Immunogenic Glycoconjugates Implicated in Parasitic Nematode Diseases

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Biochimica et Biophysica Acta 1455 (1999) 353^362 www.elsevier.com/locate/bba

Review Immunogenic glycoconjugates implicated in parasitic nematode diseases

Anne Dell a;*, Stuart M. Haslam a, Howard R. Morris a, Kay-Hooi Khoo b

a Department of Biochemistry, Imperial College of Science Technology and Medicine, London SW7 2AZ, UK b Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan

Received 13 October 1998; received in revised form 11 February 1999; accepted 1 April 1999

Abstract

Parasitic nematodes infect billions of people world-wide, often causing chronic infections associated with high morbidity. The greatest interface between the parasite and its host is the cuticle surface, the outer layer of which in many species is covered by a carbohydrate-rich glycocalyx or cuticle surface coat. In addition many nematodes excrete or secrete antigenic glycoconjugates (ES antigens) which can either help to form the glycocalyx or dissipate more extensively into the nematode's environment. The glycocalyx and ES antigens represent the main immunogenic challenge to the host and could therefore be crucial in determining if successful parasitism is established. This review focuses on a few selected model systems where detailed structural data on glycoconjugates have been obtained over the last few years and where this structural information is starting to provide insight into possible molecular functions. ß 1999 Elsevier Science B.V. All rights reserved.

Keywords: Nematode; Glycoconjugate; Antigen; Structure

Contents

1. Introduction ...... 354

2. The biology of nematodes ...... 355

3. Glycosylated nematode antigens ...... 355 3.1. Overview ...... 355 3.2. O-Methylated glycans of Toxocara ...... 356 3.3. Tyvelose as an immunodominant epitope ...... 357 3.4. Phosphorylcholine substituted glycans ...... 358 3.5. Novel fucosylated N-glycan core structures ...... 359

4. Concluding remarks ...... 359

Acknowledgements ...... 360

References ...... 360

* Corresponding author. Fax: +44-171-2250458; E-mail: [email protected]

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1. Introduction Table 1 Outline classi¢cation of the nematodes, emphasis on nematode `Parasitic helminth' is a loosely de¢ned term that is orders and families containing important human parasites commonly used to describe metazoan parasites from Phylum: Nematoda (roundworms) mainly two phyla, the Nematoda (roundworms) (see Subclass: Aphasmidia Order: Trichocephalida Table 1), and the Platyhelminths (£atworms) which Trichinella spiralis, Trichuris trichuria (whipworm) include the class Cestoda (tapeworms) and the class Subclass: Phasmidia Trematoda (£ukes). Helminth infections are highly Order: Rhabditida prevalent globally, particularly among the popula- Strongyloides stercoralis, Caenorhabditis elegans (laboratory tion of the developing world. It is estimated that model) over 3 billion cases of single or mixed infections Order: Strongylida Family: Trichostrongylidae are caused by the three most prevalent intestinal Haemonchus contortus (parasite of domestic ruminants) nematodes: large roundworm (Ascaris lumbricoides), Family: Ancylostomatidae (hookworm) whipworm (Trichuris trichuria), and hookworm (An- Necator americanus, Ancylostoma duodenale, and other Ancylos- cylostoma duodenale and Necator americanus) [5]. In toma spp. addition, about 150 million people are a¥icted by Order: Ascaridida Family: Ascaridae lymphatic ¢lariasis and onchocerciasis due to infec- Ascaris lumbricoides, Toxocara spp. (only larvae in humans) tion with one of the ¢larial nematodes (Wuchereria Order: Oxyurida bancrofti, Brugia malayi, Onchocerca volvulus) Enterobius vermicularis (pinworm) [40,41]. Order: Spirurida In humans, the most striking feature of parasitic Family: Filariidae helminths is protracted survival within the host, with Wuchereria bancrofti, Brugia malayi (causing lymphatic ¢lariasis), Onchocerca volvulus (causing river blindness and onchoder- disease severity typically related to cumulative worm matitis), Acanthocheilonema viteae (laboratory model) burden. Disease may result from local host immuno- Family: Dracunculidae logical responses to sites at which the parasites have Dracunculus mediinensis (causing dracunculiasis or guinea worm accumulated, as well as tissue damage generated by disease) the invasion, migration, and development of larvae in the host. Tissue reactions include immediate hy- persensitivity, allergic reactions, and delayed-type cell mediated reactions with granuloma and giant sion, host mimicry, evasive diversionary strategies, or cell formation. Although infection seldom leads to perhaps involvement in host lectin binding, targeting, severe acute illness or death, moderate and chronic and signalling. Any role in disease manifestation is infection does engender morbidity and signi¢cantly arguably incidental, due to improper or excessive impairs the quality of life, economic productivity, host responses to the o¡ensive antigens. and even the physical and cognitive development in This minireview is not intended to be a compre- children with high worm load. hensive coverage of all glycoconjugates identi¢ed or To date, there is no de¢nitive identi¢cation of a implicated in parasitic helminth diseases or immu- particular helminth glycoconjugate in mediating a nobiology. Rather, we focus on a few selected model speci¢c host immune response which would lead to systems where detailed structural data on glycocon- manifestation of clinical pathology or disease. Yet it jugates have been obtained over the last few years. It is well recognised that the parasite antigens, either is our ¢rm belief that only when structural data are excreted-secreted (ES antigens) or on the surface, in hand can we begin to understand the glycobiology are key modulators or targets of host immune sys- of host-parasite interactions. The trematode schisto- tems [3,28], and that the immunodominant epitopes some remains the single most well studied system and are often glycans of very unique structures [31^34]. It is separately addressed elsewhere in this volume [6]. is felt that the respective glycoconjugates must medi- We focus here on the parasitic nematodes. Several ate speci¢c parasite defense or survival mechanisms, recent general reviews on helminth immunology can possibly in the form of immune-modulation/suppres- be found elsewhere [1,10,11,14,37,38,45] and inter-

BBADIS 61869 15-9-99 A. Dell et al. / Biochimica et Biophysica Acta 1455 (1999) 353^362 355 ested readers are referred to these articles for a more at least some of the excretory/secretory (ES) prod- in-depth discussion on the immunological responses ucts. elicited by parasitic antigens.

3. Glycosylated nematode antigens 2. The biology of nematodes 3.1. Overview The important parasitic nematodes of humans are commonly grouped into two subsets, the intestinal The nematode surface and ES antigens represent nematodes and the ¢larial species. Most nematodes the major immunogenic challenge to the host and share highly conserved developmental stages. The di- may be the key to successful parasite defense strat- oecious adults sexually produce eggs that hatch to egies. It is well recognised that the immunodominant release L1 larvae which, with intervening cuticular epitopes on both sources of antigens are often peri- moults and size increases, develop through three odate- and/or peptide-N-glycosidase sensitive. The more larval phases (L2, L3, and L4) before attaining prevalence of saccharide determinants on the parasite full sexual maturity. Transmission to a new host de- surface and the ES antigens was further shown by pends upon the ingestion of mature infectious eggs numerous lectin binding studies (reviewed in [34]). or larvae, or the penetration of the skin or mucous Yet, to date, only a few of the implicated glycans membrane by the larvae. The soil-transmitted intes- have actually been structurally de¢ned. Two oppos- tinal nematodes have evolved a direct life cycle; their ing characteristics are applicable to these glycosy- eggs or larvae normally leave the host via the faeces lated epitopes, namely antigenic speci¢city and and become infective during a period of development cross-reactivity. The former implies that a particular in the soil. Infections with the insect vector-transmit- nematode species or its larval stage may harbour ted ¢larial species are initiated when the blood suck- unique saccharide sequences which are speci¢c ing vectors bite; the L3 larvae emerge from the insect enough to be clinically diagnostic, as exempli¢ed by mouth parts and actively penetrate the feeding the tyvelose containing glycans of T. spiralis (see wound in the skin before migrating to the ¢nal site Section 3.3). The latter relates to the phenomenon of infection. Not uncommonly larval stages in mam- that the same immunogenic epitope may be present malian hosts may undergo diapause or arrested de- on di¡erent core glycan structures or protein/lipid velopment, until triggered by a hormonal signal (e.g. carriers from various parasite sources, as best exem- Toxocara canis), or awaiting ingestion of one host by pli¢ed by the phosphorylcholine (PC)-containing the next (e.g. Trichinella spiralis). antigens (see Section 3.4). The cuticle which is extensively remodelled with As elegantly summarised by [37] in their review, each moult stage is a central element in the structural one of the defense strategies employed by parasites organisation of all nematodes. It is a collagen-rich including the nematodes is to avoid or block initial extracellular matrix above the epidermis, and has induction of damaging immune responses by confer- on its external surface a lipid-rich epicuticle which ring `self' status upon themselves through molecular may resemble a unit membrane. An additional outer mimicry and uptake of host antigens, or by a diver- envelope, in the form of a loosely attached carbohy- sionary tactic. The latter seems to be the most expe- drate-rich surface coat or glycocalyx, has further dient way to rationalise the synthesis and display of been identi¢ed in many nematodes [3,37]. It was highly antigenic glycans on a myriad of nematode demonstrated that in nematode species which possess surface and ES antigens examined to date. Maizels such a surface coat, their surface-labelled proteins and colleagues further advance the theory that the could be distinguished as either integral cuticle pro- nematode surface coat is dynamically responsive to teins synthesised and secreted from the underlying changing host environments or immune attack and epidermis, or those associated with the dynamic sur- can be rapidly shed. Thus, surface bound antibodies face coats derived from specialised secretory glands, and activated immune e¡ector cells recognising the therefore sharing the same biosynthetic origins with bound antibodies can both be sloughed o¡; deposits

BBADIS 61869 15-9-99 356 A. Dell et al. / Biochimica et Biophysica Acta 1455 (1999) 353^362 of discarded surface coat can act as a smokescreen, vated larval parasite [36]. Interestingly, cross-reactive diverting immune attention to static deposits and immunodominant saccharide determinants as de¢ned away from a mobile nematode. The high antigenicity by the monoclonal antibodies (Tcn monoclonals) of the nematode glycoconjugates therefore plays a were shown to be commonly present on most of role in engaging the host immune response to a futile the surface and ES antigens, as well as on those end game. In severe cases, the excessive and hyper- from the related species, Toxocara cati. Yet, among sensitivity responses lead to pathological symptoms these, one monoclonal antibody, Tcn-2, was speci¢c and diseases. enough to recognise only saccharide determinants It remains possible that the nematode glycoconju- from T. canis and not any of the T. cati ES products gates have more subtle roles in mediating other bio- [23,31]. A probable structural basis for these obser- logical events. Many of the highly immunogenic gly- vations was provided when the major glycans present coconjugates have been shown to be capable of on the heavily O-glycosylated ES glycoproteins of T. compromising selected arms of the immune system, canis and T. cati were characterised [25]. Structural disabling the short-range o¡ensives mounted by var- analysis showed that the major O-glycans from T. ious e¡ector mechanisms. Possibly the quantity and canis are two, approximately equally abundant, chemical nature of glycoconjugates produced may trisaccharides 2-O-Me-Fuc(K1-2)4-O-Me-Gal(L1-3)- interfere with antigen processing; secretions contain- GalNAc, and 2-O-Me-Fuc(K1-2)Gal(L1-3)GalNAc, ing PC may act to inhibit activation, or induce a whereas those from T. cati are predominantly the state of immunological unresponsiveness, or toler- di-O-methylated trisaccharides. Similar studies on ance, or perturb the Th1/Th2 balance. Yet, to date, the ES antigens of a related ascarid, Ascaris suum, we do not have convincing evidence to either ¢rmly showed that their major O-glycans are not O-methy- support or refute these putative roles. More structur- lated and two major components were de¢ned by al data are obviously needed to permit molecular mass spectrometric analysis as having the glycosyl dissection of the immunobiology of parasitic dis- compositions dHex1Hex1HexNAc1 and dHex1Hex1- eases. HexNAc2 [26]. The species-speci¢c unique O-methylation found 3.2. O-Methylated glycans of Toxocara on an otherwise quite common oligosaccharide sequence most likely contributes to the epitope recog- The ¢rst ever glycosylated nematode antigens of nised by the Tcn monoclonals. Thus, despite substan- which the glycan moieties were studied and structur- tial reactivity of anti-T. canis ES serum on A. suum ally characterised in any detail, and from which most L3/4 ES products, none of the anti-saccharide Tcn of the general themes discussed above originated, are monoclonals recognised the A. suum ES antigens those from the intestinal parasite of dogs, T. canis [24], consistent with the absence of O-methylation [25,26,35]. Apart from being a signi¢cant veterinary in the latter. Whilst the biological relevance of the problem, the infective L2 larvae emerging from the underlying blood group H-like sequence, namely soil-transmitted eggs of this ascarid parasite can in- Fuc(K1-2)Gal(L1-3)GalNAc, is still a moot point, vade and survive in a broad range of paratenic hosts the immunogenicity conferred by such unique mod- including human. Often, the larvae become develop- i¢cations on conserved common core structures is a mentally arrested but remain metabolically active recurring theme in nematode glycans (see later sec- and migrate through many tissues, causing muscular tions) and probably represents a common nematode weakness, eosinophilia, hepatosplenomegaly, and defense mechanism against the host immune surveil- bronchospasm, as well as optical and neurological lance, as discussed above. It has been demonstrated lesions [13,50]. that of the Tcn monoclonals raised against ES anti- Surface labelling and probing with monoclonal gens, Tcn-2 and Tcn-8 could bind to intact larvae antibodies have revealed a set of well de¢ned, signi¢- and immunoprecipitate surface-labelled TES anti- cantly glycosylated, larval stage-speci¢c, surface ex- gens. This leads to the proposal that TES glycopro- posed antigens (named TES-32, 55, 70, 120), all of teins may ¢rst appear transiently as constituents of which are also released as ES antigens by the culti- the surface coat and are then shed as ES antigens

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atode family is T. spiralis, the causative agent of trichinosis, whose L1 larval stage has the unique ability to de-di¡erentiate striated muscle cells. T. spiralis has one of the widest ranges of potential hosts of any known parasite and is capable of infecting almost any mammal. Its life cycle is completed within a single host species, without the requirement for an intermediate vector or a free-living larval stage. The commonest mode of transmission to humans is via ingestion of animal muscle tissue (usually pork) containing viable mature L1 larvae. Once inside the human host the larvae invade the mucosal epithelium of the small intestine, moult to adulthood, mate and reproduce. Despite their relatively large size (males are about 1.5 mm in length and females about 3 mm) the worms inhabit an intracellular niche. The diam- eter of the adult worms is comparable to that of the cells which they invade, but being many times longer they occupy a number of cells simultaneously, migrating through the epithelial layer in a sinusoidal manner leaving a trail of dead cells in their wake. Females can produce up to 2000 ¢rst stage larvae (L1) during their lifespan. The newborn larvae enter the general circulation, establishing transient infections in various organs before arriving at their ¢nal destination in striated skeletal muscle. Once the larva has invaded a muscle cell, de-di¡erentiation begins Fig. 1. Structures of unusual N-glycans recently identi¢ed in and conversion to a specialised cell referred to as a three types of nematode. Nurse cell occurs over a 20 day period post infection. The mechanisms by which infective larvae of T. although direct secretion is also possible. Being spiralis recognise, invade, and migrate within the in- strongly immunogenic, the prodigious production testinal epithelium are unknown. However, it is likely of the antigens would be most e¡ective in diverting that carbohydrate structures on the surface and/or in the host immune response away from the true larval ES products are important in these events. Evidence surface, the cuticle. Signi¢cantly, the cDNA from the for this comes from experiments which have shown gene encoding the apoprotein precursor of the most that monoclonal antibodies developed against ES abundant surface coat constituent, TES-120, has re- antigens e¡ect rapid expulsion of infective larvae in cently been isolated and inferred to contain a typical passively immunised neonatal rats [43]. The mono- mucin domain, consistent with it being heavily O- clonal antibodies recognise highly unusual carbohy- glycosylated [12]. Thus the surface coat may confer drate epitopes which are present in the ES glycopro- additional properties on the nematodes in a fashion teins and also on the cuticular surface of the larvae. similar to the known protective functions of mamma- The immunodominant glycans of the L1 stage are lian mucin. tri- and tetraantennary N-linked structures composed of GalNAcL1-4GlcNAc (lacdiNAc) antennae which 3.3. Tyvelose as an immunodominant epitope are capped with D-tyvelose (3,6-dideoxy-D-arabino- hexose). The majority of antennae are also fucosy- Arguably the most fascinating member of the nem- lated (Fig. 1). Tyvelose is a sugar more typically

BBADIS 61869 15-9-99 358 A. Dell et al. / Biochimica et Biophysica Acta 1455 (1999) 353^362 associated with the cell wall lipopolysaccharides of including blindness (onchocerciasis is commonly re- some pathogenic bacteria where it is a dominant ferred to as `river blindness'). antigenic determinant. Its presence in a eukaryotic Filarial nematodes require an intermediate host for glycoprotein is thus highly unusual. The structures the completion of their life cycle. The adult female of the novel ES glycans were established from com- produces thousands of micro¢lariae which pass into plementary data acquired from three groups of re- the blood and are ingested by the feeding intermedi- searchers. Firstly, the dideoxysugar was isolated and ate host. W. bancrofti and B. malayi use various spe- its structure, including absolute stereochemistry, was cies of mosquitoes as their intermediate host, where- established by [54], largely using GC-MS technology. as O. volvulus uses the black£y. The micro¢lariae Secondly the complete structures of the tri- and tet- develop into infective third stage larvae in the inter- raantennary glycans, with the exception of the tyve- mediate host and are reintroduced into humans dur- lose anomeric stereochemistry, were de¢ned by [49], ing the course of the insect vectors' feeding, where using a FAB-MS strategy. Finally, synthesis of a they migrate to the lymphatic system and complete panel of oligosaccharides capped with K- and L- their development to adults. linked tyvelose and analysis of their ability to be A characteristic of ¢larial nematode antigens is recognised by the anti-tyvelose monoclonal antibod- their immuno-cross-reactivity which is due to the ies revealed, surprisingly, that the tyvelose has L ster- shared epitope PC [33]. Attempts to characterise eochemistry in the ES antigens [9]. both the immunological function and the biochemi- Recent studies have shown that anti-tyvelose cal structure of ¢larial PC antigens is hampered by monoclonal antibodies are able to prevent larval in- obtaining enough experimental material from human vasion of MDCK tissue cultured cells thus establish- parasites. Therefore a model system was developed ing that tyvelose-speci¢c antibodies are protective in using a 62 kDa excretory-secretory glycoprotein (ES- vitro, and providing further support for the hypoth- 62) from the rodent ¢larial nematode Acanthocheilo- esis that tyvelose plays a role in in vivo tissue inva- nema viteae. Observations that peptide N-glycosidase sion [39]. Muscle-stage larvae (L1) are also rich in F removes all radioactivity from [3H]choline labelled tyvelose but it is not known whether glycans play a ES-62 and also removes binding sites for a PC spe- role in de-di¡erentiation. Nevertheless it is interesting ci¢c monoclonal antibody in conjunction with the that a tyvelosylated 43 kDa glycoprotein secreted by fact that nematodes cultured with inhibitors of N- the muscle stage larvae locates exclusively to the glycan processing secreted a protein which lacks PC Nurse cell cytoplasm from day 12 to day 15 of Nurse led to the conclusion that PC is attached to ES-62 via cell development [51]. a N-linked glycan [17]. Mass spectrometric structural analysis revealed that the PC substituted N-glycans 3.4. Phosphorylcholine substituted glycans of ES-62 are comprised of trimannosyl cores, with and without fucosylation, to which are added from Of all the diseases caused by human parasitic one to four additional N-acetylglucosamine residues worms, none are more physically striking than those (Fuc01Man3GlcNAc36) (Fig. 1) [20]. The PC com- caused by ¢larial nematodes. Lymphatic ¢lariasis ponent of ES-62 has been shown to interfere with the which is most commonly recognised by elephantiasis, activation via the Ag receptors of both murine B a painful and dis¢guring swelling of the limbs and cells [16], and a human T cell line [18], by interfering male genitals, is caused principally by infection with with key proliferative signalling pathways [8]. These W. bancrofti and B. malayi. The clinical pathology is e¡ects could contribute to the low antibody levels caused by adult nematodes inhabiting the lymphatic and poor lymphocyte responses observed in some vessels, often near the lymph nodes, leading to in- ¢lariasis patients. £ammation, distortion and dysfunction. In addition PC has also recently been characterised as a sub- a third ¢larial nematode, O. volvulus, causes oncho- stituent on carbohydrates of glycosphingolipids iso- cerciasis, a disease which manifests itself not only by lated from the porcine gastrointestinal nematode A. elephantiasis, itching, wrinkling and depigmentation suum [29]. Therefore it could be hypothesised that of the skin but also by serious visual impairment, the substitution of PC on nematode glycoconjugates

BBADIS 61869 15-9-99 A. Dell et al. / Biochimica et Biophysica Acta 1455 (1999) 353^362 359 could be a shared immunosuppressive strategy. Addi- highly antigenic epitope in both insect [44] and plant tional interesting characteristics of A. suum glyco- glycoproteins [48,53], and has also been shown to be lipids were that they were also substituted with phos- the major allergenic determinant in honeybee phos- phoethanolamine and that the oligosaccharide core pholipase A2 [27,52]. Therefore H. contortus could be belongs to the `arthro' series with a L-linked man- using these highly antigenic carbohydrate epitopes as nose. Acidic A. suum glycosphingolipids contained components of ES products or dynamic surface coat unusual phosphoinositol and 3-sulphogalactosylcere- glycoproteins to divert the host immune response broside structures [30]. away from the nematode. The characterisation of H. contortus N-glycans was extended to the infective 3.5. Novel fucosylated N-glycan core structures third stage larva. The majority of glycan structures observed in the adult were also found in L3 indicat- Haemonchus contortus is an economically impor- ing that most of the glycosyl transferases expressed tant gastrointestinal nematode that parasitises do- in the adult are also expressed at the L3 stage. The mestic ruminants. Large numbers of eggs are passed exception to this was the lack of the novel fucosyla- in the faeces of infected animals which hatch to pro- tion of the distal N-acetylglucosamine residue of the duce the non-parasitic L1 and L2 forms. After a chitobiose core [21] suggesting that the transferase further moult the infective third stage larva is in- responsible for this glycosylation is not expressed at gested by grazing animals and passes to the aboma- the L3 stage. It is not yet clear which types of struc- sum, or true stomach, where it undergoes the third tures are responsible for the larval speci¢c surface and fourth moults and reaches maturity. The life glycoprotein antigens that have been detected immu- cycle is similar to the closely related human hook- nologically [2,46,47]. As detailed structural informa- worms (A. duodenale and N. americanus), except that tion is obtained from a greater diversity of parasitic the infective third stage larva of these species can nematodes it is expected that the occurrence of stage directly penetrate the skin into the bloodstream speci¢c carbohydrate antigens and therefore stage where they migrate to the intestine via the heart speci¢c glycosyl transferase activities will be identi- and lungs. H. contortus is a blood feeding parasite ¢ed as a common characteristic. which therefore causes anaemia and a loss of animal condition; heavy infections can be fatal. Studies involving lectin binding, sensitivity of anti- 4. Concluding remarks body-binding epitopes to periodate oxidation, and susceptibility to peptide N-glycosidase F treatment, A number of structural principles are emerging indicated that immunogenic proteins in H. contortus from the recent work on nematode glycans. Firstly, were glycosylated but revealed little about the struc- oligomannosyl structures are abundant in many dif- ture of the glycans (see references contained in ferent nematodes as are truncated glycans with as [19,21]). With this in mind we set out to characterise few as one or two mannoses attached to the chito- in detail the N-glycan components of H. contortus biose core. Complex and hybrid structures are also glycoproteins. Our initial studies of the adult stage major constituents in many nematodes; these may of H. contortus revealed three families of N-glycans: have antennae truncated to a single GlcNAc. Non- high mannose structures, complex type structures truncated antennae commonly have backbones which with short antennae comprised mostly of lacdiNAc are composed of lacdiNAc (GalNAcL1-4GlcNAc), as and fucosylated lacdiNAc, and truncated structures observed in the N-glycans of Diro¢laria immitis [22] with highly unusual core structures. The cores are as well as Trichinella and Haemonchus (see above). substituted with up to three fucose residues including LacdiNAc is a relatively rare building block in higher a novel form of fucosylation on the distal N-acetyl- animals which more commonly use lacNAc (GalL1- glucosamine of the chitobiose unit [19] (Fig. 1). The 4GlcNAc); this could be due to the lack of expres- presence of N-glycans with di- and trifucosylated sion of L1;4-galactosyltransferase in nematodes [42]. cores is immunologically very interesting. The Fucose is a dominant modifying sugar and, as exem- FucK(1-3)GlcNAc moiety has been shown to be a pli¢ed by Haemonchus, it can occur in unusual loca-

BBADIS 61869 15-9-99 360 A. Dell et al. / Biochimica et Biophysica Acta 1455 (1999) 353^362 tions. The contribution of methyl groups to immu- [6] R.D. Cummings, A.K. Nyame, Schistosome glycoconju- nodominance is a common theme e.g. as integral gates, this volume (1999). components of fucose and tyvelose and as substitu- [7] R.A. DeBose-Boyd, A.K. Nyame, R.D. Cummings, Molec- ular cloning and characterization of an K1,3 fucosyltransfer- ents on the Toxocara O-glycans. Finally phospho- ase, CEFT-1 from Caenorhabditis elegans, Glycobiology 8 rylcholine is an important hapten in many glycan (1998) 905^917. epitopes. [8] M.R. Deehan, M.J. Frame, R.M.E. Parkhousr, S.D. Seatter, Knowing the structures of glycans implicated in S.D. Reid, M.M. Harnett, W. Harnett, A ¢larial nematode nematode infections is an important ¢rst step in elu- secreted product di¡erentially modulates expression and activation of protein kinase C isoforms in B lymphocytes, cidating their roles. Much progress has already been J. Immunol. 160 (1998) 2692^2699. made in this area and we anticipate a rapid growth in [9] L.A. Ellis, C.S. McVay, M.A. Probert, J. Zhang, D.R. Bun- the number of species examined and new structures dle, J.A. Appleton, Terminal L-linked tyvelose creates reported. Synthetic work will clearly be an important unique epitopes in Trichinella spiralis glycan antigens, Gly- component of parasite glycobiology because the tiny cobiology 7 (1997) 383^390. amounts of material that can normally be isolated as [10] F.D. Finkelman, T. Shea-Donohue, J. Golhill, C.A. Sulli- van, S.C. Morris, K.B. Madden, W.C. Gause, J.F. Urban pure compounds are rarely su¤cient for functional Jr., Cytokine regulation of host defense against parasitic studies. In this regard we expect the Caenorhabditis gastrointestinal nematodes: lessons from studies with rodent elegans genome project [4], which has already facili- models, Annu. Rev. Immunol. 15 (1997) 505. [11] D.O. 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