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Infect. Immun., Oct 1997, 4100-4107, Vol 65, No. 10
Y Han, T Kanbe, R Cherniak and JE Cutler
We previously reported that the immunoglobulin M (IgM) monoclonal antibody
(MAb) B6.1 protects mice against disseminated candidiasis, whereas the IgM
MAb B6 does not. Both MAbs are specific for an adhesin fraction isolated
from the cell surface of Candida albicans, but their epitope specificities
differ. In the present study, we examined the surface locations of both
epitopes and obtained structural information regarding the B6.1 epitope.
Immunofluorescence confocal microscopic analysis of C. albicans yeast forms
showed that epitope B6.1 is displayed rather homogeneously over the entire
cell surface, whereas epitope B6 appears to have a patchy distribution.
Both antibodies were essentially nonreactive with the surfaces of mycelial
forms of the fungus, indicating that neither epitope is expressed on the
surfaces of these forms. For isolation of the B6.1 epitope, the adhesin
fraction consisting of cell surface phosphomannan was subjected to mildly
acidic (10 mM HCl) hydrolysis and was fractionated into acid-labile and
acid- stable portions by size exclusion chromatography. Antibody blocking
experiments showed that the B6.1 epitope is an acid-labile moiety of the
phosphomannan and that the B6 epitope is located in the acid-stable
fraction. The B6 epitope appeared to be mannan because it was stable to
heat (boiling) and protease treatments but was destroyed by alpha-
mannosidase digestion. The B6.1 epitope eluted from the size exclusion
column in two fractions. Mass spectroscopic analyses showed that one
fraction contained material with the size of a mannotriose and that the
other was a mixture of mannotriose- and mannotetraose-size substances. Dose
response inhibition tests of the fractions indicated that the B6.1 epitope
is associated with the mannotriose. Nuclear magnetic resonance (NMR)
spectroscopic analysis of the epitope yielded data consistent with a
beta-(1-->2)-linked mannotriose. The fine structure of the B6 epitope is
under investigation. Information derived from these investigations will be
useful both in understanding protective versus nonprotective antibody
responses to C. albicans and in improving anti- Candida vaccine
formulations.
Copyright © 1997, American Society for Microbiology
Biochemical characterization of Candida albicans epitopes that can elicit protective and nonprotective antibodies
Department of Microbiology, Montana State University, Bozeman 59717- 3520, USA.
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