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Department of Microbiology and Immunology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
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Abstract |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Resistance/susceptibility to L. major depends, among other factors, upon the number of parasites employed for infection (6, 7, 8). Susceptible BALB/c mice resist a low dose infection, and resistant CBA mice develop lesions when infected with very high numbers (8). We undertook a detailed investigation of the relationship between the number of parasites employed for infection and the ensuing pathophysiological state in BALB/c mice. Our incidental observations over a period of several years following infection with low numbers of parasites suggested that immune elimination of L. major may occur, contrary to conventional views (9, 10, 11, 12, 13, 14). Given the potential importance of this tentative inference for analyzing the requirements for maintenance of immunological memory, for vaccination, and for the control of reactivation disease, we attempted to develop a more incisive and reproducible system to examine whether parasite clearance can occur and to determine what the consequences are of such clearance for immunological resistance and memory.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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BALB/c mice, 8–10 wk of age and bred at the animal facility of the Department of Microbiology and Immunology, University of Saskatchewan, were used. All mice were maintained according to the guidelines of the Canadian Council of Animal Care.
Parasites and parasite Ags
Mice were infected with stationary phase promastigotes of L. major MHOM (WHO MHOM/IL/80/Friedlin) strain as described previously (7). Soluble leishmanial Ag (SLA)3 was prepared, and protein content was determined by the Bradford method (15). SLA was used at 30 µg/ml for in vitro stimulation of splenocytes and lymph node cells for the detection of L. major Ag-specific cytokine-producing cells.
Measurement of footpad lesions and detection of lymph node (LN) swellings
The size of footpad lesions was measured with dial calipers (Oditest, Langenmesstechnik, Kroeplin, Germany), using the contralateral uninfected foot as a control. Mice were designated LN positive (LN+) if the draining popliteal lymph nodes were enlarged, as assessed by palpation.
Estimation of parasite burden
The parasite burden in the footpad, draining popliteal lymph node, spleen, and bone marrow of infected mice was estimated by limiting dilution analysis as previously described (16). To enhance sensitivity, 2 -fold dilutions of undiluted samples (up to 1/100) were used. Thereafter, the conventional 10-fold dilutions were used.
Limiting dilution assay for the frequency of L. major-specific cells
The frequency of L. major-specific precursor T cells
able to produce IL-2-, IL-4-, and IFN-
-reactive cells was measured
by limiting dilution as previously described (17) with
minor modifications. Briefly, single-cell suspensions of spleens and
draining popliteal lymph nodes from age-matched control mice or mice
previously infected with L. major and from mice in the
asymptomatic or subclinical state were serially diluted 2-fold (1000 to
50 cells/well; 32 replicate wells/dilution) and cultured in
round-bottom 96-well culture plates (Nalgene, Nunc International,
Naperville, IL) with 5 x 105 irradiated
(1500 rad from a 60Co source; Atomic Energy of
Canada, Ottawa, Canada) syngeneic spleen cells (APC), rIL-2 (20 WHO
U/ml; Genzyme, Mississauga, Canada), and SLA at 30 µg/ml. Negative
controls included irradiated spleen cells cultured in the absence of
responder cells. To assess spontaneous cytokine release, responder
cells were cultured with APC and rIL-2 in the absence of SLA. After 14
days, the cultures were washed three times and restimulated with fresh
APC (5 x 105 cells/well) and SLA in the
absence of rIL-2. Supernatant fluids were collected after 48 h and
assayed for IL-2, IL-4, and IFN- production by ELISA. In each assay,
wells were considered positive for cytokine production if the
absorbance value was >3 SD above the mean value obtained from wells
lacking responder cells only.
Assessment of protective capacity by direct challenge or by transfer of lymphocyte populations to irradiated recipients that receive a parasite challenge
Groups of mice that were previously exposed to a low dose infection of 330 L. major parasites in the right hind footpad and their age-matched controls were challenged with 106 promastigotes given s.c. into the left hind footpad, and lesion development was monitored. The protective capacity of spleen cells from mice that had been exposed to parasites was sometimes assessed by the adoptive transfer assay (18). Twenty million splenocytes from age-matched control mice or experimental mice were injected i.v. into lightly irradiated (450 rad from a 60Co source) syngeneic mice. The next day, recipient mice were challenged with 106 promastigotes given s.c. into the footpad and were monitored for lesion development.
Measurement of parasite-specific IgG1 and IgG2a Abs
At regular intervals, infected mice were tail bled, and the plasma obtained was used to determine the level of parasite-specific IgG1 and IgG2a Abs by ELISA (6, 8).
ELISPOT assay for Ag-specific IFN-- and IL-4-secreting cells
The Ag-specific IFN-- and IL-4-secreting cells in the
draining popliteal lymph nodes and spleens of infected mice were
enumerated by the ELISPOT assay as previously described
(19). Spleen cells were assayed at 5 x
105 cells/well, while lymph node cells were
assayed at 105 cells/well in 200-µl
aliquots in the presence or the absence of SLA (3 µg/well). In all
cases the total number of cells per well was made up to
106 by adding 5 x 105
or 9 x 105 unimmunized syngeneic
splenocytes to the spleen and lymph node test cells, respectively. It
has been shown previously that this allows valid enumeration of
Ag-specific cytokine-producing cells (19). The data are
presented as the number of Ag-dependent spots adjusted to the expected
number from 5 x 105 test cells unless
otherwise stated.
Cytokine determinations
The levels of IL-2, IL-4, and IFN- in supernatant fluids of
cultures from limiting dilution analysis were determined by routine
sandwich ELISA. Paired Abs against murine IL-2, IL-4, and IFN-- and
recombinant IL-2, IL-4, and IFN-, used as standards, were purchased
from PharMingen (San Diego, CA) and used according to the
manufacturer’s suggested protocol. The sensitivities of the ELISA were
3 pg/ml for IL-4 and 7.5 pg/ml for IL-2 and IFN-.
Longitudinal characterization over many months of mice infected with low numbers of parasites
Mice infected s.c. in the foot with lower numbers of parasites,
which did not often cause progressive disease, were monitored for
several months, up to 24 mo in some cases. Mice were individually
tagged and were assessed every 2 wk for lesion formation/size and for
the palpability of the lymph node draining the site of infection. Blood
samples were taken regularly, about every other month. Levels of
parasite-specific Ab in the plasma were assessed by ELISA as were the
number of parasite-specific IFN-- and IL-4-producing cells in a
million peripheral blood cells by the ELISPOT assay. Some mice were
also sacrificed so that the splenic responses and parasite burdens in
their draining lymph nodes and footpads could be assessed.
Statistical analysis
Estimates of the frequency of L. major-specific
precursor T cells able to give rise to IL-2-, IL-4-, and
IFN--producing cells were obtained by both maximum likelihood and
minimum 
2 methods, based on a Poisson
regression between the number of positive wells and the logarithm of
negative wells using the PROC GENMOD procedure of the Statistical
Analysis System (SAS Institute, Cary, NC). The maximum likelihood
results are presented, as similar results were obtained by either
method. Significance of differences for ELISPOT data and parasite
burdens was determined by ANOVA, while differences in disease outcome
were determined by repeated measure ANOVA using StatView software
(Abacus Concepts, Berkeley, CA).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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We studied infected mice longitudinally over many months,
sometimes up to 24 mo. The level of L. major-specific Abs in
plasma, the size of the infected footpad, and the palpability of the
draining popliteal lymph node were assessed periodically. We defined
four pathophysiological states, assessed at 
3 mo postinfection. 1)
The asymptomatic state is characterized by the absence of a visible
lesion, the absence of a palpable draining lymph node, and the absence
of detectable parasite-specific Abs. 2) No visible cutaneous lesion is
evident in the subclinical state, but the draining lymph node is
readily palpable, and parasite-specific IgG2a Abs predominate over IgG1
Abs. 3) Footpad lesions (0.5–2 mm) that do not change by >0.5 mm/wk
and without a consistent trend to increase or decrease over several
weeks characterize the borderline state. These mice have readily
palpable draining lymph nodes and roughly equal amounts of IgG2a and
IgG1 Ab in their plasma. Lesions in a few of these mice spontaneously
heal or become progressive. 4) Mice in a progressive state have large
palpable lymph nodes and large cutaneous lesions that continuously
increase in size, often at a rate>0.5 mm/wk. These mice produce
substantial parasitic-specific IgG1 Ab, and if mice are not euthanized,
the lesions become necrotic with consequent loss of the foot.
We first assessed the size of the infection required to favor the
generation of these distinct states. In one of three similar
experiments, groups of BALB/c mice (20–54 mice/group) were infected
with different numbers (33–106) of L.
major parasites and were assessed for lesion development,
palpability of the draining lymph node, and nature of the Ab present.
The generation of different pathophysiological states depends upon the
number of L. major parasites employed for infection, as
assessed between 3 and 15 mo postinfection (see Table I
). Infection with a million parasites
inevitably leads to progressive disease, whereas most mice infected
with 110 parasites were classified as asymptomatic/subclinical, and
over half the mice infected with 3000 parasites developed borderline
disease.
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We infected 60 BALB/c mice with 3 x
103 L. major parasites, as this
infection leads to the generation of all four pathophysiological states
defined above. Four weeks after infection, eight of eight mice had
viable parasites in their footpads and draining lymph nodes (data not
shown). Starting from 10 wk postinfection, mice were classified as
belonging to one of the four states and were sacrificed at different
times for enumeration of Ag-specific IFN-- and IL-4-secreting
parasite-specific T cells in the spleen and of parasite burden in the
footpad and lymph node and for quantitation of parasite-specific IgG1
and IgG2a Abs in the plasma. As shown in Fig. 1 (left), the number of
parasites detected in tissue extracts correlates with the different
pathophysiological states. Parasites could be detected only in the
draining lymph nodes of subclinically infected mice. These mice mounted
an IFN--dominated Th1 response and had a low ratio of IgG1/IgG2a
parasite-specific Abs (Fig. 1). Mice with borderline disease had
parasites both in the originally infected footpad and in the draining
lymph nodes (Fig. 1). Parasite-specific IFN-- and IL-4-producing
cells were equally prevalent in the spleen, and the ratio of IgG1 and
IgG2a Abs was near unity, indicating a mixed Th1/Th2 response. In
contrast, mice with progressive disease mounted a dominant Th2
response, with high numbers of parasites in their footpads and lymph
nodes (Fig. 1). Thus, different pathophysiological states are
associated with distinct Th responses.
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Some observations led us to infer that infections may have been
established and eliminated in some asymptomatic mice. We first
characterized, in four separate experiments, the immune state and the
presence of parasites in a total of 16 asymptomatic and 16 subclinical
mice as well as in eight age-matched control mice at 9 mo postinfection
with 1000 parasites. The results from one of these experiments are
presented in Fig. 2. Subclinical mice
that had palpable lymph nodes (LN+) and
parasite-specific Ab (Ab+) in their plasma always
had parasites in their lymph nodes and sometimes in their footpads, but
not in spleen and bone marrow (data not shown). However, parasites were
undetectable in all asymptomatic (Ab-,
LN-) mice as assessed by limiting dilution
analysis (16). We employed this assay rather than PCR, as
the limiting dilution assay has been shown to be as sensitive or more
sensitive than PCR (11). Spleen and lymph node cells from
subclinical mice invariably had more IFN--producing Th1 than
IL-4-producing Th2 cells, whereas the number of such cells was no
greater in asymptomatic mice than in age-matched controls (Fig. 2, A and B). Subclinical mice resisted a normally
pathogenic challenge, unlike their asymptomatic
(LN-, Ab-) and
age-matched counterparts (Fig. 2C). Similarly, when lightly
irradiated naive recipients were given splenocytes from subclinical,
asymptomatic, or age-matched normal mice and subsequently challenged
with a million parasites, only the splenocytes from mice in a
subclinical state conferred protection (Fig. 2D). We
concluded that leishmania infections were either never established in
asymptomatic mice or the infections had been established in some, but
the parasite was eliminated with consequent loss of effector T cells
and of resistance.
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A). The transfer of these
cells to lightly irradiated naive recipients also failed to protect the
recipients from a normally lethal challenge of a million L.
major parasites (Fig. 3B). In addition, the three
remaining serodeconverted mice were shown to be susceptible by direct
challenge. These observations indicate that an L. major
infection may be completely eliminated even in highly susceptible mice,
contrary to common belief. Secondly, they imply, if this primary
inference is correct, that maintenance of active resistance and
immunological memory requires the presence of L major
parasites.
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Complete elimination of L. major in lightly irradiated mice made resistant by the transfer of immune cells from subclinically infected mice results in loss of resistance
We infer from the above observations that established parasite
infections may be eliminated. A direct demonstration of such
elimination is problematical, as a mouse must be killed to establish
unequivocally that it is infected, and it is then impossible to assess
whether the infection would have been eliminated. We know that
infections are established with great reliability (>99%) upon
infecting normal BALB/c mice with a million parasites. We attempted to
examine the relationship between parasite clearance and loss of
resistance in a more controlled setting involving such a challenge. We
transferred spleen cells from mice with a subclinical infection
(Ab+/LN+) or from
age-matched control mice to irradiated, naive, syngeneic recipients.
One day after the transfer these mice were challenged with a million
parasites. All the mice that received cells from subclinical mice had
palpable lymph nodes 4 wk postinfection, but none developed any visible
cutaneous lesion. Spleen and lymph node cells were harvested from four
of these recipient mice at both 4 and 18 wk postchallenge. The mice had
predominant Th1 responses, and parasites were detectable in the
infected draining lymph nodes (Table II).
However, lymph node swelling regressed in five of the remaining 12 mice
approximately 36 wk postchallenge, and at the same time no
parasite-specific Ab could be detected. Two LN-
and three LN+ mice were sacrificed, and their
spleen and lymph node cells were assessed for L.
major-specific IL-4- and IFN--producing cells and parasite
burden. Their spleen cells were also adoptively transferred to another
set of lightly irradiated mice that was later challenged with a
normally pathogenic dose of a million L. major parasites the
next day. The remaining mice (three
Ab-/LN- and four
Ab+/LN+) were again
challenged with 2 x 106 L. major
promastigotes in the opposite hind footpad. In contrast to recipients
that remained in the subclinical state (LN+),
parasite-specific IFN-- and IL-4-producing cells were undetectable
in the spleen and lymph nodes of the
Ab-/LN- mice (Figs. 4, A and B), and no
parasites could be detected in the draining lymph nodes (Table II).
Most importantly, spleen cells from LN- mice
failed to protect a new set of naive recipients from a high dose
challenge of L. major (see Fig. 4C). Similar
results were seen in intact mice. Upon challenge with a normally
pathogenic dose of L. major, three previously protected
LN- mice were susceptible, in contrast to four
LN+ mice, which displayed a resistant phenotype
(Fig. 4E). These results demonstrate unequivocally that
elimination of L. major by a dominant Th1 response results
in loss of protection and suggests that the maintenance at least of
parasite-specific effector cells requires the continual presence of
live parasites in the animal.
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precursor T cells in the spleens and draining
popliteal lymph nodes of control mice and of these
LN- and LN+ mice, which
had been previously protected from a normally lethal challenge of
parasites by the transfer of spleen cells from subclinically infected
mice, are shown in Table III. There is no
significant difference in the frequencies of L.
major-specific reactive cells in either the spleen or draining
lymph node of LN- recipients and their
uninfected age-matched counterparts. In contrast, the frequencies of
these cells were considerably higher in LN+
mice.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The observations on clearance of parasites and its effect on resistance have important implications for strategies of vaccination and preventing reactivation leishmaniasis. It is widely believed that following healing of leishmania infections, parasites persist in tissues, resulting in a subclinical carrier state (11, 13, 14). However, immune individuals who live in a region endemic for malaria and then move to a nonendemic location for some time can become ill, sometimes fatally, upon returning to the endemic region (23, 24, 25). This suggests that such an exposed individual has immunity that can eliminate the parasite and that resistance then decays in the absence of reinfection (R. Sanderson, personal communication). The mice in this study with a subclinical infection appear resistant indefinitely unless this infection is cleared, in which case resistance is lost.
It has been shown in other systems that IL-12 is required for the maintenance of resistance to L. major as IL-12p40-/- mice, made resistance by administration of rIL-12 during the time of primary infection, develop progressive disease either spontaneously or several weeks following rechallenge (26). However, in this report, mice were infected with very high numbers of L. major parasites that normally cause fatal progressive disease and result, if the response is modulated to achieve containment, in substantial numbers of parasites in the healed foot pad and draining popliteal lymph nodes (11, 13, 14). Furthermore, it had previously been reported that IL-12 is not important in the maintenance of resistance to L. major, as healed C3H mice reinfected with L. major maintained resistance after administration of anti-IL-12 Abs at a dose that ablates resistance during primary infection of naive mice (27). Another report shows that the induction and maintenance of immunity in mice immunized with recombinant LACK protein are IL-12 dependent (28). Interestingly, it was shown in other studies by this group that the duration of immunity to L. major infection in BALB/c mice induced by recombinant LACK protein is shorter than that induced by a plasmid DNA encoding LACK protein (29). It was proposed in these studies that the superior protection achieved by DNA immunization is because LACK DNA persists longer than rLACK protein, thereby acting as a source of the continuous antigenic restimulation of LACK-specific memory T cells (29). Our results are in agreement with this explanation and support the proposal that the presence of a few viable L. major organisms might be required to maintain protective immunity to reinfection (10, 11, 30).
Rapid loss of memory in the absence of Ag is not unique to parasite infections. Recently, it has been shown that HIV-specific CD4+ memory T cells are rapidly lost following chemotherapy (31), probably due to a reduced viral load. Following viral infections, a state of active memory can probably be maintained by incomplete elimination of viruses (32, 33). In the late 1960s the term infectious immunity was used to describe the persistence of delayed-type hypersensitivity responses to pathogens that induce granulomas characteristic of tuberculosis, brucellosis, leprosy, and histoplasmosis (34). Recently, the question of whether Ag persistence is required for the maintenance of memory has drawn considerable attention (35, 36, 37, 38, 39). We suggest that a positive demonstration of a requirement for Ag to maintain memory is more likely to be valid, as maintenance of memory in the absence of the test Ag can always be explained by the presence of environmental Ags cross-reacting with the test Ag. In addition, recent investigations have led to an appreciation of homeostatic regulatory mechanisms that might complicate some analyses. For example, naive T cells placed in an in vivo lymphopenic environment, models often used to test for the requirement of Ag for the maintenance of memory T cells, acquire an activated phenotype even in the absence of Ag (40, 41, 42). Our observations for the most part are made in unmanipulated animals or in animals in which much time has elapsed after artificial conditions existed. In the latter situation the pertinent homeostatic mechanisms operating are likely to reflect those in a normal healthy individual, rather than those reflecting stress, such as might occur in lymphopenic and/or gene knockout animals.
Our findings have implications for achieving effective vaccination against leishmaniasis and other chronic infectious diseases caused by intracellular pathogens. Firstly, mice with a subclinical infection, but not asymptomatic mice, are resistant over the long term, but are likely to be susceptible, under adverse conditions, to reactivation leishmaniasis (11). For instance, inhibition of inducible NO synthase enzyme in mice in the subclinical state several months after clinical cure results in reactivation of latent leishmaniasis (13). Indeed, reactivation leishmaniasis is now common in parts of Africa where AIDS is prevalent (43, 44).
Should we strive to generate, by vaccination, a state leading to a subclinical infection or to parasite elimination? The observations discussed on susceptibility to malaria suggest that a response able to eliminate the parasite is effective as long as the immune system is continually and sufficiently stimulated by the pathogen, or cross-reacting Ags, to maintain memory and resistance. Similarly, in tuberculosis it is anticipated that exposure to environmental mycobacteria may be sufficient to maintain an effective Th1 imprint, which is believed to be required to contain Mycobacterium tuberculosis (45, 46, 47). If exposure to M. tuberculosis is relatively rare compared with exposure to environmental mycobacteria, as we suspect, a response that is able to eliminate the mycobacteria would have the advantage of minimizing the occurrence of reactivation disease. All in all, the generation of a response that can eliminate the pathogen or the attenuated pathogen employed for vaccination would seem desirable, with the maintenance of the appropriate resistant, pathogen-eliminating state by natural exposure to parasites and micro-organisms or, where necessary, by deliberate booster immunizations.
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Acknowledgments |
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Peter Bretscher, Department of Microbiology and Immunology, University of Saskatchewan, 107 Wiggins Road, Saskatoon, Saskatchewan, Canada S7N 5E5. E-mail address: bretschr{at}duke.usask.ca
3 Abbreviations used in this paper: SLA, soluble leishmanial antigen; LN, lymph node.
Received for publication June 25, 2001. Accepted for publication October 9, 2001.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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-producing cells. J. Immunol. Methods 227:99.[Medline]
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 G. F. Spath, L.-F. Lye, H. Segawa, D. L. Sacks, S. J. Turco, and S. M. Beverley Persistence Without Pathology in Phosphoglycan-Deficient Leishmania major Science, August 29, 2003; 301(5637): 1241 - 1243. [Abstract] [Full Text] [PDF]
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|
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C. Montagnoli, A. Bacci, S. Bozza, R. Gaziano, P. Mosci, A. H. Sharpe, and L. Romani B7/CD28-Dependent CD4+CD25+ Regulatory T Cells Are Essential Components of the Memory-Protective Immunity to Candida albicans J. Immunol., December 1, 2002; 169(11): 6298 - 6308. [Abstract] [Full Text] [PDF]
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 P C L Beverley Immunology of vaccination Br. Med. Bull., July 1, 2002; 62(1): 15 - 28. [Abstract] [Full Text] [PDF]
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) and draining popliteal lymph nodes (
) was determined
(A). Splenocytes from infected mice were also assessed
for the presence of L. major-specific IL-4-producing
(
