4th Jenner International Glycoimmunology Meeting

IMMUNOLOGY

4th Jenner International

Glycoimmunology

John S. Axford

TODAY

Meeting

IMMUNOLOGY

TODAY

library has been likened to diving off a high board and then, as the pool gets closer, asking if there is water in it (0. Hindsgaul,

Edmonton, Alberta); nevertheless one is being constructed and the pool is getting closer!

Sugar

therapeutics

There is much optimism within th+, biotechnology industry that syntheti, oligosaccharides may be potent and nontoxic therapeutics. A useful model to test their use is in acute cardiac graft rejection, where there is increased cardiac endothelial expression of sLe” and sLe” epitopes, which results in an increase in lymphocyte infiltration into cardiac tissue. It has been known for some time that interfering with this pro:ess, by blocking L-selectin with antibodies x removing sialic acid within the tissues, reduces lymphocyte trafficking. A synthetic tetravalent sLe” has now been manufactured and has been found to reduce lymphocyte binding (R. Renkonen, Helsinki) md therefore has the potential to be a novel anti-graft rejection drug. Two patient-based trials using a synthetic oligosaccharide called Cylexin are at a more advanced stage in trials. In one hial, which required significant optimism and product belief to perform, prevention of cardiac muscle reperfusion injury following acute myocardial infarction was attempted. Although patients derived little benefit from infusion of this suger analogue, it did prevent tissue damage following pulmonary thromboendarteriomy a. Paulson, S;n Diego, CA). Four other therapeutic trials are currently ongoing worldwide, covering a wide spectrum of disease from Escherichin coli toxin inhibition to carbohydrate vaccination to prevent growth and metastasis of breast cancer. Carbohydrate therapeutics might also be of benefit in the removal of autoantibodies that might cause graft rejection by binding to Gal-a(l,J)-Gal following organ transplantation. Once a protein-sugar interaction has been identified that may be pertinent to the disease mechanism in question, a rational approach to designing a sugar inhibitor would be to understand how such an interaction may take place. Multidimensional, multinuclear, nuclear magnetic resonance

spectroscopy is thought to be able to achieve this 6. Homans, Fife; E. Hounsell, London). However, the complexities of analysis and the potential problems involved with three-dimensional drug design, beg the question of whether a bit of luck in screening experiments would be a more palatable alternative. In addition to using sugars to block protein-sugar interactions, sugar therapeutics may be designed to inhibit glycosylation altogether. Human hepatitis B virus contains three distinct enveloped glycoproteins called L, M and S. The glycosylation of M-glycan can be inhibited by N-butyldeoxynojirimycin (NB-DNJ) and, in so doing, arrests viral particle secretion (A. Mehta, Oxford; T. Block, Philadelphia, PA). Perhaps this could be a very useful means of preventing hepatitis B pathology. Molecular manipulation may also be used to alter the expression of glycosyltransferases and this is thought to have particular PO_ tential in arresting tumour growth and metastasis (A. Mackiewicz, Poznti).

Sugars

and physiological

mechanisms

The multifaceted influences that sugars have on physiological processes is fully illush.ated by the involvement of O-GlcNAc in several important cellular processes. For example, 0-GlcNAc is found on micmtubular proteins and seems to be associated with Abheimer’s disease (G. Hart, Birmingham, AL). It may also be associated with cellcycle regulation and oncogene mutations in human lymphoma. Interestingly, the 0-GIcNAc transferase has recently been cloned, sequenced and expressed and it seems that the enzyme itself can be modified by O-GlcNAcylation. The calnexin/calreticulin proteins are involved in ensuring efficient protein pmduction by assisting folding within the spatial confines of the endoplasmic reticulum and also by directing misfolded glycopmteins out of the biosynthetic p~~ess a. Bergeron, Montreal, Quebec). They do this by their involvement in a complex chaperone apparatus that is able to recognize certain N-linked sugars and become attached to the protein during its synthesis.

Cytokines are pivotal to the inflammatory cascade and sugars may be involved in their function in a number of ways. Sugars may increase cytokine heterogeneity by the generation of glycoforms, which may have varying levels of activity; this is certainly the case with interferon a. In addition, cytokines may exert their influence by binding to sugar shuctures associated with their receptor. Indeed, tumour necrosis factor 0: (TNF-4 has been shown to bind to sugar structures on the TNF-u receptor via lectinlike domains (G. Opdenakker, Leuven). Acute phase proteins (APPs) are examples of ubiquitous serum proteins without a definite function. One role they may have is as naturally occurring anti-inflammatory molecules. This is because three APPs -

or&rated to express sLe’ determinants only in inflammatory conditions U. van LX]%, Amsterdam). This may come about by increased expression of the glycosyltransferase enzyme fucosyltrawferase VI and mesuit in the APP binding to E-selectin via its sL@ determinant. In turn, this will prevent white cell extravasation from the circulation into potential areas of inflammation.

CD59

glycosyiation

Modem technology and experimental resilience has resulted in the complementinhibiting protein CD59 being the first cell-surface glycoprotein to have its sugar structures fully characterized (P. Rudd, Oxford). Thii molecule contains all three types of post-translational modification known to involve glycosylation: addition of a glycosylphosphatidylinositol anchor, together with N-linked and O-linked glycosylation. High-pressure liquid chmmatography (HPLC) showed over 130 N-linked oligosaccharides with different compositions linked to a highly conserved N-linked glycosylation site at Asn19. It is thought that this heterogeneous array of sugars may orientate the active site of CDS9 while protecting it from protease cleavage. In a similar fashion, high-pH anion-exchange chmmatography (HPAEC) can be useo to detect 26 different oligosarrharides from cr,-protease inhibitor and haptoglobin, and has been used

IMMUNOLOGY

renal failure

TODAY

and is eswciand

IgA glycmylation sugarsarc

such

non to the N-linked U. Feehally,

mmunoglobulin gfycorytation

was

+fuch is known abut

autamtibodies

n non-arganqxiffc

autoimmune

uch as rheumatoid emit lupus s known

arthritis

they

oid faclar

disease,

xdathogerresis of disease

factors

bat the complex

bind to the

to an epitope

from both domains.

Cy2 and

remarks

Glyccbinkrgy

is goq

tobea

fmitfularw

of ways in which

plsm

and looks x4

ofrwparch.bothinternv sugars

modulate

the most

in the ratio of two

clinician

are the new thempcutifl

Cy3

factor

cvllular crcitmg

protein

pmxses

BUI

aspect

for tht that ,w

on the horizu”.

residues

mnstant-region

of this interaction

as only one edge

anhiy-binding

Concluding

and q&he

mmplising

The topology

unique

to nom~al IgA the biochemical

rrmalnr

perhaps

agatacto

Fab to o”e Fc and each rheumatoid binds

is

of the potmtial

site seems to be involved.

The number of mmact residues is also small. which results in low-affinity binding. The sugars

in this region

be fntfmately

assaiated

but perhaps

the

synthetic when

was

is a p&se

of physiological

a pmteii

possible

of galadose.

gfyemylation p-

to

the bmdm&

interactto”

due to the at)Eeaa Protein

do not appear with

such

specific glycmylation

bie

&vance.

as IgG has diseaw changes,

it is possible

Ularthe~nangemaybetnkedwithaptho logical

p-

In multiple

is h~alact~ylation this

disease

msyhtion

my&ma.

there

of IgG and, &though

is clonal profiles

in nature,

the gly-

of the pamprotein

over the COUM of the disease

vary

(R. tffetis,

Birmingham). I” RA, earlier a reduction sugars.

work

has also indicated

of gafactme

It is thought

antat

&l,+GTase

of s@fic

may

modulating mation However, the

in the inha-

activity.

RA-aswciated

v

in 1gG

that this may be due

to some form of abnormality c&lar

indicate

GTsse

activity

af isoforms,

The p~psence

serum that

GTase iso-

a method

possibly

of single

of

is via the forglycofonna.

there are other pmsibilitin,

replact?me”t

was

is whether

function

human

Londonh binds

or whether

of &I,3

8 cells

‘s not know”

It was found

R regron of a mcmoclonal iyl IgG (B. Sutton,

eiu-

has bee” used to

study how rheumatoid

levels

blood

mar-

its role in the

has remained

;ive. X-ray cry&Jography

A furtlv_: cimikwity

reduced

Rheuma-

diagnostic

ceer for RA, but unravelling

fash-

on IgC in RA

that ~cccwcr revert prints

abnormality

mechanisms

are asr;oc~ated

Wha

patients sugar

when

peripheral

dew&d.

ISLE), but little

is a” important

in

the @linked

in a similar

sugars

Leic&er).

found

G&e

(RA) and sys-

erythematoaus

about the pathogenic

vath which

found

with altered

that

agalactosylated

amino

and acids

NOVFMBFR

I997