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Infection and Immunity, March 2007, p. 1507-1511, Vol. 75, No. 3
0019-9567/07/$08.00+0 doi:10.1128/IAI.01326-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
Toll-Like Receptor-2-Mediated C-C Chemokine Receptor 3 and Eotaxin-Driven Eosinophil Influx Induced by Mycobacterium bovis BCG Pleurisy
Heloisa D'Ávila,
Patrícia E. Almeida,
Natália R. Roque,
Hugo C. Castro-Faria-Neto, and
Patrícia T. Bozza*
Laboratório de Imunofarmacologia, Departamento de Fisiologia e Farmacodinâmica, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro 21045-900, Brazil
Received 18 August 2006/
Returned for modification 15 September 2006/
Accepted 1 December 2006

ABSTRACT
An acute and persistent eosinophil infiltration is observed
during
Mycobacterium bovis BCG pleural infection in mice. Eosinophil
accumulation, lipid body formation, and eotaxin production were
significantly reduced in BCG-infected Toll-like receptor-2 (TLR2)-deficient
mice compared to wild-type mice. Neutralization of eotaxin or
CCR3 drastically inhibited BCG-induced eosinophil accumulation
and lipid body formation, indicating that BCG-induced eosinophil
recruitment and activation is largely dependent of TLR2-mediated
eotaxin generation.

TEXT
Eosinophils are fundamentally found in tissues that have an
interface with the external environment and its bacterial flora,
such as the gastrointestinal and respiratory tracts. Accumulating
evidence has established eosinophils as multifunctional leukocytes
with varied effector and immunomodulatory functions not only
in allergic or helminthic disease but also in the initiation
and amplification of numerous inflammatory and infectious responses
and as modulators of innate and adaptive immunity (
1,
22).
Mycobacterial infections frequently show eosinophil recruitment in both naturally occurring infections in human patients (11, 26) and in animal experimental infections (6, 14, 17, 20, 27). Enhanced eosinophil recruitment to sites of infection has been associated with unrestricted growth of mycobacteria observed in mouse susceptible strains in contrast to resistant ones (27) and in mice deficient in gamma interferon (IFN-
/) that are highly susceptible to infection with tuberculosis-causing organisms (13). Moreover, eosinophilia has been associated with higher rates of active tuberculosis in human immunodeficiency virus type 1-infected adults (9), suggesting that eosinophils may have roles in pathogenesis and susceptibility to mycobacterial infection. Although different studies have demonstrated that eosinophils accumulate at sites of mycobacterial infection, including celomatic cavities, skin, lungs, and airways, the mechanisms involved in eosinophil trafficking and activation are not well characterized. In the present study, we used a murine model of pleural tuberculosis to investigate the mechanism involved in eosinophil recruitment and activation.
Pleurisy in mice was induced in susceptible C57BL/6 mice by intrapleural injection of live or heat-killed Mycobacterium bovis BCG (Moreau strain, Fundação Ataulpho de Paiva, Brazil) at 5 x 106 bacilli/cavity as previously described (7), with protocols approved by the Fundação Oswaldo Cruz animal welfare committee. The first phase of pleural leukocyte accumulation induced by BCG infection was characterized by a marked increased in neutrophil numbers (mean ± the standard error of the mean [SEM]: from undetected in control animals to 0.12 ± 0.05 x 106/cavity at 1 h and 8.5 ± 0.67 x 106/cavity at 6 h). After 6 h of BCG infection a significant influx of eosinophils, macrophages, and lymphocytes was observed with a peak at 24 h (Fig. 1A to C), and the numbers of these cells remained increased for at least 15 days of infection as previously demonstrated (17, 20) (Fig. 1C). Control mice had no detectable eosinophils in the cavity (Fig. 1A and C). Although heat-killed BCG was capable of recruiting eosinophils to the pleural cavity within 24 h, the intensity of this phenomenon was reduced compared to the same dose of live BCG, suggesting that eosinophil recruitment was partially dependent on the bacterial viability (Fig. 1D).
Pattern recognition receptors involved in recognizing mycobacteria
include the mannose receptor, complement receptor, and Toll-like
receptors (TLRs) (
16). TLR2 and TLR4 and, more recently, TLR6
and TLR1 that heterodimerize with TLR2, have been shown to mediate
signaling induced by mycobacteria (
5,
15). To investigate the
role of TLR-mediated pathogen recognition in the mechanism of
eosinophil influx and lipid body formation, we infected TLR2
knockout (KO) mice (in a homogeneous C57BL/6 background) and
TLR4-deficient mouse strain C57/BL10 ScCr, along with their
wild-type controls. We observed that BCG-induced eosinophil
recruitment in TLR2-deficient mice was drastically inhibited
compared to wild-type mice (Fig.
2A). In contrast, BCG infection
in TLR4-deficient mice could induce pleural eosinophil recruitment
at levels comparable to that seen in wild-type mice (Fig.
2B).
We have recently described how intracellular lipid domains,
called lipid bodies, are specific sites involved in the synthesis
of lipid mediators during BCG infection (
7). In limited numbers,
lipid bodies are normal constituents of many cells; however,
the numbers and sizes of lipid bodies increase prominently in
cells participating in inflammatory responses. It has been demonstrated
that the lipid body formation in leukocytes is a highly regulated
event that depends on the interaction of cellular receptors
with their ligands. Also, these organelles represent specialized
intracellular domains whose induced formation is centrally related
to activating mechanisms within the cells and are dynamic sites
involved in the compartmentalization of proteins (including
protein kinases, eicosanoid-forming enzymes, and cytokines),
and lipid bodies are markers of leukocyte activation (
4). In
macrophages, it has been demonstrated that lipopolysaccharide-induced
lipid body formation occurs through TLR4 and CD14 recognition,
whereas BCG infection in vivo induced lipid body formation in
a TLR2-dependent process (
7,
18). In vivo the ability of BCG
to induce eosinophil activation, as assessed by lipid body formation,
through a TLR2-dependent pathway was observed. As shown in Fig.
2C and D, BCG significantly induced lipid body formation in
C57BL/6, C57BL/10, and C57BL/10 ScCr eosinophils but not in
TLR2
/ eosinophils. These results demonstrate an
essential role for TLR2 receptors in BCG recognition and signaling
to induce eosinophil recruitment and lipid body formation in
eosinophils.
It has been demonstrated that eosinophils do not to express TLR2, TLR4, or CD14, and consequently are not able to directly respond to TLR2 or TLR4 ligands (23). Indeed, it has been demonstrated that the TLR4 ligand lipopolysaccharide induces eosinophil accumulation in vivo through mechanisms that are largely dependent on monocyte/macrophage- and lymphocyte-derived cytokine production (3, 19). Similar monocyte/macrophage-derived cytokine dependent mechanisms could be involved in TLR2-dependent eosinophil recruitment induced by BCG. Mycobacterial infections upregulate genes encoding proteins involved in cell migration and homing (21). Furthermore, it has been demonstrated that mice deficient in IFN-
or tumor necrosis factor alpha are extremely susceptible to infection by tuberculosis-causing organisms (reviewed in reference 12). The roles of three cytokine/chemokines relevant to cell activation in Mycobacterium-induced responses were evaluated with regard to their involvement in BCG-induced eosinophil influx. In order to determine the involvement of endogenously generated proinflammatory cytokines in eosinophil recruitment induced by BCG, MCP-1/CCL2-deficient mice, TNFRI (p55)-deficient mice (Jackson Laboratories, Bar Harbor, ME), and IFN-
-deficient mice were infected intrapleurally by BCG.
As shown in Fig. 2E, no inhibition in eosinophil recruitment was observed 24 h after infection when each respective wild-type animal was compared to MCP-1/CCL2-deficient mice. In agreement with previous findings (13), in IFN-
KO mice (Fig. 2G) and also in tumor necrosis factor receptor 1 (TNFR1) (Fig. 2F)-deficient animals, we observed an increased influx of eosinophils compared to wild-type mice.
Previous findings have described the role of inteleukin-5 (IL-5) in eosinophil accumulation induced by Mycobacterium bovis BCG in wild-type and in IFN-
-deficient mice (13, 17). The involvement of TLR2 in IL-5 synthesis after BCG infection was analyzed. TLR2 KO mice produced reduced amounts of IL-5 in the pleural fluid compared to wild-type mice at 24 h after infection (Fig. 3A). Similarly, peritoneal cells from TLR-2 KO mice were unable to produce IL-5 when infected in vitro by BCG under conditions in which cells from wild-type mice produced significant levels of IL-5 when infected (from 7.6 ± 1.35 pg/ml in BCG-infected wild-type mice to undetectable levels in TLR2-deficient mice), indicating that IL-5 production induced by BCG is largely dependent on TLR2.
Eotaxin is a key mediator in the eosinophil trafficking into
inflamed tissues (
22). In addition, eotaxin-mediated CCR3 activation
is a potent inducer of lipid body formation in eosinophils (
2,
25). As shown in Fig.
3B, BCG significantly induced eotaxin
production in vivo detected in the pleural fluid of TLR2
+/+ mice but not in TLR2
/ mice (Fig.
3B). Accordingly,
eotaxin upregulation has been observed by transcriptome gene
array analysis of the macrophage cell line THP-1 infected by
M. tuberculosis (
21). To investigate the in vivo role of eotaxin
activation on BCG-induced lipid body formation and eosinophil
recruitment, we pretreated mice with neutralizing antibodies
to eotaxin or CCR3 (10 µg/cavity [intraperitoneal] 30
min before infection). Both BCG-induced eosinophil influx and
lipid body formation were dramatically inhibited by the pretreatment
with neutralizing antibodies (Fig.
3C and D), indicating that
endogenous eotaxin, acting via CCR3, elicited in vivo lipid
body formation within infiltrating eosinophils. Neutrophil and
monocyte recruitment, as well as lipid body formation within
these infiltrating cells, were not affected by pretreatment
with anti-CCR3 or with anti-eotaxin.
The role of eosinophils in mycobacterial pathogenesis is still not well defined. The bactericidal potential of eosinophils has been demonstrated by their ability to phagocytize, mount a respiratory burst, and mobilize cytotoxic proteins from specific granules after bacterial infection (8, 24), suggesting a protective role of eosinophils in bacterial infections. However, increased numbers of eosinophils at sites of mycobacterial infection has been associated with unrestricted growth of mycobacteria in animals susceptible to infection with tuberculosis-causing organisms (10), suggesting that eosinophils may exaggerate disease severity because eosinophils, which have been shown to phagocytose mycobacteria (6), may provide an intracellular environment in which mycobacteria could proliferate in an unrestricted manner and may also contribute to mycobacteria dissemination (13). Therefore, the role of eosinophils in the host immune response to mycobacterial infection in experimental and clinical tuberculosis remains to be established. The demonstration that eotaxin acting through CCR3 is critically involved in eosinophil recruitment during mycobacterial infection suggests that antibody neutralization or genetically deficient animals to eotaxin and/or CCR3 would be useful tools to address the role of eosinophils in mycobacterial pathogenesis in future studies.
The present findings demonstrate that BCG infection induces pleural eosinophil accumulation in a process requisitely dependent on TLR2 signaling. In addition, our results indicate that BCG-induced eosinophil recruitment and activation is mediated through TLR2-dependent endogenous eotaxin generation and signaling through CCR3.

ACKNOWLEDGMENTS
This study was supported by the Howard Hughes Medical Institute
(P.T.B.), PRONEX-MCT, CNPq, and FAPERJ.
We thank Bandeira-Melo for helpful comments on this study and the manuscript. We are thank S. Akira, R. Gazzinelli, J. Viola, and C. Gerard for kindly providing the animals used in this study.

FOOTNOTES
* Corresponding author. Mailing address: Laboratório de Imunofarmacologia, Departamento de Fisiologia e Farmacodinâmica, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Av. Brasil 4365, Manguinhos, Rio de Janeiro 21045-900, Brazil. Phone: 55-21-2598-4492, x221. Fax: 55-21-2590-9490. E-mail:
pbozza{at}ioc.fiocruz.br.

Published ahead of print on 11 December 2006. 
Editor: J. L. Flynn

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Infection and Immunity, March 2007, p. 1507-1511, Vol. 75, No. 3
0019-9567/07/$08.00+0 doi:10.1128/IAI.01326-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
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