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Infection and Immunity, October 1998, p. 4845-4850, Vol. 66, No. 10
Department of Microbiology and Cell and
Molecular Biology Program, School of Medicine, University of
Nevada, Reno, Nevada 89557
Received 20 March 1998/Returned for modification 10 June
1998/Accepted 24 July 1998
Candida albicans activates the classical and
alternative complement pathways, leading to deposition of opsonic
complement fragments on the cell surface. Our previous studies found
that antimannan immunoglobulin G (IgG) in normal human serum (NHS) allows C. albicans to initiate the classical pathway. The
purpose of this study was to determine whether antimannan IgG also
plays a role in initiation of the alternative pathway. Pooled NHS was rendered free of classical pathway activity by chelation of serum Ca2+ with EGTA alone or in combination with immunoaffinity
removal of antimannan antibodies. Kinetic analysis revealed a 6-min lag in detection of C3 binding to C. albicans incubated in
EGTA-chelated NHS, compared to a 12-min lag in NHS that was both EGTA
chelated and mannan absorbed. The 12-min lag was shortened to 6 min by addition of affinity-purified antimannan IgG. The accelerating effect
of antimannan IgG on alternative pathway initiation was dose dependent
and was reproduced in a complement binding reaction consisting of six
purified proteins of the alternative pathway. Both Fab and
F(ab')2 fragments of antimannan IgG facilitated alternative pathway initiation in a manner similar to that observed with intact antibody. Immunofluorescence analysis showed that addition of antimannan IgG to EGTA-chelated and mannan-absorbed serum promoted an
early deposition of C3 molecules on the yeast cells but had little or
no effect on distribution of the cellular sites for C3 activation.
Thus, antimannan IgG antibodies play an important regulatory role in
interactions between the host complement system and C. albicans.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Mannan-Specific Immunoglobulin G Antibodies in Normal Human Serum
Accelerate Binding of C3 to Candida albicans via the
Alternative Complement Pathway
*
Corresponding author. Mailing address: Department of
Microbiology/320, School of Medicine, University of Nevada, Reno, NV 89557-0046. Phone: (702) 784-6161. Fax: (702) 784-1620. E-mail: mzhang{at}med.unr.edu.
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