All healthy humans
have high levels of natural anti-α-galactosyl
(α-Gal) antibodies (elicited by yet uncharacterized glycotopes),
which may play important roles in immunoglycomics: (a) potential protection
against certain parasitic and viral zoonotic infections; (b) targeting
of α-Gal-engineered cancer cells; (c) aiding in tissue repair;
and (d) serving as adjuvants in α-Gal-based vaccines. Patients
with certain protozoan infections have specific anti-α-Gal antibodies,
elicited against parasite-derived α-Gal-bearing glycotopes.
These glycotopes, however, remain elusive except for the well-characterized
glycotope Galα1,3Galβ1,4GlcNAcα, expressed by
Trypanosoma cruzi
. The discovery of new parasitic glycotopes
is greatly hindered by the enormous structural diversity of cell-surface
glycans and the technical challenges of classical immunoglycomics,
a top-down approach from cultivated parasites to isolated glycans.
Here, we demonstrate that reversed immunoglycomics, a bottom-up approach,
can identify parasite species-specific α-Gal-bearing glycotopes
by probing synthetic oligosaccharides on neoglycoproteins. This method
was tested here seeking to identify as-yet unknown glycotopes specific
for
Leishmania major
, the causative agent of Old-World
cutaneous leishmaniasis (OWCL). Neoglycoproteins decorated with synthetic
α-Gal-containing oligosaccharides derived from
L. major
glycoinositolphospholipids served as antigens in a chemiluminescent
enzyme-linked immunosorbent assay using sera from OWCL patients and
noninfected individuals. Receiver-operating characteristic analysis
identified Gal
p
α1,3Gal
f
β
and Gal
p
α1,3Gal
f
β1,3Man
p
α glycotopes as diagnostic biomarkers for
L. major-
caused OWCL, which can distinguish with 100% specificity
from heterologous diseases and
L. tropica-
caused
OWCL. These glycotopes could prove useful in the development of rapid
α-Gal-based diagnostics and vaccines for OWCL. Furthermore,
this method could help unravel cryptic α-Gal-glycotopes of other
protozoan parasites and enterobacteria that elicit the natural human
anti-α-Gal antibodies.