René Rückert

Inhibition of keratinocyte apoptosis by IL-15 : a new parameter in the pathogenesis of psoriasis?

Keratinocytes (KC) are important source of and targets for several cytokines. Although KC express IL-15 mRNA, the functional effects of IL-15 on these epithelial cells remain to be dissected. Investigating primary human foreskin KC and HaCaT cells, we show here by semiquantitative RT-PCR and flow cytometric analysis that both translate IL-15 and IL-15R mRNA and express IL-15 and IL-15Rα protein on the cell surface, suggesting that human KC can employ IL-15 for juxtacrine signaling. While IL-15 exerted no significant effect on KC proliferation and IL-6 or IL-8 secretion, IL-15 inhibited both anti-Fas and methylcellulose-induced KC apoptosis in vitro. This is in line with the recognized potent anti-apoptotic effects of IL-15. IL-2, whose receptor shares two components with the IL-15R, failed to inhibit KC apoptosis. Together with the role of IL-15 in sustaining chronic immune reactions, this invited the question of whether a reduction of KC apoptosis by IL-15 may be involved in the pathogenesis of psoriasis, a chronic hyperproliferative inflammatory skin disease characterized by abnormally low KC apoptosis in the epidermis. Remarkably, compared with nonlesional psoriatic skin and skin of healthy volunteers, lesional psoriatic epidermis showed high IL-15 protein expression in the epidermis and enhanced binding activity for IL-15. Therefore, antagonizing the inhibitory effects of IL-15 on KC apoptosis deserves exploration as a novel therapeutic strategy in psoriasis management.

Dendritic cell-derived IL-15 controls the induction of CD8 T cell immune responses

The development and the differentiation of CD8+ T cells are dependent on IL‐15. Here, we have studied the source and mechanism of how IL‐15 modulates CD8+ T cell‐mediated Th1immune responses by employing two delayed‐type hypersensitivity (DTH) models. IL‐15‐deficient (IL‐15–/–) mice or mice treated with soluble IL‐15Rα as an IL‐15 antagonist showed significantly reduced CD8+ T cell‐dependent DTH responses, while activation of CD4+ T cell and B cell functions remained unaffected. Injection of antigen‐labeled dendritic cells (DC) fromIL‐15+/+, IL‐15–/– or IL‐15Rα–/– mice revealed that DC‐derived IL‐15 is an absolute requirement for the initiation of DTH response. The re‐establishment of the interaction of IL‐15 with the IL‐15Rα by incubating IL‐15–/– DC with IL‐15 completely restored the capacity to prime T cells for DTH induction in vivo. Moreover, IL‐15 also enhanced secretion of pro‐inflammatory cytokines by DC and triggered in vitro CD8+ T cell proliferation and IL‐2 release. Taken together, the data suggest that an autocrine IL‐15/IL‐15Rα signaling loop in DC is essential for inducing CD8+‐dependent Th1 immune responses in mice. Therefore, targeted manipulation of this loop promises to be an effective, novel strategy for therapeuticmodulation of clinically relevant DTH reactions.

High-dose proinflammatory cytokines induce apoptosis of hair bulb keratinocytes in vivo

Background Hair loss following skin inflammation may in part be mediated by keratinocyte (KC) apoptosis. While the effects of different cytokines or other apoptosis stimulating agents such as interferon (IFN)‐γ or tumour necrosis factor (TNF)‐α on KC apoptosis in vitro have been addressed in several studies, little is known about the effects of proinflammatory cytokines on KC apoptosis in vivo.

Blocking IL-15 Prevents the Induction of Allergen-Specific T Cells and Allergic Inflammation In Vivo

IL-15 has been shown to accelerate and boost allergic sensitization in mice. Using a murine model of allergic sensitization to OVA, we present evidence that blocking endogenous IL-15 during the sensitization phase using a soluble IL-15Rα (sIL-15Rα) suppresses the induction of Ag-specific, Th2-differentiated T cells. This significantly reduces the production of OVA-specific IgE and IgG and prevents the induction of a pulmonary inflammation. Release of proinflammatory TNF-α, IL-1β, IL-6, and IL-12 as well as that of Th2 cytokines IL-4, IL-5, and IL-13 into the bronchi are significantly reduced, resulting in suppressed recruitment of eosinophils and lymphocytes after allergen challenge. It is of clinical relevance that the airway hyper-responsiveness, a major symptom of human asthma bronchiale, is significantly reduced by sIL-15Rα treatment. Ex vivo analysis of the draining lymph nodes revealed reduced numbers of CD8, but not CD4, memory cells and the inability of T cells of sIL-15Rα-treated mice to proliferate and to produce Th2 cytokines after in vitro OVA restimulation. This phenomenon is not mediated by enhanced numbers of CD4+/CD25+ T cells. These results show that IL-15 is important for the induction of allergen-specific, Th2-differentiated T cells and induction of allergic inflammation in vivo.

IL-15-IgG2b fusion protein accelerates and enhances a Th2 but not a Th1 immune response in vivo, while IL-2-IgG2b fusion protein inhibits both

We have explored how IL‐15 influences Th1 or Th2 type immune response in vivo. Intraperitoneal application of an IL‐15‐IgG2b fusion protein (FP) to mice did neither significantly affect the footpad swelling nor the production of hemagglutinizing antibodies in a delayed type hypersensitivity reaction to sheep red blood cells. In contrast, in an established murine Th2 model of sensitization to ovalbumin (OVA), IL‐15‐IgG2b FP plus OVA sensitization resulted in massively accelerated and enhanced allergen‐specific IgE and IgG1 antibody production. In vitro, stimulation of spleen cells from OVA‐sensitized mice with OVA+IL‐15 or OVA+IL‐15‐IgG2b resulted in a significantly enhanced IgE production. IL‐4 secretion was significantly induced by IL‐15 but not by IL‐15‐IgG2b. An IL‐2‐IgG2b FP with the same Fc tail as the IL‐15‐IgG2b FP was used as control in both models. In striking contrast to the IL‐15‐IgG2b FP, IL‐2‐IgG2b significantly inhibited the Th2 type antibody production in vivo. The current study suggests that IL‐15‐IgG2b may be employed as a potent accelerator and enhancer of Th2 type immune responses in vivo, while IL‐2‐IgG2b can suppress the latter.

Interleukin-15 stimulates macrophages to activate CD4+ T cells: a role in the pathogenesis of rheumatoid arthritis?

Interleukin‐15 (IL‐15) is a proinflammatory cytokine that is overexpressed in rheumatoid arthritis (RA), a disease characterized by activation of monocytes/macrophages (MΦ), and by expansion of autoreactive CD4+ T cells. We hypothesized that IL‐15 plays a major role for this expansion of CD4+ T cells and modulates the phenotype of monocytes/MΦ and their interaction with CD4+ T cells. Here, we show that IL‐15 enhances the proliferation of CD4+ T cells from patients with RA in peripheral blood mononuclear cell cocultures. To further dissect the underlying mechanisms, we employed MΦ from IL‐15−/− or IL‐15 transgenic mice. These were induced to differentiate or were stimulated with IL‐15. Here we show that addition of IL‐15 during differentiation of MΦ (into ‘IL‐15MΦ’) and overexpression of IL‐15 by MΦ from IL‐15tg mice leads to increased levels of major histocompatibility complex class II expression. This resulted in enhanced stimulation of antigen‐specific CD4+ T cells in vitro and was accompanied by reduced messenger RNA expression in MΦ for immunosuppressive SOCS3. The proliferation rates of IL‐15MΦ and IL‐15tgMΦ were high, which was reflected by increased p27Kip1 and reduced p21Waf1 levels. In view of high serum and synovial levels of IL‐15 in patients with RA, our data suggest the possibility that this excess IL‐15 in RA may stimulate monocytes/MΦ to activate the characteristic autoreactive CD4+ T cells in RA.

MMP19 Is Essential for T Cell Development and T Cell-Mediated Cutaneous Immune Responses

Matrix metalloproteinase-19 (MMP19) affects cell proliferation, adhesion, and migration in vitro but its physiological role in vivo is poorly understood. To determine the function of MMP19, we generated mice deficient for MMP19 by disrupting the catalytic domain of mmp19 gene. Although MMP19-deficient mice do not show overt developmental and morphological abnormalities they display a distinct physiological phenotype. In a model of contact hypersensitivity (CHS) MMP19-deficient mice showed impaired T cell-mediated immune reaction that was characterized by limited influx of inflammatory cells, low proliferation of keratinocytes, and reduced number of activated CD8+ T cells in draining lymph nodes. In the inflamed tissue, the low number of CD8+ T cells in MMP19-deficient mice correlated with low amounts of proinflammatory cytokines, especially lymphotactin and interferon-inducible T cell α chemoattractant (I-TAC). Further analyses showed that T cell populations in the blood of immature, unsensitized mice were diminished and that this alteration originated from an altered maturation of thymocytes. In the thymus, thymocytes exhibited low proliferation rates and the number of CD4+CD8+ double-positive cells was remarkably augmented. Based on the phenotype of MMP19-deficient mice we propose that MMP19 is an important factor in cutaneous immune responses and influences the development of T cells.

Addition of pentoxifylline could reduce the side effects of fumaric acid esters in the treatment of psoriasis.

Sir, then gradually decreased to normal levels as the disease activity decreased. We report on a possible association between epidermolysis This appears to be the ® rst reported case of EBA in which bullosa acquisita (EBA) and elevated levels of circulating IgE. IgE has been evaluated. Although the potential pathophysioA 23-year-old man with a 3-month history of intensely itchy logical relevance of our ® ndings is not clear as yet, we suggest blisters ful® lled the diagnostic criteria for EBA (subepidermal that it may be useful to evaluate total immunoglobulin levels blisters, linear IgG deposits in basement membrane zone, in new patients with EBA and possibly also in other blistering circulating IgG antibodies to dermal part of the basement diseases (3, 4). membranezone in split skin test, circulatingantibodies reacting with a 290 kD component in dermal extracts by immunoblotting) (1, 2). The patient was successfully treated with a REFERENCES combination of betamethasone and dapsone. After 10 months 1. Woodley DT, Briggaman RA, O’Keefe EJ, Inman AO, Queen LL, of treatment, direct immuno uorescence had become negative, Gammon WR. Identi® cation of the skin basement-membrane and circulating antibodies to basement membrane zone comautoantigen in epidermolysis bullosa acquisita. N Engl J Med 1984; ponents could no longer be detected. Treatment was discon310: 1007± 1013. tinued after 15 months, and the patient has been in remission 2. Shimizu H, McDonald JN, Gunner DB, Black MM, Bhogal B, Leigh IM, et al. Epidermolysis bullosa acquisita antigen and the during the 2 months that have elapsed since the treatment carboxy terminus of type VII collagen have a common immunowas stopped. localization to anchoring ® brils and lamina densa of basement Interestingly, the patient had elevated serum levels of IgE membrane. Br J Dermatol 1990; 122: 577± 585. (3,480 IU/ml vs. normally <250IU/ml) at the ® rst visit. 3. Maekawa N, Hosokawa H, Soh H, Kasahara M, Izumi H, Radio-allergosorbent tests showed polyclonal IgE against a Yodoi J, et al. Serum levels of soluble CD23 in patients with wide variety of common environmental allergens such as dustbullous pemphigoid. J Dermatol 1995; 22: 310± 315. and house mites, and Candida albicans. The serum IgE levels 4. Soh H, Hosokawa H, Asada Y. IgE and its related phenomena in bullous pemphigoid. Br J Dermatol 1993; 128: 371± 377. remained high as long as the patient had skin symptoms, but