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Epitope location in the Cryptococcus neoformans capsule is a determinant of antibody efficacy.

Nussbaum G, Cleare W, Casadevall A, Scharff MD, Valadon P - J. Exp. Med. (1997)

Bottom Line: The IgM mAbs 12A1 and 13F1 originated from the same B cell and differ only by somatic mutations in their variable regions; yet mAb 12A1 protects against serotype D infection, while mAb 13F1 does not.Immunofluorescence and immunoelectron microscopy studies revealed differences in antibody localization within the capsule of serotype D strain; mAb 12A1 bound to the outer rim of the capsule resulting in an annular pattern, whereas mAb 13F1 bound throughout the capsule and had a punctate appearance.Annular binding, but not punctate binding, was associated with increased opsonic efficacy for phagocytosis of C. neoformans by J774.16 macrophage-like cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.

ABSTRACT
Monoclonal antibodies (mAbs) to the polysaccharide capsule of Cryptococcus neoformans can prolong survival in mice. However, the properties of antibodies that mediate protection are not fully understood. The IgM mAbs 12A1 and 13F1 originated from the same B cell and differ only by somatic mutations in their variable regions; yet mAb 12A1 protects against serotype D infection, while mAb 13F1 does not. Phage peptide display libraries were used to analyze the fine specificity of these two mAbs. The selection of distinct peptide motifs from identical libraries confirmed that mAbs 12A1 and 13F1 bound to two distinct epitopes. Immunofluorescence and immunoelectron microscopy studies revealed differences in antibody localization within the capsule of serotype D strain; mAb 12A1 bound to the outer rim of the capsule resulting in an annular pattern, whereas mAb 13F1 bound throughout the capsule and had a punctate appearance. The difference in the binding pattern of mAb 12A1 and 13F1 was not observed on serotype A organisms, where both mAbs bound to the capsule with an annular fluorescence pattern. The fluorescence pattern of binding correlated with protective efficacy; mAb 13F1 prolonged survival of mice infected with the J11 serotype A strain (annular fluorescence), but not serotype D strains (punctate pattern). Annular binding, but not punctate binding, was associated with increased opsonic efficacy for phagocytosis of C. neoformans by J774.16 macrophage-like cells. The correlation between capsular binding pattern, opsonic activity, and ability to prolong survival suggests that the efficacy of anticryptococcal antibodies is dependent upon where they bind in the polysaccharide capsule.

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Indirect immunofluorescence capsular pattern with mAbs  12A1 and 13F1 on different C. neoformans serotype A and D strains.
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Figure 1: Indirect immunofluorescence capsular pattern with mAbs 12A1 and 13F1 on different C. neoformans serotype A and D strains.

Mentions: In previous studies, we demonstrated that IgM mAb 12A1 protected mice from lethal infection with a serotype D strain (24067; American Type Culture Collection), whereas IgM mAb 13F1 did not (5). Indirect immunofluorescence experiments revealed that mAbs 12A1 and 13F1 produced annular and punctate fluorescence patterns, respectively, suggesting that each antibody bound to a different antigenic structure in the cryptococcal capsule. To further explore this finding, we examined additional serotype D strains and several strains representing the other serotypes (Table 2 and Fig. 1). mAb binding to strains 34873 and 34874 was similar to strain 24067; the protective mAb 12A1 bound with an annular fluorescence pattern, whereas the nonprotective mAb 13F1 produced a punctate fluorescence pattern (Fig. 1, top). However, both 12A1 and 13F1 bound in an annular pattern to a fourth serotype D strain, J22 (Table 2). J22 is an unusual strain with an unstable karyotype (26) and a GXM structure containing a novel triad repeat (16).


Epitope location in the Cryptococcus neoformans capsule is a determinant of antibody efficacy.

Nussbaum G, Cleare W, Casadevall A, Scharff MD, Valadon P - J. Exp. Med. (1997)

Indirect immunofluorescence capsular pattern with mAbs  12A1 and 13F1 on different C. neoformans serotype A and D strains.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2196155&req=5

Figure 1: Indirect immunofluorescence capsular pattern with mAbs 12A1 and 13F1 on different C. neoformans serotype A and D strains.
Mentions: In previous studies, we demonstrated that IgM mAb 12A1 protected mice from lethal infection with a serotype D strain (24067; American Type Culture Collection), whereas IgM mAb 13F1 did not (5). Indirect immunofluorescence experiments revealed that mAbs 12A1 and 13F1 produced annular and punctate fluorescence patterns, respectively, suggesting that each antibody bound to a different antigenic structure in the cryptococcal capsule. To further explore this finding, we examined additional serotype D strains and several strains representing the other serotypes (Table 2 and Fig. 1). mAb binding to strains 34873 and 34874 was similar to strain 24067; the protective mAb 12A1 bound with an annular fluorescence pattern, whereas the nonprotective mAb 13F1 produced a punctate fluorescence pattern (Fig. 1, top). However, both 12A1 and 13F1 bound in an annular pattern to a fourth serotype D strain, J22 (Table 2). J22 is an unusual strain with an unstable karyotype (26) and a GXM structure containing a novel triad repeat (16).

Bottom Line: The IgM mAbs 12A1 and 13F1 originated from the same B cell and differ only by somatic mutations in their variable regions; yet mAb 12A1 protects against serotype D infection, while mAb 13F1 does not.Immunofluorescence and immunoelectron microscopy studies revealed differences in antibody localization within the capsule of serotype D strain; mAb 12A1 bound to the outer rim of the capsule resulting in an annular pattern, whereas mAb 13F1 bound throughout the capsule and had a punctate appearance.Annular binding, but not punctate binding, was associated with increased opsonic efficacy for phagocytosis of C. neoformans by J774.16 macrophage-like cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.

ABSTRACT
Monoclonal antibodies (mAbs) to the polysaccharide capsule of Cryptococcus neoformans can prolong survival in mice. However, the properties of antibodies that mediate protection are not fully understood. The IgM mAbs 12A1 and 13F1 originated from the same B cell and differ only by somatic mutations in their variable regions; yet mAb 12A1 protects against serotype D infection, while mAb 13F1 does not. Phage peptide display libraries were used to analyze the fine specificity of these two mAbs. The selection of distinct peptide motifs from identical libraries confirmed that mAbs 12A1 and 13F1 bound to two distinct epitopes. Immunofluorescence and immunoelectron microscopy studies revealed differences in antibody localization within the capsule of serotype D strain; mAb 12A1 bound to the outer rim of the capsule resulting in an annular pattern, whereas mAb 13F1 bound throughout the capsule and had a punctate appearance. The difference in the binding pattern of mAb 12A1 and 13F1 was not observed on serotype A organisms, where both mAbs bound to the capsule with an annular fluorescence pattern. The fluorescence pattern of binding correlated with protective efficacy; mAb 13F1 prolonged survival of mice infected with the J11 serotype A strain (annular fluorescence), but not serotype D strains (punctate pattern). Annular binding, but not punctate binding, was associated with increased opsonic efficacy for phagocytosis of C. neoformans by J774.16 macrophage-like cells. The correlation between capsular binding pattern, opsonic activity, and ability to prolong survival suggests that the efficacy of anticryptococcal antibodies is dependent upon where they bind in the polysaccharide capsule.

Show MeSH
Related in: MedlinePlus