Aggregation of Streptococcus pneumoniae by a pneumococcal capsular polysaccharide-specific human monoclonal IgM correlates with antibody efficacy In Vivo

Kevin Fabrizio, Catherine Manix, Allan J. Guimaraes̃, Joshua D. Nosanchuk, Liise-anne Pirofski

Research output: Contribution to journalArticle

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Abstract

Acquired antibody immunity to Streptococcus pneumoniae (pneumococcus) has been linked to serotype (ST)-specific opsonic antibodies to the relevant pneumococcal capsular polysaccharide (PPS) that mediate protection by enhancing the bactericidal effect of host phagocytes. Despite the well-recognized role of opsonic IgG in host defense against pneumococcus, PPS-specific monoclonal antibodies (MAbs) that mediate protection against lethal challenge with ST3 pneumococcus in mice but do not promote phagocytic killing in vitro (nonopsonic antibodies) have been described. In this study, we sought to determine the biological activity of one such MAb, A7 (a human PPS3-specific IgM), and the mechanism by which it mediates protection. In vitro studies demonstrated that coincubation of A7 with ST3 in the absence of phagocytes or a complement source resulted in a reduction in CFU on blood agar plates that was largely reversible by sonication. A chromogenic cellular proliferation assay demonstrated that A7 did not affect replication of ST3 in liquid culture. The ability of A7 to induce aggregation of ST3 was confirmed by fluorescence microscopy and flow cytometry: A7 induced aggregation of ST3, and in the presence of a complement source, A7 promoted deposition of complement component 3 (C3) on aggregated bacteria in a dose-dependent fashion. Similarly, administration of preincubated mixtures of A7 and ST3 intraperitoneally to mice protected them from the lethality of ST3 in a dose-dependent fashion. These findings suggest that A7-mediated aggregation enhances resistance to ST3, most likely by enhancing C3 deposition on the ST3 capsule, thereby promoting host antipneumococcal activity in vivo.

Original languageEnglish (US)
Pages (from-to)713-721
Number of pages9
JournalClinical and Vaccine Immunology
Volume17
Issue number5
DOIs
StatePublished - May 2010

Fingerprint

Streptococcus pneumoniae
Polysaccharides
Immunoglobulin M
Agglomeration
Antibodies
Phagocytes
Chromogenics
Complement C3
Sonication
Flow cytometry
Fluorescence microscopy
Bioactivity
Agar
Capsules
Assays
Bacteria
Adaptive Immunity
Blood
Immunoglobulin G
Monoclonal Antibodies

ASJC Scopus subject areas

  • Clinical Biochemistry
  • Immunology
  • Immunology and Allergy
  • Microbiology (medical)

Cite this

Aggregation of Streptococcus pneumoniae by a pneumococcal capsular polysaccharide-specific human monoclonal IgM correlates with antibody efficacy In Vivo. / Fabrizio, Kevin; Manix, Catherine; Guimaraes̃, Allan J.; Nosanchuk, Joshua D.; Pirofski, Liise-anne.

In: Clinical and Vaccine Immunology, Vol. 17, No. 5, 05.2010, p. 713-721.

Research output: Contribution to journalArticle

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