Macrophages Extracellular Stimulation by Serum Proteins Required for Maximal Intracellular Killing of Microorganisms by Mouse Peritoneal
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INFECTION AND IMMUNITY, Dec. 1984, p. 754-758 Vol. 46, No. 3
0019-9567/84/120754-05$02.00/0
Copyright © 1984, American Society for Microbiology
Extracellular Stimulation by Serum Proteins Required for Maximal
Intracellular Killing of Microorganisms by Mouse Peritoneal
Macrophages
PETER C. J. LEIJH, THEDA L. VAN ZWET, AND RALPH VAN FURTH*
Department of Infectious Diseases, University Hospital, Rijnsburgerweg 10, 2333 AA Leiden, The Netherlands
Received 30 May 1984/Accepted 29 August 1984
Intracellular killing of catalase-positive Staphylococcus aureus by resident mouse peritoneal macrophages
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was very low in the absence of serum but maximal in the presence of fresh normal serum. A large proportion of
catalase-negative Streptococcus pyogenes were killed in the absence of extracellular serum, and maximal killing
was reached only when serum was present extracellularly. Further investigations revealed that stimulation of
intracellular killing by extracellular serum is dependent on the interaction of immunoglobulin G with Fc
receptors and of complement component C3b with C3b receptors in the macrophage membrane.
Optimal functioning of one of the important host defense were used. The peritoneal cells of five to six mice were
mechanisms, i.e., phagocytosis and intracellular killing of harvested as described elsewhere (19), pooled, suspended in
microorganisms, requires various interactions among serum Hanks balanced salt solution (HBSS) containing 0.1%
or plasma proteins, microorganisms, and phagocytic cells. (wt/vol) gelatin (gelatin-HBSS), and adjusted to a concentra-
Immunoglobulin G (IgG) alone, IgG or IgM together with tion of ca. 107 macrophages per ml. This suspension also
complement component C3b, and C3b alone can act as contained an average of 2 x 107 lymphocytes per ml and 1 x
opsonins inducing optimal attachment and ingestion of bac- 10' to 3 x 105 granulocytes per ml.
teria by granulocytes, monocytes, and macrophages (4, 11). Since incubation of resident macrophages in HBSS for 60
As previously reported, maximal killing of microorga- min at 37°C showed that the viability of these cells fluctuated
nisms by human granulocytes and monocytes requires con- between 30 and 90%, in experiments without serum, HBSS
tinuous stimulation of these cells by extracellular serum was supplemented with 2 mg of bovine serum albumin per ml
factors (i.e., IgG, C3/C3b, and B/Bb) (6-9). However, the (HBSS-Alb). Macrophages incubated in HBSS-Alb at 37°C
results of extracellular stimulation of intracellular killing for 120 min remained viable, as assessed by trypan blue
differed according to whether catalase-positive or catalase- exclusion (viability, >95%).
negative bacteria were used. The killing of catalase-positive Sera. Newborn calf serum (NBCS) was obtained from
bacteria (e.g., Staphylococcus aureus) by human monocytes GIBCO Bio-cult, Glasgow, Scotland. Adult bovine, sheep,
was almost negligible in the absence of membrane stimula- dog, pig, horse, rabbit, rat, and murine sera were prepared
tion by serum factors (8) or lectins (P. C. J. Leijh, T. L. van by clotting blood samples for 1 h at room temperature
Zwet, and R. van Furth, Clin. Exp. Immunol., in press), followed by centrifugation for 20 min at 1,100 x g, after
whereas ingested catalase-negative bacteria (e.g., Strepto- which the sera were collected and stored in 2-ml samples at
coccus pyogenes) were suboptimally killed in the absence of -20°C. Heat-inactivated serum was obtained by heating
membrane stimulation (9). These conclusions could be serum for 30 min at 56°C. An IgG fraction was prepared from
reached because the method used made it possible to mea- murine serum by the method of Fahey and Terry (3). Gamma
sure the rates of intracellular killing and ingestion of bacteria globulin levels of the various sera were determined semi-
independently. quantitatively by estimation of the gamma globulin fraction
Since macrophages originate from blood monocytes (17, in the electrophoresis patterns and were calculated on the
18), the question arose whether the maturation of monocytes basis of the serum protein content determined by the method
is accompanied by changes in the bactericidal activity of Lowry et al. (10).
these cells; in other words, are macrophages capable of Microorganisms. S. aureus (type 42 D) and Streptococcus
killing bacteria without an extracellular stimulus, and is pyogenes were cultured overnight in nutrient broth no. 2
there a difference in the intracellular killing of catalase- (Oxoid Ltd., London, England) at 37°C, harvested by cen-
positive and -negative microorganisms? Since it is almost trifugation at 1,500 x g for 10 min, washed twice with
impossible to obtain enough macrophages from a human phosphate-buffered saline (pH 7.4), and suspended in gela-
source, this investigation was carried out with mouse perito- tin-HBSS to a concentration of 107/ml. For opsonization, 5
neal macrophages. x 106 bacteria per ml were incubated with 10% serum for 30
min at 37°C under rotation (4 rpm); the cells were then
MATERIALS AND METHODS washed twice with ice-cold HBSS and suspended in HBSS
Peritoneal macrophages. Specific pathogen-free male to a concentration of 107/ml. In experiments with S. aureus,
Swiss mice (Central Institute for the Breeding of Laboratory the number of CFU was determined on diagnostic-sensitiv-
Animals, Bilthoven, The Netherlands) weighing 25 to 30 g ity-test agar plates (Oxoid Ltd.); for Streptococcus pyogenes
this was done on blood agar plates.
Phagocytosis of microorgansisms. Phagocytosis of the vari-
ous microorganisms was measured as a decrease in the
* Corresponding author. number of viable extracellular bacteria, as described in detail
754VOL. 46, 1984 KILLING OF MICROORGANISMS BY MOUSE MACROPHAGES 755
elsewhere (19). In short, 5 x 106 macrophages per ml were
incubated with 5 x 106 bacteria per ml in the presence of U)
10% serum at 37°C under rotation (4 rpm). At various time
points, a sample was taken and added to ice-cold gelatin- --A
HBSS to stop phagocytosis. Next, the noningested bacteria ._
were separated from the cell-associated bacteria by differen- a
1-
tial centrifugation for 4 min at 110 x g. Finally, the number 0 100 -
Io --_
of viable bacteria in the supernatant was determined micro- 0
D
biologically. Phagocytosis was expressed as the percentage 0
of decrease in the number of viable extracellular bacteria. 0. Murine
Phagocytosis estimates were corrected for the growth of U1) Bovine
extracellular bacteria, as described elsewhere (19). 0) Rat
Intracellular killing of microorganisms. Intracellular killing .50 10 - Bovine (Corr)
of microorganisms by peritoneal macrophages was measured
as a decrease in the number of viable intracellular bacteria as -0)
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described elsewhere (6-9, 19). In short, 5 x 106 macro- Murine (Corr)
CD0) Rat (Corr)
phages per ml were incubated with 5 x 106 preopsonized L.
bacteria per ml for 20 min at 37°C under rotation (4 rpm); the 0)
a-
20-min interval was chosen based on experimental results 1
(see below). Next, the noningested bacteria were removed 0 60 120
by differential centrifugation (4 min, 110 x g) and two Minutes
washes with ice-cold HBSS. After this procedure, no de-
crease in the number and viability of the macrophages was FIG. 1. Phagocytosis of S. aureus by resident peritoneal macro-
found. The macrophages containing ingested bacteria were phages. Macrophages (5 x 106/ml) and 5 x 106 S. aureus per ml were
suspended in HBSS to a concentration of 5 x 106/ml and incubated in the presence of 10% murine, rat, or bovine serum at
reincubated at 37°C under rotation (4 rpm). The serum under 37°C and 4 rpm. After correction for the growth of extracellular
bacteria (Corr), the results show an exponential decrease in the
study was added during this reincubation. At various time percentage of viable extracellular bacteria. No phagocytosis oc-
points a sample was taken, and after lysis of the macro- curred during incubation of bacteria without macrophages (dotted
phages by freezing in liquid nitrogen and thawing in a water lines), indicating that the serum used was not bactericidal.
bath (37°C) three times, the number of viable intracellular
microorganisms was determined microbiologically. The re-
sults showed that freezing and thawing did not affect the rocytes for Fcy and IgM- and complement-coated sheep
viability of the microorganisms. Intracellular killing was erythrocytes for C3b, as described elsewhere (2).
expressed as the percentage of decrease in the number of Calculations. All values represent the mean and standard
viable intracellular bacteria (6-9, 19). deviation of at least three experiments. Statistical analysis
Receptors. The presence of Fcy and C3b receptors on was performed with the Student t-test.
macrophages was investigated with IgG-coated sheep eryth-
(A
01)
c
0)
TABLE 1. Opsonic and killing stimulatory activities of sera from an
0
various animal species for S. aureus
Opsonic ~~Killing U)
Serum (no. Gamma globulin Opsonic stimulatory
D 100
of expt) content (jLg/ml) (a)a activity
(%)b 0
None'
0.
LI
HBSS (6) 0 -15 ± 6 32 8
Bovine (3) 3,000 62 ± 5 70 ± 11 0) Bovine
Sheep (3) 1,500 20 ± 8 63 ± 9 .0
o2 CL10
Dog (3) 600 0 ± 19 78 5 c Rat
Pig(3) 2,000 10± 12 58 ± 17
Horse (3) 1,800 10 ± 8 59 ± 15 CD Bovine (Corr)
Rabbit (3) 700 -100 ± 30 65 ± 13 0)
Murine
Mouse (6) 300 52 ± 10 67 ± 12
Rat (3) 450 44 ± 7 71 9 0)
NBCS (6) 2,000 15 ± 10 73 ± 10
0- Murine (Corr)
60 120
a
Opsonic activity was determined during incubation of 5 x 106 macro-
phages per ml and 5 x 106 S. aureus per ml in the presence of 10% serum for Minutes
60 min at 37°C and was expressed as the percentage of decrease in the number
of viable extracellular bacteria during this incubation (see text). The minus FIG. 2. Phagocytosis of Streptococcus pyogenes by resident
sign indicates extracellular growth of bacteria. peritoneal macrophages. Macrophages (5 x 106/ml) and 5 x 106
b Killing stimulatory activity was determined as the ability of serum to Streptococcus pyogenes were incubated in the presence of 10%
stimulate macrophages containig S. aureus, after phagocytosis of S. aureus murine, rat, or bovine serum at 37°C and 4 rpm. After correction for
opsonized with mouse serum at a bacteria-to-macrophage ratio of 1:1 for 20 the growth of extracellular bacteria (Corr), the results show an
min at 37°C, during incubation of these macrophages in the presence of 10%
concentrations of the various sera for 60 min at 37°C. The killing stimulatory exponential decrease in the percentage of viable extracellular bacte-
activity of a serum is expressed as the percentage of decrease in the number of ria. No phagocytosis occurred during incubation of bacteria without
viable intracellular bacteria. macrophages (dotted lines), indicating that the serum used was not
'
Incubated with HBSS-Alb instead of serum. bactericidal.756 LEIJH, VAN ZWET, AND VAN FURTH INFECT. IMMUN.
TABLE 2. Number of viable cell-associated bacteria during S. aureus or Streptococcus pyogenes during incubation in
ingestion of preopsonized bacteria by murine peritoneal the presence of sera promoting ingestion became exponen-
macrophagesa tial during the 120-min incubation period (Fig. 1 and 2; for
No. (x 106/ml) of No. (x 106/ml) of both bacteria species and various sera, r = 0.96; P < 0.01).
Duration of S. aureus incubated Streptococcus pyogenes Incubation of 5 x 106 macrophages per ml, 5 x 106 bacteria
incubation (min) with: incubated with: per ml, and 10% bovine, rat, or murine serum at 37°C
HBSS HBSS + PhB HBSS HBSS + PhB without rotation resulted in an increase in the number of
0 0.5 0.6 0.7 0.8 viable bacteria (data not shown), which indicates that inges-
10 4.0 3.6 6.2 5.0 tion requires rotation to ensure a maximal number of colli-
20 3.8 4.2 6.3 6.2 sions between phagocytes and microorganisms in such stud-
30 2.8 4.6 5.0 6.0 ies.
40 2.2 4.8 3.9 5.8 To find out whether the observed absence of phagocytosis
50 1.6 4.7 2.9 5.6 in the presence of sheep, dog, pig, rabbit, and horse sera was
60 1.2 4.9 2.0 5.9 due to insufficient opsonic activity of 10% serum, we incu-
Downloaded from http://iai.asm.org/ on February 12, 2021 by guest
a The number of viable cell-associated bacteria was determined during bated 5 x 106 macrophages per ml and 5 x 106 bacteria per
incubation of 5 x 106 macrophages per ml with 5 x 106 bacteria per ml ml with various concentrations (up to 50%) of the serum
(preopsonized with 10% murine serum) in HBSS or HBSS containing 2 mg of under investigation. No ingestion occurred in the presence
phenylbutazone (PhB) per ml.
of sheep, dog, rabbit, and horse sera, whereas with 50% pig
serum the phagocytic index was 50%, which would be
RESULTS considered suboptimal phagocytosis for mouse macro-
Phagocytosis of microorganisms by peritoneal macro- phages.
phages. The bactericidal activity of various sera to be used as Number of viable intracellular bacteria after phagocytosis.
opsonin was investigated first. S. aureus (5 x 106/ml) or Incubation of 5 x 106 macrophages per ml with 5 x 106 S.
Streptococcus pyogenes (5 x 106/ml) were incubated in the aureus or Streptococcus pyogenes per ml, preopsonized
presence of both 10 and 90% sera from the various types of with mouse or bovine serum, at 37°C and 4 rpm resulted in a
animals, at 37°C at 4 rpm. All combinations, except Strepto- maximum number of viable cell-associated bacteria-deter-
coccus pyogenes combined with 10 or 90% rat serum, led to mined after lysis of the macrophages-after 10 to 20 min
an increase in the number of viable bacteria, thus indicating (Table 2; data for bovine serum not shown). Phagocytosis of
that most sera are not bactericidal for these microorganisms preopsonized bacteria in the presence of phenylbutazone (2
(data not shown). mg/ml), a drug which has almost no effect on the rate of
The opsonic activity of various sera was studied by phagocytosis but inhibits intracellular killing (6, 9, 15),
incubation of 5 x 106 peritoneal macrophages per ml and 5 x resulted in an increase in the number of viable intracellular
106 S. aureus or Streptococcus pyogenes per ml in the bacteria during the first 10 to 20 min, and there was no
presence of 10% serum at 37°C at 4 rpm. The results show a increase after that time (Table 2). The difference between the
decrease in the number of viable extracellular S. aureus in number of viable bacteria determined after incubation with
the presence of bovine, rat, and murine sera (Table 1; Fig. and without phenylbutazone represents the number of bacte-
1). For Streptococcus pyogenes a small decrease in the ria killed during the ingestion period. Since for S. aureus and
number of viable extracellular bacteria was found in the Streptococcus pyogenes this difference was minimal during
presence of 10% NBCS, and a greater decrease was found in the first 20 min, all further experiments on intracellular
the presence of 10% bovine, rat, or murine serum (Fig. 2). killing were performed after 20 min of ingestion of preopso-
When a correction was made for the growth of extracellular nized bacteria.
bacteria, the decrease in the number of viable extracellular Effect of serum on the intracellular killing of microorga-
0
t.) (A
0 o 5x106- 5X106 -
r,
=QL
a)0
o
UL-O o HBSS-ALb HBSS - ALb
0-0
E E
cE \\ (Murine) inact.
(Bovine) inact. 106- (Bovine) inact.
\ Murine) inact. Bovine
-o x
,,, Bovine Murine
Murine
ok
D 105 105
0 60 120 0 60 120
Minutes
FIG. 3. Kinetics of intracellular killing of S. aureus by macrophages after phagocytosis of bacteria preopsonized with murine serum (left
panel) or bovine serum (right panel). The assay was performed in the presence of HBSS-Alb and 10% concentrations of murine, bovine, heat-
inactivated murine [(Murine) inact.], and heat-inactivated bovine [(Bovine) inact.] sera.VOL. 46, 1984 KILLING OF MICROORGANISMS BY MOUSE MACROPHAGES 757
To find out whether the number of bacteria ingested at the
start of the killing assay affects the dependence of macro-
2! phages on stimulation by extracellular serum factors for
m 5x1O6 maximal intracellular killing, we performed the killing assay
after phagocytosis at a bacteria-to-macrophage ratio of 10:1.
(o The results of these experiments were identical to those
L.
obtained after phagocytosis at a bacteria-to-macrophage
ratio of 1:1, i.e., maximal killing of S. aureus and Strepto-
coccus pyogenes in the presence of extracellular serum, no
COLe
_ killing of ingested S. aureus in the absence of serum, and
106 killing of only a portion of the ingested Streptococcus
L-
._.
pyogenes in the presence of HBSS-Alb (data not shown).
C's a
7O Involvement of Fc and C3b receptors in the stimulation of
D> a)0
intracellular killing. To identify the serum factors that stimu-
o e late intracellular killing by macrophages, we incubated 5 x
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za 106 macrophages containing S. aureus opsonized with mouse
serum, in the presence of 300 ,ug of purified mouse IgG per
ml. The results showed a killing index of 56 + 9% at 60 min,
which was nearly identical to the index obtained with heat-
0 60 120 inactivated serum (53 11%). These results indicate that
±
Minutes IgG is responsible for the stimulation of intracellular killing
by heat-inactivated serum. The higher killing index in the
FIG. 4. Kinetics of intracellular killing of Streptococcus pyo- presence of normal fresh serum (76%) compared with heat-
genes by macrophages after phagocytosis of bacteria preopsonized inactivated murine serum suggests that complement stimu-
with murine serum. The assay was performed in the presence of lates intracellular killing as well.
HBSS-Alb (O) and 10% murine serum (0).
To investigate this point further, we incubated macro-
nisms by macrophages. Incubation of macrophages contain- phages containing S. aureus in the presence of 1 mg of
ing S. aureus in the presence of HBSS-Alb, after phagocyto- trypsin per ml for 30 min at 37°C, followed by three washes
sis of S. aureus preopsonized with murine or bovine serum to remove the trypsin. The trypsin treatment resulted in an
at a bacteria-to-cell ratio of 1:1 for 20 min at 37°C, resulted in almost complete absence of detectable C3b receptors (Table
a negligible decrease in the number of viable intracellular 3), without affecting the viability of the macrophages. Incu-
bacteria (Fig 3). After incubation of macrophages containing bation of macrophages containing S. aureus, first with
S. aureus in the presence of 10% murine or bovine serum, trypsin for 30 min and then in the presence of 10% murine
the number of intracellular bacteria decreased by about 75% serum, 10% heat-inactivated murine, or HBSS-Alb for an
(Fig. 3). Incubation of similar macrophages in the presence additional 60 min, gave no intracellular killing. In the control
of heat-inactivated murine or bovine serum led to intermedi- experiments, macrophages containing S. aureus were incu-
ate killing indices (Fig. 3). bated with 2 mg of albumin per ml before the killing assay
To exclude the possibility that the decrease in the number was started. Under these conditions the intracellular killing
of viable bacteria was due to ingestion and subsequent killing of S. aureus was similar to that by resident macrophages
of adherent bacteria, we performed the killing assay in the (Table 3).
presence of sera without opsonic activity, i.e., 10% sheep,
dog, pig, horse, rabbit, and NBCS sera. In the presence of all DISCUSSION
of these sera, mouse peritoneal macrophages killed ingested Resident peritoneal macrophages killed ingested S. aureus
bacteria (Table 1). and Streptococcus pyogenes (representing catalase-positive
To find out whether serum stimulates intracellular killing and catalase-negative microorganisms, respectively) opti-
of catalase-negative microorganisms as it did that of cata- mally in the presence of extracellular serum. In the absence
lase-positive S. aureus, we performed a similar experiment of serum, ingested staphylococci were not killed, and only
with Streptococcus pyogenes. Incubation of macrophages about 60% of Streptococcus pyogenes were killed. Intracel-
containing ingested Streptococcus pyogenes in the presence lular killing was lower with extracellular heat-inactivated
of 10% murine serum resulted in a decrease of 82 + 6% in the serum than with fresh serum.
number of viable intracellular bacteria at 120 min (Fig. 4). The studies of the opsonic requirements of S. aureus and
This decrease was significantly greater (P < 0.01) than the Streptococcus pyogenes showed that the presence of bo-
decrease observed in the presence of HBSS-Alb (killing vine, rat, or murine serum is mandatory for optimal ingestion
index at 120 min, 61 + 5%). of these bacteria by mouse peritoneal macrophages. No
TABLE 3. Participation of Fc-y and C3b receptors in the stimulation of intracellular killing of S. aureusa
%0 %> S% Intracellular killing at 60 min (no. of expt) in the presence of:
Macrophages Macrophages
Treatment
(mg/mi)" C3b
with FC-y
receptors
with
receptors HBSS
10%lW eumIatiae
10% Serum Inactivated
(no. of expt) (no. of expt) serum
Bovine albumin (2) 98 ± 3 (6) 96 ± 3 (6) 32 + 8 (4) 78 + 10 (4) 54 + 11 (4)
Trypsin (1) 99 0.3 (3) 3 2 (3) 0 (3) 0 (3) 0 (3)
a Determined after phagocytosis at a bacteria-to-cell ratio of 1:1 for 20 min at 37°C.
bMacrophages (5 x 106/ml) containing S. aureus were incubated with albumin or trypsin for 30 min at 37°C and washed three times with gelatin-HBSS before
the intracellular killing assay was performed.758 LEIJH, VAN ZWET, AND VAN FURTH INFECT. IMMUN.
ingestion or almost no ingestion of these bacteria occurred in LITERATURE CITED
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or rabbit serum, which indicates either that these sera lack Studies of the macrophage complement receptor. Alteration of
specific antibodies against these microorganisms or that the receptor function upon macrophage activation. J. Exp. Med.
structure of the Fc part of IgG and the binding site of C3b 141:1278-1290.
surrounding opsonized bacteria are not compatible with the 2. Crofton, R. W., M. M. C. Diesselhoff-den Dulk, and R. van
Fc-y receptors and C3b receptors of mouse macrophages. Furth. 1978. The origin, kinetics and characteristics of the
The latter possibility seems unlikely, because Fcy receptors Kupffer cells in the normal steady state. J. Exp. Med. 148:1-17.
on mouse macrophages can be demonstrated with erythro- 3. Fahey, J. L., and W. E. Terry. 1978. Ion exchange chromatogra-
cytes coated with rabbit IgG antibodies (3, 4) and because phy and gel filtration, p. 8.1-8.16. In D. Weir (ed.), Handbook
NBCS promotes phagocytosis of Staphylococcus epidermi- of experimental immunology: application of immunological
methods, 3rd ed. Blackwell Scientific Publications, Ltd., Ox-
dis by macrophages (19). ford.
Ingestion of preopsonized S. aureus proved to be an 4. Griffin, F. M., Jr., C. M. Bianco, and S. C. Silverstein. 1975.
inadequate stimulus for the subsequent intracellular killing Characterization of the macrophage receptor for complement
of the microorganisms by peritoneal macrophages, as indi- and demonstration of its functional independence from the
cated by the absence of killing when macrophages containing receptor for the Fc portion of immunoglobulin 6. J. Exp. Med.
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cus pyogenes in the absence of extracellular serum stimula- tors for IgG: subclass specificity of receptors on different mouse
tion is in all probability due to the microbicidal effect of cell types and the definition of two distinct receptors on a
macrophage cell line. J. Exp. Med. 145:1316-1327.
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14). Furth. 1981. Participation of immunoglobulins and complement
Observation of the need for extracellular serum for opti- components in the intracellular killing of Staphylococcus aureus
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is dependent on the reliability of the killing assay, with the 33:714-724.
assumption that the number of viable bacteria determined 7. Leijh, P. C. J., M. T. van den Barselaar, M. R. Daha, and R. van
represents intracellular bacteria. Evidence that this is the Furth. 1982. Stimulation of the intracellular killing of Staphylo-
case has been given elsewhere (6-9, 19; Leijh, van Zwet, and coccus aureus by monocytes: regulation by immunoglobulin G
van Furth, in press), and additional evidence was provided and complement components C3/C3b and B/Bb. J. Immunol.
129:332-337.
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This indicates that the observed decrease in the number of complement and immunoglobulin for intracellular killing of
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possibly adherent bacteria during the killing assay. Since 784.
isolated IgG and inactivated serum gave equal stimulation of 9. Leijh, P. C. J., T. L. van Zwet, and R. van Furth. 1980. Effect of
intracellular killing, the killing stimulatory activity of heat- extracellular serum in the stimulation of intracellular killing of
inactivated serum must be due to the interaction of IgG with streptococci by human monocytes. Infect. Immun. 30:421-426.
10. Lowry, 0. H., U. J. Rosebrough, A. L. Farr, and R. J. Randall.
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is compatible with the decreased number of C3b receptors Phagocytosis of immune complexes by macrophages: different
found on human monocytes after trypsin treatment (8) and is roles of the macrophage receptor sites for complement (C3) and
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macrophage C3b receptors (1, 12). The observation that 12. Michl, J., J. C. Unkeless, and S. C. Silverstein. 1980. Modulation
trypsin treatment of macrophages abolishes the stimulation of macrophage plasma membrane receptors for IgG and comple-
of intracellular killing by fresh serum indicates involvement ment, p. 921-937. In R. van Furth (ed.), Mononuclear phago-
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in the presence of heat-inactivated serum after trypsin 13. Pitt, J., and H. P. Bernheimer. 1974. Role of peroxide in
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and trypsin-resistant Fcy receptors with the rosette tech- guinea pig polymorphonuclear leukocytes. J. Bacteriol.
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16. Unkeless, J. C. 1977. The presence of two Fc receptors on
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the stimulation of intracellular killing by human monocytes nomenclature in terms of sites and conditions, p. 1-30. In R. van
was correlated with the occurrence of Fc-y and C3b receptors Furth (ed.), Mononuclear phagocytes: functional aspects Mar-
on these cells (8). tinus Nijhoff Publishers, The Hague.
Comparison of the results of the present study of mouse 18. van Furth, R., and Z. A. Cohn. 1968. The origin and kinetics of
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effect of extracellular serum on intracellular killing by human 19. van Furth, R., T. L. van Zwet, and P. C. J. LeUh. 1978. In vitro
determination of phagocytosis and intracellular killing by poly-
monocytes showed no differences in intracellular killing, morphonuclear and mononuclear phagocytes, p. 32.1-32.19. In
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these cells. Publications, Ltd., Oxford.You can also read
