Published online before print September 15, 2004
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* INSERM E0225, Bichat Medical School, Paris, France; and
CNRS UMR8147, Necker Hospital, Paris, France
1 Correspondence: Bichat Medical School, 16, Rue Henri Huchard, BP 416, 75870 Paris Cedex 18, France. E-mail: monteiro{at}bichat.inserm.fr
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RI, is expressed on interstitial DC. We report here that monocyte-derived DC (Mo-DC) express another IgA receptor (IgA-R), the transferrin receptor (TfR), even in the absence of DC proliferation in vitro. Upon incubation with inflammatory cytokines such as tumor necrosis factor and interleukin (IL)-1ß or maturating agents (lipopolysaccharide, CD40 ligand), FcRI and TfR expression on Mo-DC was specifically up-regulated, whereas Fc
Rs and Fc
RI expression was down-regulated. Both IgA-Rs were functional, being able to mediate endocytosis by immature and activated Mo-DC. Although FcRI internalized IgA complexes on both types of DC, TfR was only able to mediate IgA complex internalization by immature cells. Cross-linking of FcRI but not of TfR resulted in up-regulation of major histocompatibility complex (MHC) class II/CD86 expression and secretion of IL-10 and IL-12 by immature Mo-DC. Moreover, in activated Mo-DC, cross-linking of FcRI could up-regulated MHC class II/CD86 and triggered IL-10 secretion. Our findings led us to propose that FcRI expressed by interstitial-type DC could play a critical role to sample IgA-recognized antigens and also during DC activation.
Key Words: Fc receptor • transferrin receptor • dendritic cells
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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RI, FcRII, FcRI, FcRI), receptors for heat-shock proteins, complement, scavenger receptors, and pattern-recognition receptors such as Toll-like receptors; and phagocytosis [2
]. In humans, monocyte-derived DC (Mo-DC) express FcRII, FcRn, and FcRI [3
4
5
], and Langerhans cells (LC) express FcRI and FcRI [6
7
8
].
Immunoglobulin A (IgA) is the most abundant Ig isotype in mucosal tissues and the second isotype in the blood compartment, representing one-fifth of IgG levels [9
]. IgA exists in two subclasses: IgA1 is predominant in serum in monomeric form, and IgA2 is more prevalent in mucosal secretions in dimeric form [secretory IgA (SIgA)]. Five IgA receptors (IgA-Rs) have been characterized: FcRI (CD89) is expressed on myeloid cells, including monocytes, neutrophils, eosinophils, Kupffer cells, some macrophages, and interstitial DC; the polymeric Ig-R (poly-IgR) transports polymeric IgA (and polymeric IgM) across mucosal epithelial cells; Fc/µR is expressed on monocytes/macrophages; the hepatocyte asialoglycoprotein receptor (ASGP-R); and the transferrin receptor (TfR; or CD71), which binds polymeric IgA1 [10
]. Two of these receptors have been characterized on Mo-DC, namely FcRI [5
] and ASGP-R [11
]. FcRI is expressed on native, interstitial DC and Mo-DC and at low levels on Mo-LC [5
]. Cross-linking of FcRI on DC triggers endocytosis, induces interleukin (IL)-10 production, and up-regulates CD86 costimulatory molecules, MHC class II expression, and allostimulatory activity [5
].
Here, we report that interstitial-type DC express another IgA-R, the TfR. This receptor is expressed even in the absence of DC proliferation in vitro. Upon treatment with inflammatory stimuli [tumor necrosis factor (TNF-), IL-1ß, lipopolysaccharide (LPS), CD40L], FcRI and TfR expression on interstitial-type DC is specifically up-regulated, in contrast with the other FcRs. Both IgA-Rs are functional on immature Mo-DC and mature Mo-DC, as they can be internalized. FcRI and TfR colocalize with IgA complexes in immature Mo-DC, contrary to activated Mo-DC, where IgA complex colocalization is restricted to FcRI. In addition, although FcRI aggregation results in up-regulation of MHC class II/CD86 molecules as well as secretion of IL-10 and IL-12 by immature Mo-DC, cross-linking of TfR has no effects. It is interesting that FcRI cross-linking is still able to induce an up-regulation of MHC class II and CD86 expression and IL-10 production on activated Mo-DC. These data indicated that interstitial-type DC are armed to sample antigens recognized by IgA and that these two IgA-Rs, the FcRI and the TfR, might influence the activation of DC.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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RI A77 (IgGI
) [12
], anti-CD71 A24 (IgG2b) [13
], and control isotypes IgG1 and IgG2b. Mouse anti-human FcRI mAb 15-1 was a generous gift from Jean-Pierre Kinet (Beth Israel Hospital, Boston MA). A pool of purified human serum IgA (i.e., 90% monomeric IgA, 10% poly-IgA) was obtained from ICN Biomedicals (Aurora, OH). Fluorescein isothiocyanate (FITC)-conjugated anti-CD16, -CD32, and -CD64 were from PharMingen (San Diego, CA). FITC-labeled anti-human leukocyte antigen (HLA)-DR, -DP-, DQ and phycoerythrin (PE)-labeled anti-CD86 were purchased from Beckman Coulter (France). Texas red-conjugated goat anti-IgA was from Southern Biotechnology Associates (Birmingham, AL). Rabbit anti-mouse (RAM) IgG F(ab')2 was prepared by pepsin digestion as described [14
]. Cy5-conjugated goat anti-rabbit (GAR) was purchased from Jackson ImmunoResearch (West Grove, PA). GAR IgG F(ab')2 was from Southern Biotechnology Associates. Alexa 488-wheat germ agglutinin was from Molecular Probes (Eugene, OR).
Cell culture
Peripheral blood mononuclear cells from healthy volunteers were isolated by the standard Ficoll-Paque method (Amersham Life Science, UK). Monocytes were negatively separated with the magnetic monocyte isolation kit according to the manufacturer’s instructions (Miltenyi Biotec, Germany). Monocytes were cultured in conditioned RPMI-1640 medium containing 10% fetal calf serum (FCS; Gibco-BRL, Grand Island, NY), 250 ng/ml granulocyte macrophage-colony stimulating factor (GM-CSF; Leucomax, Sanofi, France), and 10 ng/ml IL-4 (R&D Systems, UK) or 250 ng/ml GM-CSF, 10 ng/ml IL-4, and 10 ng/ml transforming growth factor-ß1 (R&D Systems) for 6 days to differentiate into interstitial-type DC or LC-type DC, as described previously [15
]. In culture, the average percentage of CD1a+/CD14–-differentiated DC is 80% [3
, 15
]. In some experiments, DC were activated for 48 h with 10 ng/ml TNF- and IL-1ß (R&D Systems), 100 ng/ml LPS (Sigma Aldrich, France), and human CD40L-transfected mouse fibroblasts (ratio 1:10).
Fluorescein-activated cell sorter analysis
Cells (2x105) were preincubated with 100 µg human polyclonal IgG for 15 min on ice to block the binding site of the Fc part of mAb used after, in phosphate-buffered saline (PBS) containing 2% FCS, 0.1% NaN3. FcRI and TfR were detected using biotinylated mAb (A77 and A24, respectively) for 20 min. After washing, cells were incubated with streptavidin–PE (Southern Biotechnology Associates) for 20 min. FcRI, FcRII, and FcRIII were stained with FITC-conjugated anti-CD64, -CD32, and -CD16, respectively. FcRI expression was detected using anti-FcRI mAb 15-1 plus FITC-conjugated goat anti-mouse (Southern Biotechnology Associates). In some experiments, cells were incubated with anti-MHC class II–PE and with biotinylated A77 or A24. After washing, cells were incubated with streptavidin-allophycocyanin (Southern Biotechnology Associates). Cells were then analyzed with a FACSCalibur flow cytometer and Cell Quest software (Becton Dickinson, San Jose, CA).
Confocal microscopy
Immature and activated Mo-DC were plated on poly-L-lysine (Sigma Chemical Co., St. Louis, MO)-coated slides for 30 min at 4°C. Cells were stained with 10 µg/ml mAb A24 or A77 or with 0.1 mg/ml serum polyclonal IgA in PBS–2% FCS for 30 min at 4°C. After washing, cells were incubated with 40 µg/ml RAM F(ab')2 and 20 µg/ml Cy5-conjugated GAR or with 50 µg/ml Texas red-conjugated goat anti-human IgA for 30 min in PBS–2% FCS. After washing, cells were incubated at 37°C for the times indicated to permit receptor internalization.
Colocalization experiments were performed using polyclonal IgA and Texas red-conjugated goat anti-human IgA plus mAb A77 or A24. Cells were then incubated for 30 min at 37°C and fixed in 4% paraformaldehyde before quenching with 0.1 M glycine. Cells were permeabilized to reveal mAb binding using 20 µg/ml goat anti-mouse–Cy5. Mounted slides were examined with a confocal laser microscope (LSM 510, Carl Zeiss, Germany).
Activation of DC by IgA
Differentiated DC (5x105) during 6 days were gently washed and incubated on ice 30 min with 10 µg/ml A77, A24, or with matched, irrelevant mouse IgG. After washing, cells were incubated on ice 30 min with 40 µg/ml RAM F(ab')2. Cells were gently washed again and incubated on ice 30 min with 40 µg/ml GAR F(ab')2. Cells were cultured at 5 x 105 cell/ml in complete medium supplemented with 250 ng/ml GM-CSF and 10 ng/ml IL-4 during 2 days. Cells were harvested, and MHC class II and CD86 expression was assessed by flow cytometry. A same experiment was performed with DC cultured for 6 days and activated for 2 days with 10 ng/ml TNF- and 10 ng/ml IL-1ß. In this experiment, after IgA-R cross-linking, cells were finally cultured for 2 days more in complete medium supplemented with 250 ng/ml GM-CSF, 10 ng/ml IL-4, 10 ng/ml TNF-, and 10 ng/ml IL-1ß.
Measurement of IL-10 and IL-12 p70 secretion
Culture supernatants was harvested after 48 h of culture and centrifuged at 14,000 rpm to remove cellular debris. IL-10 and IL-12 p70 secretion was measured by enzyme-linked immunosorbent assay (ELISA) in duplicate according to the manufacturer’s instructions using a human IL-10 and IL-12 p70 immunoassay kit (BioSource Europe, Belgium). The sensitivity of ELISA was 15 pg/ml.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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RI and TfR expression on Mo-DC by the proinflammatory cytokines TNF- and IL-1ß and IL-1ß. As TfR was recently shown to be an IgA1-R [13
], we also investigated its expression on Mo-DC. It is surprising that although monocytes do not express TfR, Mo-DC bore similar levels of TfR and FcRI, even in the absence of DC proliferation in vitro (Fig. 1A
). In the presence of TNF- and IL-1ß, Mo-DC acquired the phenotype of activated DC (CD86+, CD83+, MHC class IIhigh). It is interesting that in these conditions, Mo-DC drastically up-regulated IgA-Rs, i.e., FcRI and TfR (Fig. 1A)
. This was observed with cells from nine healthy donors. In the presence of these inflammatory cytokines, FcRI expression is increased 5.6-fold and TfR expression, 38.4-fold, as compared with immature Mo-DC (Fig. 1B)
.
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Figure 1. FcRI and TfR expression on immature and activated Mo-DC. (A) FcRI and TfR were stained with mAb A77 and mAb A24, respectively (shaded histogram), comparatively with an irrelevant antibody (open line) on human monocytes (left panel), immature Mo-DC (middle panel), and Mo-DC activated with 10 ng/ml TNF- and 10 ng/ml IL-1ß during 48 h (right panel). (B) The table shows FcRI and TfR staining of cells from nine healthy volunteers. The numbers indicate median (±SD) fluorescence intensity. *P < 0.01; Student’s unpaired t-test.
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RI and TfR on Mo-DC is specific within the IgR family, we investigated the expression of IgG-Rs and IgE-Rs on immature and activated Mo-DC. As expected, immature Mo-DC expressed FcRII and FcRI (Fig. 2A
). Incubation with TNF- and IL-1ß led to a loss of FcRI expression and markedly decreased FcRII expression, and IgA-Rs were up-regulated (Fig. 2A) . To study the regulation of IgRs on another DC population, we used Mo-LC, which possess features of LC observed in the malpighian epithelium [15
]. Comparable down-regulation of FcRII and FcRI was seen on activated Mo-LC (Fig. 2B)
. However TfR and FcRI expression was also up-regulated on activated Mo-LC (Fig. 2B)
. In particular, FcRI was only detected on activated Mo-LC (Fig. 2B)
.
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Figure 2. Regulation of FcR expression on Mo-DC and Mo-LC. FcRs and TfR were stained on Mo-DC (A) and Mo-LC (B). Cells were used when immature (left panels) or after activation with 10 ng/ml TNF- and 10 ng/ml IL-1ß during 48 h (right panels). The expression level of FcRs and TfR is shown as shaded histograms compared with the isotype control (open lines). Representative data from one of three experiments.
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RI and TfR are up-regulated by different maturing agents up-regulated TfR more potently (70%) than FcRI (15%). The opposite was seen with IL-1ß, as 80% of cells were MHC class II+/FcRI+, and only 48% were MHC class II+/TfR+. TNF- and IL-1ß together induced intermediate up-regulation of FcRI (30%) and TfR (56%; Fig. 3
). LPS preferentially increased MHC class II+/TfR+ (67%) rather than MHC class II+/FcRI+ (11%). CD40L activation strongly up-regulated FcRI+ (56%), and TfR was only minimally increased (31%; Fig. 3
). No expression of human FcRI or TfR was detected on CD40L-transfected fibroblasts (not shown).
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Figure 3. Up-regulation of FcRI and TfR expression on Mo-DC by several inflammatory stimuli. Double-staining of FcRI or TfR and MHC class II was performed on Mo-DC cultured with various activating agents (10 ng/ml TNF-, 10 ng/ml IL-1ß, 100 ng/ml LPS) or cocultured with CD40L-transfected fibroblasts (ratio 1:10) for 48 h. Percentages of MHC class II+/FcRI+ and MHC class II+/TfR+ cells are indicated in the upper-right panel of each dot plot after correction for control (Ctr) staining with an irrelevant antibody. Data are representative of five experiments.
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RI and TfR are internalized by immature and activated Mo-DCRI aggregation induces receptor internalization by interstitial DC [5
]. We therefore investigated whether TfR was similarly internalized after cross-linking by anti-TfR mAb A24 and polyclonal RAM antibody F(ab')2 on immature Mo-DC. TfR recycling is a well-established phenomenon [17
, 18
]. However, TfR aggregation by mAb A24 on Mo-DC rapidly induced submembrane localization at 5 min and cytoplasmic localization at 15 min. After 30 min, TfR did not seem to recycle to the cell surface, in contrast to FcRI (Fig. 4A
) [5
]. Similar results have been obtained after TfR cross-linking by mAb A24 on activated T cells [19
]. As both IgA-Rs were specifically up-regulated on activated Mo-DC, we attempted to determine whether FcRI and TfR aggregation could still induce internalization. Both TfR and FcRI aggregation mediated receptor endocytosis. TfR was rapidly internalized at 5 min and patched deeper in the cell at 30 min (Fig. 4B)
. The kinetics of FcRI internalization was similar to that observed with immature Mo-DC (Fig. 4B)
.
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Figure 4. FcRI and TfR internalization by immature and activated Mo-DC. Kinetics of FcRI (upper panels) and TfR (lower panels) internalization after cross-linking by 10 µg/ml mAb A77 or mAb A24, together with 40 µg/ml polyclonal RAM antibody and 20 µg/ml GAR–Cy5 [in immature Mo-DC (A) and in Mo-DC activated by TNF-/IL-1ß for 48 h (B)]. Upper panels for each condition represent midsection fluorescence, and lower panels represent the corresponding light transmission microscopy. All data are representative of at least three separate experiments.
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RI and TfR can be internalized after cross-linking on immature Mo-DC and activated Mo-DC, we examined IgA-mediated endocytosis. mAb-IgA complexes were internalized rapidly by immature Mo-DC (Fig. 5A
, upper panels). However, IgA complexes were also internalized by activated Mo-DC (Fig. 5A , lower panels). To determine which of the IgA-Rs is involved in IgA complex endocytosis, we conducted colocalization experiments. IgA complexes and FcRI or TfR were stained in immature and activated Mo-DC and examined for colocalization. As shown in Figure 5B
, in immature Mo-DC, 50% of mAb-IgA complexes colocalized with FcRI and 38% with TfR (Fig. 5B
and 5C)
. In contrast, in activated Mo-DC, mAb-IgA complexes colocalized with FcRI to a similar extent (50%) but showed weak colocalization with TfR (6%) (Fig. 5B and 5C)
.
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Figure 5. IgA endocytosis and colocalization with IgA-Rs. (A) Kinetics of IgA complex internalization in immature Mo-DC (upper panels) and in Mo-DC activated by TNF-/IL-1ß for 48 h (lower panels). mAb-IgA complexes were prepared using 0.1 mg/ml serum polyclonal IgA and 50 µg/ml Texas red-conjugated goat anti-human IgA (red fluorescence) and were incubated with cells at 37°C for the times indicated. To identify the plasma membrane, 2 µg/ml wheat-germ agglutinin conjugated to Alexa-488 was added (green fluorescence). Data are representative of three separate experiments. (B) Immature Mo-DC (left panels) and Mo-DC activated by TNF-/IL-1ß for 48 h (right panels) were incubated with mAb-IgA complexes (red fluorescence) as described above. Mo-DC were also incubated with 10 µg/ml mAb A77 or A24 as indicated. Internalization was allowed to proceed for 30 min at 37°C and cells were then fixed and permeabilized to reveal mAb binding by using 20 µg/ml goat anti-mouse–Cy5 (blue fluorescence). Simple and overlay fluorescence patterns are shown together with colocalization (white, lower panels). Data are representative of three separate experiments. (C) Fluorescence colocalization was analyzed with confocal microscopy software to determine the percentage and SD of overlaid fluorescence per pixel, corresponding to the white color in B. Percentages were calculated from three different fields in each experiment.
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RI and TfR cross-linking on MHC class II/CD86 expression and IL-10/IL-12 secretionRI and TfR on immature and activated Mo-DC, we investigated whether cross-linking of these IgA-Rs on DC could induce phenotype modulation and cytokine production. To distinguish functional effects between both IgA-Rs, we used anti-FcRI and anti-TfR mAb, which allow individual receptor aggregation.
On immature Mo-DC, FcRI cross-linking up-regulated MHC class II and CD86 molecules. 69% of cells were MHC class IIhigh/CD86high (Fig. 6A
, upper panels). Such a phenomenon was not observed after TfR aggregation, in which the percentage of MHC class IIhigh/CD86high cells was similar to controls (
10%; Fig. 6A
, upper panels). In immature Mo-DC cultivated for 48 h with TNF- and IL-1ß, the percentage of MHC class IIhigh/CD86high cells was 25% (data not shown). Activated Mo-DC cultivated for 2 additional days in the presence of TNF- and IL-1ß presented a higher percentage of MHC class IIhigh/CD86high cells (42%; Fig. 6A
, lower panels). Cross-linking of FcRI on activated Mo-DC induced MHC class II/CD86 up-regulation (73%) as compared with irrelevant antibodies (44%; Fig. 6A
, lower panels). In contrast, TfR aggregation did not change DC phenotype on activated Mo-DC cultured during 48 h with TNF- and IL-1ß. The percentage of MHC class IIhigh/CD86high cells after TfR cross-linking was 45% versus 44% for irrelevant antibodies (Fig. 6A
, lower panels). The simultaneous aggregation of both IgA-Rs on immature or activated Mo-DC showed no differences in the percentage of MHC class IIhigh/CD86high cells as compared with those of FcRI cross-linking alone (data not shown).
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Figure 6. Role of FcRI and TfR on Mo-DC activation. (A) Immature Mo-DC or activated Mo-DC (TNF-/IL-1ß for 48 h) were incubated on ice with medium, 10 µg/ml anti-FcRI mAb A77, anti-TfR mAb A24, or irrelevant control (Ctr) antibodies, as indicated. Receptor cross-linking was allowed by further incubation of cells with 40 µg/ml polyclonal RAM F(ab')2 and 40 µg/ml GAR F(ab')2. Cells were then cultured in complete medium in the presence of TNF-/IL-1ß (activated Mo-DC) or not (immature Mo-DC) for 2 days more. Cells were then analyzed by flow cytometry for CD86 and MHC class II expression. The numbers indicate the percentage of MHC class IIhigh/CD86high cells. Data are from one experiment representative of three performed with cells from different donors. (B) Cell supernatants corresponding to A were analyzed for IL-10 and IL-12 p70 concentration by ELISA. The limit of detection according to the manufacturer’s instruction was indicated on the figure. The histograms are means ± SD of three independent experiments.
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RI cross-linking results in secretion of IL-10 (211 pg/ml) but also to a lesser extent, of IL-12 (78 pg/ml; Fig. 6B
, left). As observed in Figure 6A
, no effect was observed after TfR aggregation on immature Mo-DC in secretion of IL-10 or IL-12 as compared with data from an irrelevant antibodies (Fig. 6B
, left). As control, immature Mo-DC cultured for 48 h with TNF- and IL-1ß triggered only IL-10 production but less than after FcRI cross-linking (124 pg/ml vs. 211 pg/ml; data not shown). On activated Mo-DC (Fig. 6B
, right), FcRI cross-linking still elicited IL-10 production but to a lesser extent as compared with immature Mo-DC (28 pg/ml vs. 211 pg/ml; Fig. 6B
, right). No IL-10 or IL-12 was detected in activated Mo-DC after TfR cross-linking (Fig. 6B
, right). |
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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RI, which induces DC activation after interaction with IgA complexes [5
]. This function is similar to that of FcRs, which mediate activation after cross-linking on mouse DC [20
]. FcR-mediated activation on human DC is somewhat different, probably owing to heterogenous expression of activatory (FcRI, FcRIIA, and FcRIII) and inhibitory FcRs (FcRIIB), depending on the type of in vitro DC model [21
, 22
]. Recently, it has been shown that murine DC from Peyer’s patch bind and process IgA [23
]. It is notherworthy that DC recovered from Peyer’s patch exhibit their own pattern of receptor expression and differed from Mo-DC [23
]. Morever, the IgA-R on murine DC from Peyer’s patch is not yet identified [23
], as mice do not express FcRI homologs [24
]. Another human DC subpopulation, differentiated from cord blood CD34+ precursor cells, is also reported to express FcRI [25
]. However, in this latter study, the authors showed that IgA could not induce DC activation [25
]. This apparent discrepancy can now be explained by the type of IgA used in these experiments. Indeed in our previous report, polymeric IgA activated DC [5
], whereas Heystek et al. [25
] showed that SIgA was ineffective. Recent observations suggest that SIgA do not bind efficiently to FcRI but require a mannose coreceptor [26
]. The recent crystallographic resolution of the FcRI structure favors this latter hypothesis [27
].
As the IgA-R family comprises several members [10
], we investigated on DC the expression of TfR and its role in IgA internalization. It is surprising that TfR expression, which is not detected on monocytes, was induced on Mo-DC, even in the absence of cell proliferation. The present results make TfR (after FcRI and ASGP-R) the third member of the IgA-R family to be expressed on DC. This raises the question of the respective role of these three IgA-R species on interstitial DC. Although FcRI is largely described as a conventional FcR, ASGP-R and recently, TfR were identified as accessory receptors for IgA. Particularly, TfR has been involved in pathological situations, as it is overexpressed on human mesangial cells in IgA nephropathy, where it is colocalized with IgA deposited in the mesangium [13
]. The results reported here offer the first evidence of a role of TfR in IgA-mediated endocytosis on immature DC. However, we did not observe IgA-mediated endocytosis on activated DC, despite its strong expression, and TfR aggregation did not elicit up-regulation of MHC class II and costimulatory molecules as well as cytokine production. The precise role of TfR after interaction with IgA on DC biology remains to be determined. The estimated low affinity of TfR for polymeric IgA (Ivan Cruz Moura, INSERM, unpublished data) compared with FcRI [27
] could participate by diluting the signal initiated by FcRI after IgA interaction on DC. Another explanation for the presence of TfR on DC and its high up-regulation during activation could rely on the iron cellular metabolism.
The demonstration that FcRI is specifically up-regulated on DC in the presence of several different activatory stimuli (TNF-, IL-1ß, LPS, CD40L) constitutes an intriguing observation. Indeed, although all other FcRs expressed on Mo-DC or Mo-LC are down-regulated after DC activation, the FcRI is, on the contrary, up-regulated. To our knowledge, this IgA-R is the only potential antigen-capture receptor expressed on activated DC. A recent study described some transitional stages of DC [28
]. It has been reported in mouse that after DC activation by LPS, internalization of immune complexes and cross-presentation are increased during an intermediate stage [28
]. However, the increased uptake of immune complexes did not result from increased receptor expression in intermediate DC [28
]. In our model, DC activated by TNF- and IL-1ß does not seem to correspond to the final stage of DC maturation, as we still observed receptor endocytosis.
We reported here that FcRI aggregation triggers up-regulation of MHC class II and CD86 molecules as well as IL-10 and IL-12 production on immature DC. Morever, on activated DC, FcRI cross-linking still triggers an up-regulation of MHC class II and CD86 and alters their cytokine production since the IL-12 production was shut off. Whether this could result in T cell biasing, altering T helper cell type 1 (Th1)/Th2 responses remains to be demonstrated. Depending on their maturation state, DC can induce different T cell responses [29
]. Considering the concentration of IgA in mucosae, this study particularly suggested that FcRI could play a relevant role in DC biology from immature to terminally mature DC.
This up-regulation of FcRI during DC activation and the capacity of FcRI to increase MHC class II/CD86 expression could serve as a target for immunotherapy. It has already been reported that FcRI targeting with a bispecific antibody can increase cytotoxic activity against tumor cells [30
31
32
]. However, the unique ability of DC to induce and sustain primary immune responses and to support immune memory [33
] makes them optimal candidates for anticancer vaccination. DC loaded with appropriate tumor-associated antigen are widely used in immunotherapy to induce a given immune response [34
, 35
]. The up-regulation of FcRI in this context suggests that FcRI-mediated loading of DCs might have an antitumoral, therapeutic potential.
Finally, our results point to a new line of mucosal defenses among the ones that have already been identified [36
]. The first consists of immune exclusion by SIgA at mucosal surfaces. This prevents colonization of the mucosal barrier and invasion of the epithelium. The second antigen trap involves the release of antigen–SIgA complexes from the lamina propria by poly-IgR-mediated transcytosis into the lumen [37
]. The presence of a functional FcRI on DC and its overexpression induced by proinflammatory cytokines could be considered as a mechanism designed to protect the mucosae.
Received February 20, 2004; revised July 21, 2004; accepted August 24, 2004.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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J. Exp. Med. 179,1109-1118RI J. Immunol. 155,5184-5189[Abstract]RI stimulates the production of IL-16 in Langerhans cell-like dendritic cells J. Immunol. 167,6321-6329 receptors detected by receptor-specific monoclonal antibodies J. Immunol. 148,1764-1770[Abstract] J. Immunol. 155,1606-1618[Abstract] receptor-mediated induction of dendritic cell maturation and major histocompatibility complex class I-restricted antigen presentation after immune complex internalization J. Exp. Med. 189,371-380R (CD89) binding of IgA J. Immunol. 169,3831-3836RI and its complex with IgA1-Fc Nature 423,614-620[CrossRef][Medline]RI (CD89) as a novel trigger molecule for bispecific antibody therapy Blood 90,4485-4492RI, CD89) and tumor antigens efficiently promote cell-mediated cytotoxicity of tumor targets in whole blood J. Immunol. 160,1677-1686-receptor I (CD89) recruits neutrophils as effector cells for CD20-directed antibody therapy J. Immunol. 165,5954-5961This article has been cited by other articles:
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