Molekulare Mechanismen der allergieprotektiven Wirkung durch Lactococcus lactis im Mausmodell des akuten allergischen Asthma

Both environmental and genetic factors are thought to be responsible for the increasing prevalence of asthma in industrialized countries in the last decades. Confirming the hygiene hypothesis, epidemiological studies have demonstrated a reduction of allergic disease after exposition to microbial components in a farming environment. Subsequently the apathogenic, gram-positive bacterium Lactococcus lactis (L. lactis) G121 was isolated from the stable dust of rural cow sheds. In a mouse model the intranasal application of L. lactis to Ovalbumin (OVA)-sensitized and -challenged BALB/c-mice significantly reduced the development of an asthmatic phenotype. The present work confirmed this result. Furthermore underlying molecular effects were examined. From an immunological point of view asthma is associated with a dominance of T-helper (Th)2 cytokines and a reduction of Th1- and regulatory T-cell (Treg)-specific cytokines. Consequently cytokine secretion patterns in mononuclear cells isolated out of bronchial lymph nodes (indicating local reaction) and the spleen (indicating systemic reaction) were analysed. In the lymph nodes, application of L. lactis resulted in a significant reduction of Th2-cytokines (IL 5, IL 13). In the spleen, Th2 cytokines were reduced. According to existing immunological concepts, either a Th1/Th2-imbalance or a Treg suppression is a causal factors in the development of asthma. However neither of the models could explain the protective L. lactis effect, as in addition to the reduced Th2-immune-response Th1- (interferon-gamma (IFNγ)) and Treg-specific cytokines (IL-10) tended to be likewise reduced. In the asthma pathogenesis, epigenetic changes are suspected to be the missing link between gene-environment interactions and dysfunction of the immune system. For the epigenetic mechanism of DNA methylation an association with T-cell differentiation was shown. Accordingly, having shown differences in cytokine concentrations by L. lactis treatment, in further analysis the DNA methylation in CD4+CD25+- and CD4+CD25--T-cells of CpGs in promoter regions of Th1-, Th2- and Treg-specific cytokines were analysed. No significant differences in the analysed DNA sequences were found for IL-5, IL-10 and IFNy. Further analysis could clarify, whether there are differences in DNA methylation in regulatory regions more distal to the transcription start or if the epigenetic mechanism of histone modification is associated with the protective L. lactis effect. Finally significant differences in the methylation of the IFNy promoter between OVA-sensitized and PBS (Phosphate buffered Saline) pseudo-sensitized animals indicate that the epigenetic process of DNA methylation plays a role in immunization processes. Significant differences in basic methylation of the IFNy promoter between T-cells isolated out of bronchial lymph nodes and the spleen show that separate analyses of local and systemic effects are required in this model.