The Journal of Immunology, 2007, 178: 4705-4706.
Copyright © 2007 by The American Association of Immunologists, Inc.
Comment on "Cutting Edge: Induction of B7-H4 on APCs through IL-10: Novel Suppressive Mode for Regulatory T Cells"
Noweeda Mirza and
Dmitry Gabrilovich
H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL 33612
In a recent article, Kryczek et al. (1) demonstrated that CD4+CD25+ regulatory T cells (Tregs) rendered monocytes immunosuppressive via up-regulation of B7-H4. We were particularly interested in the reported fact that Tregs were required for conditioning of human monocytes to exert suppressive effect on T cells. To investigate this phenomenon further, we have performed several experiments using conditions similar to those described by Kryczek et al. (1). We isolated CD14+ monocytes directly from peripheral blood of healthy donors and cultured them with autologous T cells stimulated with anti-human CD3 and anti-CD28 Abs. Our results were rather different from those reported by Kryczek et al. (1). Repeated experiments with the samples from three different donors demonstrated profound suppression of T cell proliferation by nonconditioned freshly isolated monocytes (Fig. 1A). It was possible that Tregs, which are present among T cells, could render monocytes immunosuppressive during that 4-day culture. To address this possibility, CD4+CD25– cells were sorted and then used in experiments as described above. However, monocytes effectively suppressed proliferation of CD4+CD25– T cells (Fig. 1B).
View larger version (7K):
[in this window]
[in a new window]
|
FIGURE 1. Effect of freshly isolated monocytes on T cell proliferation. A, Monocytes were isolated from peripheral blood of healthy volunteers using anti-CD14 microbeads (Miltenyi Biotec). T cells were isolated from the same donors using T cell enrichment columns (R&D Systems). Round-bottom 96-well plates were coated overnight with 1 µg/ml anti-CD3 and 5 µg/ml anti-CD28 Abs (BD Biosciences). T cells (2 x 105 cells/well) were cultured in triplicates with the indicated amount of monocytes. [3H]Thymidine (1 µCi/well) was added on day 3, and cells were harvested 18 h later. Three experiments with similar results were performed. B, Experiments were performed essentially exactly as described above. The only difference was that CD4+CD25– cells were isolated using cell sorter (FACSAria) with a postsort analysis showing practically 100% purity of target population.
|
|
Monocyte/macrophage-induced suppression of T cells in vitro is a well-established phenomenon, which could be mediated by many mechanisms involving cytokines, NO, etc. (2, 3). Potential contribution of Tregs to this process seems to be a very interesting possibility. However, our data indicate that this in vitro experimental system is not adequate to address the question of Treg effect on monocytes and may produce rather misleading conclusions. It is still possible that Tregs can induce monocytes to become suppressive cells, but proof of this point in the human system will require very different experimental approach.
References
- Kryczek, I., S. Wei, L. Zou, G. Zhu, P. Mottram, H. Xu, L. Chen, W. Zou. 2006. Cutting edge: induction of B7-H4 on APCs through IL-10: novel suppressive mode for regulatory T cells. J. Immunol. 177: 40-44. [Abstract/Free Full Text]
- Attwood, J. T., D. H. Munn. 1999. Macrophage suppression of T cell activation: a potential mechanism of peripheral tolerance. Int. Rev. Immunol. 18: 515-525. [Medline]
- Mantovani, A., S. Sozzani, M. Locati, P. Allavena, A. Sica. 2002. Macrophage polarization: tumor-associated macrophages as a paradigm for polarized M2 mononuclear phagocytes. Trends Immunol. 23: 549-555. [Medline]
