Accelerated decay of C3b to iC3b when C3b is bound to the Cryptococcus neoformans capsule

Pfrommer, G. S. T.; Dickens, Stijn; Wilson, Michael A.; Young, B J; Kozel, Thomas R.

doi:10.1128/iai.61.10.4360-4366.1993

Cited by 28 publications

(17 citation statements)

References 22 publications

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“…3) (55,84,105). Indeed, the percentage of bound C3 occurring as iC3b approaches 100% after 8 min of incubation in normal serum (84). In contrast, the percentage of bound C3 occurring as iC3b on nonencapsulated cryptococci does not exceed 70%, even after 60 min of incubation in normal human serum.…”

Section: Characteristics Of C3 Fragments Bound To the Cryptococcal Camentioning

confidence: 94%

“…The complete release of C3 fragments from encapsulated cryptococci by treatment with hydroxyl- amine suggests that metastable C3b binds via an ester bond to the abundant hydroxyl groups found in the cryptococcal capsule. In contrast, a significant percentage of the C3 fragments bound to nonencapsulated cryptococci are resistant to release by treatment with hydroxylamine (55,84). This suggests the presence of an amide bond.…”

Section: Characteristics Of C3 Fragments Bound To the Cryptococcal Camentioning

confidence: 96%

“…Thus, formation of iC3b is dependent on interaction between particle-bound C3b and factor H. Analysis of C3 fragments eluted from encapsulated C. neoformans showed that the vast majority (Ͼ95%) are in the form of iC3b ( Fig. 3) (55,84,105). Indeed, the percentage of bound C3 occurring as iC3b approaches 100% after 8 min of incubation in normal serum (84).…”

Section: Characteristics Of C3 Fragments Bound To the Cryptococcal Camentioning

confidence: 97%

“…Rapid conversion of C3b to iC3b suggests that an extremely efficient mechanism operates for conversion of C3b to iC3b on encapsulated cryptococci relative to the conversion that occurs on nonencapsulated cryptococci or zymosan (84). A kinetic analysis of cleavage of C3b to iC3b on encapsulated and nonencapsulated cryptococci suggests that there is a variation in the efficiency with which factor H, factor I, or both influence conversion of C3b to iC3b on these two cell types (84). Doseresponse curves of the requirements for both factor H and factor I are quite steep when cleavage of C3b to iC3b is assessed on encapsulated cryptococci.…”

Section: Characteristics Of C3 Fragments Bound To the Cryptococcal Camentioning

confidence: 99%

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Activation of the complement system by pathogenic fungi

Kozel

1996

Clin Microbiol Rev

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122

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Fungi have been studied as prototype activators of the complement cascade since the early 1900s. More recently, attention has focused on the role of the complement system in the pathogenesis of fungal infections. The interactions of Cryptococcus neoformans and Candida albicans with the complement system are the most widely characterized; however, all pathogenic fungi examined to date have the ability to initiate the complement cascade. The molecular mechanisms for initiation and regulation of the complement cascade differ from one fungus to another, most likely reflecting differences in the structure of the outer layers of the cell wall. The molecular bases for such differences remain to be identified. Studies of mycoses in experimental animals with induced or congenital deficiencies in the complement system demonstrate that complement is an important innate system for control of fungal infection. Contributions to host resistance include opsonization and generation of inflammatory mediators. Inflammation induced by chemotactic products of the complement system may contribute to the pathogenesis of some fungal infections.

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Section: Characteristics Of C3 Fragments Bound To the Cryptococcal Camentioning

confidence: 94%

Section: Characteristics Of C3 Fragments Bound To the Cryptococcal Camentioning

confidence: 96%

Section: Characteristics Of C3 Fragments Bound To the Cryptococcal Camentioning

confidence: 97%

Section: Characteristics Of C3 Fragments Bound To the Cryptococcal Camentioning

confidence: 99%

See 2 more Smart Citations

Activation of the complement system by pathogenic fungi

Kozel

1996

Clin Microbiol Rev

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122

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“…The poor complement activating capacity of LL (8,9) appears to be associated with the efficient inactivation of deposited C3b (Figure 5). In fact, the iC3b : (C3b + iC3b) ratios observed for the LL are in the range of those typical of poor complement activators, such as cells of encapsulated Cryptococcus neoformans (26); in contrast, good complement activators such as nonencapsulated cryptococci and bacterial cells reach considerably lower iC3b : (C3b + iC3b ratios) (27,28). We had previously shown, in assays employing parasite extracts, that the cofactor activity for factor I‐mediated conversion of C3b to iC3b present in the HCW is due entirely to host factor H (12).…”

Section: Discussionmentioning

confidence: 95%

Resistance of the Echinococcus granulosus cyst wall to complement activation: analysis of the role of InsP₆ deposits

Irigoı́n

Laich

Ferreira

et al. 2008

Parasite Immunology

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The larva of the cestode Echinococcus granulosus (hydatid cyst) is protected by the acellular laminated layer (LL). The mechanisms that make this thick coat a poor activator of host complement are incompletely understood. The structure binds, through unknown motifs, the host regulator of the alternative complement pathway (ACP), factor H. A second potential mechanism of ACP regulation, the inhibition of factor B activation, was detected in assays employing purified components (Immunopharmacology 42 : 91). The inhibitor was subsequently identified as myo-inositol hexakisphosphate (InsP(6)), which in the form of nano-deposits is a major component of the LL (Biochem J 362 : 297; J Cell Biochem 93 : 1272; FEBS J 273 : 3192). In this report we show that colloidal InsP(6 )solids inhibit factor B activation, through adsorption and associated impairment of C3b binding. However, this interaction is not relevant in the presence of serum proteins. In serum, InsP(6) deposits instead bind C1q, and initiate complement activation. This activation is curtailed through efficient C3b inactivation, previously shown to be entirely factor H-dependent, and now observed to be independent of the InsP(6) deposits. Therefore the complement resistance of the LL must be based on functional factor H binding sites present on the mucin-based meshwork that is its other major constituent.

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Bacterial Capsules and Evasion of Immune Responses

Merino¹,

Jm²

2010

Encyclopedia of Life Sciences

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The bacterial surface contains various structures that are capable of activating the host defences and consequently inducing host immune responses. Bacterial capsules are one of the most external structures on the bacterial surface, which may completely surround all the antigenic molecules or may be coexpressed with other bacterial antigens. They are involved in a wide range of biological processes, such as prevention of desiccation, adherence and resistance to nonspecific and specific host immunity. Gram‐negative and Gram‐positive capsular polysaccharides contribute to the bacterial resistance of host immune responses by different mechanisms. Usually, capsular polysaccharides that mask the underlying cell surface structures activate weakly or not at all the immune system, whereas bacterial capsules coexpressed with other bacterial antigens activate the immune system but mask opsonines and prevent complement attack complex formation, as well as phagocytosis. Key Concepts: Bacterial capsules completely surround bacterial cell and enhance the ability of bacteria to cause disease. Polysaccharides are polymeric carbohydrate structures, formed of one or more sugar residues repeating units joined together by glycosidic bonds. Antigenic variation modifies microorganism's surface structures and allows them to overcome the immune response.

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Accelerated decay of C3b to iC3b when C3b is bound to the Cryptococcus neoformans capsule

Cited by 28 publications

References 22 publications

Activation of the complement system by pathogenic fungi

Activation of the complement system by pathogenic fungi

Resistance of the Echinococcus granulosus cyst wall to complement activation: analysis of the role of InsP₆ deposits

Bacterial Capsules and Evasion of Immune Responses

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Accelerated decay of C3b to iC3b when C3b is bound to the Cryptococcus neoformans capsule

Cited by 28 publications

References 22 publications

Activation of the complement system by pathogenic fungi

Activation of the complement system by pathogenic fungi

Resistance of the Echinococcus granulosus cyst wall to complement activation: analysis of the role of InsP6 deposits

Bacterial Capsules and Evasion of Immune Responses

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Resistance of the Echinococcus granulosus cyst wall to complement activation: analysis of the role of InsP₆ deposits