IL-18 cDNA vaccination protects mice from spontaneous lupus-like autoimmune disease

The lupus-like autoimmune syndrome of MRL/Mp-Tnfrsf6lpr (lpr) mice is characterized by progressive lymphadenopathy and autoantibody production, leading to early death from renal failure. Activation of T helper lymphocytes is one of the events in the pathogenesis of the disease in these mice and likely in human systemic lupus erythematosus. Among T helper lymphocyte-dependent cytokines, IFN-gamma plays a pivotal role in the abnormal cell activation and the fatal development of the lpr disease. IL-18, an inducer of IFN-gamma in T lymphocytes and natural killer cells, may contribute to the disease because cells from lpr mice are hypersensitive to IL-18 and express high levels of IL-18. To assess the contribution of IL-18 to the pathogenesis in the animal model, in vivo inhibition of IL-18 was attempted. Young lpr mice were vaccinated against autologous IL-18 by repeated administration of a cDNA coding for the murine IL-18 precursor. Vaccinated mice produced autoantibodies to murine IL-18 and exhibited a significant reduction in spontaneous lymphoproliferation and IFN-gamma production as well as less glomerulonephritis and renal damage. Moreover, mortality was significantly delayed in anti-IL-18-vaccinated mice. These studies support the concept that IL-18 plays a major role in the pathogenesis of the autoimmune syndrome of lpr mice and that a reduction in IL-18 activity could be a therapeutic strategy in autoimmune diseases.     

Protection against autoimmune nephritis in MyD88-deficient MRL/lpr mice

OBJECTIVE: To determine whether innate receptor signals play an important role in the development of autoimmune nephritis in MRL/lpr mice, an experimental model of lupus nephritis. METHODS: MyD88 is a critical adaptor that is involved in signaling pathways through all of the Toll-like receptors (TLRs) except TLR-3. We therefore generated MyD88-knockout (MyD88-KO) MRL/lpr mice and examined them for histopathologic changes in the kidneys, cumulative survival rates, extent of lymphadenopathy and splenomegaly, serum chemistry, and immunologic parameters. In addition, to define the role of the MyD88-independent pathway in autoimmune nephritis, we injected MyD88-KO MRL/lpr mice intraperitoneally with either poly(I-C) (50 or 100 microg per mouse) or phosphate buffered saline and examined them for survival as well as for histopathologic, serologic, and immunologic parameters. RESULTS: In comparison with wild-type mice, MyD88-KO MRL/lpr mice exhibited a prolonged lifespan, with no apparent development of autoimmune nephritis. Their kidneys showed no glomerular cell proliferation or crescent formation, along with a drastic decrease in the mesangial matrix. Lymphadenopathy and splenomegaly were less pronounced. Serum titers of anti-double-stranded DNA (anti-dsDNA) and production of cytokines, including interferon-alpha (IFNalpha), interleukin-12 (IL-12), IL-6, and IFNgamma, in splenocytes were significantly reduced in MyD88-KO MRL/lpr mice. Interestingly, MyD88-KO MRL/lpr mice that had been treated with the MyD88-independent TLR-3 ligand poly(I-C) showed an almost complete reversion to the features of wild-type mice, demonstrating crescentic glomerulonephritis, with significant elevation of serum anti-dsDNA titers and increased cytokine production in splenocytes. CONCLUSION: The findings indicate that both MyD88-dependent and MyD88-independent innate signals play a crucial role in the development of autoimmune nephritis in MRL/lpr mice.     

Interleukin-18 is a novel mitogen of osteogenic and chondrogenic cells

IL-18 was identified due to its ability to induce interferon-gamma (IFNgamma) production by T cells. It is a pleiotropic factor that shares structural features with IL-1 and functional activities with IL-12. IL-18 has a role in T cell development, where it has been demonstrated to act cooperatively with IL-12 to regulate IFNgamma. In bone, IL-18 is mainly produced by macrophages, but is also expressed by osteoblasts and inhibits osteoclast formation through granulocyte-macrophage colony-stimulating factor (GM-CSF) and not IFNgamma production by T cells. We have investigated the effects of IL-18 on mature osteoclast activity and for potential actions on osteoblasts or chondrocytes. The effects of IL-18 on mature osteoclast activity were determined using two assays: isolated mature osteoclast cell culture and neonatal murine calvarial organ culture. IL-18 did not affect bone resorption in either assay system. The actions of IL-18 on osteogenic cells (primary cell cultures of fetal rat and neonatal mouse osteoblasts, as well as neonatal mouse calvarial organ culture) and primary chondrocytes (canine) were assessed by proliferation assays (quantification of cell numbers and thymidine incorporation). In each assay system, IL-18 acted as a mitogen to the osteogenic and chondrogenic cells. Since IL-18 signal transduction may involve IFNgamma or GM-CSF, we assessed their involvement in the IL-18 response. IL-18 did not induce IFNgamma production by primary osteoblasts, but, of greater significance, IFNgamma had the opposing action to IL-18 in that it inhibited the primary osteoblast cell proliferation. Although IL-18 rapidly induced GM-CSF production by primary osteoblasts, IL-18 was still mitogenic in osteoblast preparations established from GM-CSF-deficient mice. Combined, these studies indicate that IL-18 may have an autocrine/paracrine mitogen role for both osteogenic and chondrogenic cells, independent of the production of IFNgamma or GM-CSF.     

Antagonist of monocyte chemoattractant protein 1 ameliorates the initiation and progression of lupus nephritis and renal vasculitis in MRL/lpr mice

OBJECTIVE: To examine whether chemokine antagonists inhibit the initiation and progression of lupus nephritis in MRL/lpr mice. METHODS: NH(2)-terminal-truncated monocyte chemoattractant protein 1 (MCP-1)/CCL2 or thymus and activation-regulated chemokine (TARC)/CCL17 analogs were inserted into the pCXN2 expression vector and transfected into a nonmetastatic fibroblastoid cell line, MRL/N-1, established from an MRL/gld mouse. RESULTS: MCP-1 antagonist- or TARC antagonist-transfected MRL/N-1 cells were injected subcutaneously into MRL/lpr mice ages 7 weeks (before the onset of lupus nephritis) and 12 weeks (at the early stage of the disease). After 8 weeks, mice bearing the MCP-1 antagonist showed markedly diminished infiltration of macrophages and T cells, glomerular hypercellularity, glomerulosclerosis, crescent formation, and vasculitis compared with control mice. This seemed to be due to decreased production of interferon-gamma and interleukin-2 in the kidney. In contrast, there was no significant difference in renal damage between mice bearing TARC antagonist and control mice. CONCLUSION: We established a new system using MRL/N-1 cells that allows long-term observation of the effects of chemokine antagonists on lupus nephritis in MRL/lpr mice. We also showed that the MCP-1 antagonist ameliorated the initiation and progression of lupus nephritis and of renal vasculitis, which might provide a new approach to the treatment of the disease.     

The influence of silicone implantation on murine lupus in MRL lpr/lpr mice.

OBJECTIVE: The use of silicone breast implants has been implicated in the development of autoimmune connective tissue diseases including systemic lupus erythematosus (SLE). We examined the influence of implanted silicones in MRL lpr/lpr and MRL +/+ mice, to determine whether silicone increases autoimmunity and exacerbates experimental lupus. METHODS: Mice were implanted with either silicone gel or silicone oil (polydimethylsiloxane; PDMS), while saline injected mice were used as controls. Proteinuria levels, palpation of lymphadenopathy, serum autoantibodies, circulating cytokines, and weight change were monitored for 18 weeks, when terminal glomerulonephritis was evaluated by histopathological techniques. Proteins were extracted from the surface of recovered implants, and the composition and immune reactive status of the silicone-binding proteins (SBP) were investigated. RESULTS: No adverse influence of silicone gel or silicone oil on the clinical aspects of lupus was observed. However, anti-DNA antibodies were significantly increased in MRL mice implanted with silicone gel compared to the control animals, and rheumatoid factor titers were modestly increased in implanted MRL lpr/lpr mice. Serum cytokine levels were influenced by silicone implantation in MRL lpr/lpr mice (but not MRL +/+ mice), with interleukin 1 (IL-1) levels increased in gel implanted animals and IL-2 levels elevated in PDMS (silicone oil) implanted mice. Different SBP were detected on implants recovered from MRL lpr/lpr mice compared with MRL +/+ mice, and Western blotting revealed the presence of strong autoantibodies to SBP in sera from MRL lpr/lpr mice, but not MRL +/+ mice. CONCLUSION: These findings suggest that silicone implantation may influence immunological responses during murine lupus, including the provocation or exacerbation of autoantibodies. However, these immune modifications did not appear to influence the clinical variables of this experimental lupus model.     

Prevention of autoimmune hearing loss in MRL/lpr mice by bone marrow transplantation

We examined the effects of bone marrow transplantation (BMT) on immune-mediated inner ear diseases in MRL/Mp-lpr/lpr (MRL/lpr) mice, which manifest not only lupus nephritis but also sensorineural hearing loss (SNHL) at the age of 20 weeks. These mice were treated with cyclophosphamide (CY) and irradiation (5 Gy x 2), followed by the transplantation of bones plus bone marrow cells from allogeneic normal C57BL/6 mice at the age of 12 weeks. Hematolymphoid cells were reconstituted with donor-derived cells 3 months after BMT. Thus-treated MRL/lpr mice showed neither lupus nephritis nor SNHL even 24 weeks after BMT. No pathological findings were observed in either glomeruli or cochleae. These findings suggest that BMT can be used to prevent the development of autoimmune SNHL in MRL/lpr mice.     

Monocyte chemoattractant protein-1 activates a regional Th1 immunoresponse in nephritis of MRL/lpr mice

OBJECTIVE: Monocyte chemoattractant protein-1 (MCP-1) is upregulated and recruits and activates inflammatory cells in nephritis of MRL lpr mice. It has been shown that anti-MCP-1 gene therapy is specifically effective in nephritis, while it was apparent that an imbalance towards Th1 predominance accelerates nephritis in MRL/lpr mice. The aim of this study was to clarify whether blockade of the MCP-1 signal by anti-MCP-1 gene therapy influences the Th1/Th2 balance in MRL/lpr mice. METHOD: An NH2-terminal deletion mutant of the MCP-1 gene (7ND) was injected into the skeletal muscles of MRL/Ipr mice with advanced stage nephritis to suppress MCP-1 and its receptor (CCR2) signaling pathway. We evaluated the local tissue production of cytokines in splenocytes and microdissected infiltrating cells within the glomeruli or interstitium. RESULT: Although the production of cytokines in splenocytes was not influenced by anti-MCP-1 gene therapy, kidney glomeruli IL-12 mRNA production and interstitium-infiltrating cell production of IL-12 and IFN-gamma mRNA were significantly reduced. CONCLUSION: The blockade of MCP-1 gene therapy does not influence helper T cell polarization, but acts directly on the regional Th1 immunoreaction in MRL/lpr mice.     

Rapamycin reverses the senescent phenotype and improves immuno-regulation of mesenchymal stem cells from MRL/lpr mice and systemic lupus erythematosus patients through inhibition of the mTOR signaling pathway

We have shown that bone marrow (BM)-derived mesenchymal stem cells (BM-MSCs) from SLE patients exhibit senescent behavior and are involved in the pathogenesis of SLE. The aim of this study was to investigate the effects of rapamycin (RAPA) on the senescences and immunoregulatory ability of MSCs of MRL/lpr mice and SLE patients and the underlying mechanisms. Cell morphology, senescence associated β-galactosidase (SA-β-gal) staining, F-actin staining were used to detect the senescence of cells. BM-MSCs and purified CD4+ T cells were co-cultured indirectly. Flow cytometry was used to inspect the proportion of regulatory T (Treg) /T helper type 17 (Th17). We used small interfering RNA (siRNA) to interfere the expression of mTOR, and detect the effects by RT-PCR, WB and immunofluorescence. Finally, 1×10⁶ of SLE BM-MSCs treated with RAPA were transplanted to cure the 8 MRL/lpr mice aged 16 weeks for 12 weeks. We demonstrated that RAPA alleviated the clinical symptoms of lupus nephritis and prolonged survival in MRL/lpr mice. RAPA reversed the senescent phenotype and improved immunoregulation of MSCs from MRL/lpr mice and SLE patients through inhibition of the mTOR signaling pathway. Marked therapeutic effects were observed in MRL/lpr mice following transplantation of BM-MSCs from SLE patients pretreated with RAPA.     

Anti-monocyte chemoattractant protein-1 gene therapy attenuates nephritis in MRL/lpr mice

OBJECTIVE: Monocyte chemoattractant protein-1 (MCP-1) is up-regulated and recruits and activates inflammatory cells in human diffuse proliferative lupus nephritis (DPLN) and in nephritis of lupus model MRL/lpr mice. The aim of this study was to examine whether anti-MCP-1 gene therapy inhibits the progression of nephritis in MRL/lpr mice. METHOD: An NH(2)-terminal deletion mutant of the MCP-1 gene, 7ND, was injected into skeletal muscles of MRL/lpr mice with advanced stage nephritis to blockade MCP-1 and its receptor (CCR2) signalling pathway. RESULT: Histological findings of kidneys in treated mice, which received more than four injections of 7ND, showed that protection against renal injury resulted from reduced infiltration of leucocytes. Therefore, this therapy has been shown to prolong the life span of MRL/lpr mice. CONCLUSION: Anti-MCP-1 gene therapy is specifically effective in the localized inflammatory region. The data presented here indicate that this anti-MCP-1 gene therapy may be effective adjunct in the management of DPLN.     

Prevention and reversal of nephritis in MRL/lpr mice with a single injection of C-reactive protein

OBJECTIVE: C-reactive protein (CRP) is an acute-phase serum protein with binding reactivity to nuclear autoantigens and immunomodulatory function. The MRL/lpr mouse is an important model of human systemic lupus erythematosus (SLE). These mice develop high-titer anti-DNA antibodies and immune complex-mediated nephritis and exhibit progressive lymphadenopathy. The mortality rate among these mice is 50% by age 18-20 weeks; the most frequent cause of death is glomerulonephritis. The present study was undertaken to determine whether treatment of mice with CRP would affect the course of lupus nephritis. METHODS: MRL/lpr mice were treated with a single 200-mug injection of CRP at either age 6 weeks (before disease onset) or age 13 or 15 weeks (when proteinuria had reached high levels). Proteinuria was measured weekly, and levels of anti-double-stranded DNA autoantibodies and blood urea nitrogen were determined monthly. Glomerular immune complex deposition and renal pathology were assessed in mice ages 15 weeks and 17 weeks. RESULTS: Early CRP treatment markedly delayed the onset of proteinuria and lymphadenopathy, increased survival, and reduced levels of autoantibodies to DNA. Treatment of mice with active disease reversed proteinuria and prolonged survival. Renal disease was decreased in CRP-treated mice, with a marked suppression of glomerular pathology, tubular degeneration, and interstitial inflammation, which correlated with the decrease in proteinuria and azotemia. CONCLUSION: These findings demonstrate that systemic suppression of autoimmunity is initiated by a single injection of CRP. Long-term maintenance of CRP-mediated protection was reversed by injection of an anti-CD25 monoclonal antibody but not by macrophage depletion, suggesting that disease suppression is maintained by CD25-bearing T cells.     

MRL/lpr lupus-prone mice show exaggerated ICAM-1-dependent leucocyte adhesion and transendothelial migration in response to TNF-alpha

OBJECTIVE: Endothelial activation and dysfunctional leucocyte-endothelial interactions are thought to play key roles in the pathogenesis of systemic lupus erythematosus (SLE). The object of this study was to investigate directly the effect of increased endothelial adhesion molecule expression on leucocyte-endothelial cell interactions, using the MRL/lpr mouse model. METHODS: Leucocyte rolling, arrest and transendothelial migration were quantified in the cremaster muscle microcirculation of 20-week-old MRL/lpr mice, using intravital microscopy. Endothelial adhesion molecule expression was quantified using intravenously injected radiolabelled monoclonal antibodies. RESULTS: Basal expression of intercellular adhesion molecule 1 (ICAM-1) by cremaster endothelium was 2-fold greater in MRL/lpr than in MRL/++ mice (P<0.05). There was a 1.6-fold increase in expression of vascular adhesion molecule 1 (VCAM-1), but no increase in E-selectin or P-selectin expression. Following intrascrotal injection of saline, no difference was detected in leucocyte-endothelial interactions between MRL/lpr and control MRL/++ mice. In contrast, intrascrotal injection of tumour necrosis factor alpha (TNF-alpha) (2 h test period) led to significantly increased numbers of adherent and extravasated leucocytes in MRL/lpr (5.98+/-0.71 and 5.45+/-0.34 leucocytes per 100 micro m vessel segment respectively) compared with MRL/++ mice (3.63+/-0.26 and 2.97+/-0.24 respectively, each P<0.05). Treatment of TNF-alpha-stimulated mice with anti-ICAM-1 F(ab')2 (YN1) abolished the difference between MRL/lpr and MRL/++ mice, whereas a negative control anti-DNP F(ab')2 had no effect. CONCLUSIONS: MRL/lpr lupus-prone mice show exaggerated ICAM-1-dependent leucocyte-endothelial interactions in response to TNF-alpha. Increased leucocyte-endothelial interactions due to endothelial priming could contribute to the clinical link between infection and flares of lupus disease activity.     

Modulation of autoimmune disease in the MRL-lpr/lpr mouse by IL-2 and TGF-beta1 gene therapy using attenuated Salmonella typhimurium as gene carrier

We have investigated the effects of interleukin-2 (IL-2) and transforming growth factor-beta (TGF-beta) gene therapy on the progress of autoimmune disease in MRL-lpr/lpr mice, a murine model of systemic lupus erythematosus (SLE). These mice have uncontrolled proliferation of T cells, an impaired response to T cell mitogen and produce autoantibodies against nuclear antigens, including DNA. Immune complexes formed by these autoantibodies are believed to cause glomerulonephritis and vasculitis in lupus mice and human SLE. Since there is an imbalance of cytokine production in both SLE patients and lupus mice, we examined the effects of cytokine gene therapy on the progression of autoimmune disease in MRL-lpr/lpr mice. The mice were treated orally with a non-pathogenic strain of Salmonella typhimurium bearing the aroA-aroD- mutations and carrying the murine genes encoding IL-2 and TGF-beta. The bacteria synthesise and slowly release the cytokines in vivo. Our results show that, contrary to expectation, TGF-beta gene therapy produced no improvement in pathology and generally had opposite effects to those of IL-2. IL-2 gene therapy restored the defective T cell proliferative response to mitogen and suppressed the autoantibody response, glomerulonephritis and growth of lymphoid tumours.     

Antagonist of fractalkine (CX3CL1) delays the initiation and ameliorates the progression of lupus nephritis in MRL/lpr mice

OBJECTIVE: Lupus nephritis is characterized by immune complex deposition and inflammatory cell infiltration into the renal glomeruli. Local generation of chemokines and the presence of chemokine receptors on the infiltrating cells may be involved in this process. Fractalkine (Fkn)/CX3CL1 and its receptor, CX3CR1, form one such chemokine system. We therefore undertook this study to investigate whether Fkn antagonist inhibits the initiation and progression of lupus nephritis in MRL/lpr mice. METHODS: NH(2)-terminally truncated Fkn/CX3CL1 analogs were transfected into a nonmetastatic fibroblastoid cell line, MRL/N-1, and injected subcutaneously into MRL/lpr mice. RESULTS: Fkn analogs truncated by >/=4 amino acid residues from the N-terminus failed to induce chemotaxis and calcium influx by CX3CR1-expressing cells. Of these, the most potent antagonist (Fkn-AT) lacked the 4 N-terminal amino acid residues. Fkn expression in the glomerulus was significantly increased in 12-week-old MRL/lpr mice. Expression was localized predominantly in the glomerular endothelial cells, but was occasionally observed in the mesangial cells and, to a lesser extent, in the interstitial microvasculature. Inoculation of MRL/lpr mice with Fkn-AT before the onset or during the early stages of lupus nephritis significantly reduced glomerular hypercellularity, glomerulosclerosis, crescent formation, and vasculitis compared with control mice. This seemed to be due to a marked reduction in macrophage accumulation. In contrast, Fkn antagonist did not affect pneumonitis, sialadenitis, lymphadenopathy, or splenomegaly. CONCLUSION: We prepared a novel potent Fkn antagonist and demonstrated its ability to delay the initiation and ameliorate the progression of lupus nephritis. This agent may therefore provide a new therapeutic approach to lupus nephritis.     

Intramolecular T cell spreading in unprimed MRL/lpr mice: importance of the U1-70k protein sequence 131-151

OBJECTIVE: To analyze spontaneous T cell spreading against determinants of the U1-70K protein in young autoimmune MRL/lpr lupus mice, in comparison with the T cell spreading occurring in normal BALB/c mice immunized with peptide 131-151 of this protein. METHODS: Peripheral blood lymphocytes (PBLs) from both unprimed MRL/lpr mice and immunized BALB/c mice were tested for their ability to proliferate ex vivo in response to 18 overlapping peptides of the U1-70K spliceosomal protein, using assays for lymphocyte proliferation and secretion of interleukin-2. RESULTS: The proliferative response to peptides of the U1-70K protein evolved rapidly in MRL/lpr mice tested at different ages. At least 5 peptides were recognized by PBLs from 8-week-old autoimmune mice, whereas a different peptide was recognized by PBLs from MRL/lpr mice at 12 weeks of age. At 15 weeks, the proliferative response was weak or negative when assessed with any of the test peptides. At least 2 major peptides recognized by MRL/lpr PBLs were also recognized by PBLs generated in the BALB/c mice primed with peptide 131-151. We further demonstrated that, in preautoimmune MRL/lpr mice, repeated administration of phosphorylated peptide 131-151 (called P140), which was shown previously to be protective, transiently abolished T cell intramolecular spreading to other regions of the 70K protein. CONCLUSION: This is the first study to demonstrate that intramolecular T cell spreading effectively occurs in MRL/lpr mice with lupus, and that region 131-151 is important in the cascade of events observed in the murine lupus response. This sequence might originate a mechanism of tolerance spreading that leads to the beneficial effect observed in MRL/lpr mice after treatment with the phosphorylated peptide 131-151.     

Control of spontaneous B lymphocyte autoimmunity with adenovirus-encoded soluble TACI

OBJECTIVE: Serum B lymphocyte stimulator (BLyS) is increased in autoimmune diseases, both in animal models and in humans. This study examined the effect of BLyS blockade in 3 animal models of lupus. METHODS: Antibodies and lupus-like disease manifestations were examined in mice after administration of a single injection of an adenoviral construct for the transmembrane activator and CAML interactor receptor (AdTACI) that produces high serum levels of TACI-Fc fusion protein. RESULTS: In C57BL/6 (B6) lpr/lpr mice (B6.lpr/lpr), which were used to model autoimmunity in the absence of severe disease, treatment of younger mice with AdTACI prevented the development of hypergammaglobulinemia. In contrast, use of AdTACI for BLyS blockade had only transient effects on the levels of IgG in normal B6 mice. AdTACI blocked the development of autoantibodies in younger B6.lpr/lpr mice and reversed the production of autoantibodies in older B6.lpr/lpr mice, and also reduced the numbers of splenic plasma cells. In MRL.lpr/lpr mice, which were used to examine disease manifestations, AdTACI reduced the extent of glomerulonephritis and proteinuria and improved survival, but had little effect on T cell infiltration and interstitial nephritis. However, in (NZB x NZW)F(1) mice, AdTACI induced neutralizing anti-TACI antibodies and failed to reduce the numbers of B cells. CONCLUSION: BLyS blockade has little effect on IgG levels in normal mice, but reverses the production of spontaneously produced IgM and IgG autoantibodies in the setting of established autoimmunity. Blockade of BLyS ameliorates B cell-dependent disease manifestations even in the MRL.lpr/lpr model, but its effectiveness on autonomous T cell aspects of the disease is limited. Moreover, its effectiveness is neutralized by anti-TACI antibodies when present. These results provide a basis for understanding the potential effects of BLyS blockade in human disease.     

Sustained thymopoiesis and improvement in functional immunity induced by exogenous KGF administration in murine models of aging

Age-related thymopoietic insufficiency has been proposed to be related to either defects in lymphohematopoietic progenitors or the thymic microenvironment. In this study, we examined whether keratinocyte growth factor (KGF), an epithelial cell-specific growth factor, could increase thymopoietic capacity in aged mice by restoration of the function of thymic epithelial cells (TECs). The thymic cellularity in KGF-treated aged mice increased about 4-fold compared to placebo-treated mice, resulting in an equivalent thymic cellularity to young mice. Enhanced thymopoiesis was maintained for about 2 months after a single course of KGF, and sustained improvement was achieved by administration of monthly courses of KGF. With the enhanced thymopoiesis after KGF treatment, the number of naive CD4 T cells in the periphery and T-cell-dependent antibody production improved in aged mice. KGF induced increased numbers of TECs and intrathymic interleukin-7 (IL-7) production and reorganization of cortical and medullary architecture. Furthermore, KGF enhanced thymopoiesis and normalized TEC organization in klotho (kl/kl) mice, a model of premature degeneration and aging, which displays thymopoietic defects. The result suggests that TEC damage is pathophysiologically important in thymic aging, and KGF therapy may be clinically useful in improving thymopoiesis and immune function in the elderly.