TY - JOUR
T1 - The encapsulated strain TIGR4 of Streptococcus pneumoniae is phagocytosed but is resistant to intracellular killing by mouse microglia
AU - Peppoloni, Samuele
AU - Ricci, Susanna
AU - Orsi, Carlotta F.
AU - Colombari, Bruna
AU - De Santi, Maria Margherita
AU - Messinò, Massimino
AU - Fabio, Giuliana
AU - Zanardi, Alessio
AU - Righi, Elena
AU - Braione, Velia
AU - Tripodi, Sergio
AU - Chiavolini, Damiana
AU - Cintorino, Marcella
AU - Zoli, Michele
AU - Oggioni, Marco Rinaldo
AU - Blasi, Elisabetta
AU - Pozzi, Gianni
N1 - Funding Information:
The work was supported by the Commission of European Union (contract LSHM-CT-2005-512099 to M.R. Oggioni and G. Pozzi) and Italian MIUR ( COFIN 2004 to G. Pozzi, COFIN 2005 to S. Peppoloni). Additional financial support was obtained by the Fondazione Cassa di Risparmio di Modena (to S. Peppoloni). We have no conflicting financial interests.
PY - 2010/11
Y1 - 2010/11
N2 - The polysaccharide capsule is a major virulence factor of Streptococcus pneumoniae as it confers resistance to phagocytosis. The encapsulated serotype 4 TIGR4 strain was shown to be efficiently phagocytosed by the mouse microglial cell line BV2, whereas the type 3 HB565 strain resisted phagocytosis. Comparing survival after uptake of TIGR4 or its unencapsulated derivative FP23 in gentamicin protection and phagolysosome maturation assays, it was shown that TIGR4 was protected from intracellular killing. Pneumococcal capsular genes were up-regulated in intracellular TIGR4 bacteria recovered from microglial cells. Actual presence of bacteria inside BV2 cells was confirmed by transmission electron microscopy (TEM) for both TIGR4 and FP23 strains, but typical phagosomes/phagolysosomes were detected only in cells infected with the unencapsulated strain. In a mouse model of meningitis based on intracranic inoculation of pneumococci, TIGR4 caused lethal meningitis with an LD50 of 2 × 102 CFU, whereas the LD50 for the unencapsulated FP23 was greater than 107 CFU. Phagocytosis of TIGR4 by microglia was also demonstrated by TEM and immunohistochemistry on brain samples from infected mice. The results indicate that encapsulation does not protect the TIGR4 strain from phagocytosis by microglia, while it affords resistance to intracellular killing.
AB - The polysaccharide capsule is a major virulence factor of Streptococcus pneumoniae as it confers resistance to phagocytosis. The encapsulated serotype 4 TIGR4 strain was shown to be efficiently phagocytosed by the mouse microglial cell line BV2, whereas the type 3 HB565 strain resisted phagocytosis. Comparing survival after uptake of TIGR4 or its unencapsulated derivative FP23 in gentamicin protection and phagolysosome maturation assays, it was shown that TIGR4 was protected from intracellular killing. Pneumococcal capsular genes were up-regulated in intracellular TIGR4 bacteria recovered from microglial cells. Actual presence of bacteria inside BV2 cells was confirmed by transmission electron microscopy (TEM) for both TIGR4 and FP23 strains, but typical phagosomes/phagolysosomes were detected only in cells infected with the unencapsulated strain. In a mouse model of meningitis based on intracranic inoculation of pneumococci, TIGR4 caused lethal meningitis with an LD50 of 2 × 102 CFU, whereas the LD50 for the unencapsulated FP23 was greater than 107 CFU. Phagocytosis of TIGR4 by microglia was also demonstrated by TEM and immunohistochemistry on brain samples from infected mice. The results indicate that encapsulation does not protect the TIGR4 strain from phagocytosis by microglia, while it affords resistance to intracellular killing.
KW - Capsule
KW - Intracellular survival
KW - Microglia
KW - Phagocytosis
KW - Streptococcus pneumoniae
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U2 - 10.1016/j.micinf.2010.06.010
DO - 10.1016/j.micinf.2010.06.010
M3 - Article
C2 - 20615478
AN - SCOPUS:77958103384
SN - 1286-4579
VL - 12
SP - 990
EP - 1001
JO - Microbes and Infection
JF - Microbes and Infection
IS - 12-13
ER -