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Clinical and Diagnostic Laboratory Immunology, July 2000, p. 596-599, Vol. 7, No. 4
1071-412X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Enhancement by Ampicillin of Antibody Responses Induced by a
Protein Antigen and a DNA Vaccine Carried by Live-Attenuated
Salmonella enterica Serovar Typhi
Patrick C. Y.
Woo,1
Hoi-Wah
Tsoi,1
Harry C. H.
Leung,1
Lei-Po
Wong,1
Samson S. Y.
Wong,1
Eric
Chan,2 and
Kwok-Yung
Yuen1,*
Department of
Microbiology1 and
Pathology,2 The University of Hong
Kong, University Pathology Building, Queen Mary Hospital, Hong Kong
Received 9 November 1999/Returned for modification 24 March
2000/Accepted 24 April 2000
 |
ABSTRACT |
Live-attenuated Salmonella species are effective
carriers of microbial antigens and DNA vaccines. In a mouse model, the
immunoglobulin M (IgM) and total antibody levels directed toward the
lipopolysaccharide of Salmonella enterica serovar Typhi
were significantly enhanced at day 21 after oral immunization with
live-attenuated serovar Typhi (strain Ty21a) when ampicillin was
concomitantly administered (P < 0.05 and
P < 0.005, respectively). The heat-killed
Ty21a-stimulated lymphocyte proliferation indices for the ampicillin
group at day 21 were significantly higher than those for the normal
saline (NS) group (P < 0.005, P < 0.001, and P < 0.01) for all three doses of antigen
(104, 105, and 106 heat-killed
Ty21a per well, respectively). The 50% lethal doses for mice from the
ampicillin and NS groups immunized with Ty21a with pBR322 after
wild-type serovar Typhi challenge on day 24 were 3.4 × 107 and 5.0 × 106 CFU, respectively. The
fecal bacterial counts for the ampicillin group at days 1, 3, and 5 were significantly lower than those for the NS group
(P < 0.01, P < 0.01, and
P < 0.05, respectively), and there was a trend toward
recovery of Ty21a in a larger number of mice from the ampicillin group
than from the NS group. Furthermore, the IgG2a levels directed toward
tetanus toxoid were significantly enhanced at days 7 and 21 after oral
immunization with Ty21a that carried the fragment c of tetanus toxoid
when ampicillin was concomitantly administered (P < 0.05 and P < 0.005, respectively), and the IgM and
total hepatitis B surface antibody levels were significantly enhanced
at days 7 (P < 0.005 and P < 0.05, respectively) and 21 (P < 0.01 and P < 0.05, respectively) after oral immunization with Ty21a that carried
the DNA vaccine that encodes hepatitis B surface antigen when
ampicillin was concomitantly administered. The present observation may
improve the efficacy of the protein antigens and DNA vaccines carried
in live-attenuated bacteria, and further experiments should be carried
out to determine the best antibiotics and dosage regimen to be used, as
well as the best carrier system for individual protein antigens and DNA vaccines.
| |
INTRODUCTION |
Mucosal vaccination provides
specific advantages for ease of administration, vaccine formulation,
and potential to support mass vaccination (7). It has been
shown that live-attenuated Salmonella species are effective
carriers of microbial antigens and DNA vaccines (3, 5,
13). However, since the efficacy of oral live-attenuated
Salmonella enterica serovar Typhi vaccine (Ty21a) in
humans is only 70% (14, 15), it can be inferred that use of
strain Ty21a as a vaccine carrier for human beings is far from ideal.
Moreover, the immunogenicities of mucosal vaccines in people who reside
in developing countries are even worse (8, 12). This would
further hinder the potential use of Ty21a as a vaccine carrier for
global immunization. Therefore, new ways to improve the immunogenicity
of Ty21a as well as the protein antigens and DNA vaccines carried in it
are mandatory.
Antibiotics have been known to affect immune responses (16, 17,
18). Recently, we have shown that antibiotics, especially ampicillin, enhance the antibody response against the
lipopolysaccharide (LPS) of serovar Typhi after intraperitoneal Ty21a
immunization in a mouse model (16). In these experiments,
the effects of ampicillin on the immunogenicity of oral Ty21a and the
protein antigen and DNA vaccine carried in it were studied. We examined the effects of ampicillin on the serum antibody response against LPS of serovar Typhi, the heat-killed Ty21a-stimulated lymphocyte proliferation index (LPI), and the survival of mice upon
wild-type S. typhi challenge after oral Ty21a immunization.
We also studied the effect of ampicillin on the serum antibody response
against tetanus toxoid and hepatitis B surface antigen (HBsAg) in mice administered fragment c of tetanus toxoid and the DNA that encodes HBsAg, each of which was carried in Ty21a, respectively. The
possible mechanism of such effects is also discussed.
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MATERIALS AND METHODS |
Animals.
Female BALB/c mice (weight, 18 to 22 g) were
used in all experiments. They were housed in cages under standard
conditions with regulated day length, temperature, and humidity and
were given pelleted food and tap water ad libitum.
Experimental schedule, antibiotic administration, and
immunization.
The mice were divided randomly into two groups; one
group received ampicillin (20 mg/kg of body weight) intraperitoneally, and the other group received 0.25 ml of sterile normal saline (NS). The
doses were administered from day 
1 to day 20. To determine the effect
of ampicillin on the levels of antibodies against LPS of S. enterica serovar Typhi in serum, the heat-killed Ty21a-stimulated LPI, the survival of mice upon wild-type serovar Typhi challenge, and
the fecal aerobic bacterial and Ty21a counts after Ty21a
administration, 39 mice from the ampicillin group and 39 mice from the
NS group were immunized orally with Ty21a (Berna, Berne, Switzerland)
that had been transformed with pBR322 (Amersham Pharmacia Biotech, Piscataway, N.J.) (to make the organism ampicillin resistant) by using
a gastric tube (2.7 × 109 CFU in 0.3 ml). Fifteen
mice from each group were used for measurement of serum antibody
levels, LPI, fecal bacterial count, and Ty21a isolation; and the
remaining 24 mice in each group were used for wild-type serovar Typhi
challenge. For determination of the effect of ampicillin on the
antibody response after immunization with the expressed protein
antigen carried in Ty21a, 15 mice from the ampicillin group and 15 mice
from the NS group were immunized orally with Ty21a transformed
with pTETnir15 (a gift from A. J. Makoff)
(2.7 × 109 CFU in 0.3 ml), which contained fragment c
of tetanus toxoid under the control of a prokaryotic promoter
(2). Furthermore, for determination of the effect of
ampicillin on the antibody response after immunization with DNA carried
in Ty21a, 15 mice from the ampicillin group and 15 mice from the NS
group were immunized orally with Ty21a transformed with pRc/CMV-HBs(S)
(a gift from Robert Whalen) (2.7 × 109 CFU in 0.3 ml), which contained HBsAg under the control of a cytomegalovirus (CMV)
promoter (4).
Measurement of levels of antibodies against LPS of serovar Typhi,
tetanus toxoid, and HBsAg in serum.
Fifteen mice from each group
were bled on days 1, 7, and 21 (9). Blood was taken right
before administration of antibiotics. The blood was centrifuged at
2,700 × g for 20 min, and the serum was stored at 70°C
before antibody level measurement.
Nunc-Immuno plates (Nalge Nunc International, Roskilde, Denmark) were
used in all enzyme-linked immunosorbent assay (ELISA) experiments for
measurement of antibody levels against tetanus toxoid and LPS of
S. typhi. Each well was coated with 100 µl of diluted
antigen (50 µl of tetanus toxoid in 50 µl of 0.05 M
carbonate-bicarbonate buffer [pH 9.6] or 4 µg LPS of S. typhi in 0.05 M carbonate-bicarbonate buffer [pH 9.6]), and the
plates were incubated at 4°C overnight. After the plate was washed
with phosphate-buffered saline (PBS)-0.05% Tween 20 (washing buffer)
twice 200 µl of PBS-5% bovine serum albumin (BSA) (blocking buffer)
was added to each well and the plate was incubated at 37°C for 2 h. After the plate was washed with washing buffer three times, mouse
sera (diluted 1:25 with PBS-2% BSA) were added to the ELISA plates.
For measurement of levels of antibody against HBsAg, mouse sera
(diluted with PBS-2% BSA) were added to ELISA plates precoated with
HBsAg (Biokit, Barcelona, Spain). The plates were incubated at 37°C
for 1 h. After the plates were washed with washing buffer three
times, 100 µl of peroxidase-conjugated goat anti-mouse antibody
(anti-mouse total antibody from DAKO, Glostrup, Denmark; anti-mouse
immunoglobulin M [IgM], IgG1, and IgG2a from Serotect, Kidlington,
United Kingdom) that was diluted, according to the manufacturer's
instructions, with PBS-2% BSA was added to the each well and the
plate was incubated at 37°C for 30 min (tetanus toxoid and HBsAg) or
1 h (Ty21a). Assays for IgM and total antibody levels were
conducted to assess the primary and secondary immune responses, while
IgG1 and IgG2a levels were used to determine whether the humoral
response was inclined toward the Th2 or the Th1 pattern, respectively.
After the plate was washed with washing buffer three times, 100 µl of ortho-phenylenediamine (OPD) substrate (prepared by diluting
2 mg of OPD [Calbiochem, La Jolla, Calif.] in 2.5 ml of 50 mM citric acid [pH 5] with 2.5 µl of 30% H2O2) was
added to each well and the plate was incubated at room temperature for
30 min. A total of 100 µl of 1 M H2SO4 was
added and the absorbance of each well was measured at 492 nm, with OPD
buffer used as a blank. Each sample was tested in duplicate, and the
mean absorbance for each serum sample was calculated. All ELISAs were
optimized so that there was a linear relationship between the optical
density and the amount of antibody present in the serum at the serum
dilution for the corresponding type of antibody measured. The serum
antibody level for a particular mouse on a particular day was defined
as the absorbance obtained from the serum on that day minus that for
the corresponding mouse on day 1. Control experiments were performed
by adding ampicillin to serum samples to exclude the possibility of
interference of ampicillin with the ELISA.
Measurement of LPI.
On day 21, single-cell suspensions of
spleen cells from 15 mice in the ampicillin group and 15 mice in the NS
group that had been immunized with Ty21a with pBR322 were depleted of
erythrocytes by adding freshly prepared Gey's solution. The cells were
resuspended in RPMI 1640 medium (Gibco BRL, Rockville, Md.)
supplemented with 15% fetal calf serum and were inoculated into
microwell plates at 5 × 105 cells per well in
triplicate. The cells were stimulated with phytohemagglutinin at 5 µg
per well (positive control), heat-killed Ty21a at concentrations of
104, 105, and 106 bacteria per
well, or RPMI 1640 medium (negative control). Cells were cultured at
37°C in 5% CO2 for 3 days, and 3H-labeled
thymidine (Amersham Pharmacia, Little Chalfont, United Kingdom) was
added at 1 µCi per well for the last 18 h. The cells were
harvested onto glass-fiber filter mats with a model CH1 cell harvester
(Insel, Hampshire, United Kingdom), and radioactivity was measured in a
liquid scintillation counter (Beckman, Fullerton, Calif.). The LPI for
a particular sample is defined as the ratio of the difference in
radioactivity between the positive control and the sample and that
between the positive and negative controls.
Measurement of fecal bacterial counts.
On the day before
immunization and on days 1, 3 and 5 after immunization, the feces of 15 mice (0.01 g of feces per mouse) from the ampicillin and NS groups
immunized with Ty21a with pBR322 were collected and resuspended in 1 ml
of PBS. Each sample was further diluted 1:200,000 with PBS, and 100 µl from each diluted sample was plated onto
cystine-lactose-electrolyte-deficient agar in duplicate. The plates
were incubated at 37°C for 48 h. The number of colonies on each
plate was counted, and the fecal counts of the mice were expressed as
the number of CFU per gram of stool.
Isolation of fecal Ty21a from immunized mice.
On days 1, 2, and 3, the feces of 15 mice (0.01 g of feces per mouse) from the
ampicillin and NS groups that had been immunized with Ty21a with pBR322
were collected and resuspended in 2 ml of Selenite-F broth. After
incubation at 37°C for 24 h, 10 µl from each resuspended
sample was plated onto Luria-Bertani agar with ampicillin (100 mg/ml). The plates were incubated at 37°C for 48 h.
Suspected colonies were isolated and confirmed to be Ty21a by standard
biochemical tests and serotyping (10).
Determination of LD50 by wild-type challenge with
serovar Typhi.
On day 24, when the serum ampicillin levels of the
mice had fallen to negligible levels, groups of six mice each from the ampicillin group and the NS group that had been immunized with Ty21a
with pBR322 were challenged with graded doses (8.9 × 107, 3.4 × 107, 1.3 × 107, and 5.0 × 106 CFU) of wild-type
S. typhi. The lengths of survival of the mice were recorded.
The 50% lethal doses (LD50s) for the ampicillin and NS
groups were defined as the administered dose of wild-type S. typhi that caused the death of 50% of the mice in each groups.
Statistics.
The serum antibody levels, LPI, and fecal
bacterial counts between the mice in the ampicillin and NS groups that
received Ty21a with pBR322 were compared by Student's t
test, as were the serum antibody levels between those that received
Ty21a with fragment c of tetanus toxoid or DNA that encoded HBsAg. A
P value of <0.05 is regarded as statistically significant.
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RESULTS |
Antibodies against LPS of serovar Typhi in serum.
The levels
of total antibody and antibody subtypes against LPS of S. enterica serovar Typhi in serum at days 7 and 21 after oral
administration of Ty21a with pBR322 to mice treated with ampicillin or
NS is summarized in Table 1. The IgM
levels of the ampicillin group at days 7 and 21 and the total antibody
levels for the ampicillin group at day 21 were significantly higher
than the corresponding antibody levels for the NS group (P < 0.05, P < 0.05, and P < 0.005,
respectively).
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TABLE 1.
Levels of total antibody and antibody subtypes at days
7 and 21 after oral administration of Ty21a with pBR322 to
mice treated with ampicillin or NS
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LPI.
The heat-killed Ty21a-stimulated LPI at day 21 after oral
administration of Ty21a with pBR322 to mice treated with ampicillin or
NS is summarized in Table 2. The LPIs for
the ampicillin group at day 21 when 104, 105,
and 106 heat-killed Ty21a per well were used as antigens
were significantly higher than those for the NS group (P < 0.005, P < 0.001, and P < 0.01,
respectively).
LD50 after wild-type serovar Typhi challenge.
The
survival of mice in the ampicillin and NS groups immunized with Ty21a
with pBR322 after intraperitoneal challenge with wild-type serovar
Typhi on day 24 is shown in Table 3. The
LD50s for mice from the ampicillin and NS groups were
3.4 × 107 and 5.0 × 106 CFU,
respectively.
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TABLE 3.
Survival of mice in the ampicillin and NS groups
immunized with Ty21a with pBR322 after intraperitoneal challenge
with wild-type S. typhi on day 24
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Fecal bacterial counts.
The fecal bacterial counts at day 1
and days 1, 3, and 5 after oral administration of Ty21a with pBR322 to
mice treated with ampicillin or NS is summarized in Table
4. The fecal bacterial counts for the
ampicillin group at days 1, 3, and 5 were significantly lower than
those for the NS group (P < 0.01, P < 0.01, and
P < 0.05, respectively).
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TABLE 4.
Fecal bacterial count at day 1 and days 1, 3, and
5 after oral administration of Ty21a with pBR322 to mice
treated with ampicillin or NS
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Fecal Ty21a isolation.
The number of mice from which Ty21a was
isolated in the feces on days 1, 2, and 3 after oral administration of
Ty21a with pBR322 to mice treated with ampicillin or NS is summarized
in Table 5. There was a trend toward the
recovery of Ty21a in a larger number of mice from the ampicillin group
than from the NS group.
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TABLE 5.
Fecal Ty21a isolation on days 1, 2, and 3 after oral
administration of Ty21a with pBR322 to mice treated with ampicillin
or NS
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Levels of antibodies against tetanus toxoid in serum.
The
levels of total antibody and antibody subtypes against tetanus toxoid
in serum at days 7 and 21 after oral administration of Ty21a with
pTETnir15 to mice treated with ampicillin or NS is
summarized in Table 6. The IgG2a levels
for the ampicillin group at days 7 and 21 were significantly higher
than the corresponding antibody levels for the NS group (P < 0.05 and P < 0.005, respectively).
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TABLE 6.
Total antitetanus antibody and antibody subtypes at days
7 and 21 after oral administration of Ty21a with
pTETnir15 to mice treated with ampicillin or NS
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Levels of antibodies against HBsAg in serum.
The levels of
total antibody and antibody subtypes against HBsAg in serum at days 7 and 21 after oral administration of Ty21a with pRc/CMV-HBs(S) to mice
treated with ampicillin or NS is summarized in Table
7. The IgM and total antibody levels for
the ampicillin group at days 7 (P < 0.005 and
P < 0.05, respectively) and 21 (P < 0.01 and P < 0.05, respectively) were
significantly higher than the corresponding antibody levels for the NS
group.
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TABLE 7.
Total anti-HBsAg antibody and antibody subtypes at
days 7 and 21 after oral administration of Ty21a with
pRc/CMV-HBs(S) to mice treated with ampicillin or NS
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| |
DISCUSSION |
Ampicillin improved the B-cell response, the antigen-specific
T-cell response, and the protective immune response after oral Ty21a
immunization. Previously, we showed that antibiotics, especially ampicillin, enhanced the humoral immune response of mice immunized intraperitoneally with Ty21a (16). In the present study, we showed that ampicillin enhanced not only the humoral immune response of
mice after oral Ty21a immunization but also the heat-killed Ty21a-stimulated LPI for all three doses of heat-killed Ty21a used.
Furthermore, the LD50 for the group of mice that received ampicillin was sevenfold higher than that for the group that received NS.
The immunogenicity of the DNA vaccine or protein antigen carried in
Ty21a was also enhanced by administration of ampicillin. In our
experiments the HBsAg DNA vaccine and the fragment c of tetanus toxoid
were chosen as the DNA vaccine and the protein antigen carried in
Ty21a, respectively, because we have previously shown that ampicillin
does not affect the antibody response of mice induced by parenteral
administration of recombinant HBsAg or tetanus toxoid (16).
In the present study, we showed that ampicillin increased the serum IgM
response induced by pRc/CMV-HBs(S) carried in Ty21a. This is in line
with the evidence that the major immune response induced by a single
intraperitoneal dose of recombinant HBsAg vaccine is IgM. The IgG
response occurred only after administration of a booster dose
(16). On the other hand, ampicillin enhanced the IgG2a
response induced by tetanus toxoid fragment c carried in Ty21a. This is
probably because the tetanus toxoid fragment carried in Ty21a is
presented by the antigen-presenting cells in a manner different from
that when it is given through the subcutaneous route. When given
subcutaneously, tetanus toxoid was presented mainly through the major
histocompatibility complex class II pathway, inducing mainly antibody
responses of the Th2 type (IgM and IgG1). However, when the tetanus
toxoid fragment is carried in Ty21a, it is presented through
intracellular major histocompatibility complex class I pathways,
shifting the antibody response toward Th1. Therefore, it is not
surprising that the major serum antibody subtype level that is
upregulated is IgG2a. Furthermore, this is in line with the finding of
a previous study, which showed that a strong class I-restricted
cytotoxic T-cell response against murine lymphocytic choriomeningitis
virus was induced by the chimeric protein formed between the nuclear
protein of the virus and an S. enterica serovar Typhimurium
effector protein carried in live-attenuated serovar Typhimurium
(13).
Ampicillin enhanced the immune response of oral Ty21a probably by
giving it a survival advantage against the normal bacterial flora of
the intestine. We showed that ampicillin significantly suppressed the
normal flora of the intestine, resulting in a relatively higher rate of
recovery of Ty21a from the feces on days 1, 2, and 3. This is in line
with the M-cell sampling theory about antigen presentation in the
mucosa of the gastrointestinal tract. It has been shown that S. enterica serovar Typhi cells adhere selectively to the M cells of
mucosa-associated lymphoid tissue, which form the gateway of the
mucosal immune system (1, 6). This induces engulfment of the
bacteria by "macrocytosis." The engulfed Salmonella will
be presented to the T and B lymphocytes that form large intraepithelial pockets around the basolateral membranes of the M cells
(11). The normal flora of the murine large intestine, which
contains 108 bacteria per gram of feces, competes with
Ty21a by occupying the mucosal adhesion sites, competing with Ty21a for
nutrients, and secreting bacteriocins and bacteriocin-like substances.
When ampicillin is administered, the normal flora is transiently
suppressed 100-fold, giving Ty21a a survival advantage and a
greater chance of presenting itself and the protein antigen or
DNA vaccine carried in it to the M cells.
These observations have important applications for both prophylactic
and therapeutic vaccinations. The problem of disease transmission
through the use of reusable needles for immunization is of great
concern in developing countries. Mucosal vaccination provides specific
advantages in terms of ease of administration, vaccine formulation, and
the potential to support mass vaccination (7). Besides the
induction of an immune response to the microorganism itself,
live-attenuated bacteria that carry protein antigens are used to induce
an immune response against the protein antigen carried in them (5,
13), and the type of immune response can be further tuned with
the help of adjuvants. However, the protective efficacy of oral Ty21a
in humans is only about 70%, and this is even worse in developing
countries, where people suffer from environmental enteropathy, with
their gastrointestinal tracts, especially their upper gastrointestinal
tracts, being colonized with many more bacteria than those of people in
developed countries (8, 12). Therefore, this concept of
antibiotic enhancement of the immune response might have a place in
selective prophylactic vaccination programs, such as vaccination of
nonresponders to routine immunization. Furthermore, DNA vaccination is
considered a possible way for therapeutic vaccination, including the
treatment of cancer. Therefore, the present observations may improve
the therapeutic effect of DNA vaccines carried in live-attenuated bacteria, and further experiments should be carried out to determine the best antibiotics and dosage regimens to be used, as well as the best carrier system for individual protein antigens and DNA vaccines. However, with concerns about the increasing rate of antibiotic resistance worldwide, the incorporation of an
antibiotic as part of a routine vaccination regimen is probably not warranted.
| |
ACKNOWLEDGMENTS |
This work was partly supported by the Committee of Research and
Conference Grants, The University of Hong Kong.
We thank A. J. Makoff for providing us with the
pTETnir15 plasmid, Robert Whalen for providing us with the
pRc/CMV-HBs(S) plasmid, and Rodney Lee for comments on the manuscript.
| |
FOOTNOTES |
*
Corresponding author. Mailing address: Department of
Microbiology, The University of Hong Kong, University Pathology
Building, Queen Mary Hospital, Hong Kong. Phone: (852) 28553214. Fax:
(852) 28551241. E-mail: microgen{at}hkucc.hku.hk.
| |
REFERENCES |
| 1.
|
Baumler, A. J.,
R. M. Tsolis, and F. Heffron.
1996.
The lpf fimbrial operon mediates adhesion of Salmonella typhimurium to murine Peyer's patches.
Proc. Natl. Acad. Sci. USA
93:279-283[Abstract/Free Full Text].
|
| 2.
|
Chatfield, S. N.,
I. G. Charles,
A. J. Makoff,
M. D. Oxer,
G. Dougan,
D. Pickard,
D. Slater, and N. F. Fairweather.
1992.
Use of the nirB promoter to direct the stable expression of heterologous antigens in Salmonella oral vaccine strains: development of a single-dose oral tetanus vaccine.
Bio/Technology
10:888-892[CrossRef][Medline].
|
| 3.
|
Darji, A.,
C. A. Guzman,
B. Gerstel,
P. Wachholz,
K. N. Timmis,
J. Wehland,
T. Chakraborty, and S. Weiss.
1997.
Oral somatic transgene vaccination using attenuated S. typhimurium.
Cell
91:765-775[CrossRef][Medline].
|
| 4.
|
Davis, H. L.,
M. L. Michel, and R. G. Whalen.
1993.
DNA-based immunization induces continuous secretion of hepatitis B surface antigen and high levels of circulating antibody.
Hum. Mol. Genet.
2:1847-1851[Abstract/Free Full Text].
|
| 5.
|
Gonzalez, C.,
D. Hone,
F. R. Noriega,
C. O. Tacket,
J. R. Davis,
G. Losonsky,
J. P. Nataro,
S. Hoffman,
A. Malik,
E. Nardin,
M. B. Sztein,
D. G. Heppner,
T. R. Fouts,
A. Isibasi, and M. M. Levine.
1994.
Salmonella typhi vaccine strain CVD 908 expressing the circumsporozoite protein of Plasmodium falciparum: strain construction and safety and immunogenicity in humans.
J. Infect. Dis.
169:927-931[Medline].
|
| 6.
|
Jones, B. D.,
N. Ghori, and S. Falkow.
1994.
Salmonella typhimurium initiates murine infection by penetrating and destroying the specialized epithelial M cells of the Peyer's patches.
J. Exp. Med.
180:15-23[Abstract/Free Full Text].
|
| 7.
|
Levine, M. M., and G. Dougan.
1998.
Optimism over vaccines administered via mucosal surfaces.
Lancet
351:1375-1376[CrossRef][Medline].
|
| 8.
|
Levine, M. M., and J. B. Kaper.
1995.
Live oral cholera vaccine: from principle to product.
Bull. Inst. Pasteur
9:243-253.
|
| 9.
|
Morton, D. B.,
D. Abbot,
R. Barclay,
B. S. Close,
R. Ewbank,
D. Gask,
M. Heath,
S. Mattic,
T. Poole,
J. Seamer,
J. Southee,
A. Thompson,
B. Trussell,
C. West, and M. Jennings.
1993.
Removal of blood from laboratory mammals and birds.
Lab. Anim.
27:1-22[Free Full Text].
|
| 10.
|
Murray, P. R.,
E. J. Baron,
M. A. Pfaller,
F. C. Tenover, and R. H. Yolken (ed.).
1999.
Manual of clinical microbiology, 7th ed.
American Society for Microbiology, Washington, D.C.
|
| 11.
|
Neutra, M. R.,
A. Frey, and J. P. Kraehenbuhl.
1996.
Epithelial M cells: gateways for mucosal infection and immunization.
Cell
86:345-348[CrossRef][Medline].
|
| 12.
|
Perez-Schael, I.,
M. J. Guntinas,
M. Perez,
V. Pagone,
A. M. Rojas,
R. Gonzalez,
W. Cunto,
Y. Hoshino, and A. Z. Kapikian.
1997.
Efficacy of the rhesus rotavirus-based quadrivalent vaccine in infants and young children in Venezuela.
N. Engl. J. Med.
337:1181-1187[Abstract/Free Full Text].
|
| 13.
|
Russmann, H.,
H. Shams,
F. Poblete,
Y. Fu,
J. E. Galan, and R. O. Donis.
1998.
Delivery of epitopes by the Salmonella type III secretion system for vaccine development.
Science
281:565-568[Abstract/Free Full Text].
|
| 14.
|
Simanjuntak, C. H.,
F. P. Paleologo,
N. H. Punjabi,
R. Darmowigoto,
Soeprawoto,
H. Totosudirjo,
P. Haryanto,
E. Suprijanto,
N. D. Witham, and S. L. Hoffman.
1991.
Oral immunization against typhoid fever in Indonesia with Ty21a vaccine.
Lancet
338:1055-1059[CrossRef][Medline].
|
| 15.
|
Wahdan, M. H.,
C. Serie,
Y. Cerisier,
S. Sallam, and R. Germanier.
1982.
A controlled field trial of live Salmonella typhi strain Ty21a oral vaccine against typhoid: three-year results.
J. Infect. Dis.
145:292-295[Medline].
|
| 16.
|
Woo, P. C. Y.,
H. W. Tsoi,
L. P. Wong,
H. C. H. Leung, and K. Y. Yuen.
1999.
Modulation of vaccine-induced humoral immune response by antibiotics.
Clin. Diagn. Lab. Immunol.
6:832-837[Abstract/Free Full Text].
|
| 17.
|
Woo, P. C. Y.,
L. W. C. Chow,
E. S. K. Ma, and K. Y. Yuen.
1999.
Clarithromycin attenuates the inflammatory response induced by surgical trauma in a guinea pig model.
Pharmacol. Res.
39:49-54[CrossRef][Medline].
|
| 18.
|
Woo, P. C. Y.,
W. F. Ng,
H. C. H. Leung,
H. W. Tsoi, and K. Y. Yuen.
2000.
Clarithromycin attenuates cyclophosphamide-induced mucositis in mice.
Pharmacol. Res.
41:527-532[CrossRef][Medline].
|
Clinical and Diagnostic Laboratory Immunology, July 2000, p. 596-599, Vol. 7, No. 4
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Copyright © 2000, American Society for Microbiology. All rights reserved.
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Abstract
Introduction
