Evaluation of mite allergen-induced Th1 and Th2 cytokine secretion of peripheral blood mononuclear cells from atopic dermatitis patients: association between IL-13 and mite-specific IgE levels

There have been several reports about Th1/Th2 imbalances in atopic dermatitis (AD), but there have been few precise investigations about the differences between Th1 and Th2 cytokine secretion patterns of peripheral blood mononuclear cells (PBMCs) in such patients. We cultured PBMCs, taken from AD patients and healthy subjects, with dust mite extract (DME) and measured subsequent immunoreactive interferon (IFN)-gamma (Th1 cytokine), interleukin (IL)-4, IL-5, and IL-13 (Th2 cytokines) levels in the supernatants by ELISA assays. There is a difference between IL-4 and IL-13 secretion patterns by DME-stimulated PBMCs in AD subjects; immunoreactive IL-4 levels were detectable maximally within 24-h cultures, while IL-13 levels increased time-dependently within 7-day cultures. IL-13 levels were significantly elevated in AD subjects compared to healthy subjects, while IFN-gamma levels did not significantly differ between the two groups. IL-13 levels were significantly higher in AD patients who had high levels (>100 U/ml) of Dermatophagoides pteronyssinus-specific IgE (Dp-IgE) than in those AD patients who had low levels (<10 U/ml) of Dp-IgE. Tacrolimus (FK-506), at a concentration of 10(-8) M, significantly inhibited DME-induced IL-13 production from PBMCs. These findings suggest that IL-13 produced by Th2 cells are involved in IgE overproduction in AD subjects.     

Cytokine gene polymorphisms in psoriasis

BACKGROUND: Cytokine production is under genetic control, and certain allelic variants of cytokine genes are associated with higher or lower cytokine production in vitro and in vivo. Psoriasis is associated with an overexpression in the involved skin of T-helper cell type 1 (Th1) cytokines, e.g. interferon (IFN) -gamma and tumour necrosis factor (TNF) alpha and relative underexpression of Th2 cytokines, e.g. interleukin (IL) -4 and IL-10. Objective We investigated the hypothesis that allelic variants of genes for a high production of Th1 cytokines or TNF-alpha, or conversely low production of Th2 cytokines might represent a risk factor for developing psoriasis. METHODS: Genotyping for IFN-gamma, IL-10, IL-4 and TNF-alpha was undertaken for 84 patients with psoriasis and compared with control data on file. RESULTS: Genotype frequencies showed no differences between patients and controls for IFN-gamma, TNF-alpha or IL-4. For IL-10, patients with late onset psoriasis (over 40 years) were more likely to be heterozygous at position - 1082 (P = 0.02), corresponding to intermediate production of IL-10 in vitro and in vivo. CONCLUSIONS: Psoriasis is not determined by a genotype consistent with high production of Th1 cytokines or low production of Th2 cytokines. Thus, the Th1 cytokine profile found in psoriatic plaques is most likely a consequence of local factors.     

Cytokine expression of skin T-lymphocytes from patients with atopic dermatitis.

We analysed the cytokine profile of skin T cells by establishing 11 T-cell lines from adult patients with moderate-to-severe atopic eczema using T-cell growth factors interleukin-2 and interleukin-4. We compared T-cell lines from lesional skin of atopic dermatitis patients with those from non-atopic skin of patients with other skin diseases, observing that T-cell lines of patients with atopic dermatitis unstimulated cultures expressed a Th1 profile. After stimulation with anti-CD3 and anti-CD28 monoclonal antibodies, the cytokine expression showed rapid initial upregulation of Th2 followed by a Th1 profile. Furthermore, strong upregulation of interleukin-10 was observed after 24 h stimulation. Our findings suggest that skin T-lymphocytes from atopic dermatitis patients seem to consist of a heterogenous population of Th1 and Th2 or Th0 cells and the results for secreted cytokines indicate that T-cell lines from each inflammatory skin disease showed the corresponding disease-specific original cytokine profile.     

Interleukin 4 and interferon-gamma expression of the dermal infiltrate in patients with erythroderma and mycosis fungoides. An immuno-histochemical study

BACKGROUND: Erythroderma, or generalized erythema of the skin, may result from different causes. At present it is unclear whether the underlying patho-mechanisms that lead to erythroderma are identical or different depending on the original disease. The aim of this study was to investigate the dermal cytokine profile in different types of erythroderma and mycosis fungoides. METHODS: Snap-frozen skin biopsy specimens from 33 patients with erythroderma were studied. Thirteen had idiopathic erythroderma, 7 erythrodermic atopic dermatitis, 5 Sézary syndrome and 8 had erythroderma from miscellaneous causes. We also studied 6 patients with mycosis fungoides (5 plaques and 1 tumor) and 5 healthy non-atopic volunteers. The biopsies were immunohistochemically stained for interleukin 4 (IL-4) and interferon gamma (IFN-gamma). All positive cells for IL-4 and IFN-gamma in the dermis were counted and the number of positive cells was calculated per mm2. IL-4/IFN-gamma ratio was calculated for each biopsy. RESULTS: The patients with idiopathic erythroderma, atopic dermatitis and miscellaneous erythroderma, all showed more IFN-gamma-positive cells than IL-4-positive cells in the dermis. The median IL-4/ IFN-gamma ratio for these three groups was 0.6, 0.9 and 0.45, respectively. These differences were not statistically significant. All patients with Sézary syndrome however, showed more IL-4-positive cells than IFN-gamma-positive cells. The median IL-4/IFN-gamma ratio was 1.8, which is significantly higher than in the other groups p<0.05). In mycosis fungoides roughly the same number of cells expressed IL-4 and IFN-gamma. The median IL-4/IFN-gamma ratio was 1.0, which is significantly lower than in Sézary syndrome (p<0.05). CONCLUSIONS: The dermal infiltrate in patients with Sezary syndrome mainly shows a T-helper 2 (Th2) cytokine profile, this in contrast to T-helper 1 (Th1) cytokine profile in benign reactive erythroderma. This indicates that although a relative uniform clinical picture of erythroderma is obvious, a different patho-mechanisms may be underlying.     

Secretion of IL-2, IL-4, and IFN-γ for Dust Mite Antigens in a Patient with Atopic Dermatitis

In a 21-year-old female with severe atopic dermatitis, the secretion of interleukin-2 (IL-2), interleukin-4 (IL-4), and interferon-γ (IFN-γ) by her peripheral blood mononuclear cells (PBMC) was measured after incubation with/without antigens extracted from Dermatophagoides pteronyssinus (Dp), to which the patient had developed a positive patch-test reaction. Incubation with Dp antigen produced marked secretion of IL-2 and IFN-γ, but not IL-4. This may suggest that Dp-specific T lymphocytes present in the circulating blood cells are capable of producing IL-2 and IFN-γ, which may be relevant to the delayed-type allergic reaction occurring in the skin lesion.     

Increased frequency of intracellular interleukin (IL)-13 and IL-10, but not IL-4, expressing CD4+ and CD8+ peripheral T cells of patients with atopic dermatitis

BACKGROUND: A number of studies exist demonstrating the increased expression of type 2 cytokines and decreased capacity to produce interferon-gamma (IFN-gamma) in peripheral blood mononuclear cells (PBMCs) of patients with atopic dermatitis (AD). OBJECTIVES: To clarify the results of recent studies concerning the role of interleukin (IL)-4 and IL-13 in PBMCs of AD patients, we analysed the activation status of lymphocyte subpopulations. METHODS: We measured the intracellular expression and serum levels of certain type 1 and type 2 cytokines, using cell surface and intracellular cytokine staining, flow cytometry and enzyme-linked immunosorbent assay techniques. RESULTS: The frequency of IL-10 and IL-13 producing CD4+ and CD8+ T cells was significantly higher in patients with AD, while the frequency of IFN-gamma secreting helper and cytotoxic T cells was significantly lower in patients with AD than in control subjects. The serum levels of IL-10 and IL-13 were also significantly increased. There were no significant differences observed between the experimental groups in the frequency of IL-4 producing CD4+ and CD8+ cells. CONCLUSIONS: This study demonstrates a type 2 cytokine production in the CD4+ and CD8+ T cells of AD patients, which is characterized by an elevated IL-13, but not by IL-4 secretion, and by an increased level of the immunoregulatory IL-10, which can contribute to a decrease in IFN-gamma expression.     

A Th2 chemokine, TARC, produced by keratinocytes may recruit CLA+CCR4+ lymphocytes into lesional atopic dermatitis skin

Atopic dermatitis is an inflammatory skin disease in which the inflammation is characterized by the influx of lymphocytes into the dermis. It is generally believed that atopic dermatitis is a Th2-type disease, i.e., the T lymphocytes produce interleukin-4, interleukin-5, interleukin-10, and interleukin-13, although it has become evident in recent years that the cytokine profile in the skin changes during the course of the disease towards a Th1-Th2 mixed cytokine profile (interferon-gamma, tumor necrosis factor alpha, and interleukin-2). The lymphocytes that home into the skin express cutaneous lymphocyte-associated antigen, and it has recently been shown that most of the lymphocytes in this population express the chemokine receptor CCR4. CCR4 is the receptor for the CC chemokine TARC (thymus and activation regulated chemokine), and this chemokine is expressed predominantly by keratinocytes in the basal layer of the epidermis of lesional atopic dermatitis skin in mice. In humans, however, it was shown to be expressed in the endothelial cells of the dermis. We have examined the peripheral blood mononuclear cells of atopic dermatitis patients for the expression of cutaneous lymphocyte-associated antigen and CCR4 and compared them with peripheral blood mononuclear cells from normal controls. We found that the proportion of CLA+CCR4+ lymphocytes is upregulated in atopic dermatitis patients. In addition we have examined skin biopsies of lesional and non-lesional skin from atopic dermatitis patients and found that the keratinocytes, but not the endothelial cells, produce TARC in the lesional but not in the nonlesional skin. To gain insight in the stimulatory mechanisms for TARC production in keratinocytes, as previously observed in mice, we cultured HaCaT cells and found that interferon-gamma and tumor necrosis factor alpha work synergistically to induce TARC production. These observations suggest that the induction of TARC production in keratinocytes plays an important role in the late phase skin invasion by CCR4+CLA+ Th2-type lymphocytes in atopic dermatitis.     

IL-17 and IL-17R: an auspicious therapeutic target for psoriatic disease

The continuous discovery of new T cell subpopulations in human autoimmune diseases is making the immunopathological network more complex. Th17 cells are one such newly identified subset of T cells, characterized by the production of signature cytokine IL-17. In last few years, several studies have strongly established the regulatory role of Th17 cells and its signature cytokine IL-17 in autoimmune diseases including psoriasis, psoriatic arthritis, rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus and multiple sclerosis. Psoriasis and PsA are immune mediated hyperproliferative diseases, affecting skin and joint respectively. Before the discovery of Th17 cells, psoriasis and psoriatic diseases were thought to be chiefly Th1 mediated diseases; later on IL-17 knockout animal studies as well as human experimental data indicate the crucial role of Th17 cells and its signature cytokine IL-17 in the pathogenesis of these diseases. In vitro human studies have shown the abundance of Th17 cells in the psoriatic plaques. Subsequently our research group has extended this observation in psoriatic arthritis and found the abundance of CD4+IL-17+ T cells in the synovial fluid and majority of these T cells are of memory phenotype (CD4RO+CD45RA-CD11a+). In addition, we showed the significant presence of functional IL-17 receptor in synovial fibroblast of psoriatic arthritis patients. Considering the strong association of IL-17 and psoriatic disease, IL-17 targeted therapy have shown promises in preclinical and clinical trials. In this review article, we have discussed the pathogenic role of IL-17 in psoriatic disease and summarized the therapeutic efficacy and safety profile of different anti IL-17 therapy as an anti-psoriatic agent.     

IL-4/IL-13 antagonist DNA vaccination successfully suppresses Th2 type chronic dermatitis

Background  Atopic dermatitis (AD) is a chronic disease with a Th2-type-cytokine dominant profile. Several cytokines and related peptides have been used for the treatment of AD but they were ineffective because of their limited biological half-life. We have recently developed a highly efficient mouse dominant negative interleukin (IL)-4/IL-13 antagonist (IL-4DM), which blocks both IL-4 and IL-13 signal transductions.
Objective  To examine the effects of IL-4DM in vivo in an AD model induced by the repeated exhibition of oxazolone (OX).
Methods  Plasmid DNA was injected intraperitoneally to cause an experimental AD-like dermatitis. The effect was evaluated by ear thickness, histological findings, and mast cells counts in the inflamed skin. The plasma IgE and histamine levels were measured. Cytokine production in skin and splenocytes were also analysed.
Results  Mice treated with control plasmid developed marked dermatitis with mast cells and eosinophil infiltration, and had increased plasma IgE and histamine levels with a Th2 type splenocyte cytokine profile. Treatment with mouse IL-4 DNA augmented the ear swelling and thickness with an increased dermal eosinophil count, plasma histamine level, and production of splenocyte IL-4. However, IL-4DM treatment successfully controlled the dermatitis, decreased the mast cell and eosinophil count, and suppressed plasma IgE and histamine levels. Splenocytes produced an increased level of IFN-γ.
Conclusion  These data showed that the simultaneous suppression of IL-4/IL-13 signals successfully controlled Th2-type chronic dermatitis. IL-4DM DNA treatment is a potent therapy for AD and related diseases.     

Improvement of atopic dermatitis and reduction of skin allergic responses by oral intake of konjac ceramide

Although topical application of ceramide is effective in the treatment of atopic dermatitis, its effect is transient. Thus, the effect of oral intake of ceramide on atopic dermatitis was studied. Two groups of 25 children with moderate atopic dermatitis, who were allergic to house dust mite took either milk sugar (control group) or 1.8 mg/day of konjac ceramide in milk sugar (ceramide group) once a day for 2 weeks. Before and after 2 weeks, skin symptoms were assessed using the SCORAD index, while allergic skin responses to house dust mite were assessed by skin prick test. Moreover, production of allergen-specific IgE and various cytokines by mononuclear cells was measured. After 2 weeks, SCORAD index score, allergic skin responses to house dust mite and house dust mite-specific IgE production were significantly reduced in the ceramide group, but not in the control group. Moreover, house dust mite-induced cytokine production was skewed towards the Th1 type, since production of Th1 cytokine, IFN-gamma, and IL-12, was increased, while production of Th2 cytokine, IL-4, and IL-13, was decreased. In contrast, no change of these parameters was found in control group. Collectively, oral intake of konjac ceramide improved skin symptoms and reduced allergic responses with concomitant skewing of the cytokine pattern towards the Th1 type.     

IL-31 expression by inflammatory cells is preferentially elevated in atopic dermatitis

Interleukin-31 (IL-31) is a recently discovered cytokine expressed in many human tissues, and predominantly by activated CD4(+) T cells. IL-31 signals through a heterodimeric receptor consisting of IL-31 receptor alpha (IL-31RA) and oncostatin M receptor beta (OSMR). Earlier studies have shown involvement of IL-31 and its receptor components IL-31RA and OSMR in atopic dermatitis, pruritus and Th2-weighted inflammation at the mRNA level. The aim of this study was to investigate IL-31 protein expression in skin of such conditions. Immunohistochemical staining for IL-31, IL-31RA and OSMR was performed in formalin-fixed paraffin-embedded biopsy specimens. IL-31 expression was increased in the inflammatory infiltrates from skin biopsies taken from subjects with atopic dermatitis, compared with controls (p?≤?0.05). IL-31, IL-31RA and OSMR protein immunoreactivity was not increased in biopsies from subjects with other Th2-weighted and pruritic skin diseases. Our results confirm, at the protein level, the relationship between IL-31 expression and atopic dermatitis. Our results do not support a general relationship between expression of IL-31/IL-31R and pruritic or Th2-mediated diseases.     

Neuropeptide modulation of Th1 and Th2 cytokines in peripheral blood mononuclear leucocytes in atopic dermatitis and non-atopic controls

The neuropeptides substance P (SP) and vasoactive intestinal peptide (VIP) are present in the nerve endings in the skin and SP is thought to be present at abnormal concentrations in atopic dermatitis (AD) patients. Th1 and Th2 imbalance in AD has been the focus of recent immunological investigations and a preferential Th2 response by atopic cells on stimulation has been proposed. We wished to establish whether neuropeptides acted on T cells to affect their cytokine profile directly, using an accessory cell-independent stimulus (anti-CD3 monoclonal antibody) and neuropeptides at several concentrations. We found that interferon (IFN)-γ and interleukin (IL)-4 release were lower in AD. SP had an enhancing effect on both IFN-γ and IL-4 at physiological concentrations (10^?10–10^?6mol/L) in AD, which was significantly different from controls (P<0.05). VIP had inhibitory effects over this range in AD and in controls. We conclude that these neuropeptides have a modest effect on T-cell cytokine release and that their action is not cytokine-specific.     

Naïve CD4+ T cells from patients with atopic dermatitis show an aberrant maturation towards IL-4-producing skin-homing CLA+ cells

Abstract: Overproduction of interleukin‐4 (IL‐4) has been reported in lesional and in peripheral T cells from patients with atopic dermatitis (AD). It is not clear whether the development of IL‐4‐producing T helper type 2 (Th2) cells from naïve precursors is an intrinsic phenomenon of T cells or whether other, extrinsic factors play a significant role. To analyze these alternatives, we investigated the IL‐4 production of effector T cells generated in vitro from highly purified CD4+ CD45RA+ naïve T cells in the absence of signals derived from antigen‐presenting cells. Effector T cells generated from naïve precursors from both AD and healthy donors produced comparable amounts of IL‐4 after restimulation. Priming in the presence of exogenous IL‐4 enhanced the production of IL‐4 while neutralizing endogenously produced IL‐4 abolished IL‐4 production similarly in atopic and healthy T cells. A subset of effector T cells acquired the expression of the cutaneous lymphocyte antigen (CLA). The frequency of CLA+ T cells was not different between atopic and healthy donors. CLA+ T cells, differentiated from naïve atopic, but not healthy T cells, showed a preferential Th2 cytokine profile as assessed by intracellular cytokine staining. Also effector T cells derived from atopic patients without dermatitis tended to show this imbalance, although it was not significantly different to healthy controls. This Th2 cytokine profile did not develop when naïve T cells were cultured in the presence of IL‐12. In conclusion, high IL‐4 production in developing T cells from AD patients was associated with CLA expression, the net IL‐4 production of all effector CD4+ T cells, however, was similar to IL‐4 production by T cells from healthy donors.     

Increased frequencies of IL-31-producing T cells are found in chronic atopic dermatitis skin

Interleukin (IL)-31 has been associated with pruritus, a characteristic feature of atopic dermatitis (AD). Local T cell responses may be responsible for the increased level of IL-31 mRNA observed in AD. We investigated the frequency of IL-31-producing T cells in AD lesions, as well as their cytokine profile. T cells were isolated from chronic AD lesions, autologous blood and healthy donor skin. Intracellular expression of IL-31, IFN-γ, IL-13, IL-17 and IL-22 was measured using flow cytometry. T cells from AD lesions contained significantly higher percentages of IL-31-producing T cells compared to autologous blood and donor skin. Many IL-31-producing T cells co-produced IL-13 and to lesser extent IL-22, but rarely IFN-γ or IL-17. A substantial part of the IL-31-producing T cells did not co-produce any of the other cytokines and could therefore not be linked to any of the known functionally different T cell subsets. The T cell infiltrates were also relatively enriched for Th2/Tc2 and Th22/Tc22 cells, while frequencies of Th1/Tc1 and Th17 cells were decreased. This is the first report describing the detection of IL-31 at protein level in skin-infiltrating T cells. We show here that T cells in chronic AD skin produce IL-31 and that AD lesions contain increased levels of these IL-31-producing T cells. This suggests that a substantial part of previously reported increased IL-31 mRNA levels in AD skin is T cell derived and that these cells may be involved in the pathogenesis of AD.     

The effect of extracorporeal photopheresis on intracellular cytokine expression in chronic cutaneous graft-versus-host disease

BACKGROUND: Cytokines derived from T helper (Th)1 lymphocytes are thought to be involved in the pathogenesis of graft-versus-host disease (GVHD) and extracorporeal photopheresis (ECP) has been reported to affect Th1/Th2 lymphocyte ratios. It may also influence the balance of cytotoxic Tcells (Tc1/Tc2). OBJECTIVES: This study was formulated to assess the effect of ECP on the cytokine profiles of peripheral blood (PB) lymphocytes from patients with chronic GVHD. PATIENTS AND METHODS: Nine patients were studied. Peripheral blood was sampled at baseline and between 3 and 4 months of therapy when clinical effects are demonstrable. Intracellular cytokine production was assessed in vitro by stimulating PB lymphocytes with phorbol-12-myristate 13-acetate (PMA), inhibiting cytokine release and staining with fluorescein-labelled monoclonal antibodies to interleukin (IL)-2, interferon gamma (IFN-gamma) and IL-4. Flow cytometry analysis gave the absolute number and the percentage of cells expressing a particular cytokine within each lymphocyte subset. RESULTS: Absolute counts of CD3, CD4, CD8, CD19 and CD16+ cells per microlitre were recorded before and after ECP. There was a small but non-significant reduction in all subsets after 3 months of ECP. The percentage of cells expressing IL-2 and IFN-gamma rose following ECP in both the CD4 and CD8 subsets. However, only the percentage of CD4 cells expressing IFN-gamma reached statistical significance (P = 0.02; 95% confidence interval, CI 0.6-15.6). There were no significant changes in the percentage of CD4 cells expressing IL-4. CONCLUSIONS: Our findings appear to be inconsistent with current theories regarding the pathogenesis of GVHD as increased production of Th1 or Tc1 cytokines might be expected to exacerbate GVHD. However, chronic GVHD is characterized by a relative deficiency of IL-2 and IFN-gamma producing cells compared with other patients post-bone marrow transplantation (BMT). This indicates that Th1 and Tc1 cytokines are depleted in chronic GVHD. Thus, by reducing disease activity, ECP could allow cytokine production by these cells to recover. This indicates that the therapeutic effect of ECP is mediated by a different mechanism, and that the changes observed in this study are epiphenomena.     

Repeated topical challenge with chemical antigen elicits sustained dermatitis in NC/Nga mice in specific-pathogen-free condition

NC/Nga mice are known to develop skin lesions resembling to atopic dermatitis (AD) in conventional but not in specific-pathogen-free (SPF) condition. An epicutaneous application of 2,4-dinitrofluorobenzene (DNFB) increased skin thickness in C3H as well as NC/Nga mice in SPF environment, and the response was enlarged by repeating the challenge at weekly intervals. Although the skin reaction in C3H mice was ameliorated when the challenge was discontinued after the fifth application, the reaction in NC/Nga mice was sustained at least for 3 wk. Analyses of cytokine production by CD4+ cells from the draining lymph node proximal to the lesions revealed that, unlike C3H mice, NC/Nga mice fail to induce T helper 2 (Th2) cytokine interleukin-4 (IL-4), whereas the level of Th1 cytokine interferon-gamma in NC/Nga mice is equivalent to that of C3H mice. In addition, NC/Nga mice highly expressed IL-12, a cytokine-preventing formation of Th2 response, whereas C3H mice did not. Administration of anti-IL-12 antibody reduced duration of dermatitis in DNFB-treated NC/Nga mice. Taken together, our data suggest that IL-12 plays a role in the persistent skin reaction in NC/Nga mice. The action of IL-12 might be mediated by the decrease in IL-4 production.     

Human CD4+ T lymphocytes with remarkable regulatory functions on dendritic cells and nickel-specific Th1 immune responses

The contribution of T helper (Th) and T cytotoxic (Tc) type 1 lymphocytes in the expression of allergic contact dermatitis to haptens has been amply documented. Conversely, the existence of T cell-based regulatory mechanisms has been poorly investigated. Here, we examined the properties of a subset of nickel-specific CD4+ T cells displaying the cytokine profile (IL-10 , IL-5 , IFN-gamma+/-, IL-4+/-) of T regulatory cells 1 (Tr1) and with the potential to down-modulate immune responses to nickel. Tr1 clones were isolated from skin challenged with NiSO4 and peripheral blood of nickel-allergic patients, and from the blood of healthy individuals. Tr1 clones expressed CD25, CD28, CD30, CD26, and the IL-12 receptor beta2 chain upon activation, whereas the lymphocyte activation antigen-3 was present on 50% of the clones. Monocytes precultured with Tr1 cells in the presence of nickel, or treated with Tr1-derived supernatant, exhibited a markedly diminished capacity to stimulate nickel-specific Th1 responses. Tr1 supernatants also blocked the differentiation of dendritic cells (DC) from monocytes, as well as DC maturation and IL-12 production induced by lipopolysaccharide. As a consequence, the ability of DC to stimulate nickel-specific Th1 and Tc1 responses was greatly impaired. These inhibitory effects were completely prevented by IL-10, but not IL-5, neutralization. In aggregate, the results indicate that Tr1 cells can potently regulate the expression of Th1-mediated allergic diseases via release of IL-10.