Michael C. Byrne

CD4+CD25+ Immunoregulatory T Cells: Gene Expression Analysis Reveals a Functional Role for the Glucocorticoid-Induced TNF Receptor

CD4(+)CD25(+) immunoregulatory T cells represent a unique lineage of thymic-derived cells that potently suppress both in vitro and in vivo effector T cell function. We analyzed CD4(+)CD25(+) and CD4(+)CD25(-) T cells by DNA microarray, identifying 29 genes differentially expressed in the resting subpopulations, and 77 that were differentially expressed following activation. Most of these genes were elevated in the CD4(+)CD25(+) population, suggesting a previously activated phenotype. Among these were a number of genes that antagonize signaling, including members of the SOCS family, which may contribute to their anergic phenotype. Multiple cell surface receptors also had increased expression in CD4(+)CD25(+) cells, including GITR, a member of the TNF receptor superfamily. Importantly, antibodies to GITR abrogated suppression, demonstrating a functional role for this receptor in regulating the CD4(+)CD25(+) T cell subset.

Transcriptional Mechanisms Underlying Lymphocyte Tolerance

In lymphocytes, integration of Ca2+ and other signaling pathways results in productive activation, while unopposed Ca2+ signaling leads to tolerance or anergy. We show that the Ca2+-regulated transcription factor NFAT has an integral role in both aspects of lymphocyte function. Ca2+/calcineurin signaling induces a limited set of anergy-associated genes, distinct from genes induced in the productive immune response; these genes are upregulated in vivo in tolerant T cells and are largely NFAT dependent. T cells lacking NFAT1 are resistant to anergy induction; conversely, NFAT1 induces T cell anergy if prevented from interacting with its transcriptional partner AP-1 (Fos/Jun). Thus, in the absence of AP-1, NFAT imposes a genetic program of lymphocyte anergy that counters the program of productive activation mediated by the cooperative NFAT:AP-1 complex.

Microbial Lipopeptides Induce the Production of IL-17 in Th Cells

Naive Th cells can be directed in vitro to develop into Th1 or Th2 cells by IL-12 or IL-4, respectively. In vivo, chronic immune reactions lead to polarized Th cytokine patterns. We found earlier that Borrelia burgdorferi, the spirochaete that causes Lyme disease, induces Th1 development in αβ TCR-transgenic Th cells. Here, we used TCR-transgenic Th cells and oligonucleotide arrays to analyze the differences between Th1 cells induced by IL-12 vs those induced by B. burgdorferi. Transgenic Th cells primed with peptide in the presence of B. burgdorferi expressed several mRNAs, including the mRNA encoding IL-17, at significantly higher levels than Th cells primed with peptide and IL-12. Cytometric single-cell analysis of Th cell cytokine production revealed that IL-17 cannot be categorized as either Th1 or Th2 cytokine. Instead, almost all IL-17-producing Th cells simultaneously produced TNF-α and most IL-17+ Th cells also produced GM-CSF. This pattern was also observed in humans. Th cells from synovial fluid of patients with Lyme arthritis coexpressed IL-17 and TNF-α upon polyclonal stimulation. The induction of IL-17 production in Th cells is not restricted to B. burgdorferi. Priming of TCR-transgenic Th cells in the presence of mycobacterial lysates also induced IL-17/TNF-α coproduction. The physiological stimulus for IL-17 production was hitherto unknown. We show here for the first time that microbial stimuli induce the expression of IL-17 together with TNF-α in both murine and human T cells. Chronic IL-17 expression induced by microbes could be an important mediator of infection-induced immunopathology.

CD1d on Myeloid Dendritic Cells Stimulates Cytokine Secretion from and Cytolytic Activity of Vα24JαQ T Cells: A Feedback Mechanism for Immune Regulation

The precise immunologic functions of CD1d-restricted, CD161+ AV24AJ18 (Vα24JαQ) T cells are not well defined, although production of IL-4 has been suggested as important for priming Th2 responses. However, activation of human Vα24JαQ T cell clones by anti-CD3 resulted in the secretion of multiple cytokines notably important for the recruitment and differentiation of myeloid dendritic cells. Specific activation of Vα24JαQ T cells was CD1d restricted. Expression of CD1d was found on monocyte-derived dendritic cells in vitro, and immunohistochemical staining directly revealed CD1d preferentially expressed on dendritic cells in the paracortical T cell zones of lymph nodes. Moreover, myeloid dendritic cells both activated Vα24JαQ T cells and were susceptible to lysis by these same regulatory T cells. Because myeloid dendritic cells are a major source of IL-12 and control Th1 cell differentiation, their elimination by lysis is a mechanism for limiting the generation of Th1 cells and thus regulating Th1/Th2 responses.

Gene expression in NKT cells: defining a functionally distinct CD1d-restricted T cell subset

Since their discovery as cells bearing both TCRs and NK cell receptors, NKT cells have been intensively studied as a possible bridge between innate and adaptive immunity. Although their involvement in a wide variety of immune responses and in disease states have been well documented, molecular details of this functionality have been lacking. Recently, transcriptional profiling using microarrays has been applied to these cells, pinpointing gene-expression differences between this regulatory T cell subset and conventional T cells, and providing a framework for subset-specific therapeutic intervention in clinical settings.