Potentielle Biomarker zur Identifikation des TH2-hoch-Endotyps im Asthma bronchiale

Due to the fact that BA-patients do not benefit similarly from current pathogenesis-derived and target-based therapies it can be reasoned that there are different subsets of BA-patients within the collective of all BA-subjects, which follow according to this variable signal pathways in the pathogenesis. Subsequently the question comes up in how far responder and non-responder according to molecular based therapy strategies can be identified. Distinct BA-phenotypes can be defined by the use of clinical criteria, and beyond that there is the possibility to define a phenotype based on cytological criteria. For this purpose the percentage of eosinophils and neutrophils in the induced sputum is an essential criterion, so that an eosinophilic asthma can be distinguished from a neutrophilic BA and other cellular subtypes. There is an association or a correlation between clinical and cellular defined phenotypes. After numerous target-based therapeutic approaches proved less or not effective in the whole collective considering the specific cellular phenotypes a response to anti-IL-5-antibodies could be demonstrated with regard to a particular cellular phenotype. A further approach of phenotyping which considers the underlying signaling pathways is the definition of molecular phenotypes or endotypes respectively. By genome wide profiling using microarray analyses the up or down regulation of distinct genes can be identified in the induced sputum, whereby a molecular immunological phenotype respectively specific endotype can be derived. On the basis of the pattern of gene expression one particular endotype becomes apparent which underlies a TH2-driven inflammation. On the other side an endotype emerges where a differentiation of T-cells into TH2-cells does not occur or plays a minor role. On the basis of the expression level of the 3-gene-panel consisting of CLCA1, periostin and serpinB2 can be divided between TH2-endotypes, while there is an association of the TH2-gene-signature with eosinophilic dominated cellular phenotypes. A different response of the TH2-endotype to therapeutic approaches such as ICS as well as molecular based strategies targeting the TH2 signal pathway could be proven. In terms of stratifying of therapy it seems to be meaningful to treat patients with regard to their special endotype, the rationale here is the blockade of the cytokines involved in the TH2 signal pathway. For this purpose it is necessary to establish biomarkers which are easy to receive and to measure. It is proposed to quantify the gene products of the up regulated genes for this purpose in the serum or plasma by using ELISA. The proteins of the as up regulated identified genes such as CLCA1, periostin, serpinB2 (PAI2), the ratio of MUC5AC and MUC5B, osteopontin, CCL26 (MIP4) and carboxypeptidaseA3 are under consideration. Due to lack of suitable test systems it is required in a first step to establish and validate ELISAs for the particular proteins and to evaluate these tests in the three subsets of healthy controls, acute inflammation and atopic subjects. In a further step it will be reviewed on the basis of current studies and findings whether the particular proteins are suitable peripheral surrogate markers for a TH2-endotype by reasons of their structure, their function in the inflammation process as well as their localization. In summary the particular ELISA test systems crystallize as different suitable. With regard to their qualification as potential biomarkers to predict a TH2-endotype they seem to be heterogeneous as well. CLCA1 is a protein which appears in two distinct forms, that have a regulating function with regard to Ca2+-dependent chloride channels in the respiratory epithelium and which has influence on the composition of mucus in so far. As a membrane associated protein or a protein secreted into the ECM, CLCA1 is not suited for a systemic detection, which is proven by the measurement results. CarboxypeptidaseA3 as a protein which is systemically detectable in the plasma can be quantified reliably; however there is no evidence whether it is able to distinguish significantly between TH2-high and TH2-low. CCL26 (MIP4) is generally satisfactorily quantifiable in the plasma. In the inflammation process it has the function of a chemokine affecting eosinophils and eventually basophils. Also serpinB2 (PAI2) can be quantified reasonably in the periphery, notably in the context of an acute inflammation. On the one hand PAI2 acts as an intracellular messenger, on the other hand it exists as an extracellular protein which is involved in affairs of hemostasis. Analogous to CCL 26 and CPA3 it is questionable - with regard to the suitability to serve as a biomarker of a TH2-inflammation – if PAI2 can distinguish reliably between TH2-high and TH2-low or if the mentioned proteins occur generally on a high level within the inflammation process. To answer this question TH2-endotypes identified by molecular biology (PCR) have to be compared to non-TH2- endotypes of different specification to prove significance with regard to the assumed higher amounts of protein in the TH2-high subset. Osteopontin can be measured satisfactorily in the peripheral blood with remarkable differences in the particular subsets. Here also exists the problem if osteopontin is probably a too common marker of inflammation in general. There is evidence that osteopontin has a function in the development of TH1-inflammation and acts TH2-antagonistic. Also the point in time of the development of allergic inflammation in which osteopontin occurs is important. Altogether the role of osteopontin is very complex and less understood than to serve as a suitable biomarker. The mucins 5AC and 5B can be quantified in the peripheral blood very well. MUC5AC is up regulated in TH2-endotypes, whereas MUC5B is rather down regulated in the TH2-endotype and has probably a clearance function of the small airways. Insofar the ratio of MUC5AC and MUC5B should be shifted towards MUC5AC and therefore serves as a reasonable biomarker in theory. A significant elevated ratio can only be proven by analyses of pre-selected endotypes. Periostin can be quantified systemically in the plasma. Periostin plays a role in the development of fibrosis by interaction with ECM-proteins as well as in the migration and adhesion of eosinophils. The up regulation of POSTN proved in TH2-endotypes can be positively correlated with the eosinophilic cellular phenotype. There is also a significant correlation between the TH2-high gene-signature in general and the peripheral levels of periostin, when analyzing the molecular defined TH2-endotype (by 3-gene-panel). It can be proven that after stratifying by means of the peripheral periostin level an IL-13-blockade by mAB leads to significant results. Insofar periostin can serve as a suitable, peripheral and reliable biomarker for the identification of the TH2-endotype.