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Infection and Immunity, January 2000, p. 125-132, Vol. 68, No. 1
Department of Microbiology, Pathology, and
Parasitology, College of Veterinary Medicine, North Carolina State
University, Raleigh, North Carolina 27606
Received 25 May 1999/Returned for modification 16 July
1999/Accepted 12 October 1999
In an effort to better understand genetic and cellular factors that
influence innate immunity, we examined host and bacterial factors
involved in the nonopsonic phagocytosis and killing of Escherichia coli K-12 by mouse macrophages. Unelicited
(resident) peritoneal macrophages from five different mouse strains,
BALB/c, C57BL/6, CD-1, C3H/HeJ, and C3H/HeN, were employed. Additional macrophage populations were obtained from CD-1 mice (bone
marrow-derived macrophages). Also, for BALB/c and C57BL/6 mice,
peritoneal macrophages elicited with either thioglycolate or proteose
peptone, bone marrow-derived macrophages, and macrophage-like cell
lines derived from the two strains were employed. Two E. coli K-12 strains that differed specifically in their abilities
to produce type 1 pili containing the adhesive protein FimH were
examined. The parameters used to assess macrophage bacteriocidal
activity were (i) the killing of internalized (gentamicin-protected)
E. coli during the approximately 4-h assay and (ii) the
initial rate at which internalized E. coli were eliminated.
Data on these parameters allowed the following conclusions: (i)
unelicited or proteose peptone-elicited peritoneal macrophages were
significantly better at eliminating internalized bacteria than
thioglycolate-elicited peritoneal macrophages, bone marrow-derived
macrophages, or macrophage cell lines; (ii) the host genetic background
had no significant effect upon the ability of unelicited peritoneal
macrophages to kill E. coli (even though the mouse strains
differ widely in their in vivo susceptibilities to bacterial
infection); and (iii) the FimH phenotype had no significant effect upon
E. coli survival once the bacterium was inside a
macrophage. Additionally, there was no correlation between the
bacteriocidal effectiveness of a macrophage population and the number
of bacteria bound per macrophage. However, macrophage populations that
were the least bacteriocidal tended to bind higher ratios of
FimH+ to FimH
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Copyright © 2000, American Society for Microbiology. All rights reserved.
Host and Bacterial Factors Involved in the Innate
Ability of Mouse Macrophages To Eliminate Internalized Unopsonized
Escherichia coli
E. coli. The effect
of gamma interferon, fetal calf serum, and the recombination
proficiency of E. coli were examined as factors predicted
to influence intracellular bacterial killing. These had no effect upon
the rate of E. coli elimination by unelicited peritoneal macrophages.
*
Corresponding author. Mailing address: Department of
Microbiology, Pathology, and Parasitology, College of Veterinary
Medicine, North Carolina State University, 4700 Hillsborough St.,
Raleigh, NC 27606. Phone: (919) 513-6207. Fax: (919) 513-6455. E-mail: Paul_Orndorff{at}ncsu.edu.
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