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Infection and Immunity, November 2003, p. 6641-6647, Vol. 71, No. 11
0019-9567/03/$08.00+0 DOI: 10.1128/IAI.71.11.6641-6647.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Research Center for Infectious Diseases,1 Department of Molecular Pathology, Institute of Pathology, University of Wuerzburg, D-97080 Wuerzburg, Germany2
Received 27 January 2003/ Returned for modification 1 April 2003/ Accepted 4 August 2003
| ABSTRACT |
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Due to the binding of NFATc1 and NFATc2 to the promoters of the gamma interferon (IFN-
), IL-4, and IL-5 genes (i.e., the promoters of genes that are active either in Th1 or in Th2 cells), it has been assumed that NFATc1 and NFATc2 play an important role in driving naive T cells to effector Th1 and Th2 cells. Indeed, NFATc1-deficient (-/-) lymphocytes showed a significant decrease in Th2 responses (11, 18), and T cells doubly deficient for NFATc1 and NFATc2 were additionally defective in the synthesis of the Th1-type lymphokines IFN-
and IL-2 (9). In contrast, three lines of NFATc2-/- mice (3, 14, 17) exhibited divergent patterns of synthesized lymphokines. Whereas in all three lines no distinct decrease in Th1-type lymphokines was detected, T cells from two NFATc2-/- lines synthesized markedly more Th2-type RNAs or secreted more IL-4 than wild-type T cells (3, 11). In contrast, the third line showed a decrease in IL-4 production (14), at least after primary immune stimulation. These conflicting data prompted us to infect NFATc2-/- mice (backbred seven generations on the C57BL/6 background) (13, 14) and 5- to 8-week-old age-matched C57BL/6 control mice with a mouse-adapted strain of the helminth Nippostrongylus brasiliensis or with the Mycobacterium bovis BCG strain, which induces strong Th2 or Th1 responses in vivo, respectively, as described previously (2). All mice were kept under specific-pathogen-free conditions.
Figure 1 shows that prior to infection, T cells from the mediastinal lymph nodes (MLN), mesenteric lymph nodes (MESLN), and spleens of both types of mice secreted no or only very low amounts of IL-4 and IL-5 after in vitro stimulation with anti-CD3 (
-CD3) antibodies (Abs) and IL-2 (for descriptions of cell preparations and enzyme-linked immunosorbent assays [ELISAs], see reference 2). At 10 days following infection, in contrast, T cells from control mice or NFATc2-/- mice secreted large amounts of IL-4 and IL-5 after restimulation. Most importantly, T cells from infected NFATc2-/- mice secreted significantly more IL-4 and IL-5 than T cells from infected control mice. This clearly indicates that NFATc2 is involved in the downregulation not only of allergen-specific responses (16) but also of Th2 responses induced after infection.
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We also investigated whether NFATc2 deficiency affects RNA synthesis of lymphokines upon N. brasiliensis infection. As shown in Fig. 3, RNase protection analysis (the kit used was purchased from Pharmingen) revealed that in MLN cells infected with N. brasiliensis and stimulated for 24 h in vitro with anti-CD3 and IL-2, NFATc2 deficiency led to higher IL-4, IL-5, and IL-13 but not IL-2 or IFN-
mRNA levels. Whereas unstimulated MLN cells from infected control or NFATc2-/- mice produced no or very few cytokine-specific mRNAs (data not shown), stimulation with anti-CD3 plus IL-2 for 24 h resulted in an almost twofold increase in Th2-type lymphokine RNAs, although the effect (as assessed by analysis of variance [ANOVA]) was not significant. No increase or a very weak increase was detected for IL-2, IL-10, and IFN-
mRNA levels in the MLN cells from NFATc2-/- mice. This suggests that the potential negative effect of the presence of NFATc2 on transcription during helminth-induced immune responses might be limited to the type 2 lymphokine genes.
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-CD3 Ab and IL-2. Preparation and stimulation of cells and the ELISA for IL-4, IL-5, and IFN-
were performed as described previously (1). Figure 4A shows that the amount of IFN-
secreted by T cells from NFATc2-/- mice was significantly lower than that seen with T cells from control mice. In contrast to the ELISA results, RNase protection analysis of the RNA isolated from the MLN cells from mice infected with BCG i.n. for 14 days revealed that when activated in vitro for 14 or 24 h with anti-CD3 and IL-2 or for 24 h with PPD, the MLN cells from NFATc2-/- mice did not produce significantly reduced levels of IFN-
mRNA in comparison to MLN cells from control mice (data not shown). This suggests that although less IFN-
was secreted by NFATc2-deficient T cells, this was not reflected by reduced mRNA levels. A similar result was found when MLN cells from helminth-infected mice were analyzed (Fig. 1 and 3). Furthermore, Fig. 5 shows that although the MLN of NFATc2-/- mice infected with BCG contained fewer CD4+ T cells secreting IFN-
(as detected by intracellular FACS staining after in vitro stimulation with TPA and ionomycin) than the MLN of control mice, this difference was not significant (11.68 x 104 ± 4 x 104 CD4+ T cells for control mice versus 7.9 x104 ± 4 x104 CD4+ T cells for NFATc2-/- mice [means ± standard errors of the means by Student's t test for seven mice per group]). Taken together, these results indicated that although MLN cells from NFATc2-deficient mice infected with BCG secreted less IFN-
and fewer CD4+ cells produced IFN-
than cells from control mice, this effect was not detected on the mRNA level.
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The experimental findings presented here indicate that NFATc2 deficiency results in a decrease in Th1 responses (i.e., a decrease in IFN-
production) and in an increase in Th2 responses (i.e., an increase in IL-4 and IL-5 production and higher IgE levels after infection). These results extend and support the findings of a number of studies using three different NFATc2-deficient mouse lines (3, 13, 14, 17) and suggesting that NFATc2 exerts contrasting effects on the generation of Th1 and Th2 cells. While it had been expected that NFATc2 would promote Th1 responses (i.e., by controlling the IFN-
promoter) (5), the suppression of Th2 responses by NFATc2 was an unexpected finding. The observation that NFATc2 deficiency impairs very early IL-4 transcription (3, 14) while strongly enhancing IL-4 expression and additional Th2 responses at later stages (3, 6, 16) suggests that NFATc2 (and NFATc3) (10) controls the synthesis of one (or several) repressor(s) of Th2 cell development. The existence of such a repressor(s) remains to be shown. However, we cannot completely rule out that the increase in Th2 responses observed with the NFATc2-deficient mice might have been due to decreased IFN-
production or to other not-yet-defined mechanisms.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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