[Allergic contact dermatitis: how to re-induce tolerance?]. / Eczéma allergique de contact: comment ré-induire une tolérance?

Allergic contact dermatitis (ACD) is a skin inflammatory disease mediated by activation of CD8+ cytotoxic T cells specific for haptens in contact with the skin. CD4+ T cells behave as both regulatory and tolerogenic cells since they down-regulate the skin inflammation in patients with ACD (regulation) and prevent the development of eczema (tolerance) in normal individuals. Thus, ACD corresponds to a breakdown of immune tolerance to haptens in contact with the skin. Several regulatory CD4+ T cell subsets (Treg), especially CD4+CD25+ natural Treg cells, are involved in immunological tolerance and regulation to haptens through the production of the immunosuppressive cytokines IL-10 and TGF-beta. Ongoing strategies to re-induce immune tolerance to haptens in patients with eczema include improvement of existing methods of tolerance induction (oral tolerance, low dose tolerance, allergen-specific immunotherapy, UV-induced tolerance) as well as development of new drugs able to activate IL-10 producing Treg cells in vivo. Ongoing and future progress in this area will open up new avenues for treatment of eczema and more generally autoimmune and allergic diseases resulting from a breakdown of tolerance to autoantigens and allergens, respectively.

CpG immunostimulatory sequences enhance contact hypersensitivity responses in mice.

Bacterial DNA and synthetic cytidine-phosphate-guanosine-oligodeoxynucleotides (CpG ODN) potently activate dendritic cells (DC) and therefore have been proposed as adjuvants for vaccination strategies. Although CpG ODN are considered as safe adjuvants this study shows that CpG ODN are responsible for enhanced antigen-specific skin inflammatory reactions. We used the murine model of contact hypersensitivity (CHS) to 2,4-dinitrofluorobenzene (DNFB) in which hapten-specific CD8+T cytotoxic 1 cells are effector cells. Subcutaneous injection of CpG ODN, 1 d before sensitization enhanced the CHS response to DNFB and resulted in increased recruitment of CD8+ T cells at the challenge sites, whereas control ODN injection did not have any effect. This effect was local and not systemic as it was only observed when DNFB was applied at the same site as the CpG motifs. CpG ODN-induced enhancement of CHS was due to increased antigen-presenting cell functions of DC since: (i) CpG ODN-injected skin revealed upregulated expression of major histocompatibility complex class II, CD80, and CD86 molecules and (ii) CpG ODN treatment of DNFB-derivatized DC enhanced the intensity of CHS responses after in vivo transfer. Taken together, the results show that CpG ODN may be responsible for immune side-effects such as worsening of T cell-mediated skin diseases.

Survival after gamma interferon intratumoral injections in a model of hepatocarcinoma.

BACKGROUND/AIMS: Short-term efficacy of local gamma interferon delivered via a single injection of an adenovirus-gamma interferon vector has been reported in immunocompetent animals which develop spontaneous liver cancer. However the long-term outcome was not examined. The aim of this randomized trial was to assess in an immunodeficient mouse ectopic model the benefit, if any, of the long-term efficacy of intratumoral injections of gamma interferon itself. METHODOLOGY: 77 mice were randomly assigned to 4 groups. Gamma interferon treated groups received a dose of 5000, 10000 or 20000 IU per animal versus phosphate-buffered saline. The follow-up lasted 46 days. RESULTS: Significant differences were noted in mice receiving 20000 IU compared to controls: increase in survival (p=0.0485), slowing down of tumor growth in large tumors (p=0.009), increase in necrosis (p=0.004). The preferential staining in necrotic areas with anti-Class II antibody and the accumulation of nuclear debris indicated that neutrophils were involved. CONCLUSIONS: Gamma interferon could accentuate the migration of non-specific immune cells to necrotic areas which occur spontaneously in large tumors. These results in animals bearing large tumor suggest that it may be worthwhile to explore local gamma interferon delivery to patients with extensive hepatocarcinoma.

Enhanced TARC production by dust-mite allergens and its modulation by immunosuppressive drugs in PBMCs from patients with atopic dermatitis.

BACKGROUND: Thymus and activation regulated chemokine (TARC) is a CC chemokine that attracts CCR4+ T cells. We reported previously that TARC is an important chemokine that defines Th2 imbalance in the pathogenesis of atopic dermatitis (AD). OBJECTIVES: This study was undertaken to clarify TARC producing cells in peripheral blood mononuclear cells (PBMCs), the regulation of dust mite-allergen clude extract (DME) and different immunosuppressive drugs (Tacrolimus (FK506), cyclosporine (CsA), dexamethasone (Dex)) on TARC production by peripheral PBMCs from AD patients in vitro. METHODS: Monocyte derived dendritic cells (MoDCs) were generated from and TARC mRNA levels were examined and comapared with those from T cells in PBMCs from AD patients. PBMCs were cultured with or without DME and/or immunosuppressive drugs (Tacrolimus, CsA, Dex) for 7 days and TARC levels were measured. RESULTS: PBMCs from AD patients which were cultured with DME stimulation for 7 days showed significantly higher levels of TARC production than those from healthy controls. RT-PCR demonstrated that TARC mRNA was expressed in CD4+ T cells, CD8+ T cells and MoDCs. Tacrolimus, CsA and Dex individually suppressed TARC production by PBMCs from AD patients which were co-cultured with DME for 7 days. Gel shift analysis revealed differential inhibitory effects of these immunosuppressive drugs on NFkappaB activity in PBMCs from AD patients. CONCLUSION: Our data demonstrate that TARC producing cells are MoDCs, T cells as well as epidermal keratinocytes in AD. We suggest that MoDCs might regulate the immune responses by attracting T cells and CD25+ T cells in the pathogenesis of AD. We also showed the important role of DME on TARC production and the inhibitory effect of the immunosuppressive drugs on TARC production by PBMCs from AD patients, that can regulate ongoing immune responses in the pathogenesis of AD.

Ultraviolet A irradiation inhibits thymus and activation-regulated chemokine (TARC/CCL17) production by a human keratinocyte HaCaT cell line.

Ultraviolet A (UVA) irradiation modulates the immunological functions of skin. We examined the effect of UVA irradiation on the basal and the IFN-gamma-and TNF-alpha-stimulation-induced production of thymus-and activation-regulated chemokine (TARC/CCL17) using HaCaT cells. UVA irradiation inhibited the basal levels of both TARC mRNA expression and TARC protein production. UVA irradiation also significantly inhibited TARC mRNA expression and TARC protein secretion that were induced by co-stimulation with IFN-y and TNF-alpha. A time course study showed that: the significant suppression of TARC mRNA expression was detected 8 hours after irradiation and continued for 36 hours; the strongest inhibition of TARC protein secretion occurred in the first 8 hours after UVA irradiation and continued for 36 hours. Our data provide the first evidence that UVA inhibits TARC mRNA expression and TARC protein production by keratinocytes in a dose-dependent manner. These results may suggest an explanation for the UV-induced therapeutic effect.

Initial recruitment of interferon-gamma-producing CD8+ effector cells, followed by infiltration of CD4+ cells in 2,4,6-trinitro-1-chlorobenzene (TNCB)-induced murine contact hypersensitivity reactions.

Contact hypersensitivity (CHS) is an antigen-specific, T-cell-mediated skin reaction in sensitized individuals. Recent studies have demonstrated that the murine CHS reaction to 2,4-dinitrofluorobenzene (DNCB) is mediated by CD8+ T cells and down-regulated by CD4+ T cells. We studied cellular events and functions of infiltrating cells in CHS reactions to 2,4,6-trinitro-1-chlorobenzene (TNCB) in the skin and draining lymph nodes (LN) of BALB/c mice and compared them with the CHS reaction to a house dust mite antigen, Dermatophagoides farinae (Df). Mice were sensitized with TNCB or Df antigens, and CHS reactions elicited with the corresponding antigens were examined immunohistologically. Cytokines produced by individual cells isolated from the CHS reactions were analyzed by flow cytometry, and the expression of cytokine mRNA was assayed by reverse transcription-polymerase chain reaction (RT-PCR). Results demonstrated that the intensity of TNCB-elicited CHS skin reactions reached its peak at 24 hr after elicitation and decreased gradually. Flow cytometric analysis of isolated cells from the TNCB-elicited CHS reactions demonstrated that the infiltrating cells were composed of approximately 25% CD4+ and CD8+ cells at 12, 24, and 36 hr after challenge, although infiltrating cells became dense at 36 hr by histological observation. The percentage of IFN-gamma-producing CD8+ cells (Tc1) in the cell fractions reached its peak at 12 hr and decreased gradually. The peak infiltration of IFN-gamma-producing CD4+ cells (Th 1) was observed at 24 hr. IL-4-producing cells, however, were always below 5% in the cell fractions. The RT-PCR method demonstrated that IFN-gamma mRNA was detected in the TNCB-elicited skin reactions at 12, 18 and 24 hr after elicitation, became weak at 48 hr, and disappeared at 72 hr. No IL-4 mRNA was detected from 12 to 72 hr. In the draining LN cells, however, the percentages of both IFN-gamma-producing CD8+ (Tc1) and CD4+ cells (Th1) decreased 12 to 36 hr after TNCB elicitation. CHS reactions of Df antigens were predominantly composed of infiltrations of CD4+ cells in to the skin, associated with the expression of IL-4 mRNA from 12 to 48 hr after elicitaion. The expression of IFN-gamma mRNA was detected at 48 hr or later. Our findings indicate that the CHS skin reaction to TNCB is induced by early recruitment of IFN-gamma-producing CD8+ effector cells (Tcl), followed by infiltration of IFN-gamma-producing CD4+ cells (Th1), whereas IL-4-producing T cells (Th2) induce the early CHS response to Df antigens.

Hypersensitivity to mosquito bites with natural-killer cell lymphocytosis: the possible implication of Epstein-Barr virus reactivation.

Hypersensitivity to mosquito bites (HMB) has been recognized as one of the wide variety of Epstein-Barr virus (EBV)-associated lymphoproliferative disorders, some of which overlap with chronic active EBV infection and hydroa vacciniforme. It frequently predisposes to hemophagocytic syndrome or lymphoid malignancy with a clonal EBV replication. Here we report an 8-year-old Japanese boy who presented with a 3-year history of HMB. Every summer, he had repeated severe local skin reactions with high-grade fever, lymphadenopathy, and mild liver dysfunction after mosquito bites. Histologically, lymphoid cells overexpressing EBV-encoded small nuclear RNAs (EBER), a marker of latent EBV infection, and eosinophils infiltrated diffusely into the lesional skin. His blood tests showed a marked increase in the CD11b+ 16+ 56+ natural-killer cell population (~ 50% of the peripheral lymphocytes), but neither a clonal proliferation of EBV nor abnormal antibody titers to EBV. Quantitative PCR using a cloned EBV-determined nuclear antigen (EBNA)-1 vector revealed that a high copy number of the EBV genome is integrated into his peripheral blood cells even during the mosquito-free winter. Based on this evidence, he was diagnosed as being in a smoldering stage of HMB, in which EBV-associated NK cell lymphoproliferation might participate in its pathogenesis.

Skin inflammation during contact hypersensitivity is mediated by early recruitment of CD8+ T cytotoxic 1 cells inducing keratinocyte apoptosis.

Contact hypersensitivity (CHS) is a T cell-mediated, Ag-specific skin inflammation induced by skin exposure to haptens in sensitized individuals. Th1/T cytotoxic 1 cells are effector cells of CHS, whereas Th2/T regulatory CD4(+) T cells have down-regulating properties. We have previously shown that CHS to 2,4-dinitrofluorobenzene is mediated by specific CD8(+) effector cells, whose cytolytic activity is mandatory for induction of skin inflammation. In this study, using immunohistochemistry and RT-PCR analysis, we show that CD8(+) T cells are rapidly recruited into the skin at the site of hapten challenge before the onset of clinical and histological signs of skin inflammation. This early CD8(+) T cell recruitment is concomitant with: 1) transient IFN-gamma mRNA expression suggesting local activation of effector cells; and 2) induction of keratinocyte (KC) apoptosis which gradually increased to a maximum at the peak of the CHS response. Alternatively, skin infiltration of CD4(+) T cells occurred later and coincided with the peak of the CHS reaction and the beginning of the resolution of skin inflammation. Mice deficient in CD8(+) T cells did not develop CHS, whereas mice deficient in CD4(+) T cells developed an enhanced inflammatory response with increased numbers of CD8(+) T cells recruited in the skin associated with massive KC apoptosis. These data show that CHS is due to the early and selective recruitment in the skin of CD8(+) T cytotoxic 1 effector cells responsible for KC apoptosis.