Helge Riemann

IL-12 Suppression During Experimental Endotoxin Tolerance: Dendritic Cell Loss and Macrophage Hyporesponsiveness

Endotoxin tolerance, the transient, secondary down-regulation of a subset of endotoxin-driven responses after exposure to bacterial products, is thought to be an adaptive response providing protection from pathological hyperactivation of the innate immune system during bacterial infection. However, although protecting from the development of sepsis, endotoxin tolerance also can lead to fatal blunting of immunological responses to subsequent infections in survivors of septic shock. Despite considerable experimental effort aimed at characterizing the molecular mechanisms responsible for a variety of endotoxin tolerance-related phenomena, no consensus has been achieved yet. IL-12 is a macrophage- and dendritic cell (DC)-derived cytokine that plays a key role in pathological responses to endotoxin as well as in the induction of protective responses to pathogens. It recently has been shown that IL-12 production is suppressed in endotoxin tolerance, providing a likely partial mechanism for the increased risk of secondary infections in sepsis survivors. We examined the development of IL-12 suppression during endotoxin tolerance in mice. Decreased IL-12 production in vivo is clearly multifactorial, involving both loss of CD11chigh DCs as well as alterations in the responsiveness of macrophages and remaining splenic DCs. We find no demonstrable mechanistic role for B or T lymphocytes, the soluble mediators IL-10, TNF-α, IFN-αβ, or nitric oxide, or the NF-κB family members p50, p52, or RelB.

Inhibition of IL-12 Production in Human Monocyte-Derived Macrophages by TNF

IL-12 is a pivotal cytokine that links the innate and adaptive immune responses. TNF-α also plays a key role in orchestrating inflammation and immunity. The reciprocal influence of these two inflammatory mediators on each other may have significant impact on the cytokine balance that shapes the type and extent of immune responses. To investigate the relationship between TNF-α and IL-12 production, we analyzed the effects of exposure of human monocyte-derived macrophages to TNF-α on LPS- or Staphylococcus aureus-induced IL-12 production in the presence or absence of IFN-γ. TNF-α is a potent inhibitor of IL-12 p40 and p70 secretion from human macrophages induced by LPS or S. aureus. IL-10 is not responsible for the TNF-α-mediated inhibition of IL-12. TNF-α selectively inhibits IL-12 p40 steady-state mRNA, but not those of IL-12 p35, IL-1α, IL-1β, or IL-6. Nuclear run-on analysis identified this specific inhibitory effect at the transcriptional level for IL-12 p40 without down-regulation of the IL-12 p35 gene. The major transcriptional factors identified to be involved in the regulation of IL-12 p40 gene expression by LPS and IFN-γ, i.e., c-Rel, NF-κB p50 and p65, IFN regulatory factor-1, and ets-2, were not affected by TNF-α when examined by nuclear translocation and DNA binding. These data demonstrate a selective negative regulation on IL-12 by TNF-α, identifying a direct negative feedback mechanism for inflammation-induced suppression of IL-12 gene expression.

Modulation of Cutaneous Inflammation by Angiotensin-Converting Enzyme

Cutaneous neurogenic inflammation is a complex biological response of the host immune system to noxious stimuli. Present evidence suggests that zinc metalloproteases may play an important role in the regulation of neurogenic inflammation by controlling the local availability of neuropeptides, such as substance P (SP), that are capable of initiating or amplifying cutaneous inflammation after release from sensory nerves. To address the hypothesis that the dipeptidyl carboxypeptidase angiotensin-converting enzyme (ACE) is capable of modulating skin inflammation, we have analyzed murine allergic contact dermatitis (ACD) and irritant contact dermatitis (ICD) using wild-type C57BL/6J (ACE+/+) or genetically engineered mice with a heterozygous deletion of somatic ACE (ACE+/−). In 2,4-dinitro-1-fluorobenzene-sensitized ACE+/− mice, ACD was significantly augmented in comparison to ACE+/+ controls as determined by the degree of ear swelling after exposure to hapten. Likewise, systemic treatment of ACE+/+ mice with the ACE inhibitor captopril before sensitization or elicitation of ACD significantly augmented the ACD response. In contrast, local damage and neuropeptide depletion of sensory nerves following capsaicin, injection of a bradykinin B2, or a SP receptor antagonist before sensitization significantly inhibited the augmented effector phase of ACD in mice with functionally absent ACE. However, in contrast to ACD, the response to the irritant croton oil was not significantly altered in ACE+/− compared with ACE+/+ mice. Thus, ACE by degrading bradykinin and SP significantly controls cutaneous inflammatory responses to allergens but not to irritants, which may explain the frequently observed exacerbation of inflammatory skin disease in patients under medication with ACE inhibitors.

IL-12 Breaks Dinitrothiocyanobenzene (DNTB)-Mediated Tolerance and Converts the Tolerogen DNTB into an Immunogen

Epicutaneous application of dinitrothiocyanobenzene (DNTB) induces tolerance against its related compound dinitrofluorobenzene (DNFB), because DNTB-pretreated mice cannot be sensitized against the potent hapten DNFB. This tolerance is hapten-specific and transferable. In this study, we demonstrate that IL-12 can break DNTB-mediated tolerance. Furthermore, naive mice treated with IL-12 before DNTB application responded to DNFB challenge with a pronounced ear swelling response without previous sensitization to DNFB, showing that IL-12 can convert the tolerogen DNTB into an immunogen. No differences in numbers or regulatory activity were observed between CD4+CD25+ regulatory T cells isolated from mice treated with DNFB, DNTB, or IL-12 followed by DNTB. However, the number of CD207+ Langerhans cells in regional lymph nodes of DNTB-treated mice was significantly lower than in animals treated with DNFB or IL-12 plus DNTB. Additionally, CD11c+ dendritic cells (DC) isolated from regional lymph nodes of DNTB-treated mice had a significantly lower ability to stimulate T cell proliferation and produced reduced amounts of inflammatory cytokines. Application of both DNFB and DNTB induced apoptotic cell death of DC in the epidermis and the regional lymph nodes. However, the number of apoptotic DC in regional lymph nodes was significantly higher in DNTB-treated animals compared with mice treated with DNFB or IL-12 plus DNTB. Therefore, we conclude that DNTB-mediated tolerance is secondary to inefficient Ag presentation as a result of apoptotic cell death of DC and that IL-12 converts the tolerogen DNTB into an immunogen by preventing DNTB-induced apoptosis of DC.

Photo- und Photochemotherapie: Seltenere Indikationen

Der Einsatz von Photo- und Photochemotherapie wurde in den letzten Jahren standig erweitert. Neben den klassischen Indikationen wie z. B. Psoriasis vulgaris, atopische Dermatitis, Mycosis fungoides, polymorphe Lichtdermatose, Vitiligo wurden diese Behandlungen auch bei vielen anderen Dermatosen versuchsweise mit recht unterschiedlichen Erfolgen eingesetzt. Die Anzahl der Dermatosen, bei denen die UV-Therapie als Standardregime neben anderen etablierten Therapieverfahren angesehen werden kann, hat daher stetig zugenommen, z. B. bei Sklerodermie, Urticaria pigmentosa, Lichen ruber. Daruber hinaus gibt es eine Vielzahl von Berichten uber den erfolgreichen Einsatz von Photo- bzw. Photochemotherapie bei den verschiedensten Dermatosen. Es handelt sich allerdings oft nur um Einzelbeobachtungen, aus denen keine verallgemeinernden Schlusse gezogen werden sollten. Der endgultige Stellenwert der UV-Therapie bei diesen Dermatosen wird erst durch kontrollierte Studien mit groseren Fallzahlen zu beurteilen sein, was jedoch bei der geringen Fallzahl dieser Krankheitsbilder in nachster Zeit nicht zu erwarten sein wird. Im folgenden wird daher eine kurze Ubersicht uber diese selteneren Indikationen der Photo-und Photochemotherapie gegeben. Da aus Platzgrunden nicht die genauen, oftsehr unterschiedlichen Details der Studien bzw. Kasuistiken wiedergegeben werden konnen, sollte vor Einsatz dieser Behandlungsformen bei seltenen Indikationen auf die Originalliteratur zuruckgegriffen werden.