Whereas the usual (non-lipophilic) glycopolymers are weak immunogens, neoglycolipids Sug-PAA-PE can cause strong immune
response. Neoglycolipids bearing the haptens Ley ,SiaLea,
SiaLex, HSO3Lea adsorbed on Salmonella
minnesota (low carbohydrate mutant strain) were used as immunogens for
obtaining monoclonal and polyclonal antibodies.
The adjuvant properties of the bacteria gives strong immune response, whereas
the synthetic antigen provides a sufficient number of clones, giving rise
to the antibodies of the desired specificity. Figure 1 illustrates the absolute specificity of antibodies against the tetrasaccharide
Ley, which do not interact either
with the structurally very closely related tetrasaccharide Leb,
or with the tri- and disaccharide fragments of tetrasaccharide Ley.
Thus the approach of obtaining monoclonal antibodies with the help of synthetic
immunogen enables the generation of antibodies of custom specificity. It
should be noted that PAA-PE has several advantages over BSA, KLH and other
proteins as the matrix for an immunogen: Mabs obtained using Ley-PAA-PE
recognised the tetrasaccharide on cell membrane,
whereas Mabs raised against Ley-protein reacted strongly with
synthetic tetrasaccharide but poorly with natural Ley and also
cross reacted with Lex or H (type 2) structures. Two additional and unique advantages: i) the possibility of obtaining antibodies to masked or
immunologically "silent" antigens (e.g., alloantigens), and ii)
obtaining antibodies to defined topographical epitopes: antibodies could
be raised against the same oligosaccharide but would only recognise the
structure from a specific side or angle. The latter advantage has particular
value where in the proximity of adjacent molecules may cause steric hinderence
of the desired epitope. Thus, a correctly designed synthetic immunogen
can be used to perform primary selection of B-cells bearing the antibodies
of necessary topological specificity. The immunogen Ley-PAA-PE
with a high density of carbohydrate hapten on the polymeric chain has been
used to generate antibodies that recognise the tetrasaccharide on the surface
of Ley-positive cells. It appears,
that using more intricate immunogen construction, it would be possible
to obtain antibodies with other topographical specificity, such as those
simultaneously recognising the cluster of two or three closely located
haptens.
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