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Infection and Immunity, April 2006, p. 2423-2427, Vol. 74, No. 4
0019-9567/06/$08.00+0 doi:10.1128/IAI.74.4.2423-2427.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Department of Virology and Parasitology, Fujita Health University School of Medicine, Toyoake, Aichi 470-1192, Japan,1 Department of Protozoology, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Nagasaki 852-8523, Japan,2 Department of Pathology, Fujita Health University College, Toyoake, Aichi 470-1192, Japan,3 The Forsyth Institute, Boston, Massachusetts 02115,4 Department of Cell Biology and Neuroscience, Division of Life Sciences, Rutgers University, Piscataway, New Jersey 08854-8082,5 Division of Molecular Immunology, Institute for Genetic Medicine, Hokkaido University, Sapporo, Hokkaido 060-0815, Japan6
Received 25 May 2004/ Returned for modification 26 June 2004/ Accepted 30 December 2005
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) (5, 8, 21, 23). It has been shown that P. chabaudi chabaudi-infected mice deficient in IL-12p40 or IFN-
gene expression have a higher level of mortality with a higher level of parasitemia than wild-type (WT) mice (22, 23).
Osteopontin (OPN), a sialated phosphoprotein, is found in various tissues and is secreted into body fluids (2, 4, 11, 19, 20). OPN plays an active role in immune reactions that support the adhesion and migration of T cells and macrophages, facilitate CD3-mediated T-cell production of IL-2 and T-cell proliferation, and augment CD3-dependent IFN-
and CD40 ligand expression in T cells (7, 9, 13, 14). The roles of OPN in infectious diseases caused by Listeria monocytogenes, herpes simplex virus type 1, and Mycobacterium bovis (1, 12) have been described previously. WT mice develop herpes simplex keratitis during herpes simplex virus type 1 infection, while osteopontin knockout (OPN-KO) mice do not readily develop this disease (1). IL-12- and IFN-
-dependent Th1 responses to L. monocytogenes or M. bovis Calmette-Guérin are defective in OPN-KO mice (1, 12). These findings suggested that OPN may polarize the Th1-related cytokine response and contribute to host defense against infectious pathogens.
To our knowledge, however, there have been no reports on the role of OPN in malaria infection. By using OPN-KO mice with a resistant C57BL/6 background, in this study we examined whether OPN is secreted from the beginning of the infection and leads to suppression of P. chabaudi. Activated innate and Th1-dependent immunity in C57BL/6 mice has been found to suppress P. chabaudi chabaudi infection (5, 8, 21-23).
OPN gene homozygous(OPN+/+ C57BL/6, OPN allele a) mice were purchased from Japan SLC (Hamamatsu, Japan). The production of OPN gene-deficient (OPN/, OPN-KO) mice (C57BL/6 x 129, C57BL/6 background, F6) has been described previously (15, 16). Eight-week-old female OPN-KO mice and WT mice were used. The mice were inoculated intraperitoneally with 1 x 106 P. chabaudi chabaudi-infected erythrocytes (kindly provided by M. Suzuki, Gunma University School of Medicine, Japan). Parasitemia was monitored daily by examining Giemsa-stained thin blood smears. Blood samples were obtained via cardiac puncture under anesthesia at zero time (before infection) and on days 2, 3, and 7 postinfection. Serum was separated from clotted blood and stored at 80°C until it was used. The mice were then sacrificed, and their spleens were removed. The spleens were processed for flow cytometric, mRNA, and immunohistochemical analyses and stored at 80°C until they were used (except for the flow cytometric analysis). The experiments were carried out using five mice per group for each experimental day and were performed twice independently.
For detection of OPN mRNA by reverse transcriptase PCR (RT-PCR), total RNA was extracted from mouse spleens using ISOGEN (Nippon Gene, Tokyo, Japan) according to the manufacturer's instructions. The isolated total RNA was reverse transcribed to synthesize the first strand of cDNA using ReverTra Ace-
(Toyobo, Osaka, Japan). The cDNA was subjected to PCR using specific oligonucleotide primers to amplify cDNAs encoding ß-actin and OPN. The reaction mixtures (25 µl) contained 0.8 µg of cDNA as a template, each primer at a concentration of 0.5 µM, each deoxynucleoside triphosphate at a concentration of 200 µM, 0.625 U of Taq DNA polymerase (QIAGEN, Tokyo, Japan), and 1x PCR buffer (containing 1.5 mM MgCl2). The target cDNA was amplified using a PCR protocol consisting of denaturation at 94°C for 3 min, followed by 35 cycles of 94°C for 1 min, the optimal annealing temperature for the target primer for 30 s, and 72°C for 1 min. The final cycle was followed by extension at 72°C for 7 min. This protocol was confirmed to be optimal for amplifying mouse OPN mRNA and ß-actin mRNA by preliminary tests. The primer sequences used and optimal annealing temperatures were as follows: for ß-actin, sense primer 5'-CCA GAG CAA GAG AGG TAT CC-3', antisense primer 5'-AGT CTA GAG CAA CAT AGC ACA G-3', and 55°C; and for OPN, sense primer 5'-ATG AGA TTG GCA GTG ATT TG-3', antisense primer 5'-GTT GAC CTC AGA AGA TGA AC-3', and 54°C. A GeneAmp 2400 PCR system (Perkin-Elmer, Norwalk, CT) was used for all PCR. The PCR products were separated by electrophoresis on a 1.5% agarose gel and stained with ethidium bromide. The densities of the DNA bands were determined with the Lane & Spot Analyzer software (Atto, Tokyo, Japan). The results of OPN mRNA expression were standardized by quantification of ß-actin mRNA, which was used as an internal control.
The serum levels of IL-12 (IL-12 + p40) and IFN-
were determined with sandwich enzyme-linked immunosorbent assay kits (BioSource International, Camarillo, CA). The minimum detection levels for IL-12 and IFN-
were 2 pg/ml and 1 pg/ml, respectively.
An indirect immunofluorescence assay of spleen tissue was performed in a standard manner. Rabbit anti-mouse OPN (O-17) antibody (IBL, Gunma, Japan) and rat anti-macrophage (F4/80 specific, A3-1) monoclonal antibody (BMA Biomedicals, Augst, Switzerland) were used as primary antibodies, and labeled goat anti-rabbit immunoglobulin G (IgG) (Alexa Fluor 568; Molecular Probes, Eugene, OR) and fluorescein isothiocyanate-conjugated anti-rat IgG (MBL, Nagoya, Japan) antibodies were used as secondary antibodies. The sections were counterstained with 4',6-diamidino-2-phenylindole dihydrochloride (DAPI).
For the flow cytometric analysis, macrophages and monocytes were harvested from splenocytes by adhesion to a plate (MSP-P; JIMRO, Gunma, Japan), and the cells from five mice were pooled. Cells were first incubated with rat anti-macrophage (F4/80 specific, A3-1) monoclonal antibody and were then postfixed and permeabilized with 100% methanol. These cells were incubated with rabbit anti-mouse OPN (O-17) antibody. The cells were then treated with phycoerythrin-Cy5-conjugated anti-rabbit IgG (Santa Cruz, Santa Cruz, CA) and labeled goat anti-rat IgG (Alexa Fluor 488; Molecular Probes) antibodies. Samples were analyzed with a flow cytometer (Vantage SE fluorescence-activated cell sorter; Becton Dickinson, San Jose, CA); at least 10,000 gated macrophages were collected.
Data were expressed as means ± standard errors of the means. The statistical evaluation was performed with Student's unpaired t test (two tailed). All analyses were performed using SPSS software (SPSS Japan, Tokyo, Japan), and a P value of <0.05 was considered significant.
OPN-KO mice showed increasing parasitemia and died on days 7 and 8 postinfection (Fig. 1a), while WT mice also showed increasing parasitemia but suppressed it after day 8. Thus, the results indicated that OPN was essential for resolution of the infection; likewise, OPN has been shown to be an important factor for pathogen control in L. monocytogenes and M. bovis BCG infections (1, 12).
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FIG. 1. Kinetics of parasitemia (a) and expression of OPN mRNA (b) in WT and OPN-KO mice infected with P. chabaudi chabaudi. The parasitemia was monitored by examining Giemsa-stained thin blood smears, and OPN mRNA was measured by a semiquantitative RT-PCR. The level of OPN mRNA was expressed the ratio of OPN mRNA to ß-actin mRNA, which was used as an internal control. Each data point and bar indicate the mean of the results for 10 mice per group in two independent experiments in which five mice per group were used. An asterisk indicates that the P value is <0.001. "d" indicates death of mice.
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FIG. 2. Fluorescence-activated cell sorting analysis of splenic macrophages from WT mice infected or not infected with P. chabaudi chabaudi. (a) The splenic macrophages were stained with anti-OPN antibody. The thin line indicates the results for uninfected WT mice, and the thick line indicates the results for infected WT mice 7 days after infection. (b) The cells from WT mice on 7 day after infection were stained with anti-OPN and anti-F4/80 antibody. PE, phycoerythrin.
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FIG. 3. Fluorescence micrographs showing the localization of OPN-positive cells (a, d, and g) and F4/80 antigen (macrophage)-positive cells (b, e, and h) and merged images for OPN- and F4/80 antigen-positive cells (c, f, and i) in spleen tissue from WT mice (a to f) and OPN-KO mice (g to i) on days 2 (D2) and 7 (D7) after P. chabaudi chabaudi infection. Insets show part of the plate at higher magnification. Bars, 100 µm.
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and CD40 ligands, which augments the IL-12 production by monocytes (14). In order to evaluate the influence of OPN on Th1-related cytokine production in malaria, we measured the serum levels of IL-12 and IFN-
in mice with and without the OPN gene. WT mice had significantly increased levels of IL-12 (IL-12 + p40) on days 2 and 3, while the level of IL-12 was low in OPN-KO mice (Table 1). Serum levels of IFN-
were detected in both WT and OPN-KO mice on day 3 and increased thereafter. The levels of IL-12 and IFN-
in OPN-KO mice were significantly lower than the levels in WT mice on days 3 and 7 (Table 1). These results suggest that OPN should facilitate IL-12 and IFN-
production and secretion. It has been shown that the serum level of IL-12 is elevated early in malaria infection in mice and humans (17, 18, 22). The malaria parasite-susceptible A/J mouse strain treated with recombinant IL-12 was protected from P. chabaudi infection through upregulation of IFN-
, tumor necrosis factor alpha, and nitric oxide production (21). IFN-
gene- or IFN-
receptor gene-deficient mice with the resistant C57BL/6 background showed susceptibility to P. chabaudi infection (6, 22, 24). These findings suggest that IL-12 contributes to the protection via IFN-
. In our study, OPN-KO mice produced significantly smaller amounts of IL-12 and IFN-
than WT mice produced, which may have been responsible for the increased parasitemia and mortality in OPN-KO mice. The impairment of protective immune responses against P. chabaudi chabaudi in OPN-KO mice suggests that OPN may play a critical role in the modulation of Th1 immune responses. |
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TABLE 1. Serum levels of cytokines and expression of osteopontin mRNA in spleens of WT and OPN-KO mice infected with P. chabaudi chabaudia
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until day 7, while the level of IL-12 decreased to almost the baseline level (Table 1). Similar behavior of OPN and IFN-
was reported in a recent study in which THP-1 cells (human monocytes) or primary human monocytes treated with IFN-
were found to express OPN mRNA and protein in a time- and dose-dependent fashion (10). These findings, including our results, suggest that OPN may function in a positive feedback loop in Th1 immune responses; that is, OPN itself may upregulate the OPN gene via IFN-
expression. In conclusion, our results revealed that infection with the nonlethal murine malaria parasite P. chabaudi chabaudi induces OPN production and that OPN is involved in the clearance of the malaria parasites through Th1 immune responses at an early stage of P. chabaudi chabaudi infection.
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induction of osteopontin expression in human monocytoid cells. J. Interferon Cytokine Res. 23:259-265.[CrossRef][Medline]
and TNF-
and occurs via a nitric oxide-dependent mechanism. J. Immunol. 155:2545-2556.[Abstract]This article has been cited by other articles:
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