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Infection and Immunity, May 2001, p. 3398-3409, Vol. 69, No. 5
Division of Infectious Diseases, Department
of Medicine,1 and Departments of
Pediatrics3 and Microbiology and
Immunology,4 Albert Einstein College of
Medicine, Bronx, New York 10461, and Sidney Kimmel Cancer
Center, San Diego, California 921212
Received 22 December 2000/Returned for modification 24 January
2001/Accepted 7 February 2001
The protective efficacy of antibodies (Abs) to Cryptococcus
neoformans glucuronoxylomannan (GXM) is dependent on Ab fine
specificity. Two clonally related immunoglobulin M monoclonal Abs
(MAbs) (12A1 and 13F1) differ in fine specificity and protective
efficacy, presumably due to variable (V)-region sequence differences
resulting from somatic mutations. MAb 12A1 is protective and produces
annular immunofluorescence (IF) on serotype D C.
neoformans, while MAb 13F1 is not protective and produces
punctate IF. To determine the Ab molecular determinants responsible for
the IF pattern, site-directed mutagenesis of the MAb 12A1 heavy-chain V
region (VH) was followed by serological and functional
studies of the various mutants. Changing two selected amino acids in
the 12A1 VH binding cavity to the corresponding residues in
the 13F1 VH altered the IF pattern from annular to
punctate, reduced opsonic efficacy, and abolished recognition by an
anti-idiotypic Ab. Analysis of the binding of the various mutants to
peptide mimetics revealed that different amino acids were responsible
for GXM binding and peptide specificity. The results suggest that
V-region motifs associated with annular binding and opsonic activity
may be predictive of Ab efficacy against C. neoformans.
This has important implications for immunotherapy and vaccine design
that are reinforced by the finding that GXM and peptide reactivities
are determined by different amino acid residues.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.5.3398-3409.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Molecular Basis for Immunoglobulin M Specificity to Epitopes in
Cryptococcus neoformans Polysaccharide That Elicit
Protective and Nonprotective Antibodies
*
Corresponding author. Mailing address: Division of
Infectious Diseases, Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461. Phone: (718) 430-3665. Fax: (718) 430-8701. E-mail:
casadeva{at}aecom.yu.edu.
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