Associate Chemist, Department of Medicine
Brigham and Women's Hospital

ywang@channing.harvard.edu

Pathogen-Host Interactions: From Molecules to the Physiome

Infection and immunity are governed by an intricate network of molecular interactions between microbes and the host immune system. We are interested in both defining their fundamental molecular, structural, and cellular bases and developing rational and innovative approaches for the prevention and treatment of diseases. We employ a multidisciplinary approach which includes biological, chemical, structural, and computational principles. Our research interests, as presented below, are (I) structural biology of carbohydrate antigens and their interaction with host receptors, (II) rational design of vaccines and antoxins, (III) pathogenesis of microbe-induced arthritis and autoimmune diseases, and (IV) systems biology and physiomic description of the interplay of infection and immunity.

I. Structural biology of carbohydrate antigens and their interactions with host receptors

Complex carbohydrates (such as capsular and extracellular polysaccharides, lipopolysaccharides, glycolipids, and glycoproteins) are major entigenic and virulence determinants of a wide spectrum of microorganisms. Our goal is to identify the unique structural features of carbohydrates that define their recognition by and activity on the immune system. We envision that these findings can be beneficially exploited to design novel approaches for the regulation of microbe-host interactions. We are interested in characterizing the 3D structures of different classes of antigens with unique immunologic properties, e.g., zwitterionic, polyanionic, and neutral polysaccharides. Our recent study shows the T cell-activating zwitterionic polysaccharides assume similar 3D structures or "molecular patterns" which may account for their common property as T-cell activators.

We are also interested in characterizing the interactions between microbial carbohydrate antigens and host receptor proteins. We employ biophysical and biochemical methods (e.g., NMR, mass spectrometry, gas and liquid chromatography, FTIR, CD, and calorimetry) as well as genomic and proteomic strategies (e.g., DNA and protein arrays) in these studies.

II. Rational design of vaccines and antitoxins

We have a longstanding interest in the rational design, development, and optimization of vaccines and antitoxins. We seek to create multifunctional, hybrid-molecular constructs in which each subunit is specific for eliciting a certain molecular or cellular response. To combat the threat of biological terrorism, we are currently focusing on developing conjugate vaccines and toxin inhibitors against anthrax.

Vaccines

Many microbial antigens, such as polysaccharides, are prominent vaccine candidates but have limited application by themselves because of their inability to recruit cognate B and T helper cells for antibody production. In search for optimal molecular vaccine constructs, we are attempting to guide host immune responses by arranging epitopes specific for different immune cells in particular configurations. We have been developing chemical methods which allow the synthesis of various tailored conjugates.

Antitoxins

We are interested in creating conceptually new inhibitors of bacterial toxins. Since many toxins act via oligomeric supramolecular assemblies, singular inhibitory molecules are often insufficient to block toxin activity. We are using chemical synthetic strategies to link multiple inhibitors to a linear or branched oligomer or polymer backbone. The resulting inhibitors can block the toxin assembly with greatly increased affinity and very efficiently via cooperative and multivalent binding. We are currently developing a series of multivalent inhibitors against anthrax toxins.

III. Molecular and cellular mechanisms of GAG-mediated arthritis and autoimmunity

Rheumatoid arthritis (RA) is a systemic autoimmune disease of connective tissue with unknown etiology. While studying immune responses to carbohydrate antigens, we discovered that aberrant immune responses to glycosaminoglycans (GAGs), a major component of connective tissue, can cause RA. We developed a mouse model of GAG-induced autoreactive arthritis. To monitor cellular response to GAGs, we developed a novel carbohydrate-affinity staining technique which allows us to visualize direct binding between cells and GAGs. We discovered that certain inflammatory cells in arthritic lesions of both GAG-treated mice and patients with RA are uniquely autoreactive to GAGs. Our study, for the first time, demonstrates a direct link between carbohydrate antigens, the immune system, and a human disease. Our concept that carbohydrate self-antigens can be responsible for autoimmune diseases represents a new paradigm in immunology and medicine.

A wide variety of microorganisms, including bacteria, mycobacteria, spirochetes, fungi, and viruses, can trigger acute infectious and/or reactive arthritis and may lead to autoimmune disease such as RA as a secondary response. For example, Staphylococcus aureus and Neisseria gonorrhoeae are common bacterial causes of infectious arthritis, whereas Streptococcus pyogenes, Yersinia enterocolitica, Shigella felxneri, Campylobactor jejuni, and Salmonella and Chlamydia burgdorferi, induces arthritis in up to 70% of people who are not treated. Viruses (such as rubella, mumps, parvovirus B19, hepatitis B, and HIV) can produce arthritis by infecting synovial tissue during systemic infection or by provoking an immunologic reaction that involves joints.

Based on our recent findings, we propose the following links between infections and GAG-associated arthritis: (i) Many bacteria (e.g., S. pyogenes, Pasteurella multocida, and E. coli K5) express GAG or GAG-mimetic polysaccharide capsules. (ii) Certain intracellular bacteria (e.g., Chlamydia) promote the biosynthesis of GAGs in their host cells. (iii) Numerous pathogens secrete enzymes that degrade GAGs. (iv) A wide variety of bacteria (e.g., staphylococci and streptococci), viruses (e.g., HIV­1 and Dengue), parasite (e.g., Plasmodium falciparum), and spirochetes (e.g., B. burgdorferi) bind GAGs to facilitate their attachment or entry into host cells and tissues. Microbes may exploit GAGs to evade immune surveillance and/or to invade host tissue, but consequently also initiate GAG-associated autoimmunity.

Our research is aimed at several directions: developing animal models of arthritis using either whole pathogens or their antigens, identifying and characterizing microbial antigens that mimic or bind GAGs, and dissecting immunological responses during infection that lead to arthritis.

IV. Systems biology and physiomic description of the interplay of infection and immunity

The interplay of infection and immunity is governed by a complex, non-linear network of molecular chain reactions between microbes and the host. Traditional examination of one molecule or one interaction at a time limits our global understanding of biology. Our long-term goal is to comprehend and describe quantitatively the molecular interactions and the physiome of microbe-host networks.

Because GAGs interact with a network of molecules (e.g., adhesion molecules, cell-surface antigens, cytokines, chemokines, and growth factors), we choose GAG-mediated arthritis and autoimmunity as an initial model to explore systems biology. We will first focus on establishing mathematical models to study molecular chain reactions. Our second goal is to build E-cells that are comprised of hierarchical and intertwining molecular networks to describe microbial species and mammalian cells. Untimately, we seek to integrate different molecular networks and E-cells and derive a quantitative description of the physiology and pathophysiology of microbes and the host organism, that is, the physiome.

In conjunction, we will develop "web lab" and animal experiments to validate the accuracy, stability/robustness, dynamics, redundancy, and predictive value of the model systems. The models will be optimized through iterative experimental validation and theoretical modifications. The systems biology approach will not only help the global understanding of biology but also facilitate e.g. the identification of key molecular regulators and pathways as targets for drug discovery. A quantitative leap from the descriptive "cartoon" view of biology to systems biology and the physiome of microbe-host interplay is a fascination challenge that we look forward to exploring with our research.

Wang Y, Hollingsworth RI. An NMR spectroscopy and molecular mechanics study of the molecular basis for the supramolecular structure of lipopolysaccharides. Biochemistry 1996;35:5647-5654. [abstract]

Wang Y, Hollingsworth RI, Kasper DL. Ozonolysis for selectively depolymerizing polysaccharides containing ß-D-aldosidic linkages. Proc Natl Acad Sci USA 1998; 95: 6584-6589. [abstract]

Wang Y, Huebner J, Tzianabos AO, Martirosian G, Kasper DL, Pier GB. Structure of an antigenic techoic acid shared by clinical isolates of Enterococcus faecalis and vancomycin-resistant Enterococcus faecium Carbohydrate Research 1999;316:155-160. [abstract]

Wang Y, Hollingsworth RI, Kasper DL. Ozonolytic degradation of carbohydrates in aqueous solution. Carbohydrate Research 1999;319:141-7. [abstract]

Wang Y, Kalka-Moll WM, Roehrl MH, Kasper DL. Structural basis of the abcess-modulating polysaccharide A2 from Basteroides fragilis. Proc Natl Acad Sci USA 2000; 97: 13478-13483.

Wang Y, Kalka-Moll WM, Roehrl, MH, Kasper DL. Structural basis of the abscess-modulating polysaccharide A2 from Bacteroides fragilis. Proc Natl Acad Sci USA 2000;97:13478-13483. [abstract]

Wang JY, Roehrl MH. Glycosaminoglycans are a potential cause of rheumatoid arthritis. Proc Natl Acad Sci USA 2002; 99: 14362-14367.

Wang JY, Bhang AHC, Cuttormsen H-K, Rosas AL, Kasper DL. Construction of designer glycoconjugate vaccines with size-specific oligosaccharide antigens and site-controlled coupling. Vaccine 2002, in press.

Choi, Y-H, Roehrl MH, Kasper DL, Wang JY. A unique structural pattern shared by T-cell activating and abscess regulating zwitterionic polysaccharides. Biochemisty 2002, in press.