development of functionally active long-term monocytelike cell lines from channel catfish

Summary During the course of studies involving the in vitro manipulation of channel catfish peripheral blood leukocytes, spontaneous proliferation was observed with unexpectedly high frequency. Propagation of these spontaneously proliferating cells has resulted in the development of long-term (>11 mo.) cell lines which stain positively for nonspecific esterase and peroxidase, are phagocytic for latex beads, and morphologically resemble mammalian monocytes or macrophages. These long-term cell lines also exhibit two important additional functional features. First, induction with lipopolysaccharide results in the secretion of relatively high levels of catfish high and low molecular weight species of interleukin-1 active on channel catfish and mouse T cells, respectively. Second, these cell lines are efficient antigen-presenting cells to autologous peripheral blood leukocytes for antigen specific in vitro proliferative and antibody responses. This antigen-presenting function is blocked by inhibitors known to prevent antigen processing and presentation by mammalian monocytes. Allogeneic mixtures of cell line (used as antigen-presenting cells) and responding peripheral blood leukocytes, however, resulted in strong mixed leukocyte reaction but not in specific antibody responses. The availability of such cell lines should facilitate further studies on accessory cell functions in fish immune responses. This work was supported in part by grant 5-R37-AI-19530 from the National Institutes of Health, Bethesda, MD.     

A nanoliter-scale nucleic acid processor with parallel architecture

The purification of nucleic acids from microbial and mammalian cells is a crucial step in many biological and medical applications. We have developed microfluidic chips for automated nucleic acid purification from small numbers of bacterial or mammalian cells. All processes, such as cell isolation, cell lysis, DNA or mRNA purification, and recovery, were carried out on a single microfluidic chip in nanoliter volumes without any pre- or postsample treatment. Measurable amounts of mRNA were extracted in an automated fashion from as little as a single mammalian cell and recovered from the chip. These microfluidic chips are capable of processing different samples in parallel, thereby illustrating how highly parallel microfluidic architectures can be constructed to perform integrated batch-processing functionalities for biological and medical applications.     

T cell clones to two major T cell epitopes of myoglobin: effect of I-A/I-E restriction on epitope dominance

The murine T cell response to sperm whale myoglobin was analyzed for polyclonal and monoclonal T cells. For polyclonal T cells, the immunodominant epitope included residue Glu 109 when the antigen-presenting cells expressed I-Ad, whereas a Lys 140-containing epitope was immunodominant when the antigen-presenting cells expressed I-Ed only. Monoclonal T cells specific for each epitope were derived from a polyclonal line. T cell clones specific for the Glu 109 epitope were restricted to I-Ad, whereas the clones specific for the Lys 140 epitope were restricted to I-Ed. Thus, for an antigen that can be presented in association with either I-Ad or I-Ed, the immunodominance of particular epitopes depends strongly on the restriction element used. The immunodominance of each epitope-Ia combination may be due to a limited repertoire of T cells or selective presentation of epitope and Ia by accessory cells.     

Different antigen-presenting cells differ in their capacity to induce lymphokine production and proliferation of an apo-cytochrome c-specific T cell clone

The activation of an apo-cytochrome c-specific T cell clone was found to differ, depending on the antigen-presenting cell population. Whereas total syngeneic spleen cells and bone marrow macrophages could be shown to trigger proliferation, IL 2, and MAF production by the T cell clone, a B cell lymphoma only induced MAF secretion. Further studies demonstrated that this effect was not due to a different antigen processing by the B lymphoma or to limiting amounts of Ia and antigen molecules on the B lymphoma cell surface. The dissociation of induction of MAF production from IL-2 production/proliferation found with the different antigen-presenting cells indicates strongly that molecules other than Ia and antigen may be required for the complete functional activation of antigen-specific T cell clones.     

Immunological Properties of TtT/M-87 Cell Line Established from Murine Pituitary Tumor-Associated Macrophages

TtT/M-87 cell is a macrophage cell line established from thyrotropic pituitary tumor tissues in mouse. In this paper, we report the immunological properties of M-87 cells as a model of tumor-associated macrophage. Contrasting with resident peritoneal macrophages, M-87 cells constitutively secreted small but significant amounts of TNF-α and IL-1α, which were detectable in both biological assays (cytotoxic activity for L929 and co-mitogenic activity for Con A-induced T cell proliferation, respectively) and ELISA, and produced larger amounts of these cytokines upon stimulation with LPS. They expressed MHC class II molecules on their cell surface without stimulation by IFN-γ. The accessory or antigen-presenting cell activity in antibody-producing response of spleen lymphocytes to sheep red blood cells was shown to be much higher in M-87 cells than normal peritoneal macrophages. In addition, when normal spleen lymphocytes were cultured with allogeneic tumor cells, such as EL-4 and S-180, in the presence of M-87 cells, lymphocytes reactive to stimulator cells were activated to manifest inhibitory effect on the tumor cell growth and also to manifest specific cytotoxic effect on the allogeneic tumor cells. These results show that M-87 cells derived from tumor-associated tissue are activated macrophages and that they are inhibitory to tumor cell growth and augmentative in the induction of T-cell-mediated immune responses.     

Biological chemistry of immunomodulation by zwitterionic polysaccharides

Capsular polysaccharides isolated from pathogenic bacteria are comprised typically of many repeating units from one to eight or more monosaccharides in length. These polysaccharides stimulate the murine humoral immune system to elicit primarily IgM antibody responses. Studies conducted primarily in the mouse have characterized these polymers as T cell-independent antigens. These mouse studies and the relatively poor immunogenicity of polysaccharides in human hosts have led to the design of vaccines by coupling these polysaccharides to protein carriers to stimulate a T cell-dependent response. However, a newly described class of bacterial polysaccharides has been characterized that have the ability to modulate the cellular immune system. They are structurally diverse, but all share a zwitterionic charge motif that allows them to directly interact with T cells and antigen-presenting cells to initiate an immunomodulatory T cell response. These polymers, termed zwitterionic polysaccharides (ZPSs), elicit T cell-derived chemokines and cytokines that influence the immune response governing at least one classic host response to bacterial infection: abscess formation. This review will describe the biological and structural aspects of ZPSs that convey these activities.