168
chapter
10
Heteropolysaccharides I: Glycoproteins and Glycolipids
T A B L E 1 0 -5
ABO Blood Group System and the Agglutination Reaction
*
Blood
Type
Type of Oligosaccharide
Antigens Present
on Red Blood Cells
Antibody
in Serum
Types of Serum That Cause
Agglutination When Mixed
with Red Blood Cells
O
H
Anti-A, anti-B
None
A
A
Anti-B
O, B
B
B
Anti-A
O, A
AB
A and B
None
O, A, B
*Red blood cells from type O individuals can be donated to individuals with any other cells from type within the ABO system without causing
agglutination. Individuals with type AB can accept red blood cells from all other types but cannot donate to individuals with other types except AB.
Thus, type O individuals are known as universal donors and AB as universal acceptors.
converted to type B red blood cells. The reverse conver-
sion can be accomplished by incubation of cells in the
presence of a-galactosidase, which removes the terminal
galactose residue. Glycophorins A and B possess anti-
genic determinants for the M and N blood group antigens,
respectively.
Rh blood group antigens
are clinically important due
to their involvement in hemolytic disease of the newborn,
transfusion medicine, and autoimmune hemolytic anemia.
The designation of Rh stands for
Rhesus
because the anti-
body specificity was identical to that of antibodies gener-
ated in rabbits injected with red blood cells from Rhesus
monkeys. The Rh blood group system consists of more
than 50 nonglycosylated protein antigens; however, only
five are commonly identified; these are encoded by two
genes termed RHD and RHCED. Marked racial differ-
ences are observed for Rh alleles in different populations.
Typically, 85% of all Caucasians are Rho(D)-positive.
Anti-Rho(D) immunoglobulin G (IgG) prepared from
human plasma is administered intramuscularly as means
of passive immunization to Rho(D)-negative individuals
exposed to Rho(D)-positive cells.
Rh proteins have a molecular weight of about 32,000
and span the red blood cell membrane. Rh proteins are
incorporated into the erythrocyte membrane after palmi-
tolyation via thioester linkages involving free sulfhydryl
groups of cysteine residues. The exact function of Rh pro-
teins is not known, however, individuals lacking all Rh pro-
tein expression exhibit multiple red blood cell abnormal-
ities including abnormal morphology and survival. This
condition is known as
Rhnun syndrome. A
number of pro-
tein blood group antigens possessing a variety of functions
are shown in Table 10-6.
Blood group antigens including both oligosaccharides
and proteins are expressed on other cell surface struc-
tures as well as on erythrocytes. These antigens func-
tion as receptors for a variety of infectious agents.
Examples of oligosaccharide antigens include P antigen,
which is the receptor for B19 parvovirus; individuals who
do not express this antigen show no serological evidence
of past infections with this common childhood pathogen.
Leh
antigen is the epithelial receptor for
Helicobacter
pylori,
which is the causative agent of peptic ulcer dis-
ease (Chapter 12). Lewis antigens function as receptors
for a wide variety of pathogens including
S. aureus,
N.
meningitidis,
H.
influenzae, N. gonorrhoeae,
and
C. albicans.
Blood group antigen-bearing proteins also serve as re-
ceptors for infection agents (Table 10-7). A notable exam-
ple is the presence of receptors in the Duffy blood group
antigens to
Plasmodium vivax
and
Plasmodium knowlesi.
Individuals who do not express Duffy antigens are resis-
tant to infection by these malarial parasites.
10.4 Serum Glycoproteins
Almost all serum proteins, with the notable excep-
tion of albumin, are glycoproteins. The sugar residues
found most commonly in the outer domain of the
oligosaccharides of these glycoproteins are galactose, N-
acetylhexosamine, and sialic acid. L-Fucose is a minor
constituent. The structure of a typical oligosaccharide
chain of a serum glycoprotein is shown in Figure 10-14.
The liver plays a major role in the
synthesis and
catabolism of these proteins. Glycoproteins lose their
terminal sialic acid residues through the action of neu-
raminidase (sialidase) during circulation in the blood,
which exposes the galactose residues (Figure 10-14). The
resulting galactose-terminated glycoproteins, known as
