Systemic Autoimmunity and Lymphoproliferation Are Associated with Excess IL-7 and Inhibited by IL-7Rα Blockade

Lupus is characterized by disturbances in lymphocyte homeostasis, as demonstrated by the marked accumulation of activated/memory T cells. Here, we provide evidence that proliferation of the CD8+ precursors for the accumulating CD4–CD8– T cells in MRL-Faslpr lupus-predisposed mice is, in part, driven by commensal antigens. The ensuing lymphadenopathy is associated with increased production of IL-7 due to expansion of fibroblastic reticular cells, the primary source of this cytokine. The excess IL-7 is not, however, consumed by CD4–CD8– T cells due to permanent down-regulation of IL-7Rα (CD127), but instead supports proliferation of autoreactive T cells and progression of autoimmunity. Accordingly, IL-7R blockade reduced T cell activation and autoimmune manifestations even when applied at advanced disease stage. These findings indicate that an imbalance favoring production over consumption of IL-7 may contribute to systemic autoimmunity, and correction of this imbalance may be a novel therapeutic approach in lymphoproliferative and autoimmune syndromes

Human adult tonsil xenotransplantation into SCID mice for studying human immune responses and B cell lymphomagenesis

OBJECTIVE: To generate a human-mouse xenochimeric model where human cells remain clustered in the animal to optimize their interactions and recovery. MATERIALS AND METHODS: Severe combined immune deficient mice (SCID) were xenografted subcutaneously with human adult tonsil pieces (hu-ton-SCID mice). Such animals were: (a) compared with those receiving tonsil cells in suspension, and (b) immunized with de novo and recall antigens. RESULTS: Human tonsil pieces survived a long period of time in SCID mice, while polyclonal human T- and B-lymphocytes persisted in close vicinity within the implantation area; however, little or no graft-versus-host disease was detectable. Not surprisingly, local development of lymphoproliferative disease was often observed in animals receiving lymphoid implants from donors previously infected by the Epstein-Barr virus. One month after surgery, higher serum levels of human IgG were found in SCID mice transplanted with tonsil pieces (2x10(7) cells/animal) than in animals injected with 5x10(7) tonsil cells in suspension (1.9 vs. 0.3 mg/mL, p < 0.002). Importantly, the production of human IgG in hu-ton-SCID mice remained polyclonal for at least 6 months and was linked to the presence of cells within the implants. Immunization of hu-ton-SCID mice with hepatitis B core, a de novo antigen, did not produce a significant IgG immune response; however immunization with tetanus toxoid (TT), a thymus-dependent recall antigen, yielded high (> 700-fold increase in anti-TT IgG levels) and long-lasting (> 6 months) secondary immune responses. CONCLUSION: The hu-ton-SCID mouse xenochimeric model described in this report may improve our understanding of human lymphoid cell interactions, secondary immune responses, and lymphomagenesis

Lymphoaccumulation and T cell phenotype in MRL-<i>Fas^lpr</i> mice.

<p>(A) T cell accumulation. LN cells were obtained from MRL-<i>Fas^lpr</i> and control C57BL/6 mice at the indicated ages. Frequency and number (± SD) of CD4⁺, CD8⁺ and DN T cells were determined by flow cytometry after gating on the TCRβ⁺ cell population. (B) T cell phenotype. Expression of CD44, CD69, CD25 and CD62L by TCRβ⁺CD4⁺, TCRβ⁺CD8⁺, and TCRβ⁺DN T cells was assessed by flow cytometry in LNs of young (Y, 8 weeks of age) and older (O, 12 weeks of age) MRL-<i>Fas^lpr</i> mice. Numbers indicate percentage of positive cells (± SD). Data are representative of 3–10 independent experiments with 3–5 mice/group.</p

Cytokine receptor expression and survival of MRL-<i>Fas^lpr</i> T cells.

<p>(A) IL-7Rα and IL-2/15Rβ down-regulation in DN T cells. Lymph node T cells from young (8 weeks of age) and older (12 weeks) MRL-<i>Fas^lpr</i> mice were analyzed for expression of IL-7Rα (CD127), IL-15Rβ (CD122), γc (CD132) and IL-21R. Numbers indicate percentage of positive cells (± SD). Similar profiles were obtained with spleen cells. (B) Effect of IL-7 on T cell survival. Aliquots (5 × 10⁶) of LN cells were cultured with or without IL-7 (20 ng/ml), and numbers (± SD) of viable CD4⁺, CD8⁺ and DN T cells were determined at the indicated time-points by cell counting upon Trypan Blue staining and flow cytometry. (C) Permanent IL-7Rα down-regulation in DN T cells. LN cells (5 × 10⁶) from MRL<i>-Fas^lpr</i> mice (20 weeks of age) were analyzed either ex vivo, or after 24 hr in vitro culture in the presence of absence of IL-7 (20 ng/ml). (D) Effect of IL-21 on DN T cell survival. DN T cells (5×10⁶) were purified from LNs and cultured for 3 days in medium (control, C), or in the presence of IL-7 (20 ng/ml), IL-15 (10 ng/ml) or IL-21 (50 ng/ml, upper panel; 50-200 ng/ml, middle panel). In addition, DN T cells were CFSE-labeled, cultured with or without IL-21 (200 ng/ml), and proliferation measured by flow cytometry (lower panel). Data are representative of 2-3 independent experiments with 2–5 mice/group. Asterisks indicate statistical significance (p<0.05).</p

IL-7 excess and systemic autoimmunity in MRL-<i>Fas^lpr</i> mice.

<p>The following model is proposed: commensal and self-antigens in MRL-<i>Fas^lpr</i> lupus mice induce proliferation of CD8⁺ T cells and conversion to double-negative (DN) T cells that irriversibly down-regulate IL-7R. Lymphoaccumulation causes reorganization of the lymphoid organ microarchitecture and expansion of the stromal cell compartment, including fibroblastic reticular cells (FRCs), the main source of IL-7. The resulting excess of IL-7 is not used by DN cells, but instead promotes autoreactive T cell activation and proliferation. Consequently, antibody-mediated blockade of IL-7R signaling reduces autoimmunity in this model.</p

IL-7R blockade inhibits disease in MRL-<i>Fas^lpr</i> mice.

<p>(A) IL-7R blockade by anti-IL-7Rα antibody. MRL-<i>Fas^lpr</i> mice (6 weeks old) were treated with anti-IL-7Rα antibody or PBS, 3 times weekly for 4 weeks, and expression of IL-7Rα was determined. (B–E) Prophylactic anti-IL-7Rα antibody treatment. Young female MRL-<i>Fas^lpr</i> mice (6 weeks old) were treated with anti-IL-7Rα or PBS for 6 to 10 weeks. Antibody levels (E) were assessed after 6 weeks, dermatitis (B) after 8 weeks, and weights (± SD) of inguinal, axillary and cervical LNs and spleen (C) after 10 weeks of treatment. B and T cell subsets (D) were examined in LNs and spleen after 10 weeks of treatment. (F-G) Therapeutic anti-IL-7Rα antibody treatment. Female MRL-<i>Fas^lpr</i> mice (14 weeks old) with established disease (lymphadenopathy and anti-chromatin autoantibodies) were treated with anti-IL-7Rα or PBS for 3 to 10 weeks. Proteinuria, glomerulonephritis (GN) and lymphocytic infiltration (LI) were determined between 14 and 20 weeks of age (E), and survival at 24 weeks of age (F). Data are representative of 1–5 independent experiments with 3–9 mice/group.</p