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Summary: Interleukin-2 (IL-2) has multiple, sometimes opposing, functions during an inflammatory response. It is a potent inducer of T-cell proliferation and T-helper 1 (Th1) and Th2 effector T-cell differentiation and provides T cells with a long-lasting competitive advantage resulting in the optimal survival and function of memory cells. In a regulatory role, IL-2 is important for the development, survival, and function of regulatory T cells, it enhances Fas-mediated activation-induced cell death, and it inhibits the development of inflammatory Th17 cells. Thus, in its dual and contrasting functions, IL-2 contributes to both the induction and the termination of inflammatory immune responses.

Activation of the TCL1 oncogene has been implicated in T cell leukemias/lymphomas and recently was associated with AIDS diffuse large B cell lymphomas (AIDS-DLBCL). Also, in nonmalignant lymphoid tissues, antibody staining has shown that mantle zone B cells expressed abundant Tcl1 protein, whereas germinal center (GC; centrocytes and centroblasts) B cells showed markedly reduced expression. Here, we analyze isolated B cell subsets from hyperplastic tonsil to determine a more precise pattern of Tcl1 expression with development. We also examine multiple B cell lines and B lymphoma patient samples to determine whether different tumor classes retain or alter the developmental pattern of expression. We show that TCL1 expression is not affected by Epstein-Barr virus (EBV) infection and is high in naïve B cells, reduced in GC B cells, and absent in memory B cells and plasma cells. Human herpesvirus-8 infected primary effusion lymphomas (PEL) and multiple myelomas are uniformly TCL1 negative, whereas all other transformed B cell lines tested express moderate to abundant TCL1. This observation supports the hypothesis that PEL, like myeloma, usually arise from post-GC stages of B cell development. Tcl1 protein is also detected in most naïve/GC-derived B lymphoma patient samples (23 of 27 [85%] positive), whereas most post-GC-derived B lymphomas lack expression (10 of 41 [24%] positive). These data indicate that the pattern of Tcl1 expression is distinct between naïve/GC and post-GC-derived B lymphomas (P < 0.001) and that the developmental pattern of expression is largely retained. However, post-GC-derived AIDS-DLBCL express TCL1 at a frequency equivalent to naïve/GC-derived B lymphomas in immune-competent individuals (7 of 9 [78%] positive), suggesting that TCL1 down-regulation is adversely affected by severe immune system dysfunction. These findings demonstrate that TCL1 expression in B cell lymphoma usually reflects the stage of B cell development from which they derive, except in AIDS-related lymphomas.

The TCL1 protooncogene is overexpressed in many mature B cell lymphomas, especially from AIDS patients. To determine whether aberrant expression promotes B cell transformation, we generated a murine model in which a TCL1 transgene was overexpressed at similar levels in both B and T cells. Strikingly, transgenic mice developed Burkitt-like lymphoma (BLL) and diffuse large B cell lymphoma (DLBCL) with attendant Bcl-6 expression and mutated J H gene segments at a very high penetrance beginning at 4 months of age. In contrast, only one mouse developed a T cell malignancy at 15 months, consistent with a longer latency for transformation of T cells by TCL1. Activation of premalignant splenic B cells by means of B cell antigen receptor (BCR) engagement resulted in significantly increased proliferation and augmented AKT-dependent signaling, including increased S6 ribosomal protein phosphorylation. Transgenic spleen cells also survived longer than wild-type spleen cells in long-term culture. Together these data demonstrate that TCL1 is a powerful oncogene that, when overexpressed in both B and T cells, predominantly yields mature B cell lymphomas.T he TCL1 (T cell leukemia 1) protooncogene is expressed in CD3 Ϫ CD4 Ϫ CD8 Ϫ precursor T cells and is extinguished at the CD4 ϩ CD8 ϩ stage of thymocyte development (1). In B cells, TCL1 is first expressed in pro-B cells and remains high in naive mantle zone B cells of peripheral lymphoid tissues (1-4). Downregulation of TCL1 expression in follicle center centroblasts and centrocytes is followed by gene extinction in post-germinal center (GC) memory B cells and plasma cells (4, 5).Continued high-level TCL1 expression, because of chromosomal rearrangements, was implicated in mature peripheral T cell malignancies (6, 7). Polyclonal and oligoclonal T cell expansions preceded clonal outgrowth by many years, suggesting that additional lesions were required for transformation (8,9). Supporting this tumorigenic mechanism, transgenic mice expressing TCL1-familymember proteins exclusively in T cells developed polyclonal T cell expansions before the evolution of clonal malignancies at 15 to 20 months (10, 11). Overexpression of TCL1, or MTCP1 (mature T cell proliferation 1), in mouse T cells did not affect B cell development or produce B cell lymphomas. These findings indicate that aberrant expression of TCL1 or MTCP1 in T cells perturbs T cell homeostasis through cell autonomous pathways without inducing premalignant or malignant changes in bystander B cells.About 15% of AIDS patients develop aggressive B cell nonHodgkin lymphoma (AIDS-NHL) (12, 13). Most AIDS-NHL originate from GC or post-GC B cells, but the early events leading to AIDS-NHL remain poorly defined (13,14). Diffuse large B cell lymphoma (DLBCL) is the most prevalent type of AIDS-NHL, and these tumors generally lack consistent genetic and͞or viral tumorpromoting alterations. Recently, abundant TCL1 expression was shown in a high percentage of AIDS-NHL of post-GC origin (3,4). This discovery led us to postulate that TCL1 dy...

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CD8 T cells can play both a protective and pathogenic role in inflammation and autoimmune development. Recent studies have highlighted the ability of CD8 T cells to function as T follicular helper (Tfh) cells in the germinal center in the context of infection. However, whether this phenomenon occurs in autoimmunity and contributes to autoimmune pathogenesis is largely unexplored. In this study, we show that CD8 T cells acquire a CD4 Tfh profile in the absence of functional regulatory T cells in both the IL-2-deficient and scurfy mouse models. Depletion of CD8 T cells mitigates autoimmune pathogenesis in IL-2-deficient mice. CD8 T cells express the B cell follicle-localizing chemokine receptor CXCR5, a principal Tfh transcription factor Bcl6, and the Tfh effector cytokine IL-21. CD8 T cells localize to the B cell follicle, express B cell costimulatory proteins, and promote B cell differentiation and Ab isotype class switching. These data reveal a novel contribution of autoreactive CD8 T cells to autoimmune disease, in part, through CD4 follicular-like differentiation and functionality.

IntroductionThe interleukin-2 knockout (IL-2-KO) mouse provides a powerful model for defining the signals involved in the development of spontaneous autoimmune disease in the absence of regulatory T cells. IL-2-KO mice on the BALB/c background develop a systemic autoimmune disease, dying by 5 weeks from complications of autoimmune hemolytic anemia (AIHA). 1 The principal immunologic defects in these mice are a deficiency of regulatory T lymphocytes (Tregs) leading to a breakdown of self-tolerance and failure of T-cell homeostasis, resulting in uncontrolled activation and proliferation of CD4 ϩ T cells. 2,3 It has been shown that AIHA progression in these animals is mediated by autoantibodies and is dependent on abnormal helper T-cell (Th) activity. 1,4,5 We used this mouse model of spontaneous, acute systemic autoimmunity to define the cytokine milieu that influences the development of autoimmune disease.A tightly controlled balance between activation and suppression normally maintains immune homeostasis. Dysregulated cytokine expression is documented in various autoimmune and inflammatory diseases, and in the expansion of autoreactive T cells. 6-10 Our understanding of the cytokine network required to induce, amplify, and control self-reactive lymphocytes continues to evolve. Autoimmune manifestations have traditionally been thought to be mediated by Th1 cells and their abundant interferon-␥ (IFN-␥) and tumor necrosis factor (TNF) production. With the more recent identification of the Th17 subset, the role of cytokines in autoimmunity is being re-evaluated. Th17 cells are potent inducers of tissue inflammation, and dysregulated expression of IL-17 appears to initiate organ-specific autoimmunity; this has been best characterized in mouse models of colitis, 11 experimental autoimmune encephalomyelitis, 12 and rheumatoid arthritis. 13 The specific roles and interactions of Th subsets during the development of autoimmunity are a topic of great interest at present. 14,15 In this study, we set out to evaluate the contributions of Th1 and Th17 cytokines in the development of inflammation and autoimmunity in the absence of Tregs using the IL-2-KO mouse model. We demonstrate a clear role for IFN-␥ in the production of autoantibodies and progression of AIHA. In the absence of IFN-␥, IL-2-KO mice show delayed AIHA but, over time, develop intestinal inflammation, whereas elimination of IL-17 has no impact on the kinetics of AIHA development. Thus, our studies reveal that different cytokines play distinct roles in various manifestations of autoimmunity in the absence of Tregs. Methods MiceMice lacking IL-2, IFN-␥, IL-17, IL-2/CD28, IL-2/CD40L, IL-2/IFN-␥, and IL-2/IL-17 were used on the BALB/c background. Mice were bred and maintained in our specific pathogen-free facility at the Animal Barrier Facility in accordance with the guidelines of the Laboratory Animal Resource Center of the University of California San Francisco. Lymphocyte isolationLymph nodes (LNs) and spleens were pressed through a nylon mesh filter, red blood ...