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Infection and Immunity, March 2002, p. 1627-1630, Vol. 70, No. 3
0019-9567/02/$04.00+0 DOI: 10.1128/IAI.70.3.1627-1630.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
and Eckhart Kämpgen2
Institute for Molecular Biology of Infectious Diseases, University of Würzburg, 97070 Würzburg,1 Department of Dermatology, University of Würzburg, 97080 Würzburg, Germany2
Received 27 June 2001/ Returned for modification 15 August 2001/ Accepted 26 November 2001
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) predominate in resistant C57BL/6 mice, whereas Th2 cells producing interleukin 4 (IL-4), IL-5, IL-10, and IL-13 are associated with the susceptibility of BALB/c mice. The development of Th1 cells in leishmaniasis is primarily directed by IL-12 (12, 17), and the differentiation of Th2 cells is driven by IL-4 (9, 10). In the mammalian host, Leishmania parasites are obligatorily intracellular and reside within macrophages and dendritic cells (DC). Langerhans cells (LC), the DC of the skin, are critical for the initial triggering of the parasite-specific T-cell response (13). Within a few days of infection, they transport L. major from the newly infected skin to the draining lymph nodes (14) while differentiating into mature DC with potent antigen presentation functions and the capacity to activate resting T cells. Furthermore, parasite infection stimulates DC to produce IL-12 (4, 5, 8, 20). In fact, since macrophage IL-12 production is impaired by Leishmania infection (1, 5, 16, 22), DC are likely to be the sole source of IL-12.
The migration and concomitant differentiation of LC are tightly regulated by cytokines. The different functional states can be analyzed with LC cultured in the presence of growth factors in vitro. By use of this model, it has been shown that differential expression of cytokine receptors controls DC responsiveness and thus affects their activities (7, 21). However, it is not known whether infection of DC with microbial pathogens modulates their expression of cytokine receptors. To elucidate the molecular consequences of DC interaction with infectious agents and their potential impact on the ensuing immune response, we analyzed whether infection of LC with L. major induces changes in their expression of cytokine receptors.
Parasites and infection of LC. Amastigotes of the L. major isolate MHOM/IL/81/FE/BNI were obtained from skin lesions as described previously (3). Single-cell suspensions of epidermal cells were prepared from the ear skin of BALB/c or C57BL/6 mice by trypsinization procedures (4, 18). These preparations contained 3 to 5% LC that constitutively express major histocompatibility complex class II (MHC-II) as well as MHC-II-negative keratinocytes, a source of cytokines that are essential for LC differentiation. For infection of LC with L. major, 3 x 106 epidermal cells were incubated with amastigotes at a ratio of three parasites per cell in 2 ml of culture medium (RPMI 1640 medium supplemented with 10% heat-inactivated fetal calf serum, 2 mM L-glutamine, 10 mM HEPES buffer, 60 µg of penicillin/ml, 20 µg of gentamicin/ml, 17 mM NaHCO3, and 0.05 mM 2-mercaptoethanol). The nonadherent population, 30 to 50% of which was LC, was harvested after 1 to 6 days of culture.
Analysis of LC cytokine receptor expression by flow cytometry.
LC were identified by labeling 1 x 106 to 2 x 106 cells in 100 µl with biotin-conjugated mouse anti-I-Ad or anti-I-Ab monoclonal antibody (MAb) (PharMingen, Hamburg, Germany) and streptavidin-conjugated CyChrome (PharMingen). The expression of the cytokine receptors of LC was analyzed by staining with rat MAb directed against the IL-1 receptor (IL-1R) of type I or type II (PharMingen), the IL-4R (R&D, Wiesbaden, Germany), the tumor necrosis factor receptor of type I or type II (Genzyme, Rüsselsheim, Germany), or the IFN-
receptor (IFN-
R) (PharMingen) or with isotype-matched control antibodies and phycoerythrin-conjugated donkey anti-rat antibodies (Dianova, Hamburg, Germany). Primary MAbs were used at 10 µg/ml, and secondary antibodies were used at 5 µg/ml diluted in phosphate-buffered saline containing 2% heat-inactivated fetal calf serum (30 min at 4°C). Two-color flow cytometry was performed on a FACSCalibur (Becton Dickinson, Heidelberg, Germany) by using Cell Quest software.
ELISA for detection of IL-12 production by LC. LC were infected with L. major on day 0. In some experiments, LC cultures were supplemented with anti-IL-4 MAb (from hybridoma 11B11) until day 3. From day 3 to day 6 of culture, the cells were incubated with lipopolysaccharide (LPS) (100 ng/ml; Roth, Karlsruhe, Germany) and/or IL-4 (5 ng/ml; R&D). Kinetic studies demonstrated that this protocol resulted in higher activities than did shorter periods of LC culture (1 to 4 days). On day 6, culture supernatants were harvested for the determination of IL-12 p40 by sandwich enzyme-linked immunosorbent assay (ELISA) as previously described (4). Tris buffer (50 mM; pH 7.6) containing 0.05% Tween 20 was used for the washing and blocking steps. Rat MAbs against IL-12 p40 were used as capture antibodies, and biotinylated rat anti-IL-12 p40 MAbs were used as detection antibodies (both from PharMingen). Standard curves were generated using serial dilutions of murine recombinant IL-12 p40 (PharMingen). The detection threshold was 2.4 pg of IL-12 p40 per ml.
L. major modulates IL-4R expression by LC.
Differences in patterns of cytokine receptor expression by LC regulate their responsiveness to the corresponding factors and their functional activities (7, 21). However, there has been no information on the receptor profile of LC from L. major-resistant mice compared to that of LC from susceptible mice. We therefore analyzed the expression of receptors for cytokines relevant to LC growth and differentiation or to the activities of Th1 or Th2 cells. Flow cytometric analysis of gated MHC-II+ LC showed that the patterns of expression of IL-1R (type I and type II), tumor necrosis factor receptor (type I and type II), and IFN-
R by LC from resistant C57BL/6 and susceptible BALB/c mice were comparable and were not modulated by infection with L. major parasites (data not shown). In contrast, the expression of IL-4R was significantly upregulated by infection of LC from BALB/c but not from C57BL/6 mice (Fig. 1). Thus, infection with L. major modulated IL-4R expression by LC in a mouse strain-dependent manner. Interestingly, although not all LC take up L. major (2), exposure of LC to parasites did not result in a bimodal profile of IL-4R expression, suggesting that IL-4R upregulation in LC from BALB/c mice is not confined to LC infected with parasites.
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The present study revealed that IL-4R expression was increased on infected LC from susceptible BALB/c mice but not on those from resistant C57BL/6 mice. Enhanced IL-4R levels correlated with suppression of LPS-induced IL-12 expression by DC after treatment with IL-4. These data provide the first evidence that infection of DC results in a mouse strain-dependent modulation of cytokine receptor expression, a mechanism that may contribute to the development of Th2 cells and to susceptibility to L. major in BALB/c mice via its effect on the ability of DC to express IL-12.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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Present address: GSF-Institute for Molecular Immunology, KKG Hyperthermia, Munich, Germany. ![]()
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