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Infection and Immunity, September 1999, p. 4646-4654, Vol. 67, No. 9
Groupe de Recherche sur les Maladies
Infectieuses du Porc (GREMIP),
Received 12 February 1999/Returned for modification 26 March
1999/Accepted 2 July 1999
Streptococcus suis capsular type 2 is an important
etiological agent of swine meningitis, and it is also a zoonotic agent. Since mononuclear phagocytes have been suggested to play a central role
in the pathogenesis of meningitis, the objective of the present study
was to evaluate the capacity of whole killed S. suis type 2 organisms to induce the release of the proinflammatory cytokines tumor
necrosis factor alpha (TNF-
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Heat-Killed Streptococcus suis Capsular
Type 2 Strains Stimulate Tumor Necrosis Factor Alpha and Interleukin-6
Production by Murine Macrophages
) and interleukin-6 (IL-6) by murine
macrophages. Induction of cytokines was evaluated in the presence or
absence of phorbol ester (phorbol 12-myristate 13-acetate [PMA])
costimulation. Results showed that S. suis type 2 stimulated the production of both cytokines in a concentration- and
time-dependent fashion. Although large doses of bacteria were required
for maximal cytokine release, titers were similar to those obtained
with the lipopolysaccharide (LPS) positive control. An increase in
cytokine release was observed with both S. suis and LPS
with PMA costimulation. Experiments with cytochalasin-treated
macrophages showed that the stimulation of cytokine production was
phagocytosis independent. When macrophages were stimulated with an
unencapsulated mutant, an increase in TNF production was observed, but
the absence of the capsule had no effect on IL-6 production. In fact,
whereas purified capsular polysaccharide of S. suis failed
to induce cytokine release, purified S. suis cell wall
induced both TNF and, to a lesser extent, IL-6. IL-6 secretion probably
requires some distinct stimuli which differ from those of TNF. Finally,
the S. suis putative virulence factors suilysin and
extracellular protein EF showed no cytokine-stimulating activity. The
ability of S. suis to trigger macrophages to produce
proinflammatory cytokines may have an important role in the initiation
and development of meningitis caused by this microorganism.
*
Corresponding author. Mailing address: GREMIP,
Faculté de Médecine
Vétérinaire, Université de Montréal, 3200 rue
Sicotte, C.P. 5000, Saint-Hyacinthe, Québec J2S 7C6, Canada.
Phone: (450) 773-8521, ext. 8374. Fax: (450) 778-8108. E-mail:
gottschm{at}medvet.umontreal.ca.
Infection and Immunity, September 1999, p. 4646-4654, Vol. 67, No. 9
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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