Virulent serotypes of Streptococcus pneumoniae rank as the leading pathogen in childhood bacteremias, in adult pneumonias, and in life-threatening infections in the immunocompromised host. Host defense against pneumococcal infection requires the binding of C3b, the opsonic fragment of the third component of complement (C3), to the microbial surface in preparation for ingestion by phagocytic cells. In previous studies with virulent serotypes of Streptococcus pneumoniae (3,4,6A,14), we have shown how a particular biochemical structure of C3 --- the reactive thiolester bond --- directs the covalent binding of opsonic C3b to the organism by means of a transacylation reaction. We have also described serotypic differences in the amount, biochemistry (ester vs. amide) and degradation of covalently deposited C3b and have demonstrated how C3b and iC3b on the pneumococcal capsule serve as ligands for membrane complement receptor on phagocytic cells. We therefore propose to analyze, at the molecular level, the functional mechanisms directing deposition and degradation of C3b on the pneumococcal surface and the membrane receptors which, in recognizing these C3 ligands, regulate intracellular functions in phagocytosis and in antibody production. We shall first investigate the role of C3 and its active fragments in the phagocytosis of virulent Streptococcus pneumoniae. Using prototypic surfaces bearing purified C3b and iC3b with ester- or amide-modification at the thiolester site, we shall derive principles of phagocytosis which can then be applied to the study of ester-linked or amide-linked C3b and iC3b on the capsule or cell wall of genetically related pneumococci differing only in the presence or absence of capsule. Secondly, we shall examine how C3 and its active fragments may affect the production of type-specific anticapsular antibody to pneumococcal polysaccharides. We shall test our hypothesis that C3d, covalently bound to the pneumococcal surface as a result of opsonization, serves as an immunogenic ligand for the C3d receptor on the B lymphocyte. Our preliminary studies in a serum-free culture system may lead to the development of more broadly immunogenic polysaccharide vaccines. By focusing on the molecular mechanisms of C3 deposition and degradation on the surface of virulent pneumococci, we hope to elucidate the biochemical principles by which surface-bound C3 ligands interact with cellular receptors to direct phagocytic and immunogenic responses of the normal host.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
1R01AI024162-01A1
Application #
3136924
Study Section
Bacteriology and Mycology Subcommittee 1 (BM)
Project Start
1987-07-01
Project End
1990-06-30
Budget Start
1987-07-01
Budget End
1988-06-30
Support Year
1
Fiscal Year
1987
Total Cost
Indirect Cost
Name
University of Minnesota Twin Cities
Department
Type
Schools of Medicine
DUNS #
168559177
City
Minneapolis
State
MN
Country
United States
Zip Code
55455
Zhang, Y; Masi, A W; Barniak, V et al. (2001) Recombinant PhpA protein, a unique histidine motif-containing protein from Streptococcus pneumoniae, protects mice against intranasal pneumococcal challenge. Infect Immun 69:3827-36
Madsen, M; Lebenthal, Y; Cheng, Q et al. (2000) A pneumococcal protein that elicits interleukin-8 from pulmonary epithelial cells. J Infect Dis 181:1330-6
Cheng, Q; Finkel, D; Hostetter, M K (2000) Novel purification scheme and functions for a C3-binding protein from Streptococcus pneumoniae. Biochemistry 39:5450-7
Hostetter, M K (1999) Opsonic and nonopsonic interactions of C3 with Streptococcus pneumoniae. Microb Drug Resist 5:85-9
Hostetter, M K (1996) Adhesion and morphogenesis in Candida albicans. Pediatr Res 39:569-73
Hostetter, M K (1996) An integrin-like protein in Candida albicans: implications for pathogenesis. Trends Microbiol 4:242-6
Michael, E J; McClellan, M; Huebner, H et al. (1995) Expression of CD21 and synthesis of its ligands by HeLa cells after growth in serum-free medium. J Lab Clin Med 125:102-12
Hostetter, M K (1994) Society for Pediatric Research presidential address 1994: yeast as metaphor. Pediatr Res 36:692-8
Angel, C S; Ruzek, M; Hostetter, M K (1994) Degradation of C3 by Streptococcus pneumoniae. J Infect Dis 170:600-8
Hostetter, M K (1993) The third component of complement: new functions for an old friend. J Lab Clin Med 122:491-6

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